Abstract:
A structure for reducing or eliminating electrostatic discharge from a finger into the platen of a biometric sensor is disclosed. The structure is designed to be positioned above and around the platen such that conductive components in the structure stimulate corona discharge and dielectric breakdown from an approaching finger into the conductive components of the structure rather than into the platen itself. The structure is designed to eliminate, reduce or otherwise neutralize the charge on an approaching finger prior to the finger coining into contact with the platen of the biometric sensor and prior to the finger coming close enough to the platen so that the electrostatic discharge causes an are to strike the platen.

Description:
BACKGROUND 
     Fingerprint detection has long been used as a method of identification. In the time that fingerprints have been examined and compared, no two areas of friction ridge skin on any two fingers or palms have been found to have the same friction ridge characteristics. As such, fingerprinting has been accepted as a primary method of identifying an individual. 
     Although fingerprinting was initially used for forensic purposes, computerized identification, verification and authentication systems that utilize the digital analysis of fingerprints have been developed more recently to protect personal property such as laptops, computers and cellular phones, prevent credit card and calling card fraud, limit access to secure computers, information and areas, and ensure security for network based financial transactions. 
     The technology for the actual scanning or sensing of fingerprints has also advanced over time. For example, ink roller methods were replaced with optical and mechanical sensing technologies. Such technologies generally used scanners or cameras to capture a fingerprint image and then digitize the image for subsequent processing. One problem with such technologies is that the lighting conditions available at the time of image capture can affect the quality of the resulting fingerprint image. 
     More recently, capacitive fingerprint sensors have been introduced. Such sensors are typically silicon semiconductor-based devices that have an array of capacitor electrodes covered by a protective coating at the surface of the sensor (i.e., the platen). The sensor detects varying capacitor charges that correspond to die distance between the ridges and valleys of a, fingerprint and the electrodes when a finger is pressed against the platen. These measurements are then converted into a digital image of the fingerprint. An early capacitive fingerprint sensor is disclosed in U.S. Pat. No. 4,353,056 to Tsikos, which is incorporated herein by reference in its entirety. 
     One issue with capacitive fingerprint sensors is that placing a linger that holds a sufficient level of electrostatic charge onto the sensor has the potential to significantly damage sensitive electronic components in the sensor, other electronic components coupled to the sensor (including circuitry in any authentication computer systems coupled to the sensor) or otherwise interfere or affect the operation of the sensor. This effect is known as electrostatic discharge (“ESD”). Conventionally, sensor manufacturers have sought to control ESD by placing electrodes or an internal metal grid underneath the sensor to dissipate electrostatic charge received from a finger. Exemplary patents incorporating such methods include U.S. Pat. No. 6,628,812 to Setlak et al. and U.S. Pat. No. 6/737,329 to Lepert et al, each of which is incorporated herein by reference in its entirety. However, such methods do not reduce the electrostatic charge received at the surface of sensors. As such, despite the potential of such electrodes or metal grids to distribute or dissipate current once the finger contacts the surface of the sensor, substantial ESD effect or damage may still occur to any sensitive components in the sensor that tire not in adequate proximity to the electrodes or grid. In particular, sensors placed in environments that have the potential to produce ESD finger events that result in high voltages (e.g., greater than 12 kV) may not be adequately protected by such conventional solutions. What is therefore needed is a structure or architecture where ESD is dissipated prior to contact by the finger with the platen. 
     SUMMARY 
     The present disclosure relates to a structure for dissipating ESD from a finger approaching the platen of a fingerprint sensor prior to the finger&#39;s contact with the platen. Such a structure reduces the risk that sensitive electronic components within the fingerprint sensor or coupled to the sensor are damaged or otherwise cease to function properly. 
