CN110956923A - Low-temperature polycrystalline silicon flat panel detector pixel circuit and flat panel detection method - Google Patents

Low-temperature polycrystalline silicon flat panel detector pixel circuit and flat panel detection method Download PDF

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CN110956923A
CN110956923A CN201911348859.0A CN201911348859A CN110956923A CN 110956923 A CN110956923 A CN 110956923A CN 201911348859 A CN201911348859 A CN 201911348859A CN 110956923 A CN110956923 A CN 110956923A
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switch
reset switch
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flat panel
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CN110956923B (en
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解海艇
金利波
朱翀煜
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Iray Technology Co Ltd
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    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/24—Measuring radiation intensity with semiconductor detectors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/24—Measuring radiation intensity with semiconductor detectors
    • G01T1/247—Detector read-out circuitry

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Abstract

The invention provides a low-temperature polysilicon flat panel detector pixel circuit and a flat panel detection method, wherein the method comprises the following steps: the first reset switch and the transmission gate are sequentially connected in series between the reset signal and the cathode of the photosensitive diode, and the anode of the photosensitive diode is connected with a bias voltage; the second reset switch, the source electrode follower and the selection switch are sequentially connected in series between the power signal output ends; a compensation switch connected between the source and the gate of the source follower; and a storage capacitor connected between the drain of the first reset switch and the gate of the source follower; the first reset switch and the control end of the first reset switch are connected with a first control signal, and the transmission gate and the control end of the compensation switch are connected with a second control signal; the control end of the selection switch is connected with a third control signal. The invention carries out internal compensation on the threshold voltage drift of the source follower in the circuit, reduces the off-state leakage current of the first reset switch, and can realize dynamic flat-panel detection with high frame rate, high sensitivity and low dosage.

Description

Low-temperature polycrystalline silicon flat panel detector pixel circuit and flat panel detection method
Technical Field
The invention relates to the field of flat panel detection, in particular to a low-temperature polycrystalline silicon flat panel detector pixel circuit and a flat panel detection method.
Background
The flat panel detector is generally applied to a plurality of fields such as medical X-ray radiation imaging, security inspection and security protection, industrial nondestructive inspection and the like. Generally, flat panel detectors can be classified into a direct type and an indirect type. The direct flat panel detector can directly convert X-rays into electric signals and can realize direct conversion of X-ray energy, is typically represented by an amorphous selenium (a-Se) flat panel detector, combines an amorphous selenium material and a Thin Film Transistor (TFT) technology, has high spatial resolution, but needs to add high voltage on an amorphous selenium thin film, possibly causes elements to be easily burned out and lose efficacy, and has poor system stability. The indirect flat panel detector converts X-rays into visible light through a scintillator, and converts the visible light into an electrical signal through a Photodiode (PD), so as to realize indirect conversion of X-ray energy.
Flat panel detectors typically consist of millions to tens of millions of pixels. Each pixel for an indirect flat panel detector is generally composed of 1 Photodiode (PD) and several Thin Film Transistors (TFTs). For the pixel unit circuit, the circuit can be divided into a passive pixel unit sensing circuit (PPS) and an active pixel unit sensing circuit (APS). A passive pixel cell sensing circuit typically consists of 1 PD and 1 TFT (1T1D), while an active pixel cell sensing circuit typically consists of 1 PD and more than 3 TFTs. Compared with the PPS pixel circuit, the APS pixel circuit has the advantages of higher signal-to-noise ratio, higher sensitivity and the like; in addition, the APS pixel circuit generally uses high-performance and high-mobility TFTs, which have a smaller pixel size and can achieve a higher integration level. Therefore, the APS flat panel detector can meet the application requirements of low dosage, low noise, dynamic detection and the like.
For a conventional amorphous silicon flat panel detector, the field effect mobility of the amorphous silicon (a-Si) TFT adopted by the conventional amorphous silicon flat panel detector is low (about 0.5 cm)2V-1s-1) Therefore, the integrated capacity is low, and the PPS flat panel detector (1T1D) can be prepared only by general method. LTPS TFTs have very high field-effect mobilities (50-200 cm) compared to a-Si TFTs2V-1s-1) Therefore, it can realize the integration of the APS pixel circuit, but it has a disadvantage of large off-state leakage current, which may result in the loss of electrical signals generated after exposure and high noise.
