Double junction photodiode for X-ray CMOS sensor IC
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 r...
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Published in | Journal of semiconductors Vol. 35; no. 7; pp. 84 - 89 |
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Main Author | |
Format | Journal Article |
Language | English |
Published |
01.07.2014
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Subjects | |
Online Access | Get full text |
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Summary: | 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. |
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Bibliography: | Xu Chaoqun, Sun Ying, Han Yan, Zhu Dazhong(Department of Information Science and Electronic Engineering, Institute of Microelectronics and Optoelectronics, Zhejiang University, Hangzhou 310027, China) 11-5781/TN 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. double junction photodiode; indirect X-ray sensor; CMOS X-ray sensor IC; fluorescence detection ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 1674-4926 |
DOI: | 10.1088/1674-4926/35/7/074011 |