• 专利附录
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    • 专利摘要:
    A method and apparatus for driving a radiation sensor pixel are disclosed. The sensor pixel includes a detection element capable of charge production in response to incident radiation, a floating diffusion node, a transfer gate between the detection element and the floating diffusion node, and a charge storage device connected to the floating diffusion node via a switch. The method includes biasing the transfer port to three or more biases OFF, ON and an intermediate bias between OFF and ON. During the period when the transfer port is biased to the intermediate bias, if the sensor reaches saturation, the overflowed charges may be collected and some of them stored in the charge storage device for further analysis and aggregation.
    公开号:BE1023468B1
    申请号:E2015/5771
    申请日:2015-11-26
    公开日:2017-03-29
    发明作者:Bart Dierickx；Benoit Dupont；Jiaqi Zhu；Kalgi Ajit Kumar；Diang Yao；Koen LIEKENS；Gaozhan Cai；Bert Luyssaert；Aken Dirk Van；Peng Gao
    申请人:Caeleste Cvba；
    IPC主号:
    专利说明:

    Transfer port with three levels
    FIELD OF THE INVENTION
    The present invention relates to the field of radiation sensor pixels that are suitable for use in sensor arrays. The present invention relates in particular to a sensor with a high dynamic range and to a drive method for such a sensor.
    BACKGROUND OF THE INVENTION
    Through miniaturization, sensor arrays usually suffer from leakage currents that degrade an image captured by the sensor arrays. The use of integrated microelectronic elements (such as transistors or photodiodes) in monolithic sensors is an important technique that allows the fabrication of very small radiation sensor pixels, but leakage currents can often occur due to the type of materials and the very small dimensions and distances between electronic elements . One of the characteristics of the detection element that contribute to this effect is its limited sensitivity. When incident radiation exceeds a predetermined threshold limit, the sensor becomes saturated and a further increase in radiation intensity can lead to leakage. Some solutions have been proposed. For example, the use of pixels with a wide surface can lead to an increase in the saturation limit. This solution is very limited due to the fact that a sensor array should be able to have high sensor density (e.g., high number of pixels per inch) in order to be competitive.
    Other solutions remove excess charge by draining, thus avoiding leakage, in saturated pixels. Although leakage and related effects (such as intermodulation or haze) are reduced, the sensor becomes saturated and the image quality is not optimal.
    Dynamic range can be defined as the ratio between the lowest and highest radiation intensity that is capable of producing a variation in the radiation sensor. It is desirable to have high dynamic range (HDR) in a sensor while at the same time reducing leakage currents in a sensor array in order to obtain an optimum configuration suitable for sensor arrays. Various alternatives and sensor configurations have been proposed. US2012 / 0193516 discloses a pinned photodiode (PPD) with capacitors for storing charge, thereby increasing dynamic range. The capacity of the capacitors is higher than the capacity of the sensor. Furthermore, a lateral overflow barrier can be used to reduce leakage current during charge production and collection in the photodiode.
    The manufacture of a sensor suitable for sensor arrays, which allows a reduced leakage and high dynamic range, is desirable, while at the same time avoiding increasing the surface of the sensor (thus avoiding a reduction in resolution), reducing the sensitive surface is avoided (thus obtaining good saturation) and expensive production routes are avoided.
    Summary of the invention
    It is an object of embodiments of the present invention to provide a radiation sensor pixel and a method for driving a radiation sensor pixel suitable for sensor arrays to achieve good image quality, low leakage currents and enabling imaging with high dynamic range.
    The above object is achieved by a method and a device according to embodiments of the present invention.
    In a first aspect, embodiments of the present invention relate to a method for driving a radiation sensor pixel. The radiation sensor pixel comprises a detection element capable of charge production in response to incident radiation, a floating diffusion node, a transfer gate between the detection element and the floating diffusion node, and a charge storage device connected to the floating diffusion node via at least one switch for controlling the current through an ON bias to allow charge current, and an OUT bias to prevent charge current between the charge storage device and the floating diffusion node. The method comprises sequentially biasing the transfer port to at least three different bias voltages, the at least three different bias voltages comprising at least one OFF bias voltage, an ON bias voltage, and at least one intermediate bias voltage. The at least one intermediate bias has a value within the range between the OFF bias and the ON bias. The ON bias allows the charge in the detection element to be transferred to the floating diffusion node while the switch is OFF. The method further comprises enabling the charge storage device to accept charges, at least while biasing the transfer port to the intermediate bias. It is an advantage of embodiments of the present invention that any possible overflow through the selectable intermediate bias can be controlled by a single transistor, thereby avoiding leakage of currents and related negative effects, while simultaneously collecting and accounting for the overflowed charges of their influence is made possible.
    In specific embodiments of the present invention, the method may include at least one integration period in which charges are integrated on the detection element. Successively biasing the transfer port to at least three different bias voltages may include biasing the transfer port to the intermediate bias during at least a portion of the integration period, thus a portion of the integrated charges that may overflow the transfer port (corresponding to a predetermined threshold), transferring to the floating diffusion node and the charge storage device. It is an advantage of embodiments of the present invention that the charges produced by supersaturation of the pixel can be measured. It is an advantage of embodiments of the present invention that the value of the saturation level of the pixel during charge integration can be arbitrarily set low, thereby allowing a large control at different intensities of incident radiation. It is an additional advantage that the charges produced by supersaturation of the pixel can be collected.
    Some embodiments of the present invention may include transfer of charge from the detection element to an intermediate node, via the transfer port. During integration, charges can, for example, overflow through a transfer port with intermediate bias to the intermediate node. Charges from the intermediate node can then be transferred to at least one floating diffusion node via a transfer port, which can be biased to at least two bias voltages.
    Some embodiments may include (a) overflowing charges from the detection element directly to the storage device, or (b) overflowing charges from the detection element to an intermediate node and from the intermediate node to the storage device and / or the floating diffusion node . The present invention is not limited to the examples mentioned, and a mixture of both can also be designed. It is an advantage of embodiments of the present invention that charges are not lost, but are stored for future use.
    In the first case (a), the overflow of charges from the detection element to the storage device can be done via a fixed barrier, which preferably reduces energy consumption; or via a further transfer port that can be biased to three voltages, preferably controlling the amount of charge that can be integrated into the detection element.
    In the second case (b), transferring an amount of charge through the at least first transfer port to the at least one intermediate node may include transferring or overflowing charge exceeding the maximum capacity from the at least one intermediate node to the storage device (e.g., the capacitor node) via an overflow barrier, e.g. via a fixed barrier (which preferably reduces energy consumption) or via a transfer port that can be biased to three voltages, preferably controlling the amount of charge that can be accumulated in the integration node.
    Some embodiments of the method of the present invention may include additional periods. They may, for example, comprise an integration period and furthermore a read-out period. Each period can include different phases, which will be described within the scope of different embodiments of the present method.
    For example, certain embodiments of the first aspect of the present invention may further include a readout period. This readout period, according to some embodiments of the method of the present invention, may include reading out the charges previously integrated on the detection element. It may also, in further embodiments of the present invention, include combining charges stored on the charge storage device with charges present on the floating diffusion node. It is an advantage of embodiments of the present invention that charges collected during integration may be part of the signal reading.
