Double junction photodiode for X-ray CMOS sensor IC

作者：Xu Chaoqun; Sun Ying^*; Han Yan; Zhu Dazhong

来源：Chinese Journal of Semiconductors, 2014, 35(7): 074011.

DOI：10.1088/1674-4926/35/7/074011

• Capacitive transimpedance amplifiers
• Fluorescence detection
• Fluorescence spectra
• Integration time
• Photocurrent signals
• Spectral response
• Spectrum response
• X ray sensors

A CMOS compatible P+/Nwell/Psub double junction photodiode pixel was proposed, which can efficiently detect fluorescence from CsI(Tl) scintillation in an X-ray sensor. Photoelectric and spectral responses of P+/Nwell, Nwell/Psub and P +/Nwell/Psub photodiodes were analyzed and modeled. Simulation results show P+/Nwell/Psub photodiode has larger photocurrent than P+/Nwell photodiode and Nwell/Psub photodiode, and its spectral response is more in accordance with CsI(Tl) fluorescence spectrum. Improved P+/Nwell/Psub photodiode detecting CsI(Tl) fluorescence was designed in CSMC 0.5 μm 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+/N well/Psub photodiodes (13 pA and 11 pA respectively). The sensitivity of P+/Nwell/Psub photodiode is about 20 pA/lux under white LED. The spectrum response of P+/N well/Psub photodiode ranges from 400 nm to 800 nm with a peak at 532 nm, which is in accordance with the fluorescence spectrum of CsI(Tl) 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·m2/W or 5097e-/pixel @ 8.05 keV considering the pixel size, integration time and average energy of X-ray photons.

• 出版日期2014
• 单位浙江大学