Patent Description:
Fingerprint sensors comprising electrodes for measuring characteristics in a finger surface are well known. For example, <CIT>, <CIT>, <CIT>, <CIT> and <CIT> describe sensors based on different impedance or capacitance measurement principles with strip-shaped or matrix sensors comprising a number of individual sensor elements. <CIT> describes a single-sided capacitive fingerprint sensor comprising a first layer of pickup lines, a first layer of drive lines and an AC voltage source which is connected to the drive lines and causes an electric field to radiate from the drive lines to the pickup lines. <NPL>, describes a fingerprint sensing method that uses a double-sided fingerprint sensor configured to be held between a thumb and an index finger of a user. <CIT> describes a continuous biometric authentication system comprising a sensor which may be a double-sided touch sensor.

Fingerprint sensors are found in all kind of devices such as PC's, tablets, smart phones and smart cards for the security and ease of use it provides. The widespread use of fingerprint sensors may also provide a security problem as fingerprint sensors have been spoofed by spoof fingerprints produced from latent fingerprints. Current art fingerprint sensors typically attempt to mitigate this problem with additional security measures, such as live finger detection, at the cost of increased false rejection of fingerprints and reduced ease of use. There is, therefore, a need in the industry for an improved fingerprint sensor that is specifically architected to improve the anti-spoof protection without degrading the ease of use of the fingerprint sensor.

The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments of the subject matter of this disclosure. In the drawings, like reference numbers indicate identical or functionally similar elements.

While aspects of the subject matter of the present disclosure may be embodied in a variety of forms, the following description and accompanying drawings are merely intended to disclose some of these forms as specific examples of the subject matter. Accordingly, the subject matter of this disclosure is not intended to be limited to the forms or embodiments so described and illustrated.

Unless defined otherwise, all terms of art, notations and other technical terms or terminology used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this disclosure belongs.

Unless otherwise indicated or the context suggests otherwise, as used herein, "a" or "an" means "at least one" or "one or more.

This description may use relative spatial and/or orientation terms in describing the position and/or orientation of a component, apparatus, location, feature, or a portion thereof. Unless specifically stated, or otherwise dictated by the context of the description, such terms, including, without limitation, top, bottom, above, below, under, on top of, upper, lower, left of, right of, in front of, behind, next to, adjacent, between, horizontal, vertical, diagonal, longitudinal, transverse, radial, axial, etc., are used for convenience in referring to such component, apparatus, location, feature, or a portion thereof in the drawings and are not intended to be limiting.

Furthermore, unless otherwise stated, any specific dimensions mentioned in this description are merely representative of an exemplary implementation of a device embodying aspects of the disclosure and are not intended to be limiting.

The present disclosure relates to an electronic sensor for detecting proximally located objects. In an embodiment, the sensor is a fingerprint sensor that detects surface features (e.g., ridges and valleys) of two fingers placed on the electronic sensor. In an embodiment, the electronic sensor operates based on interaction between a pair of electrodes that include a drive element and a pickup element. The pickup element may be capacitively coupled to the drive element and may sense a signal that passes from the drive element to the pickup element. Features of a proximally located object can be detected based on whether the sensor detects a change in a signal being received at the pickup element.

In an embodiment, the electronic sensor includes a top, or upper, conductive grid and a bottom, or lower, conductive grid configured to detect surface features of two proximally located objects at a plurality of locations on two sides of the sensor. The top and bottom grids each include a plurality of parallel drive lines, which are each connectable to a drive source, and a plurality of parallel pickup lines that are oriented transversely (e.g., perpendicularly) to the drive lines. The drive lines are separated from the pickup lines by an insulating (e.g., dielectric) layer. Each drive line may thus be capacitively coupled to a pickup line. In the embodiment, the drive lines can form one axis (e.g., X-axis) of the grid, while the pickup lines form another axis (e.g., Y-axis) of the grid. Each location where a drive line and a pickup line cross may form an impedance-sensitive electrode pair. This impedance-sensitive electrode pair may be treated as a pixel (e.g., an X-Y coordinate) at which a surface feature of the proximally located object is detected. The top and bottom grids form a plurality of pixels that can collectively be scanned to create a map of the surface features of the proximally located object. For instance, the pixels of the grid can differentiate locations where there is a ridge of a fingertip touching the electronic sensor and locations where there is a valley of the fingerprint. The map can be used as a pattern to match with ridge/valley patterns stored in a database. The grid sensor may create maps of two different fingers at the same time, typically a thumb and an index finger pinching the grid sensor. This makes it very difficult to find, develop, and align individual latent prints at the correct angles in order to spoof the sensor. The biomechanical angle of index print to thumb print may also be used as a secondary biometric. A prior art version of a fingerprint sensor with overlapping drive lines and pickup lines is discussed in more detail in <CIT>, entitled "Electronic imager using an impedance sensor grid array and method of making" and <CIT>, entitled "Fingerprint sensor employing an integrated noise rejection structure,".