Each pixel point in a typical APS pixel circuit structure includes 3 LTPS TFTs (P-type) and 1 photodiode PD; taking the P-type LTPS TFT as an example, the APS circuit is shown in fig. 1. Wherein, TRSTA reset switch for supplying a reset signal to the photodiode PD; t isSFA source follower, which amplifies the electric signal generated by exposure and generally works in a saturation region; t isSELFor selecting the switch, the signal generated after exposure and passing through TSFAn amplified electrical signal; PD is a photosensitive diode, which works in a reverse bias state; cPDIs the junction capacitance of the photodiode; vCOMIs the level at the cathode of the photodiode, here the positive level; vDDProviding a negative level for a power supply; vRSTIs a reset signal, here a negative level; vGRSTTo reset the switch TRSTA gate level signal of (a); vSELFor selecting a switch TSELThe gate level signal of (1). The timing of the APS pixel circuit is shown in FIG. 2 when 2| V is satisfiedRST-VTH|＞＞ΔVGIn the case of (3), the change value of the pixel circuit output current with or without the X-ray exposure satisfies the following relation:
ΔIOUT＝ΔID≈μP·Cox·W/L·(VRST-VTH)·ΔVG，
wherein, Delta IOUTFor varying value of output current of pixel circuit, Δ IDIs a source follower TSFDrain current variation value of (d), muPIs a source follower TSFField effect mobility of (2), CoxIs a source follower TSFW is the capacitance value of the gate insulating layer per unit area, W is the source follower TSFL is the source follower TSFChannel length of the tube, VTHIs a source follower TSFThreshold voltage of, Δ VGFor post-exposure at the source follower TSFPotential change generated by gridThe value is obtained. From the above formula, when the source follower T is usedSFThreshold voltage V ofTHWhen drifting, it will change the output current value Δ I of the pixelOUTProduce a large influence, produce a large interference signal, and possibly cause Δ IOUTAnd Δ VGThe phenomenon of nonlinear change is presented between the two detectors, and the accuracy and the reliability of the detector are influenced.
In addition, the reset switch T adopting a single gateRSTLarge leakage current in the off state, which results in the electrical signal collected by the exposed photodiode from TRSTLeaking out and causing loss of the electrical signal generated by the exposure.
Therefore, how to suppress the influence of the threshold voltage drift of the source follower on the output current variation value and reduce the leakage current when resetting the off state of the switch has become one of the problems to be solved by those skilled in the art.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a pixel circuit of a low temperature polysilicon flat panel detector and a flat panel detection method, which are used to solve the problems in the prior art that the variation value of the output current of an APS pixel unit circuit is affected by the drift of the threshold voltage of a source follower, and the electric signal loss is caused by the leakage current when the reset switch is in an off state.
To achieve the above and other related objects, the present invention provides a low temperature polysilicon flat panel detector pixel circuit, which at least comprises:
the circuit comprises a first reset switch, a storage capacitor, a transmission gate, a photosensitive diode, a second reset switch, a compensation switch, a source electrode follower and a selection switch;
the first end of the first reset switch is connected with the reset signal, the control end of the first reset switch is connected with the first control signal, and the second end of the first reset switch is connected with the first polar plate of the storage capacitor;
the first end of the transmission gate is connected with the first polar plate of the storage capacitor, the control end of the transmission gate is connected with a second control signal, the second end of the transmission gate is connected with the cathode of the photosensitive diode, and the anode of the photosensitive diode is connected with a bias voltage;
the first end of the second reset switch is connected with a power supply signal, the control end of the second reset switch is connected with the first control signal, and the second end of the second reset switch is connected with the first end of the compensation switch;
the control end of the compensation switch is connected with the second control signal, and the second end of the compensation switch is connected with the second polar plate of the storage capacitor;
the first end of the source electrode follower is connected with the second end of the second reset switch, the second end of the source electrode follower is connected with the first end of the selection switch, and the control end of the source electrode follower is connected with the second polar plate of the storage capacitor;
and the control end of the selection switch is connected with a third control signal, and the second end outputs current change values before and after exposure.
Optionally, the first reset switch is a dual gate switch.
Optionally, the first reset switch, the transmission gate, the second reset switch, the compensation switch, the source follower, and the selection switch use low temperature polysilicon thin film transistors.
