Research Of X-ray Sensor Array With On-chip Scintillator

X-ray sensors are widely used in medical radiograph, industrial exploration and scientific researches, help people get an insight into the internal structure of human body and objects that are invisible to our eyes. The mainstream of the current X-ray sensors are mostly scintillator based, the scintillator converses the incident X-ray into fluorescence firstly, the fluorescent are visible light, and then the fluorescence be detected by semiconductor photoelectric detector, thereby form the X-ray sensor. Cesium Iodide doped with Thallium (CSI (Tl)) becomes the one of choice among the many types of scintillators due to its high light yield and difficulty of deliquescence. To match the fluorescence spectral range of Csl (Tl) and detect the weak fluorescent intensity, research on photoelectric sensor arrays suited for the detection of Csl (Tl) fluorescence are carried out.Through theoretical analysis, device modeling, circuit simulation, and preliminary testing, the design of X ray sensor based on the6x6P+/Nwell/Psub photodiode arrays chip has been completed; The8x8CMOS photoelectric sensor array based on CSMC0.5um process was developed which is suitable for forming CMOS X-ray sensors of, simulation and test results indicate that the design of the circuit meet the detection of weak light.The main research includes:1、To match the Csl (Tl) fluorescence spectroscopy the junction depth of P+/Nwell is designed to be0.2um to absorb400nm-550nm incident light and Nwell/PSub0.8um to absorb550nm-800nm incident light. ISE-TCAD software is used to simulate the fabricate process and come to the process conditions. High-temperature diffusion and photolithography are used to develop6x6P+/Nwell/PSUb photodiode arrays chip. Chip test results show that the leakage current is less than1.5nA under4V reverse bias, sensitivity approximates lnA/lux under white LED lamp (the same structure in CSMC0.5um process has leakage current about11pA and sensitivity about19pA/lux). The photoelectric response model of P+/Nwell/PSUb is proposed, the measured results show that responses differs for incident light of different wavelengths.2, For testing characteristics of the X-ray sensor based on the6×6photodiode, a36-channel weak current acquisition system is developed with the digitized result output and the system acquisition accuracy is lnA.3、A paster-coupled X-ray sensor based on the developed P+/Nwell/Psub photodiode array chip is produced with6nA background current. The sensitivity of the sensor to X-ray irradiation is about1.034X10-9A·m2/W.4, A X-ray sensor integrated with on-chip pixilated Csl (Tl) based developed P+/Nwell/PSub photodiode array chip is produced. SU-8photoresist constitutes the light separating wall with height85um and thickness20um, the trough area is100×lOOum2.5, A8×8photoelectric sensor array chip using CSMC0.5um CMOS process is designed to detect the fluorescence of Csl (Tl). Optimization of photodiode is carried out to reduce the leakage current without increasing the layout area and improve the weak light detection capability, using the CTIA pixel structure to improve the sensitivity of the photoelectric sensing unit.The sensitivity of the sensor is0.21V·m2/W.