    In some embodiments of the present invention, successively biasing the transfer port to at least three bias may further include temporarily biasing the transfer port to ON bias, thus transferring the integrated charges to the floating diffusion node while not allowing the charge storage device to charge and then the charge levels in the floating diffusion node are read. This phase can be included in the read phase, although the present invention is not limited thereto. It is an advantage of embodiments of the present invention that the total charge produced by the incident radiation can be collected above the pixel saturation level.
    The readout period can bias the transistor (ON state) between the intermediate node and the floating diffusion node, and read the charges, followed by bias the transistor (ON state) between the storage device and the diffusion node and read off of the charges. The charges in the storage node can be collected in preceding steps directly from the detection element (first case (a) explained earlier) or they can be collected from an overflowing intermediate node (second case (b)). The transfer step can be performed via a transfer port with an intermediate bias or via a fixed barrier.
    Specific embodiments of the present invention may further comprise additional steps or periods. For example, certain embodiments may include biasing the transfer port by the OFF bias between the integration period and a subsequent readout period. It is an advantage of embodiments of the present invention that it allows the measurement of reset levels. It is an advantage of embodiments of the present invention that not only the total accumulated charge can be collected and measured, but also the level of saturation can be obtained and corrected for increasing the dynamic range of the pixel.
    The charge on different phases can be analyzed in different ways. Certain embodiments of the present invention include, for example, obtaining correlated double sampling output (CDS). In certain embodiments of the present invention, the CDS output is calculated from the difference in charges present on the floating diffusion node before and after biasing the transfer port ON. It is an advantage of embodiments of the present invention that the total charge accumulated during the preceding step can be additionally collected.
    In preferred, non-limiting embodiments of the present invention, the transfer of a portion of the integrated charges is performed only through the transfer port. In such embodiments, the pixel can preferably be compact. No additional design features such as lateral overflow ports are required.
    Other embodiments can make it possible to reset the detection element, for example by incorporating a flushing gate, to obtain the favorable properties of a sensor shutter. It is an advantage of embodiments of the present invention that high dynamic range and reduced negative effects from charge leak can be obtained without the need to include additional transistors, hence compact pixel circuits can be used.
    In a second aspect of embodiments of the present invention, the present invention also relates to a radiation sensor pixel. The radiation sensor pixel according to embodiments of the present invention can preferably be driven according to a method embodiment of the first aspect of the present invention. Said device according to embodiments of the present invention may comprise a detection element capable of charge production in response to incident radiation, a floating diffusion node, a single transfer port between the detection element and the floating diffusion node, a charge storage device connected to the floating diffusion node via a switch, and preferably a driver circuit adapted for successively biasing the single transfer port at at least three different bias levels, the connections between the detection element and the floating diffusion node and between the charge storage device and the floating diffusion node being adapted to transfer charges in the detection element to the floating diffusion node while the switch is OFF. It is an advantage of embodiments of the present invention that a limited number of transistors can be used in a pixel, thereby reducing the size of the sensor and thus enabling higher sensor density in a sensor array. For example, in certain embodiments that include pixels, a higher pixel density can be achieved in a camera set. It is an additional advantage that the sensitivity of the sensor can be manipulated, so in a small and compact device high dynamic range can be obtained.
    Certain embodiments of the present device according to the second aspect of the present invention may include an output stage configured to produce a signal representative of the amount of electrical charge on the floating diffusion separately, on the charge storage device individually, or on both. This may include analog-to-digital converters, analog readers, integrated circuits, the present invention not being limited by such examples, and may be suitable for measuring the signal level of radiation received by the radiation sensor pixel. It is an advantage of embodiments of the present invention that the sensor may have radiometry applications. It is an additional advantage that the present invention can have photometry applications.
    The device according to some embodiments of the present invention can be manufactured in a substrate with semiconductor properties, for example a semiconductor, for example Si or Ge, or a mixture of different elements such as SiGe; GaAs or InGaAs, or any other suitable combination. In preferred embodiments of the present invention, the detection element may comprise a surface of the substrate, it may, for example, comprise at least one photoelectric diode, for example a pegged photodiode. It is an advantage of embodiments of the present invention that low dark current and high quantum efficiency can be obtained. It is an additional advantage that standard manufacturing methods for embedded or pinned photo diodes can be used. The photodiode can be made, for example, by layered p-n doping in a light p-doped substrate. The present invention can include other types of semiconductor structures, or even different detection elements.
    According to embodiments of the present invention, the device comprises a charge storage device coupled to the output. In various embodiments of the present invention, this charge storage device may comprise, for example, one capacitor, or a capacitor node comprising at least one capacitor coupled to the output via a switch, for example a transistor such as a MOSFET, TFET or any other type of switch. The capacitor can be an external switching element, or can be integrated in a substrate in embodiments including integrated sensors, for example in monolithic devices. The present invention is not limited to such a structure and it may comprise more than one capacitor, as well as other elements and switches. The charge storage device may, for example, comprise a pair of capacitors connected in parallel between them, thereby increasing the capacity. It is an advantage of embodiments of the present invention that the charge storage device can be easily implemented in a circuit.
    According to embodiments of the present invention, the device may further comprise an intermediate node between the detection element and the floating diffusion node. The intermediate node can store charges overflowed from the detection element through the transfer port, and it can include a further transfer port and a drive circuit adapted for successively biasing the further transfer port at two different bias levels, which is charge transfer between the intermediate node and the floating diffusion. In some embodiments, the driver circuit can bias the further transfer port at at least three different bias levels.
    Furthermore, the device may comprise an overflow port for electrically connecting the detection element (e.g. a pinned photodiode) and the at least one storage node. The overflow port may, for example, comprise a transfer port for selectively overflowing charges directly or indirectly from the detection element, allowing selectivity of charge-at-full-well (QFw) ranges. In alternative embodiments, the overflow port may comprise at least one fixed barrier between the pinned photodiode and the at least one capacitor node, which preferably reduces the size of the circuit by implementing the barrier via doping, deposition or patterning.
    According to embodiments of the present invention, the device comprises an overflow port for electrically connecting the charge storage device and an intermediate node. The overflow port may, for example, comprise a transfer port for selectively overflowing charges from the intermediate node. Thus, the dynamic range can be adjusted, allowing different levels of sensitivity of the pixel to different lighting conditions. The overflow port may alternatively comprise a fixed barrier, which reduces space and energy consumption while reducing haze to the floating diffusion.
    In some preferred embodiments of the present invention, the charge storage device may include an integrated transistor configured to selectively open a conductive path between the charge storage device and the floating diffusion node, thereby preferably collecting the overflowed charges that can be measured for estimation of supersaturation levels. Other possible configurations may include, for example, three capacitors in parallel configuration connected to each other via a switch. It is a further advantage of embodiments of the present invention that different levels of saturation can be checked and measured for the same intermediate voltage [voltage] VM, further reducing any potential leakage current that may still occur. For example, in certain embodiments, the additional capacitors are used (for example, their switches are opened) in case the main capacitor of the storage device becomes saturated.