<FIG> illustrates a portion of an exemplary sensor structure <NUM>. The sensor <NUM> includes a middle conductive layer comprising a plurality of drive elements <NUM>, an upper conductive layer comprising a plurality of upper pickup elements <NUM>, and a lower conductive layer comprising a plurality of lower pickup elements <NUM>. In one embodiment, the drive elements <NUM> may be formed or etched as elongated, flat strips (i.e., width greater than thickness) of conductive material (e.g., copper, aluminum, gold) that are substantially parallel to each other and which may also be referred to as drive lines or drive plates. The upper and lower pickup elements <NUM>, <NUM> may be formed or etched as elongated, flat strips of conductive material (e.g., copper, aluminum, gold) that are substantially parallel to each other and which may also be referred to as pickup lines or pickup plates. In an embodiment, the upper pickup elements <NUM> may be aligned with the lower pickup elements <NUM>. A first insulating layer <NUM> made of a dielectric material separates the drive lines <NUM> and the upper pickup lines <NUM>. The drive elements <NUM> and the upper pickup elements <NUM> are oriented transversely to each other, and in one embodiment, are substantially perpendicular to each other, thereby forming an area of overlap between the drive lines <NUM> and the crossing upper pickup lines <NUM>. A second insulating layer <NUM> made of a dielectric material separates the drive lines <NUM> and the lower pickup lines <NUM>. The drive elements <NUM> and the lower pickup elements <NUM> are oriented transversely to each other, and in one embodiment, are substantially perpendicular to each other, thereby forming an area of overlap between the drive lines <NUM> and the lower crossing pickup lines <NUM>.

Each location where a drive element <NUM> and a pickup element <NUM>, <NUM> cross forms an impedance-sensitive electrode pair - drive elements <NUM> and upper pickup elements <NUM> forming upper electrode pairs and drive elements <NUM> and lower pickup elements <NUM> forming lower electrode pairs. When no object is in contact with or in close proximity to the impedance-sensitive electrode pair, the impedance-sensitive electrode pair has a first impedance determined by the size of the parallel plate capacitor formed by the electrode pair, which is a function of the dimensions of the drive element <NUM> and dimensions of the pickup elements <NUM>, <NUM> and the thickness and dielectric properties of the insulating layers <NUM>, <NUM>. In one embodiment, the widths of the drive elements <NUM> and the pickup elements <NUM>, <NUM> are equal, and thus the area of overlap defined by the width of the drive line and the width of the pickup line has equal width and length. Other configurations are possible in which the width of the drive elements <NUM> and the pickup elements <NUM>, <NUM> are different. For example, in one embodiment, the width of each of the drive elements <NUM> is greater than (e.g., twice) the width of each of the pickup elements <NUM>, <NUM>, or vice versa.

<FIG> illustrates a portion of an exemplary sensor structure <NUM> according to an alternate embodiment. The sensor <NUM> includes a first upper conductive layer comprising a plurality of upper drive elements <NUM>, a second upper conductive layer comprising a plurality of upper pickup elements <NUM>, a first lower conductive layer comprising a plurality of lower drive elements <NUM>, and a second lower conductive layer comprising a plurality of lower pickup elements <NUM>. In one embodiment, the drive elements <NUM>, <NUM> may be formed or etched as elongated, flat strips of conductive material (e.g., copper, aluminum, gold) that are substantially parallel to each other and which may also be referred to as drive lines or drive plates. The pickup elements <NUM>, <NUM> may be formed or etched as elongated, flat strips of conductive material (e.g., copper, aluminum, gold) that are substantially parallel to each other and which may also be referred to as pickup lines or pickup plates. A first insulating layer <NUM> made of a dielectric material separates the upper drive elements <NUM> and the upper pickup elements <NUM>. A second insulating layer <NUM> made of a dielectric material separates the lower drive elements <NUM> and the lower pickup elements <NUM>. The drive elements <NUM>, <NUM> and the pickup elements <NUM>, <NUM> are oriented transversely to each other and, in one embodiment, are substantially perpendicular to each other, thereby forming an area of overlap between the drive elements <NUM>, <NUM> and the crossing pickup elements <NUM>, <NUM>.

In one embodiment, the sensor <NUM> includes a third insulating layer <NUM> separating the first upper conductive layer of substantially parallel electrodes <NUM> and the first lower conductive layer of substantially parallel electrodes <NUM>. The upper drive elements <NUM> and lower drive elements <NUM> are pairwise connected by interconnects <NUM> to form drive elements <NUM>. In one embodiment, the upper drive elements <NUM> and lower drive elements <NUM> may be interconnected by a via extending through the third insulating layer <NUM>. In another embodiment the upper drive elements <NUM> and lower drive elements <NUM> may be interconnected by a conductive element extending beyond the third insulating layer <NUM>. In one embodiment the third insulating layer <NUM> may be made of glass, fiberglass, polycarbonate glass, polymer, semiconductor material or a layered composite material.

