Evaluation of ESD hardness of fingerprint sensor LSIs

We used three kinds of fingerprint sensor LSIs, i.e., a conventional planar sensor LSI, a sensor LSI with a grounded wall (GND wall) structure where each sensor plate was surrounded by a lattice-like wall, and a sensor where some of the sensor plates had been replaced with GNDs. In human body model (HBM)-based contact discharge tests, the sensor LSI with the GND wall structure and the one with the GNDs demonstrated a high ESD hardness compared with the planar sensor LSI. An air discharge test was also carried out in accordance with IEC61000-4-2 specifications because other ESD tests cannot be used to estimate over ±8 kV. The ESD hardness of the GND wall structure was ±20 kV, whereas that of the other sensor with the GND structure was below ±12 kV. It was evident from our findings that the ESD hardness of sensor LSIs obviously depends on the number of GNDs in the sensor region, their arrangement, and the GND structure, and that the sensor LSI with the GND wall had the highest ESD hardness.