A Back-Illuminated 4μm P⁺N-Well Single Photon Avalanche Diode Pixel Array With 0.36Hz/μm² Dark Count Rate at 2.5 V Excess Bias Voltage

This article introduces a high fill factor (FF) and low dark count rate (DCR) back-illuminated single photon avalanche diode (SPAD) pixel array fabricated in customized 55nm CMOS technology. In the SPAD array, all pixels use the same deep N-well (DNW) and adjacent pixels share the same N ⁺ and N-well. The fill factor reaches 41.6%. Furthermore, deep trench isolation (DTI) is used to reduce optical crosstalk. For a single SPAD design, the shallow trench isolation (STI) is isolated away from avalanche multiplication zone to reduce the DCR. The array contains of ${8}\,\,\times \,\,{8\,4}\,\,\mu \text{m}$ pixels whose active area diameter is $2.6~\mu \text{m}$ . At room temperature, the DCR of the SPAD is only 0.03Hz $/ \mu \text{m}^{{2}}$ at 1.0 V excess bias and 0.36Hz $/ \mu \text{m}^{{2}}$ at 2.5 V excess bias. The full width at half maximum (FWHM) jitter at 640nm wavelength is 180 ps and the photon detection efficiency (PDE) at 905nm wavelength is 5%. The SPAD array shows excellent performance for time-of-flight (ToF) applications.