Monolithic Integration of CMOS Capacitive Tactile and Optical Proximity Sensors for Multiaxis Force and Distance Sensing

This study presents a complementary metal–oxide–semiconductor (CMOS)-based tactile–proximity sensing platform that integrates a $4\times 4$ capacitive tactile sensor array with optical proximity sensors to enable both in-plane and out-of-plane detection. By leveraging the maturity and scalability of CMOS processes, the system achieves high integration density and excellent spatiotemporal resolution. This work demonstrates the first monolithic integration of photodiodes with capacitive tactile sensors within a standard CMOS process. The tactile sensor design demonstrates average sensitivities of 1.5 fF/mN (in-plane) and 163 fF/mN (out-of-plane), with corresponding force resolutions of 233 and $2.2~\mu $ N, respectively. The integrated photodiodes achieve a proximity detection range of up to 11 cm, with a spatial resolution of approximately $339~\mu $ m. These results demonstrate the potential of CMOS-integrated tactile–proximity sensors for compact, high-performance applications.