    It is an advantage of embodiments of the present invention that the basics of a general electronic shutter capable of performing CDS readout without being limited by the relatively high dark current of a surface diode can be combined with a linear high dynamic range, by creating multiple linear CW ranges, thereby reducing noise and increasing storage capacity of the pixel, without increasing the pixel surface. Furthermore, haze formation can be reduced while most or all of the integrated photo charges are being used at the same time.
    Some embodiments of the present invention include at least one reset transistor. For example, a transistor can control the connection between the floating diffusion and the source VDD, so that the detection element can be quickly depleted of charge and prepared for new use. This is particularly advantageous in photography or video applications where the radiation sensor pixel may have reduced image delay. Embodiments of the present invention may include at least one alternative or additional transistor for the depletion of the charge storage device CS, which preferably allows depletion of overflowed charge at a different time than the floating diffusion region. This allows for greater control of the accumulation, thereby making it possible, for example, to control the moment at which charge accumulation starts, or whereby, if desired, different cycles of charge accumulation are made possible.
    The device according to a second aspect of the present invention can include other configurations and structures, to the extent that these features enable operation according to embodiments of the first aspect of the present invention. For example, some embodiments may include a coil port connected to the detection element, thereby allowing more control during the integration and read periods, and whereby rapid processing with good sensitivity and a compact optical system are obtained. In pixel sequences that use the sensor according to these embodiments, an electronic general shutter effect can be obtained.
    The present invention may comprise other elements, for example a second storage node connected to a second floating diffusion node, both connected to the detection element via a further overflow barrier. This configuration can enable shutter mode with pipeline.
    Embodiments of the present invention may include detection of any type of radiation, for example ionizing radiation, particulate radiation (alpha particles, beta particles, neutrons, etc.). Some embodiments of the present invention include a method and apparatus for detecting electromagnetic (EM) radiation, for example, gamma radiation, x-rays, or within the range between far infrared and ultraviolet, for example, within the range of visible radiation. In the case of these specific embodiments for EM radiation, the detection element would comprise a photoelectric detection element and the charges would comprise photo charges.
    Specific and preferred aspects of the invention are included in the appended independent and dependent claims. Features of the dependent claims can be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly stated in the claims.
    These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment (s) described below.
    BRIEF DESCRIPTION OF THE FIGURES FIG. 1 shows a flow chart of a method according to embodiments of the present invention for driving a radiation sensor pixel. FIG. 2 shows a potential diagram of a radiation sensor pixel during an integration period according to embodiments of methods of the present invention. FIG. 3 shows a potential diagram of a radiation sensor pixel during a first part of a readout period according to embodiments of methods of the present invention. FIG. 4 shows a potential diagram of a radiation sensor pixel during a second part of a readout period according to embodiments of methods of the present invention. FIG. 5 shows a potential diagram of a radiation sensor pixel during charge assembly, according to embodiments of methods of the present invention. FIG. 6 shows an optional discharge cycle for reading the low gain levels, according to embodiments of methods of the present invention. FIG. 7 is a schematic illustration of a radiation sensor pixel with one storage device according to embodiments of the present invention. FIG. 8 is a schematic illustration of a radiation sensor pixel with one storage device, a charge storage reset switch, and an electronic shutter according to embodiments of the present invention. FIG. 9 is a schematic illustration of a radiation sensor pixel with a storage device comprising three capacitors and selector switches, according to some embodiments of the present invention. FIG. 10 shows an exemplary sequence according to embodiments of the present invention, for driving a radiation sensor pixel as schematically illustrated in FIG. 7. FIG. 11 shows another sequence according to embodiments of the present invention for driving the schematic in FIG. 9 illustrated radiation sensor pixel.
    The figures are only schematic and non-limiting. In the figures, the dimensions of some parts may be exaggerated and not represented to scale for illustrative purposes.
    Reference numbers in the claims may not be interpreted to limit the scope of protection.
    In the various figures, the same reference numbers refer to the same or similar elements.
    Detailed description of illustrative embodiments
    The present invention will be described with reference to particular embodiments and with reference to certain drawings, however, the invention is not limited thereto but is only limited by the claims. The described drawings are only schematic and not restrictive. In the drawings, the dimensions of some elements may be increased for illustrative purposes and not drawn to scale.
    The dimensions and the relative dimensions sometimes do not correspond to the current practical embodiment of the invention.
    The terms first, second and the like in the description and in the claims are used to distinguish similar elements and not necessarily for describing a sequence, neither in time, nor spatially, nor in ranking, or in any other way. It is to be understood that the terms used in this way are suitable under interchangeable conditions and that the embodiments of the invention described herein are capable of operating in a different order than described or depicted herein.
    Moreover, the terms upper, lower and the like in the description and claims are used for description purposes and not necessarily to describe relative positions. It is to be understood that the terms so used may be interchanged under given circumstances and that the embodiments of the invention described herein are also suitable to operate in other orientations than described or shown herein.
    It is to be noted that the term "comprises," as used in the claims, is not to be construed as limited to the means described thereafter; this term does not exclude other elements or steps. It can therefore be interpreted as specifying the presence of the listed features, values, steps or components referred to, but does not exclude the presence or addition of one or more other features, values, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices that consist only of components A and B. It means that with regard to the present invention, A and B are the only relevant components of the device.
    Reference throughout this specification to "one embodiment" or "an embodiment" means that a specific feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, occurrence of the expressions "in one embodiment" or "in an embodiment" at various places throughout this specification may not necessarily all refer to the same embodiment, but may do so. Furthermore, the specific features, structures, or characteristics may be combined in any suitable manner, as would be apparent to those skilled in the art based on this disclosure, in one or more embodiments.
    Similarly, it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together into a single embodiment, figure, or description thereof for the purpose of streamlining disclosure and assisting in understanding one or several of the various inventive aspects. This method of disclosure should not be interpreted in any way as a reflection of an intention that the invention requires more features than explicitly mentioned in any claim. Rather, as the following claims reflect, inventive aspects lie in less than all the features of a single prior disclosed embodiment. Thus, the claims following the detailed description are hereby explicitly included in this detailed description, with each independent claim as a separate embodiment of the present invention.
    Furthermore, while some embodiments described herein include some, but not other, features included in other embodiments, combinations of features of different embodiments are intended to be within the scope of the invention, and constitute different embodiments, as would be understood by those skilled in the art . For example, in the following claims, any of the described embodiments can be used in any combination.
    Numerous specific details are set forth in the description provided here. It is, however, understood that embodiments of the invention can be practiced without these specific details. In other cases, well-known methods, structures and techniques have not been shown in detail to keep this description clear.
    Where in embodiments of the present invention reference is made to detection element, reference is made to the element in a radiation sensor pixel that generates charges when radiation impinges on the element. In preferred embodiments of the present invention, the detection element is a photoelectric detection element that generates photo charges after collision of electromagnetic (EM) radiation (X-ray radiation, gamma radiation, a radiation range between infrared and ultraviolet, for example visible light in applications related to pixel devices). Accordingly, when reference is made to charges, reference is made to electric charges, e.g., photo charges produced by EM radiation in those embodiments that include a photoelectric detection element. The present invention is not limited thereto and the detection element can produce charges after colliding other types of radiation, such as ionizing radiation, corpuscular radiation (e.g. alpha radiation), etc.
