Research On Single Photon Avalanche Diode Based On CMOS Technology

Single photon detection has wide application prospect in military,scientific research and civil life field,such as key distribution in quantum communication,laser ranging in astronomy,and fluorescence lifetime imaging in medicine.In these emerging applications,the signal's energy is only several photon level,even lower than the background noise.So rigorous demands were being placed on single photon detectors which act a core component in the single photon detection system.Among the available photon detectors,single photon avalanche diode?SPAD?has attracted much attention for its high sensitvity,low power consumption and high detection efficiency.Using modern CMOS technology,SPAD and its peripheral circuits can be integrated on one chip,thus improving the system performance,reducing the noise,and achieving higher integration level.With the development of the CMOS technology in the direction of deep submicron,the device has smaller size,higher doping concentration,and less annealing time.These factors give a challenge to SPAD structural design and performance optimization.The existing structure has also shown some drawbacks.In order to solve this problem,this thesis has studied the main factors that affect the performance of SPAD based on existing structure,and designs a new SPAD structure based on UMC 0.18?m CMOS technology.The main works are as follows:First,we elaborated the working mechanism of SPAD and summarize classical protection ring structures.Two different SPADs with classical protection were designed based on UMC 0.18?m CMOS.Basic electrical characteristics,such as breakdown voltage,electric field distribution,quantum efficiency,and impact generation were analyzed by using Silvaco Atlas.Through comparison and analysis,their drawbacks were pointed out and the difficulty of making SPAD based on CMOS technology was discussed.Secondly,a new SPAD structure with non-contact guard ring was proposed on the basis of the above work.The non-contact guard ring can not only improve the electric field distribution,but also effectively solve the problem of premature breakdown of the edge.The results shown that the device has low breakdown voltage and good spectral response within the spectral range wavelength of 400 nm to 700 nm.When the excess bias voltage V_ex=2.5V,the peak photon detection efficiency is up to39%.Thirdly,quenching circuit which can be used in CMOS was studied in this thesis.The electrical model of SPAD was established,and the single-transistor passive quenching-passive recovery circuit,active quenching-active recovery circuit and passive quenching-active recovery circuit were analyzed and simulated.Finally,the passive quenching-active recovery circuit was selected as the external quenching circuit of Proposed SPAD,since this circuit has the virtues of large photosensitive area,few transistors and compact circuit,which is helpful to improve the utilization of the chip and integration level of arrays.