Patent ID: 7084642

Claim:
A fingerprint sensing device having a plurality of pixels formed within semiconductor and dielectric material, the dielectric material disposed atop the semiconductor material and having flat exposed surface portions, one or more of said pixels comprising: a surface plate retained by dielectric material at a sensing surface, the surface plate having an upper surface that defines the sensing surface with surrounding surface portions of the dielectric material; first and second electrodes embedded in the dielectric material at a level beneath the surface plate; and an amplifier having an input connected to the second electrode and an output for generating a pixel output signal in response to an input pulse applied to the first electrode; wherein a fingerprint sensor having a variable impedance is formed by the surface plate and a portion of a fingerprint-bearing skin of a user's finger applied to the sensing surface, said portion being disposed above the surface plate with the skin applied to the sensing surface, wherein first and second sensors are formed between the surface plate and the respective first and second embedded electrodes, and wherein the pixel output signal varies with the impedance value of the fingerprint sensor to indicate the proximity of the skin of the user's finger to the surface plate when an input pulse is applied to the first electrode; and further comprising a third embedded electrode lying between the first and second embedded electrodes, wherein the third embedded electrode is connected to the surface plate and has edges facing respective opposed edges of the first and second electrodes.