    When in embodiments of the present invention reference is made to a charge storage device (or CS, for conciseness), reference is made to any element or circuit configuration capable of storing charges (e.g., photo charges) and selectively discharging them according to needs of the user, or the specific operating stages of the radiation sensor pixel. In some non-limiting embodiments of the present invention, the charge storage device may include switching elements such as capacitors.
    Where in embodiments of the present invention reference is made to a switch, reference is made to a device (e.g., a transistor, while the present invention is not limited thereto) that can control the current between two states (ON or OFF), e.g. switch or switches that control the cycle of charge to and from the storage device. They can be externally regulated, or programmed, and can be used to merge the charges in the charge storage device and in a floating diffusion node, and they can also be used to control the reset of the radiation sensor pixel.
    Where "haze formation" is referred to in embodiments of the present invention, a process is referred to where the charge in a pixel exceeds the saturation level of the pixel, and the charge begins to fill adjacent pixels.
    With floating diffusion node (FD), in embodiments of the present invention, reference is made to a portion of the radiation sensor pixel connected to the readout circuit (or output), and it may include other connections, such as connections to the charge storage device or a reset switch. In embodiments of the present invention that include monolithic sensors, it may be embedded in the same substrate as the detection element, for example comprising a doped region.
    Where in embodiments of the present invention reference is made to a transfer gate (TG), reference is made to any device that controls the circulation of the current between a detection element and an FD. This can be achieved by a bias electrode and an insulating (e.g., oxide) layer on a channel between the FD and the detection element, although the present invention is not limited by these examples.
    In radiation sensor pixels, a low intensity threshold can be defined below which the detection element is unable to produce enough charges for meaningful reading. A high threshold can also be defined, showing the maximum amount of charges produced by the detection element, beyond which this amount would not increase despite receiving a higher radiation dose. It is then said that the radiation sensor pixel reached saturation. The ratio between the low and the high threshold is the dynamic range. Within the scope of the present invention, the saturation value can be varied to change the dynamic range. For example, the dynamic range of the radiation sensor pixel can be increased. In embodiments of the present invention, the saturation value during integration may be selected by biasing the transfer port to a given bias voltage Vm, which would result in a smaller saturation than the maximum sensor saturation value obtained when the transfer port is biased to an OFF bias voltage, e.g. zero volts.
    Excessive charges above the selected saturation can be transferred (by overflowing the transfer port) to the floating diffusion node. When in embodiments of the present invention reference is made to defects in charge, reference is made to these abundant charges that exceed the selected saturation value of charges that can be held in the detection element.
    A first aspect of embodiments of the present invention relates to a method for driving a radiation sensor pixel comprising at least one photoelectric detection element, a floating diffusion node and a transfer port between the detection element and the floating diffusion node. A charge storage device is connected to the floating diffusion node via at least one switch. The method allows for sequential bias of the transfer port to at least three different bias voltages, including at least OFF (V0), ON (Vi) and one or more intermediate bias voltages (VM). The intermediate bias can for example be a fixed value, or can be selected within a range of possible values between V0 and Vj. The values V0, Vi, VM can be selected depending on specific technology parameters, desired functionality and specifications.
    In specific embodiments, the values used can be, for example, V0 = 0 V, Vi = 3 V and the intermediate voltage VM can be 0.8 V.
    The method 100, illustrated in the flow chart of FIG. 1, may include: - an integration step 110. During this step 110, charges (e.g., photo charges, e.g., photo charges generated by incident radiation, e.g., but not limited to visible light) are integrated on the detection element, during an integration period. At the start of the integration period, the charge storage device CS is brought into contact 111 with the floating diffusion node FD, for example, by closing a switch ("opening the gate") between the charge storage device CS and the floating diffusion node FD. The integration period further comprises driving 112 the transfer port between the detection element and the floating diffusion node to a predetermined intermediate bias voltage Vm, according to the desired saturation value of the detection element. All possible defected loads can be transferred to the FD and the CS loads are allowed to receive. At the end of the integration period and before the next period begins, the transfer port can optionally be driven 113 to an OFF bias (thus opening the switch, or "closing the port"). - a read-out step 120. During a read-out period corresponding to the read-out step, the charge storage is turned off 121, for example by opening a switch between the charge storage device and the floating diffusion node. All charge collected in the floating diffusion node FD during the integration period can optionally be read 122 from the FD via an output stage, which can be configured to produce a signal representative of the amount of electrical charge, for display or data storage. The integrated charges from the detection element are transferred to the floating diffusion node by driving the transfer port 123 to an ON bias (closing the switch, or "opening" the port). Once the charges have been transferred, the transfer port is biased 124 to an OFF bias (again closing the port, opening the switch). The charges can be read 125 from the floating diffusion node FD. Correlated double sampling (CDS) can optionally be performed 126, preferably reducing kTC noise. In addition, a merging step can be performed by connecting 127 of the charge storage device CS to the floating diffusion node FD. Thereafter, the charge level of the CS combined with the charges that may have been collected in floating diffusion node FD during the integration period can be obtained 128. The method may include resetting 129 the radiation sensor pixel at the end of the readout period.
    The above steps are not limiting for the present invention, as long as the transfer port is sequentially biased to at least three different biases. Other steps may also be included in methods according to embodiments of the present invention. For example, during the readout period (e.g. after merging the charges in the FD, or after the first reading), a cycle of biasing the transfer port to OFF-ON-OFF states can be performed to include loads that be integrated in the phases in the detection element in which the transfer port was 'open'. It may also be possible to understand a coil port that acts as a shutter, for example to obtain a general shutter in a sensor array. For example, the coil port can be used to determine the time when the integration period starts. The joining of the charges can include various joining steps, for example, in the case that multiple storage elements include the CS. Other additional or alternative steps could be to read the charge directly from the CS, thereby creating a CS signal representative of the stored charge alone, which could then be compared or added to the FD signal alone without the assemble loads yourself. Reading the level and producing the signal could, for example, be done with analogue means such as a voltmeter, or with analog-to-digital converters. Additional reset switches can be added in the charge storage device.
    In embodiments of the present invention, there is no readout of charges during the integration period and during each sequence a single integration period (including biasing the transfer port) takes place that the data shown in FIG. 1 includes steps. FIG. 2 shows two potential diagrams 200, 210 of a radiation sensor pixel according to embodiments of the present invention, corresponding to one exemplary bias configuration, during the integration period. Operations during the integration period may, in embodiments of the present invention, include sequentially biasing the transfer port on the intermediate bias VM, thereby the height of the potential barrier 202, 212 of the transfer port VM will be. Charges 203, 213 produced by incident radiation 204, 214 can first be integrated on the detection element 205, 215. If the charges 203 do not exceed the potential barrier 202, the detection element 205 is not saturated, which corresponds to the potential diagram 200. Depending on the value of VM with respect to the radiation intensity received by the detection element, the charges 213 may be the sensor 215 saturation, which corresponds to the potential diagram 210. The bias voltage VM can be selected from a range of values, allowing different levels of saturation during integration. If low values are selected, the radiation sensor pixel will be saturated for corresponding low radiation intensity.
