CN201852941U - Radiation detector and imaging device and electrode structure thereof - Google Patents
Radiation detector and imaging device and electrode structure thereof Download PDFInfo
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- CN201852941U CN201852941U CN2010205369857U CN201020536985U CN201852941U CN 201852941 U CN201852941 U CN 201852941U CN 2010205369857 U CN2010205369857 U CN 2010205369857U CN 201020536985 U CN201020536985 U CN 201020536985U CN 201852941 U CN201852941 U CN 201852941U
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Abstract
The application discloses a radiation detector and an imaging device and an electrode structure thereof. The radiation detector comprises a radiation-sensitive thin film, a top electrode positioned on the radiation-sensitive thin film and an array of pixel units, which is electrically coupled with the radiation-sensitive thin film, wherein each pixel unit comprises a pixel electrode, a storage capacitor, a reset transistor, a buffer transistor, a column gating transistor and a line gating transistor, wherein the pixel electrode is used for collecting charge signals in one pixel region of the radiation-sensitive thin film; the storage capacitor is used for storing the charge signals collected by the pixel electrode; the reset transistor is used for emptying charges in the storage capacitor; the buffer transistor is used for converting the charge signals on the pixel electrode to voltage signals and transmitting the voltage signals onto a signal wire; and the column gating transistor and the line gating transistor are connected between the buffer transistor and the signal wire in series, and used for transmitting the voltage signals of the corresponding pixel unit by responding to a column gating signal and a line gating signal. The radiation detector can be used for X-ray digital imaging and the like.
Description
Technical field
The utility model relates to radiation detector and imaging device and electrode structure, relates to for example X ray digitized video flat panel detector and imaging device particularly.
Background technology
In the past, people utilize radiosensitive flash layer to convert ray to light signal, use the television camera receiving optical signals, and show through display screen, thus the real time imagery when realizing the x radiation x perspective.Along with the development of technology, the appearance of CCD makes this real time imagery mode optimize more.CCD has very superior performance on stability, integrated level, consistance and high speed acquisition.But because the radiation hardness damage problem of CCD itself, this real time imagery mode has an inevitable shortcoming, that is the device that needs the radiation-sensitive films or the transmission light path of adequate thickness, conversion, transmitting device commonly used have image amplifier, lens, optical fiber etc., these conversions, transmitting device are positioned at the CCD front in workflow, factors such as inconsistent, the noise of being introduced make many advantages of CCD to display fully, also increase simultaneously the complexity of imaging system, reduced the reliability of system.
Since 20th century the nineties, how the technician who is engaged in the radiant image field begins to be conceived to study on radiation imaging detector the advantages such as simplification of high speed, high image quality, high integration, high reliability, large tracts of land and operation, develops thus large-area digitized video flat panel detector.
The product of digitized video flat panel detector can be realized the large tracts of land of thousands of square centimeters of levels, the reading speed of tens micron-sized spatial discriminations and per second frames up to a hundred at present.
First kind of known technology of digitized video flat panel detector is to adopt the amorphous silicon diode to combine with TFT.The amorphous silicon diode absorbs ray, produces electron hole pair, and the charged particle of certain polarity floats on the TFT pel array under electric field action, and the switch scanning by TFT reads each picture element signal successively.
The ionization energy of amorphous silicon very low (about 5eV) can produce a large amount of electron hole pairs under radiation exposure, can still obtain good signal to noise ratio (S/N ratio) under low dosage.
Yet, the atomic number of silicon very little (Z=14), to the blocking capability of ray very a little less than, need very thick silicon layer ray effectively could be stopped, this makes that this method is difficult for realizing on technology, and cost is very high.
Second kind of known technology of digitized video flat panel detector is to combine with TFT with the amorphous selenium film.Amorphous selenium absorbs ray, produces electron hole pair, and the charged particle of certain polarity floats on the TFT pel array under electric field action, and the switch scanning by TFT reads each picture element signal successively.
The atomic number of selenium is 34, and amorphous selenium is stronger to the relative amorphous silicon of blocking capability of ray, but still only is adapted to survey 50KeV with interior ray, and this main application fields that has limited amorphous selenium flat-bed detector is low-yield field (as a breast imaging).
The ionization energy of amorphous selenium with adding field intensity and the ray energy of incident change and change, in medical diagnosis field intensity and ray energy zone commonly used, its ionization energy is about 50eV, has limited the lowest dose level of ray and the signal amplitude of output thus.
In addition, the amorphous selenium temperature stability is poor, and easily deliquescence and crystallization are not so good as the flat panel detector of other structures serviceable life.
The third known technology of digitized video flat panel detector is to adopt scintillator to combine with photodiode and TFT.Scintillator converts ray to light signal, and the photodiode receiving optical signals is converted to electric signal, and the switch scanning by TFT reads each picture element signal successively again.
