Inoue Akito, Okino Toru, Koyama Shinzo, Hirose Yutaka
Panasonic Corporation, 1 Kotari-yakemachi, Nagaokakyo City, Kyoto 617-8520, Japan.
Sensors (Basel). 2020 May 25;20(10):3007. doi: 10.3390/s20103007.
We present an analysis of carrier dynamics of the single-photon detection process, i.e., from Geiger mode pulse generation to its quenching, in a single-photon avalanche diode (SPAD). The device is modeled by a parallel circuit of a SPAD and a capacitance representing both space charge accumulation inside the SPAD and parasitic components. The carrier dynamics inside the SPAD is described by time-dependent bipolar-coupled continuity equations (BCE). Numerical solutions of BCE show that the entire process completes within a few hundreds of picoseconds. More importantly, we find that the total amount of charges stored on the series capacitance gives rise to a voltage swing of the internal bias of SPAD twice of the excess bias voltage with respect to the breakdown voltage. This, in turn, gives a design methodology to control precisely generated charges and enables one to use SPADs as conventional photodiodes (PDs) in a four transistor pixel of a complementary metal-oxide-semiconductor (CMOS) image sensor (CIS) with short exposure time and without carrier overflow. Such operation is demonstrated by experiments with a 6 µm size 400 × 400 pixels SPAD-based CIS designed with this methodology.
我们对单光子雪崩二极管（SPAD）中从盖革模式脉冲产生到其猝灭的单光子探测过程的载流子动力学进行了分析。该器件由一个SPAD和一个电容的并联电路建模，该电容既代表SPAD内部的空间电荷积累，也代表寄生元件。SPAD内部的载流子动力学由与时间相关的双极耦合连续性方程（BCE）描述。BCE的数值解表明，整个过程在几百皮秒内完成。更重要的是，我们发现串联电容上存储的总电荷量会导致SPAD内部偏置电压的摆动幅度是相对于击穿电压的过偏置电压的两倍。这反过来又给出了一种精确控制产生电荷的设计方法，并使人们能够在互补金属氧化物半导体（CMOS）图像传感器（CIS）的四晶体管像素中，将SPAD用作传统光电二极管（PD），实现短曝光时间且无载流子溢出。使用这种方法设计的基于6 µm尺寸400×400像素SPAD的CIS进行的实验证明了这种操作。
