A Back-Illuminated 4<i>μ</i>m P⁺N-Well Single Photon Avalanche Diode Pixel Array With 0.36Hz/<i>μ</i>m² Dark Count Rate at 2.5 V Excess Bias Voltage
Wenbo Sun, Yuxin Wang, Maliang Liu, Yintang Yang
Abstract
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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${8}\,\,\times \,\,{8\,4}\,\,\mu \text{m}$ </tex-math></inline-formula> pixels whose active area diameter is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.6~\mu \text{m}$ </tex-math></inline-formula> . At room temperature, the DCR of the SPAD is only 0.03Hz <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$/ \mu \text{m}^{{2}}$ </tex-math></inline-formula> at 1.0 V excess bias and 0.36Hz <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$/ \mu \text{m}^{{2}}$ </tex-math></inline-formula> 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.