Scintillator can absorb ray energy and launch the optical photon of certain wavelength coverage, and the photon number of launching is directly proportional with the energy of absorption.The atomic number of scintillator material is generally than higher, and is stronger to ray absorption capacity.Scintillator can be fluorescence membrane material (such as some rare earth material) or scintillation crystal (such as cesium iodide, cadmium tungstate etc.).
The atomic number of cesium iodide crystal is all bigger than amorphous silicon and amorphous selenium, ray is had well stop, receptivity; The cesium iodide crystal emission spectrum peak position of thallium of mixing simultaneously is 565nm, and identical substantially with the absorption spectrum peak position of amorphous silicon photodiodes, both being combined in the same kind product has the highest quantum efficiency.These advantages make that modal in the present digitized video flat panel detector all is the structure that is combined with silicon photoelectric diode and TFT by cesium iodide crystal.
When scintillator is the homogeneous film material, in order to increase detectable energy range and detection efficiency, need to increase the thickness of film, and along with the increase of film thickness, the scattering of optical photon can increase to the influence of detector spatial resolution.When scintillator is cesium iodide crystal, can be by with crystal growth being high density needle-like array (needle tubing of 10-20 μ m size), to suppress the scattering of photon.
Yet along with the increase of cesium iodide film thickness, the needle tubing depth-to-width ratio increases, and the collection efficiency of photon can reduce greatly in the pipe, thereby has reduced the quantum efficiency of detector.Simultaneously because the size matching problem between needle tubing and the photodiode, the shared ratio regular meeting in such detector dead band is bigger than normal.
The energy that optical photon of every generation need about 20-50eV in the scintillator, consider the quantum efficiency of photodiode again to visible light wave range, the a pair of electron hole pair of the every generation of the detector of this structure need about 100eV even more energy, and this performance has determined to adopt scintillator can obtain relatively poor signal to noise ratio (S/N ratio) as radiation-sensitive films.
The 4th kind of known technology of digitized video flat panel detector is to adopt scintillator to combine with CMOS.Scintillator can be directly overlayed on the CMOS, also can large-area scintillator be combined with the CMOS of small size by the different optical fiber of two ends diameter.
Adopt CMOS technology to replace traditional silicon technology, can improve the integrated level of system greatly, the spatial resolution of detector, dutycycle, picking rate etc. all improve a lot, each pixel cell is all integrated independently electric charge-voltage conversion circuit and amplifying circuit can obtain better signal to noise ratio (S/N ratio).
Yet, being subjected to the restriction of CMOS technology, such flat panel detector is difficult for lower
Cost under obtain big sensitive area, but in the small size field of detecting, such as dentistry CT, toy CT etc., its advantage is very tangible.
In sum, in the digitized video flat panel detector of prior art, consider factors such as dynamic range (detectable energy range), detection efficiency, signal to noise ratio (S/N ratio), spatial discrimination, main ray conversion regime is to use the caesium iodide scintillator of high density needle-like, ray is converted to optical photon earlier, by photodiode optical photon is converted to electric signal again.
Electric signal read that main employing TFT reads or CMOS reads, factors such as area according to actual needs, spatial resolution, picking rate, integrated level, cost are selected one of TFT and CMOS.
The utility model content
The utility model proposes a kind of digitized video flat panel detector and imaging device of simple in structure, high-quantum efficiency, wherein needn't use scintillator and electrooptical device.
According to one side of the present utility model, a kind of radiation detector is provided, comprise radiation-sensitive films, be positioned on the radiation-sensitive films top electrodes and with the array of the pixel cell of radiation-sensitive films electric coupling, wherein each pixel cell comprises; Pixel electrode is used for collecting the charge signal of a pixel region of radiation-sensitive films; Storage capacitors is connected with pixel electrode, is used to store the collected charge signal of pixel electrode; Reset transistor is connected with pixel electrode, is used for emptying the electric charge of storage capacitors; Buffer transistor is connected with pixel electrode, is used for the charge signal on the pixel electrode is converted to voltage signal and is sent to signal wire; Transistor is led in column selection, is used to select the pixel electrode of predetermined column; And row gate transistor, be used to select the pixel electrode of predetermined row, wherein, logical transistor of column selection and row gate transistor are connected in series between buffer transistor and the signal wire, and response column selection messenger and row gating signal transmit the voltage signal of corresponding pixel cell.
Preferably, in radiation detector, radiation-sensitive films is a patterning, comprise and the corresponding pixel region of each pixel electrode, and pixel region is electrically insulated from each other.
Preferably, in radiation detector, reset transistor responds reset signal and pixel electrode is connected on the fixing original levels.
