Radiation detector, imaging device and electrode structure thereof, and method for acquiring an image

Abstract

The present invention discloses a radiation detector, an imaging device and an electrode structure thereof, and a method for acquiring an image. The radiation detector comprises: a radiation sensitive film, a top electrode on the radiation sensitive film, and an array of pixel units electrically coupled to the radiation sensitive film, wherein each pixel unit comprises: a pixel electrode, which is configured to collect a charge signal in a pixel area of the radiation sensitive film; a storage capacitor, which is connected to the pixel electrode, and is configured to store the charge signal collected by the pixel electrode; a reset transistor, which is connected to the pixel electrode, and is configured to clear the charge in the storage capacitor; a buffer transistor, which is connected to the pixel electrode, and is configured to convert the charge signal on the pixel electrode into a voltage signal and transfer the voltage signal to a signal line; a column strobe transistor, which is configured to select a predetermined column of pixel electrodes; and a row strobe transistor, which is configured to select a predetermined row of pixel electrodes, wherein, the column strobe transistor and the row strobe transistor are connected in series between the buffer transistor and the signal line, and transfer the voltage signal of the corresponding pixel unit in response to a column strobe signal and a row strobe signal. The radiation detector may be used for, for example, X-ray digital imaging.

What is claimed is: 
     
         1 . A radiation detector, comprising: a radiation sensitive film, a top electrode on top of the radiation sensitive film, and an array of pixel units electrically coupled to the radiation sensitive film, wherein each pixel unit comprises:
 a pixel electrode, which is configured to collect a charge signal in a pixel area of the radiation sensitive film;   a storage capacitor, which is connected to the pixel electrode, and is configured to store the charge signal collected by the pixel electrode;   a reset transistor, which is connected to the pixel electrode, and is configured to clear charges in the storage capacitor;   a buffer transistor, which is connected to the pixel electrode, and is configured to convert the charge signal on the pixel electrode into a voltage signal and transfer the voltage signal to a signal line;   a column strobe transistor, which is configured to select a predetermined column of the pixel electrodes; and   a row strobe transistor, which is configured to select a predetermined row of the pixel electrodes,   wherein the column strobe transistor and the row strobe transistor are connected in series between the buffer transistor and the signal line, and transfer the voltage signal of the corresponding pixel unit in response to a column strobe signal and a row strobe signal.   
     
     
         2 . The radiation detector according to  claim 1 , wherein the radiation sensitive film is formed of one material selected from the group consisting of mercuric iodide, lead iodide, cadmium zinc telluride, cadmium telluride, gallium arsenide, thallium bromide, indium phosphide, cadmium selenide, cadmium sulphide, indium arsenide, lead sulphide, indium antimonide, lead telluride, and mercury selenide. 
     
     
         3 . The radiation detector according to  claim 1 , wherein the radiation sensitive film is patterned and comprises pixel areas corresponding to each pixel electrode, and the pixel areas are electrically isolated from each other. 
     
     
         4 . The radiation detector according to  claim 1 , wherein the reset transistor connects the pixel electrode to a fixed initial level in response to a reset signal. 
     
     
         5 . The radiation detector according to  claim 1 , wherein a gate electrode of the buffer transistor is connected to the pixel electrode, a drain electrode of the buffer transistor is connected to a fixed bias level, and a source electrode of the buffer transistor is connected to the column strobe transistor. 
     
     
         6 . The radiation detector according to  claim 1 , wherein the radiation detector consists of a monolithic CMOS integrated circuit that is integrated with the radiation sensitive film. 
     
     
         7 . The radiation detector according to  claim 1 , wherein the radiation detector consists of a monolithic TFT integrated circuit that is integrated with the radiation sensitive film. 
     
     
         8 . The radiation detector according to  claim 1 , wherein the radiation sensitive film and the pixel electrode are located on one side of a circuit board, at least a part of the storage capacitor, the reset transistor, the buffer transistor, the column strobe transistor and the row strobe transistor are integrated in the integrated circuit, and the integrated circuit is mounted on the other side of the circuit board. 
     
     
         9 . The radiation detector according to  claim 1 , wherein a shape of the pixel electrode is one selected from circular, ellipse and polygon. 
     
     
         10 . The radiation detector according to any one of  claims 1  to  9 , further comprising: a grid-like steering electrode that surrounds at least one pixel electrode, wherein the pixel electrode and the steering electrode are electrically isolated from each other. 
     
     
         11 . The radiation detector according to  claim 10 , wherein a grid shape of the grid-like conductive electrode is the same as the shape of the pixel electrode. 
     
     
         12 . The radiation detector according to  claim 1 , further comprising: a protection layer enveloping the radiation sensitive film and the top electrode; and a cover enveloping the protection layer. 
     
     
         13 . The radiation detector according to  claim 12 , further comprising: a first intermediate protection layer located between the radiation sensitive film and the array of pixel units, and a second intermediate protection layer located between the radiation sensitive film and the top electrode. 
     
