Design Of High Detection Efficiency SPAD Based On CMOS Technology

The Single Photon Avalanche Diode is one of the core components of a single photon detector and can be used to detect optical signals.With the maturity of photo detection technology,single-Photon avalanche diodes based on 180 nm CMOS technology have been characterized by fast response,low power consumption,small size,mass production and easy integration.All the time,they draw high attention in the Science and industry.It is often used in many fields such as fluorescence lifetime imaging,near-infrared optical radiography(NIROT),early disease detection,medical diagnosis and Raman spectroscopy and Silicon(Si)is a common material for single photon avalanche diodes which can be used to detect optical signals in the range of 300 nm to 1100 nm.However,due to the nature of the silicon,the photon detection efficiency of the device is not high,especially in the long wavelength range,the absorption of light is not ideal.How to improve the wavelength detection of single photon avalanche diodes by using innovative structure,it has become the focus of research today.Firstly,this paper introduces the working principle of single photon avalanche diode and the performance parameters of single photon avalanche diode for breakdown voltage,spectral response,avalanche incidence,photon detection efficiency,quantum efficiency and so on.What's more,list two existing innovative single photon avalanche diode structures and analyze their advantages and disadvantages.Then,the structure of single photon avalanche diode is proposed which having double electric layers.The P+ region is the light absorbing region,the main PN junction is formed by P-charge/deep n-well contact,and in order to prevent premature breakdown by using p-/deep n-well contact in edge region.The N-charge is formed at the convergence of the Deep N-well and the N-isolation layer(N-iso),which can improve the spectral response and improve the photon detection efficiency much further.When the device in operation,N-iso,N-well/p-epi(p-epitaxial)can isolate the central region of the device from the substrate,effectively reducing coupling noise and solving latch-up effects.The semiconductor device simulation software silvaco TCAD was used to simulate I-V characteristics.In addition,the microscopic mechanism of photocurrent generation is studied to optimize P-charge concentration and the position of N-charge,and then high photon detection efficiency is obtained.Comparing its performance with other different single-photon avalanche diode,the single-photon avalanche diode proposed in this paper can achieve high photon detection efficiency and improve photon detection capability in long wavelength range.Finally,based on the structure of the double-charged single photon avalanche diode,a trench type of single photon avalanche diode structure is proposed.The main junction is formed by N-charge/deep p-well.The poly silicon(poly)layer and the trench electrode are added in the device.At the same time,using the existence of the poly silicon layer and the type of the trench electrode as variations to analyze the performance parameters under four different structures: breakdown voltage,electric field strength,collision generation rate,current flow path and so on.Then the principle of photo-carrier transit time and diffusion current is analyzed.Finally,under 5V excess-bias,the photon detection efficiency in the range of 300nm?900nm can more than 30%,and the photon detection efficiency peak is 70%.When the wavelength is 900 nm,there is still nearly 16% photon detection efficiency.It proves that the structure proposed in this paper can achieve better photon detection in the visible and near-infrared range.