Preferably, in radiation detector, the grid of buffer transistor is connected with pixel electrode, and drain electrode is connected with the bias level of fixing, and source electrode is connected with the logical transistor of column selection.
Preferably, in radiation detector, radiation detector is made of the monolithic cmos integrated circuit that is integrated with radiation-sensitive films.
Preferably, in radiation detector, radiation detector is made of the monolithic TFT integrated circuit that is integrated with radiation-sensitive films.
Preferably, in radiation detector, radiation-sensitive films and pixel electrode are positioned on the one side of circuit board, at least a portion of storage capacitors, reset transistor, buffer transistor, the logical transistor of column selection and row gate transistor is integrated in the integrated circuit, and integrated circuit is installed on the another side of circuit board.
Preferably, radiation detector also comprises the latticed guiding electrode around at least one pixel electrode, and wherein pixel electrode is electrically insulated from each other with the guiding electrode.
According to another aspect of the present utility model, a kind of digital imaging apparatus is provided, comprising: radiation source produces radiation; Aforesaid radiation detector, the radiation dose behind the testee is passed in detection; Data-acquisition system, the analog signal conversion that radiation detector is exported becomes digital signal; Image processor processes digital signals into image.
Preferably, digital imaging apparatus also comprises collimating apparatus, and wherein radiation source, collimating apparatus and detector move with respect to testee, thereby testee is carried out linear sweep.
Preferably, in digital imaging apparatus, described radiation source, collimating apparatus and detector synchronously move along the direction of scanning.
According to another aspect of the present utility model, a kind of electrode structure that is used for radiation detector is provided, comprising: pixel electrode; And latticed guiding electrode, around at least one pixel electrode, and pixel electrode is electrically insulated from each other with the electrode that leads.Preferably, electrode structure is positioned on the one side of integrated circuit or circuit board.
Preferably, in electrode structure, the current potential of guiding electrode is identical with the current potential of pixel electrode.
Preferably, in electrode structure, the current potential of guiding electrode is different with the current potential of pixel electrode.
Preferably, in electrode structure, when the charge signal that produces in pixel region was produced by the hole, the current potential of guiding electrode was lower than pixel electrode.
Preferably, in electrode structure, when the charge signal that produces in pixel region was produced by the hole, the current potential of guiding electrode was higher than pixel electrode.
Detector that the utility model proposes and imaging device thereof are guaranteeing detection efficiency, are surveying under the prerequisite of energy range, signal to noise ratio (S/N ratio) and spatial resolution on the one hand, utilize radiation-sensitive films (as the mercuric iodixde film) directly ray to be converted to electric signal, removed ray has been converted to optical photon is converted into electric signal again by optical photon step, simplified the structure of detector, reduce the loss of pilot process useful signal, improved the quantum efficiency of detector.And, there is not the sunset glow problem of scintillator, detector is responsive more to the variation meeting of irradiation dose, and sweep velocity can further improve.
On the other hand, by comprising the pixel cell of four transistors (4T), realize collection, output and the data processing of electric signal, and can be implemented as TFT pel array, cmos pixel array, circuit board and signal processing IC.The integrated level that this has improved system makes it more superior on performance index, adapts to more with practical application area.
Because 4T pixel cell direct voltage output signal can reduce the interference of external circuit to simulating signal, improve the signal to noise ratio (S/N ratio) of system, reduce the complexity of follow-up ASIC design simultaneously, improve the reliability of equipment.
Utilization comprises the cmos pixel array or the TFT pel array of 4T pixel cell, improves the integrated level of system, to satisfy the more requirement of high-space resolution in the zonule.
Utilization comprises the signal processing IC of 4T pixel cell, form pel array with circuit board, the pixel electrode in a certain zone is caused a signal processing IC collect electric signal and handle, can reduce the design scale of signal processing IC, farthest reduce cost.
The latticed guiding electrode of certain structure is set between the pixel or between the pixel region and pel array periphery, can collects the detector surface leakage current, reduce the noise of detector.Simultaneously, feasible guiding electrode potential is slightly different with the pixel electrode current potential, and (the guiding electrode potential is a little less than pixel electrode when collecting electronics, the guiding electrode potential is a little more than pixel electrode when collecting the hole), there is weak electric field between guiding electrode and the pixel electrode, can effectively prevent electric charge accumulation, improve the charge-trapping rate, reduce the dead band of detector, alleviate the polarization effect of detector.Further optimized the performance of detector.
Description of drawings
Fig. 1 a to 1c shows the schematic structure according to three kinds of digitized video flat panel detectors of prior art respectively.
Fig. 2 a to 2b shows the schematic structure according to two kinds of digital imaging apparatus of prior art respectively.
Fig. 3 a to 3b shows the more detailed structure according to the digitized video flat panel detector of prior art.
Fig. 4 shows the TFT pel array according to the digitized video flat panel detector of prior art.