     
         14 . The radiation detector according to  claim 1 , wherein the radiation sensitive film is overlaid on the array of pixel units by employing a method of vacuum physical vapor deposition, sputtering, spray coating, hot pressing, screen printing, or the like. 
     
     
         15 . A digital imaging device, comprising:
 a radiation source, which is configured to generate radiation;   a radiation detector according to any one of the above claims, which is configured to detect a dosage of the radiation that passes through an object to be detected;   a data acquisition system, which is configured to convert an analog signal outputted from the radiation detector into a digital signal; and   an image processor, which is configured to process the digital signal into an image.   
     
     
         16 . The digital imaging device according to  claim 15 , further comprising a collimator, wherein the radiation source, the collimator and the detector move relatively to the object to be detected, so as to perform a linear scanning with respect to the object to be detected. 
     
     
         17 . The digital imaging device according to  claim 16 , wherein the radiation source, the collimator and the detector move in a scanning direction synchronously. 
     
     
         18 . An electrode structure for a radiation detector, comprising:
 pixel electrodes; and   a grid-like steering electrode, which surrounds at least one pixel electrode, and the pixel electrodes and the steering electrode are electrically isolated from each other.   
     
     
         19 . The electrode structure according to  claim 18 , wherein a shape of the pixel electrodes is one selected from circular, ellipse and polygon. 
     
     
         20 . The electrode structure according to  claim 19 , wherein a grid shape of the grid-like conductive electrode is the same as the shape of the pixel electrodes. 
     
     
         21 . The electrode structure according to  claim 18 , wherein the steering electrode and the pixel electrodes are formed of the same or different metallic layers. 
     
     
         22 . The electrode structure according to  claim 21 , wherein the steering electrode and the pixel electrodes are located on the same plane and are formed of the same metallic layer. 
     
     
         23 . The electrode structure according to any one of  claims 18  to  22 , wherein the electrode structure is located in an integrated circuit or on one side of a circuit board. 
     
     
         24 . The electrode structure according to any one of  claims 18  to  22 , wherein an electric potential of the steering electrode is the same as or different from that of each pixel electrode. 
     
     
         25 . The electrode structure according to  claim 24 , wherein, when a charge signal generated in a pixel area is generated by electrons, the electric potential of the steering electrode is lower than that of the pixel electrode. 
     
     
         26 . The electrode structure according to  claim 24 , wherein, when a charge signal generated in a pixel area is generated by holes, the electric potential of the steering electrode is higher than that of the pixel electrode. 
     
     
         27 . A method for acquiring an image by using a radiation detector according to any one of  claims 1  to  14 , comprising the steps of:
 a) applying a reset signal to each column of pixel units to reset all pixel units; 
 b) turning off reset transistors, column strobe transistors and row strobe transistors of all the pixel units, collecting charge signals by pixel electrodes, and accumulating the charge signals on storage capacitors; 
 c) applying a column strobe signal, to a first column of pixel units after predetermined integrating time is reached, and then applying row strobe signals to the corresponding pixel units in the column sequentially, thereby turning on the column strobe transistor and the row strobe transistor of the corresponding pixel unit, so that electric potentials of pixel electrodes in the first column of pixel units are read one by one as sensing signals; 
 d) turning off the column strobe transistor and the row strobe transistors of the first column of pixel units, and applying a reset signal to the first column, thereby turning on the reset transistors of the first column of pixel units, that is, resetting the first column of pixel units; 
 e) turning off the reset transistors of the first column of pixel units, applying a column strobe signal to the first column of pixel units, and then applying row strobe signals to the corresponding pixel units in the column sequentially, thereby turning on the column strobe transistor and the row strobe transistor of the corresponding pixel unit, so that the electric potentials of the pixel electrodes of the first column of pixel units are read one by one as background signals; 
 f) repeating steps c) to e), and for other columns, reading the charge signals collected on the pixel electrodes on a pixel-by-pixel basis; and 
 g) obtaining a frame of image by data processing after reading all the pixels. 
 
     
     
         28 . The method according to  claim 27 , wherein, the step g) comprises subtracting the background signals from the sensing signals. 
     
     
         29 . The method according to  claim 27 , wherein, during step a) to step g), a constant first bias voltage is applied to a top electrode of the radiation sensitive film, so that a collecting electric field with a sufficient intensity is formed in a sensitive region of the radiation detector. 
     
     
         30 . The method according to  claim 29 , wherein, when the charge signals generated in a pixel area are generated by electrons, the first bias voltage is a negative bias voltage. 
     
     
         31 . The method according to  claim 29 , wherein, when the charge signals generated in a pixel area is generated by holes, the first bias voltage is a positive bias voltage. 
     
     
         32 . The method according to any one of  claims 27  to  31 , wherein, steps c) to g) are repeated to acquire multiple of consecutive frames of images. 
     
     
         33 . The method according to  claim 32 , further comprising: applying a constant second bias voltage to a top electrode of the radiation sensitive film between each frame of image or every several frames of images, so as to eliminate the polarization phenomenon of the detector during an operation procedure, wherein a polarity of the second bias voltage is opposite to that of the first bias voltage.