SPADs are fabricated with standard 90 nm CMOS technology

For the first time, single-photon avalanche diodes (SPADs) have been created using a standard 90 nm complementary metal-oxide semiconductor (CMOS) process and mask set; the achievement is a step towards the creation of high-dynamic-range, high-timing-resolution megapixel-scale SPAD arrays. Developed by researchers at the Technical University of Delft (Delft, the Netherlands) and Ecole Polytechnique Fédérale Lausanne (Lausanne, Switzerland), the SPAD structure was the result of a systematic study in which 162 different types of SPADs with differing arrangements of doping layers and varying guard-ring sizes were fabricated on one chip (which the researchers called a "SPAD farm"); 45 of the structures worked properly in the single-photon counting mode.

Forming a well-functioning guard ring (which confines the electric field to the SPAD's active area) was one of the biggest challenges, due to limitations of standard CMOS technology. The optimum 8 μm diameter device had a dark-count rate of 8.1 kHz, a maximum photon-detection probability of 9%, and a jitter of 398 ps at a 637 nm wavelength. It functioned over a 360-800 nm wavelength range and had a breakdown voltage of 10.4 V. Potential uses include time-of-flight 3D vision, fluorescence-lifetime imaging microscopy, and fluorescence-correlation spectroscopy. Contact Mohammad Azim Karami at [email protected].