Fig. 5 shows the pel array according to digitized video flat panel detector of the present utility model.
Fig. 6 shows the vertical view according to the pixel electrode in the digitized video flat panel detector of prior art.
Fig. 7 shows the vertical view according to the pixel electrode in the digitized video flat panel detector of the present utility model.
Fig. 8 a and 8b show the sectional view according to the pixel electrode in the digitized video flat panel detector of the present utility model respectively.
Fig. 9 a and 9b show the sectional view according to the pixel electrode in the digitized video flat panel detector of the present utility model respectively.
Embodiment
Following with reference to accompanying drawing, the utility model is described in further detail, embodiment of the present utility model has been shown in the accompanying drawing.But the utility model can adopt multiple different form specific implementation, and should not be considered as the embodiment that the utility model only limits in this proposition.
Fig. 1 a to 1c shows three kinds of digitized video flat panel detectors according to prior art respectively.Mercuric iodixde (HgI
2) film 1 is continuous films or is patterned to and the corresponding discrete pixel region of pixel electrode, utilizes the electrod-array of cmos pixel array 2, TFT pel array 3 and circuit board (PCB) 6 that the pixel cell of digitized video is provided respectively.The picture element signal that obtains by detector is sent to image processor 9 (for example computing machine) via cable 8, forms digitized video, and shows on display.
As shown in Figure 1a, mercuric iodixde film 1 is positioned at cmos pixel array 2 tops, for example directly forms at the top of cmos pixel array 2 by evaporation, as the part of integrated circuit.The visit that utilizes cmos pixel array 2 to realize to each pixel region in the mercuric iodixde film 1.
Shown in Fig. 1 b, mercuric iodixde film 1 is positioned at TFT pel array 3 tops, for example directly forms at the top of TFT pel array 3 by evaporation, as the part of integrated circuit.Via electrode 4 and 5 visits that realize each pixel region in the mercuric iodixde film 1.
Shown in Fig. 1 c, mercuric iodixde film 1 is positioned at the one side of circuit board 6, provides signal processing IC 7 at the another side of circuit board, is connected mercuric iodixde film 1 and signal processing IC 7 with via hole via the wiring on the circuit board.Further, signal processing IC 7 is connected to image processor 9.Utilize the electrod-array (not shown) that forms on the circuit board to realize visit to each pixel region in the mercuric iodixde film 1.
The atomic number of mercuric iodixde is than cesium iodide height, and density is bigger than cesium iodide, and is stronger to the blocking capability of ray, and the radiation-sensitive films that is used as ray can obtain higher detection efficiency.Under the same radiation-sensitive films thickness, the ray energy that the mercuric iodixde detector can detect also higher (dynamic range headroom).Simultaneously because its atomic number height, the photon in the 500KeV scope and the interaction of mercuric iodixde are mainly photoelectric effect, the ratio that Compton scattering takes place is very little, under certain electric field action, so in the Duan migration distance, the lateral excursion of charge carrier can be ignored, and the positional information of ray and matter interaction can obtain more accurate measurement.
Because mercuric iodixde is a semiconductor material, its ionization energy and amorphous silicon the same order of magnitude (＜10eV), it obtains the required ray energy of electron hole pair much smaller than cesium iodide or amorphous selenium, under same energy/rays with doses irradiation, electron hole pair quantity that produces and amorphous silicon are at the same order of magnitude, far more than cesium iodide or amorphous selenium.The mercuric iodixde energy gap is about 2 times of silicon, and resistivity can reach 10 simultaneously
14Ω .cm, so the leakage current under its room temperature is very little, noiseproof feature is much better than silicon photo diode, therefore adopts mercuric iodixde can obtain better signal to noise ratio (S/N ratio) as radiation-sensitive films, can measure more low-energy ray (dynamic range lower limit).
The inventor recognizes, under identical irradiation dose, adopts mercuric iodixde can obtain more excellent picture quality as radiation-sensitive films.
Can adopt methods such as physical vacuum vapour deposition, sputter, spraying, hot pressing, silk-screen, on pel array, cover the mercuric iodixde film.
Yet,, can use lead iodide (PbI according to practical application area (for example ray energy, detection efficiency, technological requirement etc.)
2), tellurium zinc cadmium (CdZnTe), cadmium telluride (CdTe), gallium arsenide (GaAs), thallium bromide (T1Br), indium phosphide (InP), cadmium selenide (CdSe), cadmium sulfide (CdS), indium arsenide (InAs), vulcanized lead (PbS), indium antimonide (InSb), lead telluride (PbTe), mercury selenide (HgSe) wait other semiconductor materials to replace mercuric iodixde.