     In particular, the present disclosure describes an apparatus that comprises a raised molded structure that surrounds or is otherwise proximate to the platen, wherein an initial distance between the approaching finger and the internal sides of the raised molded structure is less than the distance between the area on the approaching finger and the platen. Given its shorter distance to the approaching finger, conductive structures within the raised molded structure will he able to stimulate or otherwise encourage electrostatic activity prior to the conductive traits of the platen doing so itself. The apparatus also includes a frame for the aforementioned conductive structures, wherein the frame is affixed underneath the raised molded structure and connected to ground and the conductive structures are positioned in a manner such that their end portions are substantially flush against (e.g., almost protruding completely through) the surface, of the raised molded structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects, features, benefits and advantages of the disclosed embodiments will be apparent with regard to the following description, appended claims and accompanying drawings where: 
         FIG. 1  depicts a molded structure with ports designed to reduce the amount of electrostatic buildup discharged to a platen according to an embodiment. 
         FIG. 2  depicts a top-side view of the molded structure. 
         FIG. 3  depicts a lateral-side view of the molded structure, 
         FIG. 4  depicts a frame including conductive structures placed under the molded structure according to an embodiment. 
         FIG. 5  depicts the molded structure and frame in an exploded and separated view. 
         FIG. 6  depicts exemplary conductive structures according to embodiments. 
         FIGS. 7 and 8  depict swipe sensors including exemplary electrostatic discharge structures according to embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is directed towards a structure for reducing ESD that may be drawn into a sensor by an approaching finger. Although reference is made to a fingerprint sensor herein, any sensor that comes into contact with electrostatically charged objects may be protected from ESD using a device designed according to the principles of the disclosed embodiments as will be apparent to one of ordinary skill in the art. 
       FIG. 1  depicts an exemplary structure configured to reduce or eliminate the amount of electrostatic buildup discharged from a finger into a fingerprint sensor. As shown in the particular structure of  FIG. 1 , the raised molded structure  100  may be placed around the platen  105  of a fingerprint sensor  110 . Those with ordinary skill in the art will recognize that such a structure  100  would be effective when used with a capacitive, piezoelectric, pyroelectric or any other electrically sensitive fingerprint, sensor. Such fingerprint sensors may take a variety of forms known to those of ordinary skill in the art, including, without limitation, area fingerprint sensors, such as the one  110  depicted in  FIG. 1 , and swipe fingerprint sensors, such as depicted in the embodiment of  FIG. 7 . 
     The structure  100  may be mounted or otherwise affixed onto the fingerprint sensor  110  so that the position of the structure  100  with respect to the platen  105  is constant. The structure  100  may be designed in order to increase the probability that an approaching finger is nearer to the structure  100  than the platen  105  such that electrostatic buildup on the finger may be drawn towards the structure  100  rather than the platen  105  in accordance with the teachings herein but simultaneously does not cause an impediment for the finger to be placed on the sensor (e.g., create too narrow a channel for the finger to reach the platen  105 , etc.). For example, in the particular embodiment of  FIG. 2 , the lateral walls  205  of the molded structure  100  are designed similarly to the walls of a slanted trough such that the internal sides  210  (i.e., closest to the platen  105 ) of the lateral walls  205  are angled slightly outwards. Such an angled design is intended to roughly approximate the contours and curvature of a finger such that as the finger approaches the platen  105 , the distance of the approaching finger to the internal sides  210  of the structure  100  is anticipated to be less than the distance of the finger to the platen  105  (at least until the finger touches the platen  105  or is substantially close to touching the platen  105 ). Similarly, as depicted in  FIG. 3 , the top and bottom portions  305  of the structure  100  are also similarly inclined at a slight angle such that the base and top portions of the fingertip approach the top and bottom portions of the molded structure  100  and may ultimately touch such portions as the finger reaches the platen  105  or before the finger reaches the platen  105 . The structure  100  may additionally be further economically designed to guide a user&#39;s finger into the platen  105  in an appropriate position. For example, as depleted in  FIG. 1 , the structure  100  may include a grooved fingertip area  115  to provide guidance for proper finger placement. 
