低过偏压下高增益单光子雪崩二极管的设计与验证

Design and Verification of Single-Photon Avalanche Diode with High Gain at Low Overbias Voltage

单光子雪崩二极管(SPAD)可以检测到异常微弱的光信号,可广泛应用于目标跟踪、自动驾驶、荧光检测等领域。本文基于180 nm标准双极-互补金属氧化物半导体-双扩散金属氧化物半导体(BCD)工艺,设计了一种低过偏压下具有高光子检测概率(PDP)的SPAD器件。该器件在440~740 nm范围内具有良好的光谱响应。采用半径为10μm的N+/P阱形成PN结作为感光区域,由N阱形成一个能有效防止边缘击穿的保护环。应用计算机技术辅助设计(TCAD)软件对SPAD的基本工作原理进行了定性分析,并通过建立的测试平台获得了设备的实际电气参数。测试结果表明,在1 V的过量偏置电压下,在480~660 nm的波长范围内,该器件可达到30%以上的PDP。在560 nm时,PDP峰值为42.7%,暗计数率为11.5 Hz/μm^(2)。最后通过设计VerilogA混合模型验证了器件的模拟结果和实测结果之间具有良好一致性。

Objective Photoelectric detection plays an important role in various fields such as fluorescence microscopes,photodetectors,and medical three-dimensional imaging.With the emergence of photomultiplier tubes(PMTs),avalanche photodiodes(APDs),and other new photoelectric devices,the photoelectric detection effect is further strengthened.PMT achieves high sensitivity detection by photoelectron multiplication,but it features expensiveness,fragility,large size,and high pressure operation,which makes it have limited practical applications.Meanwhile,APDs based on the avalanche effect can generate avalanche current amplification under light excitation,but it is limited by gain,volume,process compatibility,and other factors in practical applications.Single-photon avalanche diode(SPAD)has been applied to various fields such as robotic radar detection,target tracking,and autonomous driving due to its low power consumption,high sensitivity,and low noise characteristics.Most of the SPADs proposed in recent years have high photon detection probability(PDP)under high overbias voltage or enlarge the multiplication region to achieve higher detection probability,but this will affect the junction capacitance and then the time jitter of the device.Thus,we design a SPAD device compatible with most of the processes,which can achieve high PDP at low overbias voltage and has a small dark count rate(DCR).Methods The basic working mechanism of SPAD is characterized by applying technology-computer-aided-design(TCAD)software.Silvaco TCAD software is employed to simulate the device structure and obtain electrical characteristic results from the Atlas Simulator.The Selberrherr model(impact ionization model)built into TCAD software is adopted for analyzing the operating mechanism,and the Newton iteration method is for numerical calculation.Then,a SPAD device with N+/P-well is designed based on a 180 nm standard bipolar CMOS-DMOS(BCD)process,and the device performance is tested by qE-IPCE-K6517B UV detector photoelectric response system and semiconductor analyzer.Additionally,based on the Cadence circuit simulation platform,VerilogA programming language and circuit combined hybrid model are built to simulate SPAD quenching and I-V curve,which provides guidance for SPAD design in the future.Results and Discussions Simulation results show that the N+/P-well structure has a large electric field and current density in the avalanche multiplication region.The breakdown voltage of the device is about 12.8 V,and photo-generated carriers in the depletion region collide with lattice atoms to create new electron-hole pairs. This chain reaction makes the number of charge carriers in the depletion layer increase in an avalanche manner, and the current flowing through the PN junction rises sharply. Breakdown voltage testing of the flow sheet device indicates that the photocurrent in the linear region of the SPAD can reach the sub-microamperage level. The test results show that the device's PDP can reach 42. 7% under the overbias voltage of 1 V, peak wavelength is 560 nm, and DCR is 11. 5 Hz/µm^(2). The built model is verified to be consistent with the measured principle of the device, and an avalanche pulse can be generated when a photon arrives and is passively quenched by a quench resistor. The matching results of light and dark currents can well fit the measured I-Vcharacteristics of SPAD.Conclusions A SPAD device with high PDP is designed based on a 180 nm standard BCD process. The device has good spectral responses in the range of 440-740 nm. An N+/P-well with a radius of 10 μm is adopted to form a PN junction as the sensing region, and a protective ring that effectively prevents edge breakdown is formed by the N-well. The basic working mechanism of SPAD is characterized by applying TCAD software. The actual electrical parameters of the device are also obtained by the established test platform. The test results show that more than 30% PDP can be achieved in the wavelength range of 480-660 nm at an overbias voltage of 1 V. At 560 nm, the peak PDP is 42. 7% and the DCR is 11. 5 Hz/µm^(2). Finally, the VerilogA hybrid model verifies the good agreement between the simulated and measured results.