More optionally, the first reset switch, the transmission gate, the second reset switch, the compensation switch, the source follower, and the selection switch employ P-type transistors.
In order to achieve the above and other related objects, the present invention further provides a flat panel detection method, using the pixel circuit of the low temperature polysilicon flat panel detector, the flat panel detection method at least includes:
a reset stage: closing the selection switch, and opening the first reset switch, the transmission gate, the second reset switch, the compensation switch and the source follower; the potential on the first polar plate of the storage capacitor is reset to a positive level, and the potential on the second polar plate is reset to a negative level; the photosensitive diode is in a reverse bias state;
and (3) compensation stage: turning off the first reset switch and the second reset switch, and turning on the transmission gate, the compensation switch, the source follower, and the selection switch; the potential on the first plate of the storage capacitor is kept, and the potential on the second plate is released and locked at the threshold voltage of the source follower;
and (3) an exposure stage: turning off the first reset switch, the second reset switch, the source follower and the selection switch, and turning on the transmission gate and the compensation switch; after exposure is completed, the potential on the first polar plate of the storage capacitor is changed;
a reading stage: closing the transmission gate and the compensation switch, and opening the first reset switch, the second reset switch, the source follower, and the selection switch; and resetting the potential on the first polar plate of the storage capacitor to zero, correspondingly jumping the potential on the second polar plate of the storage capacitor, amplifying the variable quantity by the source electrode follower and then outputting the variable quantity to obtain the current change value before and after exposure.
Optionally, the source follower operates in a saturation region during a reset phase, a compensation phase and a read phase.
Optionally, the first reset switch, the transmission gate, the second reset switch, the compensation switch, and the selection switch operate in a linear region when turned on.
More optionally, the current variation before and after the exposure is in a linear relationship with the potential variation generated by the cathode of the photodiode after the exposure.
More optionally, the current change values before and after the exposure satisfy the following relation:
ΔIOUT＝μP·Cox·W/L·(VRST0·ΔVPD+ΔVPD 2/2)≈μP·Cox·W/L·VRST0·ΔVPD，
wherein, 2VRST0＞＞|ΔVPD|，ΔIOUTThe current change before and after exposure, μPIs the field effect mobility of the source follower, CoxIs the capacitance value of the gate insulating layer per unit area of the source follower, W/L is the width-to-length ratio of the source follower, VRST0For the voltage value, Δ V, of the reset signal on the first plate of the storage capacitor during the reset phasePDFor potential generated by the cathode of the photodiode before and after exposureThe value of the change.
As described above, the pixel circuit and the flat panel detection method of the low temperature polysilicon flat panel detector of the invention have the following advantages:
1. the low-temperature polysilicon flat panel detector pixel circuit and the flat panel detection method can carry out internal compensation on the threshold voltage drift of the source follower in the circuit, and inhibit the interference of the threshold voltage drift of the source follower on the change value of the pixel output current.
2. According to the pixel circuit of the low-temperature polycrystalline silicon flat panel detector and the flat panel detection method, the first reset switch adopts a double-gate LTPS TFT (low-temperature polycrystalline silicon technology thin film transistor), so that off-state leakage current of the first reset switch can be reduced; the loss of the electric signal generated after exposure can be suppressed in conjunction with the designed operation timing.
3. The low-temperature polysilicon flat panel detector pixel circuit and the flat panel detection method adopt the low-temperature polysilicon technology to prepare the APS flat panel detector pixel circuit, and the LTPS TFT has high field effect mobility, so that the low-temperature polysilicon flat panel detector pixel circuit can realize dynamic flat panel detection with high frame rate, high sensitivity and low dose.
Drawings
Fig. 1 is a schematic diagram of an APS pixel circuit structure in the prior art.
Fig. 2 is a schematic diagram of the operation timing of the APS pixel circuit structure in the prior art.
FIG. 3 is a schematic structural diagram of a pixel circuit of a low temperature polysilicon flat panel detector according to the present invention.
FIG. 4 is a timing diagram illustrating the operation of the flat panel inspection method according to the present invention.
Fig. 5 is a schematic diagram of the flat panel detection method of the present invention in the reset phase.
FIG. 6 is a schematic diagram of the flat panel inspection method of the present invention in the compensation stage.