In addition, just as known in the art, factors such as area according to actual needs, spatial resolution, picking rate, integrated level, cost are selected one of TFT and CMOS.For example, in small size imaging field (dentistry), CMOS is most preferred.
In addition, under less demanding situation, even can replace tft array with circuit board (PCB) to spatial resolution.
Schematic structure according to the digital imaging apparatus of the planar imaging of prior art has been shown in Fig. 2 a.Pass testee 300 from the radiation of radiation source 200, arrive detector 100 then.Detector 100 comprises the pel array of two dimension, and this can be the pel array of the two dimension of an integral body, also can be spliced by the pel array of a plurality of one dimensions or two dimension.Each picture element signal is relevant with the radiation dose of pixel region, obtains system (DAQ) 400 through subsequent data then and converts digital signal to, is sent to image processor 900.
The digital imaging apparatus that utilizes the linear sweep imaging has been shown in Fig. 2 b.Be shaped as the radiation beam of wire from the radiation of point-like radiation source 200 via collimating apparatus 201, pass testee 300 then, arrive detector 100, obtain system (DAQ) 400 through subsequent data then and convert digital signal to, be sent to image processor 900.
Different with the digital imaging apparatus shown in Fig. 2 a, digital imagery among Fig. 2 b utilizes testee 300 relatively moving with respect to radiation source 200, collimating apparatus 201 and detector 100, testee 300 is carried out linear sweep, to be formed on the digital picture of the two dimension of expanding on the direction of scanning.
For example radiation source 200, collimating apparatus 201 and detector 100 synchronously move along the direction of scanning, and testee 300 is fixing.Alternatively, radiation source 200, collimating apparatus 201 and detector 100 are all fixing, and only testee 300 moves along the direction of scanning.
As a result, this digital imaging apparatus can utilize the testee 300 of 100 pairs of large-sizes of detector of reduced size to carry out planar imaging, thereby has reduced the manufacturing cost of digital imaging apparatus.
Referring to Fig. 3 a; detector 100 comprises pel array 110, is positioned at the mercuric iodixde film 101 of pel array 110 tops, the protective seam 112 that is positioned at top electrodes 111, encirclement mercuric iodixde film 101 and top electrodes 111 on the mercuric iodixde film 101 and the shell 113 that surrounds protective seam.Pel array 110 can be tft array, CMOS array or circuit board.
Radiation can be passed shell 113, protective seam 112 and top electrodes 111 and be arrived mercuric iodixde film 101.The interaction of radiation and mercuric iodixde film produces electron hole pair, drifts about to pel array 110 and top electrodes 111 respectively under electric field action, and is directly collected by electrode, is handled by signal processing circuit.
In the modification of the detector shown in Fig. 3 b 100; further comprise at first intermediate protective layer 114 between mercuric iodixde film 101 and the pel array 110 and second intermediate protective layer 115 between mercuric iodixde film 101 and top electrodes 111, to realize the long-time stability of detector.First intermediate protective layer 114, second intermediate protective layer 115 are formed by dielectric, can be identical or different with the material of aforesaid protective seam 112.
For the detector 100 shown in Fig. 3 a and Fig. 3 b, preferably, by periodically (for example between every frame or every multiframe signal) pixel region is applied reversed electric field, in and the residual charge in the mercuric iodixde film 101, make that detector 100 can work steady in a long-term.
Fig. 4 shows the TFT pel array according to the sensor element in the digitized video flat panel detector of prior art.Each pixel cell is made up of a pixel electrode 311, a transistor Q10 and a storage capacitors C1.The drain electrode of transistor Q10 links to each other with pixel electrode 311, and pixel electrode 311 is via storage capacitors C1 ground connection.
Storage capacitors C1 is used for store charge.When transistor Q10 by the time, the Charge Storage of collecting via pixel electrode 311 is in storage capacitors C1.When transistor Q10 conducting, can read the charge signal Signal among the storage capacitors Cl.
The grid of transistor Q1 is connected to outside control signal V
Gate, and source electrode is connected to and reads circuit (for example integrating amplification circuit).Control signal V
GateCan provide by programmable logic chip, realize relevant logic control in the following way:
A) when transistor Q10 ends, pixel electrode 311 is collected charge signals, is accumulated on the storage capacitors C1;
B) reach predetermined integral time after, apply gating signal V to the first row pixel cell
Gate, the first rowed transistor Q10 conducting, the storage capacitors C1 discharge of first each unit of row, thereby reading electric charges signal;
C) repeating step b), at other row, by the charge signal of collecting on the row read pixel electrode.
D) after all row read and finish, can obtain a two field picture through data processing.
Usually inconsistent owing to respectively being listed as integral time in first two field picture, first frame image data is given up, and each two field picture is valid data later on.
Fig. 5 shows the pel array according to the sensor element in the digitized video flat panel detector of the present utility model.Each pixel cell comprises pixel electrode 311, four transistors (Q21, Q22, Q23, Q24) and storage capacitors C1.
