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Abstract

A fingerprint sensor includes an integrated circuit die and a protective covering of a z-axis anisotropic dielectric material. The die includes a conductive layer defining an array of electric field sensing electrodes. The z-axis anisotropic dielectric layer focusses an electric field at each of the electric field sensing electrodes. In other words, the dielectric covering may be relatively thick, but not result in defocussing of the electric fields propagating through the dielectric covering because of the z-axis anisotropy of the material. The z-axis anisotropic dielectric layer may be provided by a plurality of oriented dielectric particles in a cured matrix. For example, the z-axis anisotropic dielectric layer may comprise barium titanate in a polyimide matrix. The conductive layer preferably comprises a plurality of capacitive coupling pads for permitting capacitive coupling with the integrated circuit die. Accordingly, the dielectric covering is preferably continuous over the capacitive coupling pads and the array of electric field sensing electrodes. The z-axis dielectric layer also advantageously reduces cross-talk between adjacent capacitive coupling pads.

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