FIG. 7 is a schematic diagram of the flat panel inspection method of the present invention in the exposure stage.
FIG. 8 is a schematic diagram of the flat panel detection method of the present invention in the reading stage.
Description of the element reference numerals
1 APS pixel circuit structure
2 low-temperature polysilicon flat panel detector pixel circuit
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Please refer to fig. 3 to 8. It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the components related to the present invention are only shown in the drawings rather than drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.
Example one
As shown in fig. 3, the present embodiment provides a low temperature polysilicon flat panel detector pixel circuit 2, where the low temperature polysilicon flat panel detector pixel circuit 2 includes: first reset switch TRST1Storage capacitor CSTTransmission gate TXPhotodiode PD, second reset switch TRST2Compensating switch TCMPSource follower TSFAnd a selection switch TSEL。
Wherein the first reset switch TRST1Is connected to the reset signal VRSTThe control end is connected with a first control signal VGRSTThe second end is connected with the storage capacitor CSTA first plate of (a);
the transmission gate TXIs connected to the storage capacitor CSTThe control end of the first polar plate is connected with a second control signalNumber VCMPThe second end is connected with the cathode of the photosensitive diode PD, and the anode of the photosensitive diode PD is connected with a bias voltage VCOM；
The second reset switch TRST2Is connected with a power supply signal VDDThe control end is connected with the first control signal VGRSTThe second end is connected with the compensation switch TCMPA first end of (a);
the compensation switch TCMPIs connected with the second control signal VGRSTThe second end is connected with the storage capacitor CSTA second electrode plate of (1);
the source electrode follower TSFIs connected to the second reset switch TRST2A second terminal connected to the selection switch TSELA control terminal connected to the storage capacitor CSTA second electrode plate of (1);
the selection switch TSELIs connected with a third control signal VSELThe second end outputs the current change value delta I before and after exposureOUT。
It should be noted that the photodiode PD includes a junction capacitor CPDSaid junction capacitance CPDThe junction capacitor C is illustrated in fig. 3 for convenience of illustration, and is a capacitor inside the photodiode PD and is not independent from the outside of the photodiode PD in practical usePD。
Specifically, in the present embodiment, the first reset switch TRST1Is a dual gate switch, thereby reducing the first reset switch TRST1The off-state leakage current of the semiconductor device can further suppress the loss of the electric signal generated after exposure. In practical use, the first reset switch TRST1A general switch may be used without being limited to the present embodiment.
Specifically, in the present embodiment, the first reset switch TRST1The transmission gate TXThe second reset switch TRST2The compensation switch TCMPThe source follower TSFAnd the selection switch TSELThin film transistor using low temperature polysilicon。
It should be noted that the first reset switch T is providedRST1The transmission gate TXThe second reset switch TRST2The compensation switch TCMPThe source follower TSFAnd the selection switch TSELThe material of the second electrode can be set according to the requirement, including but not limited to low temperature polysilicon material, and is not limited to this embodiment.
Specifically, in the present embodiment, the first reset switch TRST1The transmission gate TXThe second reset switch TRST2The compensation switch TCMPThe source follower TSFAnd the selection switch TSELP-type transistors are adopted; when the control end receives a high level, each switch is turned off, and when the control end receives a low level, each switch is turned on. In practical use, the first reset switch TRST1The transmission gate TXThe second reset switch TRST2The compensation switch TCMPThe source follower TSFAnd the selection switch TSELAn N-type transistor may be used, but not limited to this embodiment.
Example two
As shown in fig. 4 to 8, the present embodiment provides a flat panel detection method, which is implemented based on the pixel circuit of the low temperature polysilicon flat panel detector of the first embodiment, and the flat panel detection method includes:
1) a reset stage: close the selector switch TSELOpening the first reset switch TRST1Transmission gate TXA second reset switch TRST2Compensating switch TCMPAnd source follower TSF(ii) a Storage capacitor CSTThe potential on the first polar plate is reset to a positive level, and the potential on the second polar plate is reset to a negative level; the photodiode PD is in a reverse-biased state.
