Effect of ground-wall structure in capacitive fingerprint sensor on electrostatic discharge tolerance

This paper describes the electrostatic discharge (ESD) tolerance of capacitive fingerprint sensor or sensor/identifier LSIs in which the sensor is stacked on a CMOS LSI. The ground-wall structure that we proposed as a capacitive sensor structure for ESD tolerance was investigated. The contact discharge method was used for the fingerprint sensor ESD test. The dependence of ESD failure voltage on the distance between the sensor surface and the ESD electrode was measured. In the planar-type structure, ESD failure voltage decreased as the electrode approached the sensor surface and reached its minimum when the electrode touched the surface. Results for the ground-wall type show a high ESD tolerance regardless of the distance. Moreover, in the test on the fingerprint sensor and sensor/identifier LSIs, the ground-wall effect was obtained with a high ESD tolerance. In conclusion, it was revealed that fingerprint sensor LSI or the fingerprint sensor/identifier LSI with a ground-wall structure has a high ESD tolerance of more than +/- 20.0 kV.