Silicon integrated electrical micro-lens for CMOS SPADs based on avalanche propagation phenomenon

Abstract– The design and fabrication of integrated microlenses for CMOS single-photon avalanche diodes (SPADs) is presented in this paper. The micro-lens exploits the avalanche propagation phenomenon occurring in abrupt single-sided junctions and is achieved by carful design of the SPAD in a standard CMOS process. In contrast to an optical micro-lens, the proposed technique is more robust to manufacturing tolerances and can scale in principle to large arrays, providing a better concentration factor and concentration uniformity. Measurement results show a photon detection probability (PDP) as high as 64.85 % at 600 nm when the SPAD is biased at 2 V of excess bias. The micro-lens configuration is compatible with backside illumination and the use of integrated devices on guard rings, thereby enabling the high density pixels and extremely high fill factors.