Specifically, as shown in fig. 4 and 5, in the present embodiment, the third control signal VSELSet to high level, the selection switch TSELClosing; the first control signal VGRSTAnd said second control signal VCMPIs provided withAt a low level, the first reset switch TRST1The transmission gate TXThe second reset switch TRST2And the compensation switch TCMPAnd conducting. The source electrode follower TSFWorking in a saturation region; the first reset switch TRST1The transmission gate TXThe second reset switch TRST2And the compensation switch TCMPOperating in the linear region. The storage capacitor CSTIs controlled by the reset signal VRSTReset, at which time the storage capacitor CSTThe potential on the first polar plate is VRST0(positive level); and the storage capacitor CSTIs controlled by the power supply signal VDDReset, the power supply signal VDDIs at a negative level. The photodiode PD is in a reverse-biased state, and its cathode collects electrons and anode collects holes.
2) And (3) compensation stage: closing the first reset switch TRST1And the second reset switch TRST2Opening said transfer gate TXThe compensation switch TCMPThe source follower TSFAnd the selection switch TSEL(ii) a The storage capacitor CSTThe potential on the second plate is released and locked on the source follower TSFThe threshold voltage of (2).
Specifically, as shown in fig. 4 and 6, in the present embodiment, the first control signal VGRSTSet to high level, the first reset switch TRST1And the second reset switch TRST2Turning off; the second control signal VCMPAnd said third control signal VSELSet to low level, the transmission gate TXThe compensation switch TCMPAnd the selection switch TSELAnd conducting. The source electrode follower TSFWorking in a saturation region; the transmission gate TXThe compensation switch TCMPAnd the selection switch TSELOperating in the linear region. At this time, the storage capacitor CSTIs maintained at a potential of V on the first plate (point A)RST0(positive level); and the storage capacitor CSTGradually releases the potential on the second plate (point B) to the source follower TSFThreshold voltage V ofTH. The source electrode follower TSFDiode-connected, so that at the beginning of the compensation phase, the source follower TSFOperating in saturation region and then gradually releasing the storage capacitor CSTPotential on the second plate (point B); when the storage capacitor CSTTo the source follower TSFThreshold voltage V ofTHWhile, the source follower TSFOff, the storage capacitor CSTIs locked at a potential V on the second polar plate (point B)TH。
3) And (3) an exposure stage: turning off the first reset switch, the second reset switch, the source follower and the selection switch, and turning on the transmission gate and the compensation switch; and after the exposure is finished, the potential on the first plate of the storage capacitor is changed.
Specifically, as shown in fig. 4 and 7, in the present embodiment, the first control signal VGRSTAnd said third control signal VSELSet to high level, the first reset switch TRST1The second reset switch TRST2And the selection switch TSELTurning off; the second control signal VCMPSet to low level, the transmission gate TXAnd the compensation switch TCMPConducting; the source electrode follower TSFAnd (6) turning off. The transmission gate TXAnd the compensation switch TCMPOperating in the linear region. Before exposure, the storage capacitor CSTIs maintained at a potential of V on the first plate (point A)RST0(positive level); after exposure, the cathode of the photodiode PD collects electrons, the storage capacitor CSTThe first polar plate (point A) generates potential change △ VPD(ii) a Thus, the storage capacitor CSTThe first polar plate (point A) has a potential drop of VRST0+△VPDAnd said storage capacitor CSTIs kept constant and remains the source follower TSFThreshold voltage V ofTH。
4) A reading stage: closing the transmission gate TXAnd the compensation switch TCMPOpening the first reset switch TRST1The second reset switch TRST2The source follower TSFAnd the selection switch TSEL(ii) a The storage capacitor CSTThe potential on the first polar plate is reset to zero, and the storage capacitor CSTThe potential on the second plate jumps correspondingly, the variation quantity is through the source electrode follower TSFAmplified and output to obtain the current change value delta I before and after exposureOUT。
Specifically, as shown in fig. 4 and 8, in the present embodiment, the second control signal VCMPSet to high level, the transmission gate TXThe compensation switch TCMPTurning off; the first control signal VGRSTAnd said third control signal VSELSet to low level, the first reset switch TRST1The second reset switch TRST2And the selection switch TSELConducting; the source electrode follower TSFWorking in a saturation region; the first reset switch TRST1The second reset switch TRST2And the selection switch TSELOperating in the linear region. The storage capacitor CSTIs controlled by the reset signal VRSTReset to 0, at which time the storage capacitor CSTFrom the first plate of (2) to potential from VRST0+△VPDThe abrupt change is 0, the storage capacitor CSTFrom point B to point VTHMutation to VTH-(VRST0+△VPD)。
At this time, we calculate the variation of the output current with or without X-ray exposure, and then know the variation and the source follower TSFThreshold voltage V ofTHThere is no relation. In particular, in the case of no X-ray exposure, during the reading phase, the source follower TSFThe drain output current of (a) satisfies the following relation:
Figure BDA0002334144420000081
wherein, muPIs the field effect mobility of the source follower, CoxIs the capacitance value of the gate insulating layer per unit area of the source follower, W/L is the width-to-length ratio of the source follower, VGSIs the gate-source voltage, V, of the source followerTHIs the threshold voltage of the source follower, VRST0The voltage value of the reset signal on the first plate of the storage capacitor in the reset phase is shown. In the case of X-ray exposure, the source follower T is in the read phaseSFThe drain output current of (a) satisfies the following relation:
Figure BDA0002334144420000082
wherein, Delta IDIs the drain current variation value of the source follower, Δ VPDIs the potential variation value of the point A in the pixel circuit after exposure. Then there is X-ray exposure, and during the reading phase, the source follower TSFThe drain output current variation value satisfies the following relation:
ΔIOUT＝μP·Cox·W/L·(VRST0·ΔVPD+ΔVPD 2/2)
when in use
Figure BDA0002334144420000083
I.e. 2VRST0＞＞|ΔVPDIf there is X-ray exposure, in the reading stage, the source follower TSFThe drain output current variation value satisfies the following relation:
ΔIOUT＝ΔID≈μP·Cox·W/L·VRST0·ΔVPD
as can be seen from the above formula, the following formula satisfies 2VRST0＞＞|ΔVPDUnder the condition of |, the change value delta I of the output currentOUTAnd the potential change DeltaV generated after the cathode of the photosensitive diode is exposedPDLinear relationship, Δ IOUTFree from source follower threshold voltage driftThe function of internally compensating for the threshold voltage drift of the source follower can be realized.
In summary, the present invention provides a pixel circuit of a low temperature polysilicon flat panel detector and a flat panel detection method, including: the circuit comprises a first reset switch, a storage capacitor, a transmission gate, a photosensitive diode, a second reset switch, a compensation switch, a source electrode follower and a selection switch; the first end of the first reset switch is connected with the reset signal, the control end of the first reset switch is connected with the first control signal, and the second end of the first reset switch is connected with the first polar plate of the storage capacitor; the first end of the transmission gate is connected with the first polar plate of the storage capacitor, the control end of the transmission gate is connected with a second control signal, the second end of the transmission gate is connected with the cathode of the photosensitive diode, and the anode of the photosensitive diode is connected with a bias voltage; the first end of the second reset switch is connected with a power supply signal, the control end of the second reset switch is connected with the first control signal, and the second end of the second reset switch is connected with the first end of the compensation switch; the control end of the compensation switch is connected with the second control signal, and the second end of the compensation switch is connected with the second polar plate of the storage capacitor; the first end of the source electrode follower is connected with the second end of the second reset switch, the second end of the source electrode follower is connected with the first end of the selection switch, and the control end of the source electrode follower is connected with the second polar plate of the storage capacitor; and the control end of the selection switch is connected with a third control signal, and the second end outputs current change values before and after exposure. The low-temperature polysilicon flat panel detector pixel circuit and the flat panel detection method can carry out internal compensation on the threshold voltage drift of the source follower in the circuit, and inhibit the interference of the threshold voltage drift of the source follower on the change value of the pixel output current; the first reset switch adopts a double-gate LTPS TFT (low-temperature polysilicon technology thin film transistor), so that off-state leakage current of the first reset switch can be reduced; the loss of the electric signal generated after exposure can be inhibited by combining the designed working time sequence; the APS flat panel detector pixel circuit is prepared by adopting a low-temperature polysilicon technology, and the LTPS TFT has high field effect mobility, so that the low-temperature polysilicon flat panel detector pixel circuit can realize high-frame-rate and high-sensitivity dynamic flat panel detection. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Claims (9)

1. A low temperature polysilicon flat panel detector pixel circuit, comprising at least:
the circuit comprises a first reset switch, a storage capacitor, a transmission gate, a photosensitive diode, a second reset switch, a compensation switch, a source electrode follower and a selection switch;
the first end of the first reset switch is connected with a reset signal, the control end of the first reset switch is connected with a first control signal, and the second end of the first reset switch is connected with the first polar plate of the storage capacitor;
the first end of the transmission gate is connected with the first polar plate of the storage capacitor, the control end of the transmission gate is connected with a second control signal, the second end of the transmission gate is connected with the cathode of the photosensitive diode, and the anode of the photosensitive diode is connected with a bias voltage;
the first end of the second reset switch is connected with a power supply signal, the control end of the second reset switch is connected with the first control signal, and the second end of the second reset switch is connected with the first end of the compensation switch;
the control end of the compensation switch is connected with the second control signal, and the second end of the compensation switch is connected with the second polar plate of the storage capacitor;
the first end of the source electrode follower is connected with the second end of the second reset switch, the second end of the source electrode follower is connected with the first end of the selection switch, and the control end of the source electrode follower is connected with the second polar plate of the storage capacitor;
and the control end of the selection switch is connected with a third control signal, and the second end outputs current change values before and after exposure.
