Research On Low Noise SPAD Detector Based On BCD Technology

Single photon avalanche diodes(SPADs),with picosecond response time and high internal gain,are widely applied in Light Detection and Ranging(LiDAR),3-D imaging,and fluorescence lifetime imaging.In recent years,SPAD detectors are highly developing towards low-cost and high-density integration.However,there are still many challenges to be solved,such as eye safety threshold,longrange,and rejection of background light for SPAD detectors.Therefore,to address the above problems,this thesis proposes the following solutions:(1)Research on calculation models for crucial statistical performance.Based on the P-well/Deep N-well structure of SPAD devices,the generation rate of photon-generated carriers and avalanchetriggering probability in different regions were simulated and calculated.By analyzing the mechanism of photon detection probability(PDP)and dark count rate(DCR),the calculation models of PDP and DCR were proposed by Matlab.According to the derived models described,the performance parameters of the simulated SPAD were calculated and compared with tested data.The results show that the accuracy of the calculation model reaches 99%,which verifies the accuracy of the models.(2)Research on Silicon-based SPAD device structure with high sensitivity in the near-infrared spectrum.The SPAD based on high-voltage P-well/N+ buried layer junction in 180 nm BipolarCMOS-DMOS(BCD)technology was designed.The photon detection probability in the nearinfrared is enhanced owing to the deep junctions formed by the high-voltage P-well and buried N+layer.The virtual guard ring is formed by the epitaxial layer,which prevents premature breakdown of the electric field at the edge of the multiplication region and greatly decreases the dark count rate of the SPAD.It is experimentally found that the PDP of the SPAD can obtain 41% at 600 nm and maintain 12% at 850 nm at 5 V excess bias,which can work in the near-infrared and enhance the safety threshold of human eyes.The DCR is only 200 Hz at 5 V excess bias at room temperature.It solves the disadvantages of high dark count rate and low photon detection probability in near-infrared of traditional SPAD.(3)Research on analog-to-digital mixed-mode circuits with background light noise rejection and wide dynamic range.The circuit of Time of Flight(TOF)was designed utilizing a mixed-mode approach combining a Time-to-Amplitude Converter(TAC)and digital counter to achieve a wide dynamic range and high-resolution simultaneously,which solves the contradiction of detection distance and resolution.A smart triggering logic for concurrent events detection is attached to the detection circuit,which can distinguish the photon echo signal from the background photon signal by setting the threshold,reducing the influence of background light noise.The simulation results demonstrate that the designed circuit can achieve a dynamic range of 96 m,and a time resolution of39 ps.The DNL and INL of the TAC are less than 0.15 LSB and 1LSB respectively in the full-scale range of 10 ns.It can operate in a 70 klux strong background light environment.