A pixel region electric coupling of pixel electrode 311 and mercuric iodixde film is used to collect charge signal.As mentioned above, the mercuric iodixde film is as radiation-sensitive films, and the deposition ray energy produces charge signal through raying the time, is collected by pixel electrode 311 then.
Storage capacitors C1 is used for store charge.When electric charge accumulated on storage capacitors C1, the current potential of pixel electrode 311 can change.The variable quantity of current potential is directly proportional with the quantity of electric charge of accumulative total, promptly is directly proportional with the ray energy that deposits in the pixel region.
Transistor Q21 is used to reset, its grid and reseting controling signal (V
Reset) link to each other.When transistor Q21 conducting, the electric charge that storage capacitors C1 goes up accumulation is cleared, and pixel electrode 311 returns to fixing original levels V
1, detector restPoses.
Transistor Q22 is used for buffering, and to drive follow-up circuit, its grid links to each other with pixel electrode 311.In drain electrode, apply fixing bias level V
2, make transistor Q22 work in following state.Because Q22 stateless in the course of the work changes, therefore, fixing level V
2All the time be applied in the drain electrode of transistor Q22.
It is logical that transistor Q23 is used for column selection, its grid and column selection messenger (V
Col) link to each other the order that control is read and the integral time and the time for reading of every row; Transistor Q24 is used for the row gating, its grid and row gating signal (V
Row) link to each other, be used for need selecting the row of output.
Transistor Q23 and 24 is connected in series.If when while gate transistor Q23 and Q24, then the charge signal that stores in the storage capacitors is sent on the signal wire Signal the feasible current potential that can read the pixel electrode 311 of corresponding pixel cell via pixel electrode 311, buffer transistor Q21, the logical transistor Q23 of column selection, row gate transistor Q24 successively.
The grid of the transistor Q21 of same row pixel cell is connected to same reset signal (V
Reset) on; The grid of the transistor Q23 of same row pixel cell is connected to same column selection messenger (V
Col) on; Grid with the transistor Q24 of delegation's pixel cell is connected to same capable gating signal (V
Row) on; Source electrode with the transistor Q24 of delegation's pixel cell is connected to the follow-up circuit in same road (for example, multi-way switch, level conversion or ADC).
(transducing signal) and the variable quantity of (background signal) pixel electrode 311 current potentials afterwards that resets before resetting by measurement can calculate the energy of the ray that deposits, thereby obtain the image information of this pixel in this pixel region.
The output of this read method be magnitude of voltage, read mode with traditional transistor and compare, antijamming capability can be stronger, data processing circuit can be simpler simultaneously.
Realize relevant logic control in the following way:
A) apply reset signal V to each row pixel cell
Reset, make all pixel cells reset;
B) transistor Q21, Q23, the Q24 of all pixel cells end, and pixel electrode 311 is collected charge signal, is accumulated on the storage capacitors C1;
C) reach predetermined integral time after, apply column selection messenger V to the first row pixel cell
Col, apply capable gating signal V to the corresponding pixel cell of these row successively then
Row, make transistor Q23, the Q24 conducting of corresponding pixel cell, thereby one by one read the current potential of the pixel electrode 311 of the first row pixel cell, as transducing signal;
D) transistor Q23, the Q24 of the first row pixel cell end, and apply reset signal V to first row
Reset, make the transistor Q21 conducting of the row pixel cell of winning, promptly the first row pixel cell resets;
E) the transistor Q21 of the first row pixel cell ends, and applies column selection messenger V to the first row pixel cell
Col, apply capable gating signal V to the corresponding pixel cell of these row successively then
Row, make transistor Q23, the Q24 conducting of corresponding pixel cell, thereby one by one read the current potential of the pixel electrode 311 of the first row pixel cell, signal as a setting;
F) repeating step c) to e), at other row, by the charge signal of collecting on the pixel ground read pixel electrode.
G) all pixels read finish after, through certain data processing (for example, subtracting background signal from transducing signal), can obtain a two field picture.
Usually inconsistent owing to respectively being listed as integral time in first two field picture, first frame image data is given up, and each two field picture is valid data later on.
In step a) to g) during, can apply constant bias voltage by the top electrodes on radiation-sensitive films, make the collection electric field that forms sufficient intensity in the radiation detector sensitive volume.The charge signal that produces in pixel region is during by electron production, and this bias voltage is a negative bias.When the charge signal that produces in pixel region was produced by the hole, this bias voltage was a positive bias.
Degree of polarization and residual charge amount according to detector, between every frame or every several two field picture, the bias polarity (reverse biased) that further comprises the periodically-varied top electrodes, in the detector sensitive volume, form the opposite electric field of direction, eliminating detector polarization phenomena in the course of the work, in and residual charge.