    In case saturation is reached (the right-hand side of FIG. 2), to avoid leakage of charges, all possible defects in charge 216 can be transferred via transfer port 211 (biased by the intermediate bias Vm and potential barrier 212) to the floating diffusion node FD . If a switch is closed between the floating diffusion node FD and the charge storage device CS, part of these overflowed charges 216 can preferably be collected on a charge storage device (CS), thereby avoiding some of the effects that adversely affect sensors such as charge haze or leak that can, for example, reduce resolution in sensor arrays or saturate nearby detection elements or, in some types of sensors such as pixel arrays in cameras, produce intermodulation and reduce image quality.
    The storage charge device may thereby comprise a single capacitor connected to a switch connected at its other end to a floating diffusion node FD, or may comprise more than one capacitor, for example in a parallel configuration with switches regulating the charge transfer between them and the floating diffusion node . FIG. 3 shows two potential diagrams 300, 310 of the radiation sensor pixel according to embodiments of the present invention, corresponding to one exemplary bias configuration during the readout period.
    Before the readout period begins, the transfer port 201, 211 may optionally be biased to an OFF bias V0, effectively closing the transfer port by potential 301, 311 and interrupting the flow of charges 203, 213 to the FD. Embodiments of the present invention are not limited to this configuration.
    The switch coupled to the CS can be closed (thereby creating the barrier 302, 312) so that all charge from the previous period can be kept in the storage CS.
    In the floating diffusion node FD, pre-reading of charges can optionally be performed. If the reading does not yield a significant value, the case in the first diagram 200 of FIG. 2 and the first diagram 300 of FIG. 3 shown. On the other hand, if the reading results in a significant value, it can be foreseen that the radiation sensor pixel reached saturation during the integration phase (thus corresponding to the situation depicted in the second diagram 210 of FIG. 2 and in the second diagram 310 of FIG. 3). The amount of 313 charges that exceeded the saturation level can be estimated or measured. This value can be used, for example, with adjustment techniques applied to radiation sensors, for example, to dynamically reduce the sensitivity of the pixels of a camera (thereby lowering VM in transfer port 211 and raising barrier 212 in subsequent exposures during integration , Fig. 2), or alternatively increasing sensitivity if no saturation is achieved, while the present invention is not limited to this example. Alternatively, the pre-reading of the amount of 313 charges cannot optionally be performed.
    The readout period may further, as shown in FIG. 4, a complete transfer 401, 411 of charges from the detection element 205, 215 to the floating diffusion node FD. This transfer is performed by biasing the transfer port 201, 211 to an ON bias Vi (by turning on the transfer port), thereby removing the barrier. Flet reading of these charges can be interpreted as the "signal level" 403, 413. If the detection element did not become saturated during the integration period, the signal level 403 only includes the charges integrated into the detection element during the integration period (left side of FIG. 4) , while if the saturation level is exceeded during the integration period, the signal level readings 413 are a combination of the read level (arising from the charges from the photodiode transferred to the FD during the read period) and the level of the overflowed charges transferred to the floating diffusion node during the integration period (right side of FIG. 4).
    As seen in FIG. 5, the readout period may further "close" the transfer gate 201, 211 (biasing the gate to an OFF potential 301, 311) and then merging the charges of the floating diffusion node FD with the ones held in the charge storage device CS loads. This can be done, for example, by opening a switch that couples the charge storage device CS to the floating diffusion node FD, thus eliminating the barrier 302, 312. Charges in the floating diffusion node after biasing the switch between CS and FD with an ON voltage would coincide with the stored charges. After merging, the charges can be read as a "total" radiation level 501, 511, which can be higher than the maximum saturation level allowed by the detection element, thus effectively and preferably increasing the dynamic range of the radiation sensor pixels. It will be clear to those skilled in the art that the charges thus combined all arise from the same integration period.
    In accordance with embodiments of the present invention, as opposed to some prior art solutions, the integration period is independent of the captured signal levels and is the same for high and low light levels.
    In addition, as shown in FIG. 6, allowing the transfer port 201, 211 to cycle during the readout period, e.g. after merging the charges on the FD and the CS (e.g. after the steps of connecting 127 of the CS to FD and obtaining 128 of the charge level, or after obtaining 128 the charge level, as shown in FIG. The cycle may include a cycle of bias voltages (OFF-ON-OFF), indicated by an arrow, to read off all possible charge 601 generated by radiation 602 that collides with the sensor during the readout period. These charges can be interpreted as "low-gain" radiation level 603, which can also be aggregated and read, or read before merging. The present invention is not limited to these examples and other cycles may be used at the same or different times of the readout period.
    By subtracting two signal levels from each other, optionally correlated double sampling (CDS) can be performed, resulting in a more accurate readout value. CDS can be easily performed if the optional pre-reading of the floating diffusion node is performed between the last read signal 403, 413 or 501, 511 and pre-reading of charges as shown in FIG. 2. Alternatively, the charge level can be read from the storage load device CS and subtracted from the signal level.
    At the end of the readout period, the radiation sensor pixel can be reset, i.e., all available charge removed.
    A method according to embodiments of the first aspect of the present invention is not limited by the above steps and periods. For example, a separate transfer port can be added, creating a more versatile electronic shutter, depending on each specific application, which accurately defines the duration of charge integration, for example.
    The method uses a single transfer port between the floating diffusion node and the detection element, which can be biased to at least three bias voltages to allow charge overflow. The method according to further embodiments may include the use of further structures that allow overflow, for example, fixed barriers or further transfer ports that accept three bias voltages. In this case, after integration of charges in the detection element, overflowed charges can be transferred directly from the detection element to a storage device via a fixed barrier or a transfer port between the storage device and the detection element. At the end of the integration period, the charges from the detection element can be read via the floating diffusion node and the stored charges can also be read afterwards. In another embodiment, charges are transferred via the first transfer port TG to an intermediate node which is connected to the storage device via an overflow barrier, such as a fixed barrier or a further transfer port. If the charge reaching the intermediate node exceeds the maximum allowable charge, in order to avoid parasitic currents and other adverse effect, the excess charge is transferred to the storage device (e.g., a condenser node). This transfer can be done either by overflow or via a transfer port or a transistor port. The detection element can be exhausted from photo charges, thus reducing blurring. All charge transferred to the storage device can be kept in a capacitor. This allows, for example, reading of the charges using correlated double sampling (CDS). The method may further include transferring the charges from an intermediate node to a floating diffusion node FD via the second TG, the charges being read, e.g., by a readout circuit. The method may further include transferring the charges from the capacitor node to the FD via the merge switch (e.g., closing the switch) and reading the charge in the FD. It is an advantage of embodiments of the present invention that the full-state charge (Qfw) can be linearly increased.
    Other steps may be included. Retaining the charge in a capacitor may, for example, include retaining the charge in a number of capacitors connected in parallel. Optionally or additionally, using alternating frames, the charge can alternately be transferred to a first capacitor or transferred to a second capacitor. For odd frames, for example, the charges can be transferred to a first capacitor and for even frames, the charges can be transferred to a second capacitor. The readout can follow a similar assignment and the charges from a first capacitor can be transferred to the FD by opening the first switch and the combining switch, while the charges from a second capacitor can be transferred to the FD by opening the second switch and the merge switch.
