Study On X-ray Image Sensor With CMOS Process

Because of the strong transmission, X-ray is the ideal light source fornondestructive testing and security detection.Besides, X-ray is also widely used inmedical assay and radiation imaging. X-ray is with high energy,it will cause damage tothe semiconductor devices.All of the traditional X-ray image sensors choose fluorescentscreen as the medium to translate the X-ray into visible light and then detect the light.The transfer of the information and the quality of imaging were affected because of themedium. Because of the scattering, the resolution ratio was hard to improve. Theafterglow effect affects the real time of image sensor.In order to solve the above problem, CMOS active pixel sensor was studied withthe support of NSFC. Without the effect of medium, this structure could be used todetect X-ray directly. The spatial resolution and real time of the image sensor wereimproved. In order to overcome the radiation damage in semiconductor device,Sentaurus TCAD was used for modeling analysis. The MOSFET structure weremodeled with SDE. The effect of X-rays on the threshold voltage shift are simulatedthrough the method of charge incorporation. Technology was used for radiationhardening. Multiple performance parameters, such as sensor area, power consumptionand filling rate were compared between CMOS active pixel sensor and passive pixelsensor. The CMOS APS structure with3-T,4-T and5-T were compared.CMOS active pixel image sensor array were designed with improved3T structure.8×8pixel array are simulated and analyzed. The response curve with different currentequivalent and the linearity analysis of parameter curve were finished. The layout of128×128pixel array were designed with0.5um standard CMOS process. Sample pixelcolumns were packaged with DIP for testing the imaging performance. The X-ray with80KV-250uA was used as the light source for radiation imaging. PCI6115dataacquisition card of NI were chosen as the equipment for image data acquisition. AlteraEP2C8Q208C8N FPGA provides digital timing control signal. The digital sequentialdetection signal were generated with Verilog.240pixel array were spliced. Objectsmoving through the traction displacement platform with the help of shift imagingplatform. X-ray source and image sensor keep relative static. Two dimensional datawith240×400array were collected.The collected data array is passed into the LabVIEW program of PC machine through the data acquisition card PCI6115. The data were processed by LabVIEW,voltage data was converted to gray level signal with8bit. By constructing imagingsoftware, the signal were presented in three-dimensional structure and2D gray image.Based on the experimental material’s data measurement, reading, processing andimaging, not only test the design of image sensor, but also reflects the accuracy of theinformation collection and imaging system.