Double junction photodiode for X-ray CMOS sensor IC  

作　　者：许超群 孙颖 韩雁 朱大中 

机构地区：[1]Department of Information Science and Electronic Engineering,Institute of Microelectronics and Optoelectronics,Zhejiang University

出　　处：《Journal of Semiconductors》2014年第7期84-89,共6页半导体学报（英文版）

基　　金：supported by the National Natural Science Foundation of China(No.61076075);the Natural Science Foundation of Zhejiang Province(No.Y1100287)

摘　　要：A CMOS compatible P＋/Nwell/Psub double junction photodiode pixel was proposed, which can effi- ciently detect fluorescence from CsI（T1） scintillation in an X-ray sensor. Photoelectric and spectral responses of P＋/Nwell, NweE1/Psub and P＋/Nwell/Psub photodiodes were analyzed and modeled. Simulation results show P＋/Nweu/Psub photodiode has larger photocurrent than P＋/Nwetl photodiode and Nweu/Psub photodiode, and its spectral response is more in accordance with CsI（T1） fluorescence spectrum. Improved P＋/Nweu/Psub photodiode detecting CsI（T1） fluorescence was designed in CSMC 0.5 #m CMOS process, CTIA （capacitive transimpedance amplifier） architecture was used to readout photocurrent signal. CMOS X-ray sensor IC prototype contains 8 × 8 pixel array and pixel pitch is 100 × 100 μm2. Testing results show the dark current of the improved P＋/Nwell/Psub photodiode （6.5 pA） is less than that of P＋/Nwell and P＋/Nwell/Psub photodiodes （13 pA and 11 pA respectively）. The sen- sitivity of P＋/Nwell/Psub photodiode is about 20 pA/lux under white LED. The spectrum response of P＋/Nwell/Psub photodiode ranges from 400 nm to 800 nm with a peak at 532 nm, which is in accordance with the fluorescence spectrum of Csl（T1） in an indirect X-ray sensor. Preliminary testing results show the sensitivity of X-ray sensor IC under Cu target X-ray is about 0.21 V.m^2/W or 5097e-/pixel @ 8.05 keV considering the pixel size, integration time and average energy of X-ray photons.A CMOS compatible P＋/Nwell/Psub double junction photodiode pixel was proposed, which can effi- ciently detect fluorescence from CsI（T1） scintillation in an X-ray sensor. Photoelectric and spectral responses of P＋/Nwell, NweE1/Psub and P＋/Nwell/Psub photodiodes were analyzed and modeled. Simulation results show P＋/Nweu/Psub photodiode has larger photocurrent than P＋/Nwetl photodiode and Nweu/Psub photodiode, and its spectral response is more in accordance with CsI（T1） fluorescence spectrum. Improved P＋/Nweu/Psub photodiode detecting CsI（T1） fluorescence was designed in CSMC 0.5 #m CMOS process, CTIA （capacitive transimpedance amplifier） architecture was used to readout photocurrent signal. CMOS X-ray sensor IC prototype contains 8 × 8 pixel array and pixel pitch is 100 × 100 μm2. Testing results show the dark current of the improved P＋/Nwell/Psub photodiode （6.5 pA） is less than that of P＋/Nwell and P＋/Nwell/Psub photodiodes （13 pA and 11 pA respectively）. The sen- sitivity of P＋/Nwell/Psub photodiode is about 20 pA/lux under white LED. The spectrum response of P＋/Nwell/Psub photodiode ranges from 400 nm to 800 nm with a peak at 532 nm, which is in accordance with the fluorescence spectrum of Csl（T1） in an indirect X-ray sensor. Preliminary testing results show the sensitivity of X-ray sensor IC under Cu target X-ray is about 0.21 V.m^2/W or 5097e-/pixel @ 8.05 keV considering the pixel size, integration time and average energy of X-ray photons.

关 键 词：double junction photodiode indirect X-ray sensor CMOS X-ray sensor IC fluorescence detection 

分 类 号：TP212[自动化与计算机技术—检测技术与自动化装置] TN432[自动化与计算机技术—控制科学与工程]