    A second aspect of embodiments of the present invention relates to a radiation sensor pixel comprising a detection element, for example an integrated detection element, for example a photodiode such as a PPD, a monolithic photodiode, while the present invention is not limited to these examples. The detection element is capable of generating charges in response to incident radiation; for example, when corpuscular radiation such as alpha or beta particles, positrons, etc. collide with it; or electromagnetic radiation such as gamma radiation, x-ray radiation, or a radiation of a wavelength range between far-infrared and ultraviolet. In specific embodiments of the second aspect of the present invention, the detection element is a photoelectric sensor that is substantially sensitive to visible radiation.
    The radiation sensor pixel further comprises a floating diffusion node (FD) connected to at least one output of the radiation sensor pixel and to at least one charge storage device. In specific embodiments of the present invention, the FD may be integrated in the substrate; it may be, for example, a surface of n + doping in a p-substrate, separated from the detection element by a substrate space, the space being covered by the transfer port. The transfer port may comprise an electrode and an insulating layer, for example an oxide layer.
    In embodiments of the present invention, a single transfer port is provided between the detection element and the floating diffusion node for controlling all charge transfer from the detection element to the floating diffusion node (FD). In particular, the single transfer port can control the transfer of defected loads to the FD. Hence, the charges can be transferred to a charge storage device, depending on the operational status of a switch between the floating diffusion node and a charge storage device. In specific embodiments of the second aspect of the present invention, the transfer port may be connected to a driver circuit which can successively bias the transfer port at at least three different bias levels, e.g. bias levels corresponding to an ON state, an ÜIT state and also at least one intermediate state. For example, if the transfer port has transistor characteristics, the intermediate voltage can be obtained by varying the voltage in the ohmic region, although the present invention is not limited thereto.
    A charge storage device is an element or circuit configuration that is capable of storing charges. It may, for example, comprise at least one capacitor, e.g. an integrated capacitor, a metal-insulator-metal, polysilicon-insulator-polysilicon, MOS, integrated capacitor, while other types are also possible. The charge storage device may also comprise a system of capacitors, for example a number of capacitors in a parallel configuration, or connected via switches. The charge storage device can be connected to the output of the radiation sensor pixel. The charge storage device may be provided with means for resetting its value, for example, it may be connected to a reset transistor.
    The output may include a readout circuit, analog-to-digital converters, etc.
    In some embodiments of the present invention, a coil port (e.g., an electronic shutter) may be connected to the detection element (e.g., connected to the PPD).
    In some embodiments of the present invention, a reset transistor is connected to the floating diffusion node FD, for depletion of charge in the FD and restart. In some embodiments, an alternative or additional reset may, if desired, be connected to the charge storage device CS for depletion of the charge independently of the storage, for example to create different saturation cycles. FIG. 7 schematically shows a configuration of a radiation sensor pixel according to an embodiment of the second aspect of the present invention. A detection element 701 is shown, for example a pegged photodiode PPD (p + n) on a lightly doped p-substrate 702, although the present invention is not limited thereto. The floating diffusion node 703 may, for example, be a highly doped n + region, while the present invention is not limited thereto, connected to an output 704, e.g., a readout circuit. Between the floating diffusion node 703 and a voltage source VDD, a reset transistor 705 can be connected for exhausting charges in the floating diffusion node 703. A transfer port 706 is adapted to control the transfer of charges from the detection element 701, e.g. the floating diffusion node 703. The transfer port 706 is controlled by a driver circuit 707, for example a selector, which is capable of sequentially biasing the transfer port 706 to an ON bias Vi, an intermediate or barrier voltage VM, and an OUT bias Vo . The driver circuit 707 may include an additional check for selection of the level of the barrier value VM, thereby enabling control of the saturation level of the radiation sensor pixel, for example during the process shown in FIG. 2 described integration period. A charge storage device, for example a capacitor 708, is connected via a switch 709, for example a transistor, to the floating diffusion node 703 for controlling the charging of the capacitor 708 and, for example, also for checking all the charges flowing together in the FD 703, e.g. during the time shown in FIG. 5 described reading phase.
    Other features may be present in a radiation sensor pixel according to embodiments of the second aspect of the present inventions. FIG. 8 shows, for example, a separate transfer port that acts as an electronic shutter 801 connected to the detection element 701, e.g., a photodiode that can empty the charges from the detection element to a drain region, e.g., 802. The electronic shutter can be, for example, a general shutter and it can improve the control of the timing of certain phases (eg the integration phase). The present invention includes other possibilities, such as connection of the electronic shutter 801 with an alternating current or signal node instead of a direct voltage.
    Alternatively or additionally to the reset switch 705 connected to the output 704, a storage reset system 803, for example a transistor, can be added to the charge storage device 708 (e.g. a capacitor), for example between the charge storage device 708 and the switch 709 for controlling the storage device 708 (and checking the merging process).
    Yet another possibility, shown in FIG. 9, shows an alternative charge storage device 901 connected to the output 704 and the floating diffusion node 703, as before. The alternative charge storage device 901 comprises a plurality of capacitors, for example, three capacitors 911, 912, 913, all connected to each other with combination switches 923, 922 between them. Although in this example the capacitors and switches are in series, the present invention is not limited thereto and other configurations (e.g. parallel connection of capacitors and switches) are also possible. The alternative charge storage device 901 is, as in other embodiments, connected via a switch 709 to the floating diffusion node 703.
    A possible sequence of gate bias and reading of the floating diffusion node is shown in FIG. 10. The schematic sensor of FIG. 7 taking into account, RESET graph 1001 shows the switching sequence of the reset transistor 705, JOIN graph 1002 shows the switching sequence of the switching transistor 709 between the floating diffusion node 703 and the charge storage device, TG graph 1003 shows the switching sequence of the transfer port 706, the graph FD 1004 shows the signal reading in the floating diffusion node 703 and the TG2 graph 1005 shows the switching sequence of an optional electronic shutter. Graph FD 1004 can be considered as the read signal.
    It can be seen that in the period to t0, which corresponds to the integration period, the reset transistor 705 is low biased, therefore, the reset switch is closed. It is assumed that before the start of operation, the floating diffusion node is reset to a high level (VDD), as can be seen from graph 1004. The pool transistor is biased to high, thereby driving the charge storage device 708 to accept charges. The transfer port 706 is biased to a VM bias that is lower than the ON signal. Charges produced by the detection element 701 in response to incident radiation can flow through the transfer port 706 to the floating diffusion node 703, and from there via the merge switch 709 to the charge storage device 708. The signal on the floating diffusion node (graph 1004) shows or overflow occurred; which is not the case in the specific illustrated embodiment. At time t0, which is the end of the integration period, the transfer gate 706 closes (TG is driven to an OFF bias voltage, e.g., a small voltage, or a 0 voltage, while the present invention is not limited by these values) and the charge storage device (JOIN 1002) does not accept charges by opening the merge switch 709 (e.g., by biasing a merge transistor to low). The integration period has ended.