The pixel cell of digitized video flat panel detector of the present utility model be the 4T structure (promptly, comprise four transistors), with respect to the digitized video flat panel detector of prior art shown in Figure 4 (wherein, pixel cell is the 1T structure), digitized video flat panel detector of the present utility model both can read signal by row, also can read signal by individual element.
And, when the testee area is very little, can optionally only read signal to the corresponding pixel region of testee, reducing effective imaging area of detector, thereby reduce the redundancy of data, improve the speed of data processing.
When bad point appears in detector, can be by row gating and logical this bad point of functional shielding of column selection.Particularly bad point can be exported big voltage under some situation, and is very big to follow-up influence circuit, will badly put with follow-up circuit by row gating function to disconnect, and neither influences follow-up circuit, also do not influence peripheral any pixel.
Pel array shown in Figure 5 can be implemented as the arbitrary example in the combination of the circuit board 6 shown in the TFT pel array 3 shown in the cmos pixel array 2 shown in Fig. 1 a, Fig. 1 b and Fig. 1 c and signal processing IC 7.Further, the detector that constitutes thus can be used for arbitrary example of the digital imaging apparatus of the digital imaging apparatus of the planar imaging shown in Fig. 2 a and the linear sweep shown in Fig. 2 b.
Fig. 6 shows the vertical view according to the pixel electrode in the digitized video flat panel detector of prior art.For example on circuit board 210, form the array of pixel electrode 311.Each pixel electrode 311 is as the part of a pixel cell shown in Figure 5, and is electrically coupled to a pixel region of mercuric iodixde film.Electrical isolation between each pixel electrode 311.
Fig. 7 shows the vertical view according to the pixel electrode in the digitized video flat panel detector of the present utility model.Different with pixel electrode shown in Figure 6, electrode structure shown in Figure 7 comprises pixel electrode 311 and the latticed guiding electrode 314 around each pixel electrode 311.Between each pixel electrode 311 and pixel electrode 311 and the guiding electrode 314 between electrical isolation.
Fig. 8 a shows the sectional view according to the pixel electrode in the digitized video flat panel detector of the present utility model.Formed the transistor of each pixel cell in cmos pixel array or the TFT pel array in the active layer 212 aspect on substrate 211.Interlayer insulating film 213 is between pixel electrode 311, guiding electrode 314 and active layer 212.Pixel electrode 311 and guiding electrode 314 are electrically connected with transistor in the active layer 212 via the passage in the interlayer insulating film 213 (via) (not shown).
Fig. 8 b shows the modification of pixel electrodes, and each grid of wherein latticed guiding electrode 314 comprises at least two pixel electrodes 311.
Fig. 9 a shows the sectional view according to the pixel electrode in the digitized video flat panel detector of the present utility model.On the one side of circuit board 214, formed pixel electrode 311 and guiding electrode 314, provide the signal processing IC (not shown), pixel electrode 311 and guiding electrode 314 have been connected to signal processing IC via wiring on the circuit board and via hole at the another side of circuit board.
Signal processing IC comprises transistor Q21-24 and the storage capacitors C1 in the pixel cell.
Fig. 9 b shows the modification of pixel electrodes, latticed at least two pixel electrodes 311 that comprise of each of wherein latticed guiding electrode 314.
The shape that should be noted that pixel electrode 311 is not limited to rectangle, can also be circle, rhombus, hexagon etc.
Electrode structure shown in Fig. 7 to 9 can be implemented as the pixel electrode in arbitrary example in the circuit board shown in the TFT pel array 3 shown in the cmos pixel array 2 shown in Fig. 1 a, Fig. 1 b and Fig. 1 c.Further, the detector that constitutes thus can be used for arbitrary example of the digital imaging apparatus of the digital imaging apparatus of the planar imaging shown in Fig. 2 a and the linear sweep shown in Fig. 2 b.
Know that large-area flat panel detector exists serious tracking current.In detector of the present utility model, adopted the latticed guiding electrode 314 that surrounds each pixel electrode 311, can collect the leakage current of detector surface effectively, reduce the influence of leakage current to pixel electrode 311, reduce the noise of detector.
Preferably, the current potential of guiding electrode 314 is slightly different with the current potential of pixel electrode 311, and (current potential of guiding electrode 314 is a little less than pixel electrode 311 when collecting electronics, the current potential of guiding electrode 314 is a little more than pixel electrode 311 when collecting the hole), thus between guiding electrode 314 and pixel electrode 311, there is weak electric field.Guiding electrode 314 can prevent effectively that electric charge from not having the blank area of electrode to pile up between pixel, and and then prevent that the electric field of the charge generation of piling up from weakening the charge-trapping electric field intensity that adds, reduce the dead band of detector, and the polarization effect that alleviates detector.