2. The low temperature polysilicon flat panel detector pixel circuit of claim 1, wherein: the first reset switch is a dual gate switch.
3. The low temperature polysilicon flat panel detector pixel circuit of claim 1, wherein: the first reset switch, the transmission gate, the second reset switch, the compensation switch, the source follower and the selection switch are low-temperature polysilicon thin film transistors.
4. The pixel circuit of the low-temperature polysilicon flat panel detector according to any one of claims 1 to 3, wherein: the first reset switch, the transmission gate, the second reset switch, the compensation switch, the source follower and the selection switch are P-type transistors.
5. A flat panel detection method using the pixel circuit of the low temperature polysilicon flat panel detector according to any one of claims 1 to 4, wherein the flat panel detection method at least comprises:
a reset stage: closing the selection switch, and opening the first reset switch, the transmission gate, the second reset switch, the compensation switch and the source follower; the potential on the first polar plate of the storage capacitor is reset to a positive level, and the potential on the second polar plate is reset to a negative level; the photosensitive diode is in a reverse bias state;
and (3) compensation stage: turning off the first reset switch and the second reset switch, and turning on the transmission gate, the compensation switch, the source follower, and the selection switch; the potential on the first plate of the storage capacitor is kept, and the potential on the second plate is released and locked at the threshold voltage of the source follower;
and (3) an exposure stage: turning off the first reset switch, the second reset switch, the source follower and the selection switch, and turning on the transmission gate and the compensation switch; after exposure is completed, the potential on the first polar plate of the storage capacitor is changed;
a reading stage: closing the transmission gate and the compensation switch, and opening the first reset switch, the second reset switch, the source follower, and the selection switch; and resetting the potential on the first polar plate of the storage capacitor to zero, correspondingly jumping the potential on the second polar plate of the storage capacitor, amplifying the variable quantity by the source electrode follower and then outputting the variable quantity to obtain the current change value before and after exposure.
6. The flat panel detection method according to claim 5, characterized in that: in a reset phase, a compensation phase and a reading phase, the source follower works in a saturation region.
7. The flat panel detection method according to claim 5, characterized in that: the first reset switch, the transmission gate, the second reset switch, the compensation switch and the selection switch work in a linear region when being conducted.
8. The flat panel detection method according to any one of claims 5 to 7, characterized in that: the current change value before and after exposure and the potential change value generated by the cathode of the photosensitive diode after exposure are in a linear relation.
9. The flat panel detection method according to claim 8, characterized in that: the current change values before and after exposure satisfy the following relational expression:
ΔIOUT＝μP·Cox·W/L·(VRST0·ΔVPD+ΔVPD 2/2)≈μP·Cox·W/L·VRST0·ΔVPD，
wherein, 2VRST0＞＞|ΔVPD|，ΔIOUTThe current change before and after exposure, μPIs the field effect mobility of the source follower, CoxIs the capacitance value of the gate insulating layer per unit area of the source follower, W/L is the width-to-length ratio of the source follower, VRST0Resetting the first plate of the storage capacitor for a reset phaseVoltage value of signal, Δ VPDThe potential change value generated by the cathode of the photosensitive diode before and after exposure is obtained.
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