    Between t0 and t1, the reset switch 705 and the combination switch 709 are off, for example by biasing the corresponding transistors to low, and the transfer port 706 is also biased to low. Charges produced by the detection element 701 are no longer transmitted to the floating diffusion node 703. The FD 1004 shows the overflow level R1 (due to the interference of the COMPOSITION switch, this level may be slightly lower than the RESET level before t0), which may are read out by means of the output circuit 704.
    Next, at tl, the transfer gate 706 is biased to an ON bias (in the case of a transistor, for example, the voltage would be the saturation characteristic of the transistor), as can be seen in the TG graph 1003, while the reset switch 705 and the reset switch 705 merge switch 709 is still OFF. The charge present in the detection element 701 is transferred from the detection element to the floating diffusion node 703.
    At time t2, after the detection element has been exhausted, the transfer port 706 is again driven to an OFF bias and the amount of charges present at the floating diffusion node 703 can be read out. The read signal S1 corresponds to the amount of charges transferred from the detection element 701 to the floating diffusion node 703 during the charge transfer period t1-t2, together with some charges already present on the floating diffusion node by overflow of the detection element. The reading S1 of the floating diffusion node can be used together with the previous reading R1 of the reset level or the overflow level to obtain a downstream CDS output.
    At t3, the combination switch 709 is closed, for example, by biasing a combination transistor at high. The charges from the charge storage device are merged with the charges present on the floating diffusion node 703 and a further reading S2 can be taken from the floating diffusion node. Both readout signals S1 and S2 result in a readout that has a higher dynamic range than the readout of the detection element alone.
    At t4, the reset switch 705 is closed, for example, by biasing a reset transistor to high, thus resetting the floating diffusion node to reset level. Optionally, the transfer port 706 can also be biased to high, whereby the detection element 701 is also reset. A new cycle integration + readout can begin.
    If an electronic shutter is present, graph TG2 1005 shows an additional control of the process during the integration and readout periods. When the TG2 is high, so 'on', it constantly removes the photo charges from the photodiode. The integration period actually only really starts when TG2 goes low, so 'off'. That is why the TG2 electronic shutter makes it possible to change the start of the integration period.
    Another possible sequence is shown in FIG. 11 is shown. This sequence refers to the schematic in FIG. 9, wherein the JOIN 1 graph 1101 refers to the state of the JOIN switch 709, the JOIN 2 graph 1102 refers to that of the second switch 922, and the JOIN 3 chart 1103 refers to that of the third switch 923.
    The integration period (to t0), the readout period of the reset or overflow level (between t0 and t1) and the charge transfer period (between t1 and t2) are the same as in the example of FIG. 10. However, during the actual signal reading period of the present example, consecutive merging of the charges stored in the three capacitors 911, 912 and 913 with the charges in the floating diffusion node 703 is performed. First, a read-out of the signal level S1 on the floating diffusion node 703 takes place between times t2 and t3, just as in the example of FIG. 10. Thereafter, at time t3, the merge switch 709 is turned on, for example, by biasing a corresponding merge transistor at high, and a signal level S2 corresponding to merged charges from the floating diffusion node and the first charge storage node 911 is read out, also like in the example of FIG. 10. At time t3 ', while the combining switch 709 remains ON, a second combining switch 922 is turned on, and then a signal level S3 is read out corresponding to the previous merged charges together with the charges previously stored on the second charge storage device 912. On time t3 ", while the combining switches 709 and 922 remain on, a third combining switch 923 is turned on, a signal level S4 is read out corresponding to the previous merged charges together with the charges previously stored on the third charge storage device 913. The integration period is shown as arrows in the lower diagram of Fig. 10. Each sequence can include a single integration period in which the gate 706 is sequentially biased on 3 levels, as explained.After the sequence ends, a new sequence and a new integration period can start.
    The present invention is not limited by the above illustrative embodiments, and additional or alternative sequences may be included (e.g., using two-step charge storage, additional reset sequences, etc.). In FIG. 12 to FIG. 15, for example, the plan view of further radiation sensor pixel configurations is shown. In the figures, active areas (e.g., photodiode, sources, drains) are patterned, while barriers (e.g., transistor ports, transfer ports, fixed barriers) are shown with a white box. FIG. 12 shows an implementation of a pixel according to embodiments of the present invention, with a detection element such as a pinned photodiode (PPD) 701, connected to an optional intermediate node 1201 via a first transfer port (TG) 706. The intermediate node 1201 is via a second TG 1202 connected to the floating diffusion (FD) 703. The capacitor node 1203 of the CS is via the transistor 709, previously presented in FIG. 7, connected to the FD 703. In the embodiment shown in FIG. 12, the capacitor node 1203 of the CS can be connected to the intermediate node 1201 via a barrier 1204 (e.g., a fixed or passive potential barrier, a transfer port, etc.). When the first TG 706 is pulsed, photo charges integrated into the detection element 701 are transferred to the intermediate 1201. If the charge exceeds the maximum capacity of the intermediate node 1201, it passes over the potential set by the barrier 1204 to the capacitor node 1203. The potential of the barrier 1204 can preferably be lower than the potential of the second TG 1202, which allows charges to overflow first from the intermediate node 1201 to the CS node 1203 instead of to the FD or to a random surrounding substrate (e.g. in integrated device), thereby reducing haze formation and other parasitic effects.
    The capacitor node 1203 can each be connected via a switch 1207,1208 to a single capacitor or to a number of (e.g. two) capacitors 1205, 1206 in parallel. A further switch 705, or "reset switch", can connect the FD to a voltage Vdd to reset the FD to a start value when required. FIG. 13 shows an alternative embodiment where photo charges in the detection element 701 can be transferred to a storage node 1201 and then to a floating diffusion node 703 via a transfer port 706 according to embodiments of the present invention. Furthermore, the capacitor node 1203 of the CS is connected to the detection element 701 via a fixed or variable barrier 1301, which may be, for example, a transistor gate, a fixed (e.g. passive potential) barrier, or any other suitable barrier. The capacitor node 1203 is further connected to parallel capacitors 1205, 1206 which are further connected to their corresponding switches 1207, 1208 and to a plurality of capacitors 1302, 1303. A pair of switches or barriers 1304, 1305 are added so that the capacitors 1205, 1206 do not overcharge, allowing the additional charges to pass and be stored in the further capacitors 1302, 1303. Other embodiments with similar configuration may include an intermediate node (such as the node 1201 shown in FIG. 12) separated from the floating diffusion 703 by a second TG. FIG. 14 and FIG. 15 shows embodiments of pixel circuits according to the present invention, comprising a pinned photo diode, and two branches, each comprising a CS. In these embodiments, each branch comprises an optional intermediate node. Photo charges from the detection element (e.g., a PPD) 701 can be stored in both branches and read in a unique FD 703 (FIG. 14), or in two FDs 1503, 703, one for each branch (FIG. 15). This parallelized topology makes 'pipeline shutter' possible, allowing photo charge of alternating frames or integration times to be stored alternatively in one branch or the other, thereby increasing readout flexibility and dynamic range. FIG. 14 shows an embodiment with two intermediate nodes 1201, 1401 which are connected to the detection element 701 via a first pair of TGs 706, 1402. Both intermediate nodes 1201, 1401 are further connected via a second pair of TG 1202, 1402 to a unique FD 703. Each capacitor node 1203, 1403 of the CS is connected to a capacitor 708, 1404 in each branch. The capacitor nodes are further connected to the detection element 701 by two potential barriers 1301, 1405 which may be one of a gate, a fixed barrier such as a passive potential barrier, etc. The capacitor nodes and the unique FD 703 are connected via two combination switches 709, 1406 of any suitable type. FIG. 15 shows the two intermediate nodes 1201,1501 which are connected to the detection element 701 via a first pair of TGs 706,1502. Both intermediate nodes 1201, 1501 are further connected to a corresponding (separate) FD 703, 1503 in each branch, via a second pair of TG 1202, 1504. This allows two readings per pixel. Each capacitor node 1203, 1505 is connected to a capacitor 708, 1506 in each branch, and to the intermediate node through two potential barriers 1204, 1507 (which may be any suitable barrier, e.g., a variable or fixed potential barrier). The capacitor nodes 1203, 1506 and FDs 703, 1503 are connected via two combination switches 709,1508 of any suitable type.