     As depicted in  FIG. 4 , a frame  400  comprising a plurality of conductive structures of varying lengths and angles, such as  405  and  410 , is substantially covered by the structure  100 . The frame  400  and its protruding conductive structures may comprise a metal or an alloy, such as aluminum or copper, or any other conductive materials known to those with ordinary skill in the art. Alternatively, a metallic coating or a coating comprising an alloy may be used to form an appropriate conductive structure if, for example, the portion of the conductive structure underlying the coating is not conductive. As depicted in the particular embodiment of  FIG. 5 , the frame  400  may be a separate component from the molded structure  100 . The frame  400  and its conductive structures may be electrically connected to a ground voltage. For example and without limitation, the shield of a cable connected to the fingerprint sensor may be used as the ground. This connection may be internal to the fingerprint sensor  110 , such as via a wire from one or more screws that affix the molded structure  100  to tire sensor housing to a direct connection to the cable shield. Alternatively, the ground path may also be connected externally to the fingerprint sensor  110  via a dedicated ground wire. The conductive structures of the frame  400  may have pointed tips as in  FIG. 4  and may be positioned in various angular positions relative to the base of the frame  400  such that the tips of such conductive structures may slightly protrude though the various ports (e.g., slots or openings) in the molded structure  100 , such as depicted in  120  of  FIG. 1  and  FIG. 4 . Nevertheless, the pointed tips of the conductive structures may be substantially flush with the exterior surface of the molded structure  100  such that a user is unable to feel the pointed tips when a finger is placed on the surface of the structure  100 . As shown in the particular embodiment of  FIG. 4 , the overall configuration of the conductive structures beneath the lateral walls  205  of the molded structure  100  may alternate between conductive structures in a raised position that are, for example, perpendicular or nearly perpendicular to the base of the frame  400  (such as  405 ) and conductive structures in a position prone and level or nearly prone and level with the frame  400  (such as  410 ). Similarly, the conductive structures beneath the top and bottom portions  305  are angled in such a manner as to also slightly protrude though ports  120  of the molded structure  100 . Those with ordinary skill in the art will recognize that other angled configurations for conductive structures are possible within the scope of the present disclosure and that the shape and number of conductive structures used in any particular embodiment may differ from the shape and number shown in the particular embodiments represented by  FIGS. 1 through 5  herein. For example and without limitation, conductive structures protruding from the internal sides  210  of the lateral walls  205  of the molded structure  100  may be at intermediate angles and with greater or lesser distances from the platen  105  than the depicted conductive structures  405  and  410 . 
     As depicted in  FIG. 1 , the molded structure  100  may be made of material having a low dielectric constant. The dielectric constant is the ratio of the amount of electrical energy stored in a particular material, when a static electric field is imposed across it, relative to a vacuum. Accordingly, materials having low dielectric constants essentially act as a shield against electric fields. Creating the molded structure  100  with materials of low dielectric constant may improve the performance of ESD dissipation as taught herein because such materials will interfere less with the creation of high electric fields at the tips of the conductive structures that protrude through the structure  100 . For example and without limitation, the molded structure  100  may be manufactured from a plastic having a dielectric constant in the range from about 1.5 to about 2.5, such as polypropylene and/of polytetrafluorocthylene. Other embodiments may utilize a material with, a higher dielectric constant such as aerylonitrile butadiene styrene (“ABS”) plastic, which has a dielectric constant of 4.5. Those with ordinary skill in the art will recognize that the performance of the ESD dissipation as taught herein may depend upon the combination of the dielectric constant of material of the structure  100  as well as the placement of the conductive structures in relation to the structure  100 . For example, for a structure  100  made of material with a higher dielectric constant, the performance of ESD dissipation may be better when the conductive structures protrude further out of the ports  120  and are exposed to the air since such an embodiment would decrease the interference of the material of the structure  100  with the electric fields created by the tips of the conductive structures. Similarly, those with ordinary skill in the art will recognize that a structure  100  made of a material with a very low dielectric constant (e.g., the dielectric constant of air) could obviate the need for creating the ports  120  from which the pointed tips of the conductive structures of the frame  400  can protrude in order to stimulate and encourage corona discharge and possible subsequent dielectric breakdown (i.e., arcing) as further detailed below. In such an embodiment, since the conductive structures would not protrude through the structure  100 , the thinner the thickness of the walls of the structure (e.g., in the order of a few microns), the better the performance of corona discharge and possible dielectric breakdown through the thin walls of the structure  100  into the conductive structures. 
