A Multilayer Interdigitated Spiral Structure to Achieve Inductive Force and Capacitive Proximity Dual-Sensing

This study presents a tactile sensor featuring interdigitated spiral structure. Using different electrical routings, the interdigitated spiral structure achieves both inductive force and capacitive proximity dual-sensing capabilities on the same chip. The sensing device is implemented using the Taiwan Semiconductor Manufacturing Company (TSMC) 0.18- $\mu $ m 1P6M standard complementary metal-oxide–semiconductor (CMOS) process, along with in-house post-CMOS processes. Key features of the tactile sensor include: 1) force sensing mode (two-end signal input): acting as a magnetic coil to provide magnetic flux and 2) proximity sensing mode (single-end signal input): acting as interdigitated electrodes to generate fringe electric field. Leveraging the advantages of the CMOS platform, this study presents a multilayer interdigitated spiral structure to enhance the performance of the sensors. Measurements indicate that the device has a sensitivity of 5.1 nH/N under a 0–1-N load with one magnetic-coil sensing unit in the inductive force sensing mode, and a sensitivity of 0.54 fF/mm over a 0–3-mm distance range with a single-layer interdigitated electrode in the capacitive proximity sensing mode. Moreover, increasing the magnetic-coil sensing units from one to eight results in a nearly 64-fold enhancement in the sensitivity of force sensing. The proximity sensing can also be improved by increasing the stacked layers in interdigitated electrodes; however, this may result in a relatively unstable sensing signal, leading to larger error bars, which is a concern for applications.