    According to embodiments of the present invention, the TG between the detection element and the FD or the intermediate node can be set to three states, and the TGs and variable barriers that act as charge ports between the charge storage and FDs, intermediate nodes or detection elements, can be on one of two states (ON or OFF, allowing or blocking the flow of charges) or on three or more states (ON, OFF and at least one further intermediate overflow state, allowing only loads over a predetermined charge threshold to flow ) be set. This can be achieved through transistors, transfer ports, direct current ports, etc.
    权利要求:
    Claims (24)
    [1]
    Conclusions
    A method for driving a radiation sensor pixel comprising a detection element capable of charge production in response to incident radiation, a floating diffusion node connected to a readout circuit, at least one transfer port between the detection element and the floating diffusion node, and a charge storage device connected to the floating diffusion node via at least one switch for controlling the current through an ON bias to allow charge current, and an OFF bias to prevent charge current between the charge storage device and the floating diffusion node, the method comprising sequentially biasing of the transfer port at at least three different bias voltages, wherein the at least three bias voltages include at least one OUT bias voltage, at least one intermediate bias voltage and an ON bias voltage to allow the charge in the sensing element to float to diffuse noop is transferred while the switch is OFF, the method further comprising causing the charge storage device to accept charges at least while biasing the transfer port to the intermediate bias voltage.
    [2]
    The method of claim 1, wherein driving the radiation sensor pixel further comprises at least one integration period during which charges are integrated on the detection element, wherein successively biasing the at least one transfer port to at least three different bias voltages biasing the transfer port on the intermediate bias during at least a part of the integration period, thus transferring to the floating diffusion node and the charge storage device a part of the integrated charges that can overflow the transfer port.
    [3]
    The method of claim 2, wherein transferring to the floating diffusion node and the charge storage device of a portion of the integrated charges comprises transferring to a intermediate node and the charge storage device a portion of the integrated charges that can overflow the transfer port, charges from the intermediate node to the floating diffusion node are further transferred.
    [4]
    The method of any preceding claim, wherein the transferring to the charge storage device of a portion of the integrated charges comprises transferring a portion of the integrated charges directly from the detection element to the charge storage device via a potential barrier or a second transfer port between the detection element and the charge storage device.
    [5]
    The method of any one of the preceding claims, further comprising merging charges stored on the charge storage device with charges present on the floating diffusion node.
    [6]
    The method of claims 2 to 5, wherein driving the radiation sensor pixel further comprises at least one readout period during which charges previously integrated on the detection element are read, wherein successively biasing the transfer port to at least three biases biasing the transfer port to ON bias, thus transferring the integrated charges to the floating diffusion node, while not allowing the charge storage device to accept charges, and then reading the charge levels in the floating diffusion node.
    [7]
    The method of claims 2-6, wherein driving the radiation sensor pixel comprises at least one readout period during which charges previously integrated on the detection element are read out, wherein successively biasing the transfer port to at least three biasing voltages the transfer port comprises the OFF bias between the integration period and the subsequent readout period.
    [8]
    The method of any of claims 6 or 7, wherein correlated double sampling is performed on the difference in charges present on the floating diffusion node before and after biasing the transfer port ON.
    [9]
    The method of any of claims 2 or 3, wherein the transfer of a portion of the integrated charges from the detection element is performed only through one transfer port.
    [10]
    The method of any one of the preceding claims, wherein an electronic shutter port is capable of resetting the charge of the detection element.
    [11]
    A radiation sensor pixel comprising: a detection element capable of charge production in response to incident radiation, a floating diffusion node connected to a readout circuit, a single transfer port between the detection element and the floating diffusion node, a charge storage device connected to the floating diffusion node via a switch, wherein the radiation sensor pixel further comprises a driver circuit adapted to sequentially bias the single transfer port at at least three different bias levels, the connections between the detection element and the floating diffusion node and between the charge storage device and the floating diffusion node being adapted to transfer charges into the detection element to the floating diffusion node while the switch is OFF.
    [12]
    The sensor pixel of claim 11, further comprising an output stage configured to generate a signal representative of the amount of electrical charge on the floating diffusion node separately, on the charge storage device separately, or on both.
    [13]
    The sensor pixel of any of claims 11 or 12, wherein the detection element comprises at least one pinned photodiode.
    [14]
    The sensor pixel of any of claims 11-13, further comprising an intermediate node between the detection element and the floating diffusion node.
    [15]
    The sensor pixel of any one of claims 11 to 14, wherein the charge storage device comprises a capacitor node connected to at least one capacitor.
    [16]
    The sensor pixel of claim 15, further comprising an overflow port between the capacitor node and the detection element or between the capacitor node and the floating diffusion node.
    [17]
    The sensor pixel of claim 16, wherein the overflow port is a fixed barrier or a transfer port that includes a driver circuit adapted for sequentially biasing the transfer port at two or three different bias levels.
    [18]
    The sensor pixel of any of claims 11-17, wherein the charge storage device comprises an integrated transistor configured to selectively open a conductive path between the charge storage device and the floating diffusion node.
    [19]
    The sensor pixel of any of claims 11-17, further comprising an intermediate node between the detection element and the floating diffusion node, and a transfer port to allow charge transfer between the intermediate node and the floating diffusion node.
    [20]
    The sensor pixel of claims 11-19, further comprising a reset transistor.
    [21]
    The sensor pixel of claim 20, wherein the reset transistor is connected to the floating diffusion node.
    [22]
    The sensor pixel of claim 20, wherein a reset transistor is connected to the charge storage device.
    [23]
    The sensor pixel of any of claims 11 to 22, further comprising a coil port connected to the detection element.
    [24]
    The sensor pixel of any one of claims 11 to 23, wherein the detection element is equipped for detection of electromagnetic radiation, particles or both.
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    优先权:
    申请号 | 申请日 | 专利标题
    US14/554,327|US9780138B2|2014-11-26|2014-11-26|Three level transfer gate|
    US14/554,327|2014-11-26|
    US201562171468P| true| 2015-06-05|2015-06-05|
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