Fingerprint sensor-compatible overlay material
A fingerprint sensor-compatible overlay material which uses anisotropic conductive material to enable accurate imaging of a fingerprint through an overlay is disclosed. The anisotropic conductive material has increased conductivity in a direction orthogonal to the fingerprint sensor, increasing the capacitive coupling of the fingerprint to the sensor surface, allowing the fingerprint sensor to accurately image the fingerprint through the overlay. Methods for forming a fingerprint sensor-compatible overlay are also disclosed.
1. An apparatus comprising:
a fingerprint sensor comprising a plurality of capacitive sense elements disposed adjacent to a sensor surface, wherein the plurality of capacitive sense elements are configured to measure changes in capacitance corresponding to fingerprint features; and
an overlay, comprising:
a first overlay surface disposed adjacent to the sensor surface; and
a first conductivity in a first direction between the first overlay surface and a second overlay surface wherein the first conductivity is greater than a second conductivity in at least one other direction;
wherein the overlay is configured to:
receive a fingerprint in direct contact with or in close proximity to the second overlay surface; and
increase a capacitive coupling of fingerprint features to the plurality of capacitive sense elements such that the plurality of capacitive sense elements measure changes in capacitance corresponding to fingerprint features.
2. The apparatus of claim 1 , wherein the overlay is flexible.
3. The apparatus of claim 1 , wherein the second overlay surface is configured to conform to the curvature of a finger.
4. The apparatus of claim 1 , wherein the first conductivity is substantially constant.
5. The apparatus of claim 1 , wherein the overlay comprises conductive pillars comprising conductive elements disposed in a material wherein the conductive pillars are aligned in the first direction.
6. The apparatus of claim 5 , wherein the conductive pillars are disposed in the material symmetrically around an axis in the first direction.
7. The apparatus of claim 5 , wherein the conductive pillars are disposed in the material asymmetrically around an axis in the first direction.
8. The apparatus of claim 7 , wherein the conductive pillars are further disposed randomly in the material.
9. The apparatus of claim 1 , further comprising a processor configured to receive measurements of changes in capacitance corresponding to fingerprint features and, based on measurements of changes in capacitance, generate a set of data values that represents the fingerprint in digital format.
10. A method, comprising:
disposing an overlay material over a sensor wherein:
the sensor comprises a plurality of capacitive sense elements disposed adjacent to a sensor surface, wherein the plurality of capacitive sense elements are configured to detect changes in capacitance corresponding to a presence of an object;
the overlay material has a first conductivity in a first direction between a first overlay surface and a second overlay surface wherein the first conductivity is greater than a second conductivity in at least one other direction, and
the first overlay surface is adjacent to the sensor surface and the second overlay surface is disposed to receive the object in direct contact with or in close proximity to the second overlay surface, such that the first conductivity increases a capacitive coupling of the object to the plurality of capacitive sense elements; and
detecting, by the capacitive sense elements through the overlay material, changes in capacitance corresponding to the presence of the object in direct contact with or in close proximity to the second overlay surface;
coupling the sense elements to a capacitance measurement circuit;
receiving, by the capacitance measurement circuit, a plurality of voltage or current signals from the capacitive sense elements corresponding to changes in capacitance; and
generating, based on the plurality of voltage or current signals, a set of data values that represents the object in digital format.
11. The method of claim 10 , wherein the overlay material is flexible.
12. The method of claim 10 , wherein the second overlay surface is configured to conform to the curvature of the object.
13. The method of claim 10 , wherein the first conductivity is substantially constant.