Capacitive fingerprint sensor with protective coating containing a conductive suspension

摘要

A capacitive fingerprint sensor includes a polymeric protective coating defining a sensing surface and having conductive particles suspended therein. The conductive particles act as parallel strings of series capacitors to couple the capacitance the fingerprint-bearing skin of a user's finger applied to the sensing surface to capacitive sensing elements beneath the protective coating. The polymeric material of the coating is durable and scratch resistant. The conductive particles enable use of a protective coating of 10 to 20 microns in thickness while providing a high degree of sensitivity and image resolution.