The Research Of High Photon Detection Efficiency CMOS Single Photon Avalanche Diode

In recent years,with the improvement of technology level and the rapid development of science and technology,single photon detection technology is developing in the direction of integration,miniaturization and array.However,the traditional structure of the photomultiplier tube(PMT)and avalanche photodiode(APD)detectors have been unable to meet the specific requirements of engineering application.In order to accurately detect the low-level light signal or single photon signal,it is necessary to study the high sensitivity single photon detector.At present,national scholars have carried out extensive research on the APD under the Geiger mode,namely the single photon avalanche diode(SPAD).Because of its high speed,superior timing resolution performance and exceptional photon sensitivity,SPAD can effectively detect the extremely weak optical signal with single photon magnitude,becomes the ideal device of a single photon detector.In this thesis,the structure and performance of SPAD devices are studied in depth in view of the detection requirements of high-sensitivity and low-intensity light signal from 650 to 950 nm.To achieve this goal,this device is designed with 0.18?m standard CMOS technology.Using dual diode structure of P~+/deep N-well as the basic structure,the depth of the deeper P~+layer deepens the depth of PN junction,which is helpful to improve the detection efficiency of the longer wavelength.The guard ring which formed by low-doped p-well material around P~+active region can avoid premature edge breakdown.Avalanche multiplication occurs in the P~+/deep N-well breakdown region to achieve photoelectric conversion.The deep N-well/P-sub junction is used as shielding diode to prevent the photo-generation carriers from substrate diffusing into the work PN junction,thus,the effect of the substrate slow propagation carrier diffuser on the response speed of the device is reduced.Although the P~+/deep N-well structure has a good detection efficiency in the range of 650-950 nm,the dark count rate is high,the overall performance of the device needs to be optimized.After the basic structure is determined,according to the performance characteristics of the device,through theoretical analysis and simulation design,the structure of the device and the related parameters are optimized.The following work has been carried out in the following aspects:First of all,due to the diffused guard-ring technique occupies large space and lower the fill-factor.Therefore,in order to optimize the compactness and scalability of the device,employing virtual guard ring formed by the lateral diffusion of n-well instead of the p-diffused guard ring formed by heavily doped edge light doping,decreasing the edge electric field,and then inhibits the edge breakdown.Secondly,in order to improve the characteristic of device noise,high doping central N-well layer is injected underneath the center of P~+layer to enhance the electric field in the anode central active area,reduce breakdown voltage of the device,effectively control the dark count rate.In addition,the retrograde deep N-well structure with low surface concentration can enhance the collection effect of the active region carriers,and some optical carriers are formed in the deep N-well,which extends the optical absorption region,and then improving the overall detection efficiency of the device.Through the simulation analysis of the optimized SPAD device,the results show that:the breakdown voltage of the optimized SPAD device is obviously reduced.At room temperature,the breakdown voltage changed from-18.4 V before optimization to-8.2 V.Under the incident light of 0.001 W/cm~2,when the reverse bias voltage increases to the breakdown voltage,the photocurrent increases rapidly from 1×10~-1212 A to macroscopic current(mA magnitude),which marks the effective conversion of the ultra-low amplitude light signal into a detectable electric signal.The peak response is around 650 nm with a maximum value of 0.64 A/W,the spectral responsivity in650-950 nm is higher than 0.45 A/W.At 1 V excess bias,the photon detection efficiency has a peak of 75%,and there is a visible plateau from 550 nm to 600 nm,the PDE in 650-950 nm is higher than 35%.At room temperature,the dark count rate dropped to about 1.3 kHz.Compared with the pre optimized device,the overall performance is obviously improved.