More preferably, the bias potential that applies to guiding electrode 314 provides the shaping electric field for each pixel region, further improves the collection efficiency of electric charge.By changing the shape of pixel electrode and guiding electrode, can obtain the shaping electric field of ideal form.For example, the shape of pixel electrode can be selected from any one in circle, ellipse, the polygon.Preferably, pixel electrode be shaped as square.The mesh shape of latticed conductive electrode and the shape of pixel electrode are roughly the same.
Describe some embodiment hereinbefore, person of skill in the art will appreciate that, under the situation of the spirit that does not depart from claim of the present utility model, can use various modification, alternative structure and equivalent.Therefore, top description should not be used for limiting scope of the present utility model.
Claims (14)
1. radiation detector is characterized in that: described radiation detector comprises radiation-sensitive films, be positioned on the radiation-sensitive films top electrodes and with the array of the pixel cell of radiation-sensitive films electric coupling, wherein each pixel cell comprises;
Pixel electrode is used for collecting the charge signal of a pixel region of radiation-sensitive films;
Storage capacitors is connected with pixel electrode, is used to store the collected charge signal of pixel electrode;
Reset transistor is connected with pixel electrode, is used for emptying the electric charge of storage capacitors;
Buffer transistor is connected with pixel electrode, is used for the charge signal on the pixel electrode is converted to voltage signal and is sent to signal wire;
Transistor is led in column selection, is used to select the pixel electrode of predetermined column; And
The row gate transistor is used to select the pixel electrode of predetermined row,
Wherein, logical transistor of column selection and row gate transistor are connected in series between buffer transistor and the signal wire, and response column selection messenger and row gating signal transmit the voltage signal of corresponding pixel cell.
2. radiation detector according to claim 1 is characterized in that: described radiation-sensitive films is formed by a kind of material that is selected from the group that mercuric iodixde, lead iodide, tellurium zinc cadmium, cadmium telluride, gallium arsenide, thallium bromide, indium phosphide, cadmium selenide, cadmium sulfide, indium arsenide, vulcanized lead, indium antimonide, lead telluride, mercury selenide constitute.
3. radiation detector according to claim 1 is characterized in that: described radiation-sensitive films is a patterning, comprise and the corresponding pixel region of each pixel electrode, and pixel region is electrically insulated from each other.
4. radiation detector according to claim 1 is characterized in that: described reset transistor responds reset signal and pixel electrode is connected on the fixing original levels.
5. radiation detector according to claim 1 is characterized in that: the grid of described buffer transistor is connected with pixel electrode, and drain electrode is connected with the bias level of fixing, and source electrode is connected with the logical transistor of column selection.
6. radiation detector according to claim 1 is characterized in that: radiation detector is made of the monolithic cmos integrated circuit that is integrated with radiation-sensitive films.
7. radiation detector according to claim 1 is characterized in that: radiation detector is made of the monolithic TFT integrated circuit that is integrated with radiation-sensitive films.
8. radiation detector according to claim 1, it is characterized in that: radiation-sensitive films and pixel electrode are positioned on the one side of circuit board, at least a portion of storage capacitors, reset transistor, buffer transistor, the logical transistor of column selection and row gate transistor is integrated in the integrated circuit, and described integrated circuit is installed on the another side of circuit board.
9. radiation detector according to claim 1 is characterized in that: the shape of pixel electrode is selected from a kind of in circle, ellipse, the polygon.
10. according to each described radiation detector in the claim 1 to 9, it is characterized in that: described radiation detector also comprises the latticed guiding electrode around at least one pixel electrode, and wherein pixel electrode is electrically insulated from each other with the guiding electrode.
11. radiation detector according to claim 10 is characterized in that: the mesh shape of latticed conductive electrode is identical with the shape of pixel electrode.
12. radiation detector according to claim 1 is characterized in that: described radiation detector further comprises protective seam that surrounds radiation-sensitive films and top electrodes and the shell that surrounds protective seam.
13. radiation detector according to claim 12 is characterized in that: described radiation detector further comprises at first intermediate protective layer between the array of radiation-sensitive films and pixel cell and second intermediate protective layer between radiation-sensitive films and top electrodes.
14. radiation detector according to claim 1 is characterized in that: adopt physical vacuum vapour deposition, sputter, spraying, hot pressing, silk-screen, on the array of pixel cell, cover radiation-sensitive films.
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| CN102401906A (en) * | 2010-09-19 | 2012-04-04 | 同方威视技术股份有限公司 | Radiation detector, imaging device thereof, electrode structure and method for acquiring image |
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| CN103860184A (en) * | 2012-12-11 | 2014-06-18 | 三星电子株式会社 | Photon-counting detector and readout circuit |
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