Research Of CMOS Single Photon Avalanche Diode And Peripheral Circuit

With application scope expanding of the single photon detection technology,greater demands are being placed on the core component of photoelectric detector.Traditional PMT,APD and other photoelectric devices can't meet these requirements of detecting the extremely weak light even only a few photons accurately and measuring photon picosecond time resolution precisely and so on.Consequently,the researchers put forward a kind of APD operated in geiger mode,which is called single photon avalanche diode?SPAD?,it has big internal gain,high sensitivity and low noise,the CMOS SPAD devices overcame the problem such as difficult to compatible with CMOS circuits and devices expensive,can be large-scale production and application.Therefore,the study of CMOS SPAD is of great significance.This thesis is based on 0.18?m CMOS process to design a p+/n-well/p-sub planar structure SPAD device,with p-well guard ring structure.The p+/n-well is avalanche area for photoelectric conversion,n-well is the main area of the light absorption,p substrate facilitated integration,and p-well guard ring is used to prevent the edge breakdown in advance.Due to p+/n-well/p-sub structure of SPAD devices exist these problems such as long wavelength detection efficiency is low,dark count rate is high and so on,on this basis structure optimal design is made.Firstly,in the middle of the p+/n-well structure to increase a p-well structure,make the p-well/n-well as an avalanche diode,it not only increased the junction depth,the detection of the longer wavelength light is improved,but also reduced the electric field in the multiplication area,the avalanche breakdown voltage and dark count rates are reduced;Secondly,the deep n-well structure is introduced to increase the light absorption area,detection efficiency is increased;Finally,the edge breakdown is prevented by p-sub virtual guard ring,formed a kind of p+/p-well/n-well/DNW/p-sub SPAD structure.At the same time the influences of different doping of deep n-well on the I-V characteristics is explored,different optical window areas influence on detection efficiency is researched,the influence of different bias voltage on the dark counts rates is discussed and so on.Through the simulation analysis of the p+/n-well/p-sub structure of SPAD device,the results showed that:At Kelvin temperature 300k,the window area length is of 20?m,the breakdown voltage is of-22.0V,responsivity between 300 nm and 600 nm wavelength range is good;when excess bias voltage is 1V,at wavelength of 420 nm the maximum detection efficiency is 30%,the dark count rate is of 28.3kHz.The performances simulation results of the modified SPAD device showed that in the same temperature,deep n-well concentration is of 2.0×10¹⁶cm^-3 when the I-V curve is the steepest;the p-sub virtual guard ring width in 1.0?m device breakdown characteristic is best;window area has little effect on breakdown voltage,but the larger the area,the higher the dark current as well as the detection efficiency,this thesis decided to compromise the window area length is 20?m.The avalanche breakdown voltage is of-12.0V,the responsivity between the wavelength of 300 nm and 800 nm are bigger than0.2A/W,the best responsivity is 0.45A/W at wavelength of 550nm;the maximal detection efficiency is as high as 55%at 2V excess bias voltage,the dark count rate is of16.5kHz,compared with the first device structure the performances are all improved.Due to the avalanche of SPAD device would not automatically quenching,so the three kinds of commonly used peripheral quenching circuit are analyzed.Peripheral passive quenching circuits in combination with the SPAD device equivalent circuit model,using cadence software transient simulation with dead time is 20ns.Owing to quenching circuit output is a discrete pulse signals,peripheral counting circuit is designed and analyzed.The peripheral digital counting circuit designed frequency is 500MHz,satisfied the requirement of single photon avalanche pulse counting.