Each location where a drive element <NUM>, i.e., upper drive element <NUM> and lower drive <NUM>, and an upper and lower pickup element <NUM>, <NUM> cross forms an impedance-sensitive electrode pair - upper drive elements <NUM> and upper pickup elements <NUM> forming upper impedance-sensitive pairs, and lower drive elements <NUM> and lower pickup elements <NUM> forming lower impedance-sensitive pairs. When no object is in contact with or in close proximity to the impedance-sensitive electrode pair, the impedance-sensitive electrode pair has a first impedance determined by the size of the parallel plate capacitor formed by the electrode pair, which is a function of the dimensions of the drive elements <NUM>, <NUM> and dimensions of the pickup elements <NUM>, <NUM>, and the thickness and dielectric properties of the insulating layers <NUM>, <NUM>, <NUM>. In one embodiment, the widths of the drive elements <NUM>, <NUM> and the pickup elements <NUM>, <NUM> are equal, and thus the area of overlap defined by the width of the drive elements <NUM>, <NUM> and the width of the pickup elements <NUM>, <NUM> has equal width and length. Other configurations are possible in which the width of the drive elements <NUM>, <NUM> and the pickup elements <NUM>, <NUM> are different. For example, in one embodiment, the width of each of the drive elements <NUM>, <NUM> is greater than (e.g., twice) the width of each of the pickup elements <NUM>, <NUM> or vice versa.

<FIG> illustrates a portion of a sensor system comprising a sensor <NUM> and an ASIC <NUM>. Sensor <NUM> is comparable to the sensor <NUM> shown in <FIG>. Alternatively, the sensor system as illustrated in <FIG> could encompass a sensor <NUM> as shown in <FIG>.

Referring to <FIG> and <FIG>, the ASIC <NUM> includes a signal source connected to the drive elements <NUM>, <NUM> by a connector <NUM> to provide a signal to at least one of the drive elements <NUM>, <NUM>. ASIC <NUM> further includes a detection system configured to detect a resultant impedance on at least one of the upper electrode pairs and one of the lower electrode pairs, where the resultant impedances are indicative of the presence of a ridge and valley features of a first object over the upper electrode pairs and a second object under the lower electrode pairs. In one embodiment the first object and second object are sensed simultaneously or sequentially in rapid succession. In an embodiment, the first and second objects are alternately sensed in subsections that can be reconstructed into complete images. In another embodiment, the first and second objects are one thumb and one non-thumb finger of the same hand and the angular relationship between the two is measured as a secondary user biometric.

In one embodiment the first object and second object are two different fingers, e.g., a thumb and an index finger.

In one embodiment the insulating layer <NUM> constitutes a part of a substrate material larger than the finger print sensing area, i.e., a substrate that encapsulates the ASIC <NUM> and covers connectors <NUM>, <NUM> and <NUM> to create an integrated finger print sensor module. In the integrated sensor module, the upper pickup lines <NUM> are connected to the ASIC by connectors <NUM> and vias <NUM>, and the lower pickup lines <NUM> are connected to the ASIC <NUM> by connectors <NUM> under the insulating layer <NUM> and vias <NUM> through insulating layer <NUM>. The upper drive elements <NUM> and lower drive elements <NUM> of the drive elements <NUM> are interconnected by vias <NUM> through the insulating layer <NUM> and connected to the ASIC <NUM> by connectors <NUM>.

Claim 1:
A sensor assembly for detecting biometric images, the sensor assembly comprising:
a first sensor side comprising first pickup elements comprising a first plurality of substantially parallel pickup lines (<NUM>, <NUM>);
a second sensor side comprising second pickup elements comprising a second plurality of substantially parallel pickup lines (<NUM>, <NUM>);
a plurality of drive elements comprising a plurality of substantially parallel drive lines orientated transversely to the first and second pluralities of pickup lines, comprising either (i) a first layer of drive elements (<NUM>), a second layer of drive elements (<NUM>), a first insulating layer (<NUM>, <NUM>) separating the first layer of drive elements and the first pick up elements, a second insulating layer (<NUM>, <NUM>) separating the second layer of drive elements and the second pickup elements, a third insulating layer (<NUM>) separating the first layer of drive elements from the second layer of drive elements and a plurality of interconnects (<NUM>) connecting the first layer of drive elements to the second layer of drive elements, or (ii) a single layer of drive elements (<NUM>), a first insulating layer (<NUM>, <NUM>) separating the single layer of drive elements and the first pick up elements, a second insulating layer (<NUM>, <NUM>) separating the single layer of drive elements and the second pickup elements; and
a signal source (<NUM>) configured to provide a drive signal to at least one of the drive elements resulting in a signal that passes from the drive elements to the first and second pickup elements,
wherein the sensor assembly is configured to scan the first pickup elements to generate a first map of features of a first object located proximately to the first sensor side based on changes in the signal received by the first pickup elements from the drive elements and scan the second pickup elements to create a second map of features of a second object located proximately to the second sensor side based on changes in the signal received by the second pickup elements from the drive elements.