高响应度的NMOS型栅体互连光电探测器

NMOS-Type Gate/Body-Tied Photodetector with High Responsivity

针对硅基光电探测响应度低的问题,设计了一款与标准CMOS工艺兼容的、可用于弱光探测的高响应度的NMOS型光电探测器(NMOS-PD).该探测器由栅体互连的NMOS管和T-well/N-well结光电二极管构成,利用光电二极管的光生伏特效应改变T阱电势,进而控制NMOS管的栅压和阈值电压,以此实现光信号的探测与倍增放大,故所设计光电探测器具有更高的光电流增益和更宽的动态范围.经理论模拟计算和优化设计,本文设计了总面积为20μm×20μm的NMOS-PD,选用整个T阱区作为光敏区域(16μm×16μm),以增加光的吸收量,所设计光电探测器经UMC 0.18μm CMOS工艺流片制备.测试结果表明,所设计探测器在400～700 nm波长范围内具有较好的响应度.采用630 nm LED作为光源,当输出光功率密度P_(opt)=5 mW/cm^2、漏源偏压V_(DS)=0.4 V时,NMOS-PD的响应度达到1 550 A/W,并实现了200 kHz的信号探测.尽管随着光强增大,光电探测器响应度逐渐降低,但整体上仍超过10~3A/W.与硅基CMOS工艺制备的传统光电探测器相比,所设计光电探测器结构不仅可在低压、低功耗下正常工作,且在弱光条件下具有极高的倍增放大能力,有望应用于弱光探测的图像传感领域.

This study aims to design a novel N-channel metal oxide semiconductor transistor-type photodetector (NMOS-PD)with high responsivity for ultra-weak light detection based on standard CMOS technology to improve the responsivity of photodetectors in optoelectronic integrated circuits. NMOS-PD comprises a gate/body-tied NMOS transistor and photodiode formed by a T-well/N-well junction. The photovoltage induced by the photodiode controls the gate and threshold voltages of the NMOS transistor,thereby improving the sensitivity of NMOS-PD. After simulation calculation and optimization,a total area of 20 μm×20 μm was adopted for the NMOS-PD. Moreover,the whole T-well region was selected as the photosensitive area(16 μm×16 μm)to increase light absorption. The designed NMOS-PD was fabricated in UMC 0.18 μm CMOS technology. Results showed that the output characteristics of NMOS-PD were as similar to that of the NMOS transistor,and the designed NMOS-PD demonstrated a good spectral response between 400 and 700 nm. When the device was biased by a drain voltage of 0.4 V and illuminated by a 630 nm LED source with an average output power density of 5 mW/cm2 ,a responsivity of 1 550 A/W was obtained. The device could normally operate up to 200 kHz. Although the responsivity gradually decreased as the light intensity was enhanced,it still exceeded 103 A/W. In comparison with traditional silicon photodetectors fabricated in standard CMOS,the designed NMOS-PD could operate properly under low voltage with low power consumption and exhibited high multiplying amplification capability under weak light conditions. Therefore,the proposed NMOS-PD has potential applications in the field of ultra-weak light imaging detection.