     As depicted in the particular embodiments of  FIGS. 1 through 5 , the tips of the conductive structures are pointed to stimulate or otherwise encourage corona discharge from a finger as it approaches the platen  105 . As would be apparent to one of ordinary skill in the art, such pointed tips encourage the creation of localized high electric fields and as an electrically charged finger approaches the molded structure  100  (and therefore the ports  120  and tips of the conductive structures), local electric fields between the tip&#39;s of the conductive structures nearest to the finger and the finger may steadily increase. When an electric field reaches a sufficient level, an electrical arc (also known as dielectric breakdown) may result between the finger and at least one conductive structure, thereby dissipating ESD prior to the finger touching the platen  105 . The ports  120  from which the conductive structures protrude are situated on the molded structure  100  in a manner so as to increase the probability that the various protruding conductive structures cause corona discharge and dielectric breakdown to be diverted from the platen  105  and directed towards the conductive structures. For example and without limitation, in the embodiments of  FIGS. 1 through 5 , the ports  120  that are intended to initially encourage corona discharge as a finger first approaches the platen  105  are those that are placed near the top of the molded structure  100  and are associated with the longest conductive structures  405  of the frame  400  which have been positioned, for example, nearly perpendicular to the base frame  400 . As the finger passes through the initial horizontal plane created by the plateau of the lateral walls  205  and draws nearer to the platen  105  itself, the lower situated conductive structures  410  related to the lower ports  120  on the internal sides  210  of the lateral walls  205  and the conductive structures  310  of various lengths and angles protruding through the ports of the top and bottom portions  305  of molded structure  100  provide additional opportunities to attract and stimulate corona discharge and dielectric breakdown from the finger into such conductive structures prior to ultimate contact with the sensor. As further depicted in  FIG. 6 , those with ordinary skill in the art, consistent with the scope of the present disclosure, may envision alternative embodiments of the frame  400  that utilize different conductive structures having alternate and/or additional shapes with varying effect in dissipating ESD. For example and without limitation, rather than having conductive structures with points protruding through the center of the ports  120  as depicted in  FIG. 1 through 5  and as detailed in  605 , an alternative embodiment  610  may have two points from two conductive structures protruding through a single port, but positioned at the edges of the port such that the valley between the two conductive structures is centered over the center of the slot. In such an embodiment, because the points of the two conductive structures are tangent to, and in contact with, the inner wall of the port, they may be less exposed than a point protruding from the center of the port, thereby providing a smoother feel when a finger comes into contact with the port. Alternatively, rather than having pointed conductive structures protruding from the frame  400 , an embodiment  610  may simply utilize a conductive bar that passes across the ports in the molded structure  100 . 
     With respect to an embodiment that may be similar to the embodiments set forth in  FIGS. 1 to 5 , the tips of the raised conductive structures  405  may be, for example, approximately one-third of an inch above the platen  105  of the fingerprint sensor  110 . The tips of the lowered conductive structures  410  may be, for example, approximately 0.02 inches above the platen  105  of the fingerprint sensor  110 . A port  120  may be approximately 0.01 inches to approximately 0.05 inches in diameter and maybe any shape, such as circular, rectangular, or the like. Each port  120  exposes a portion (e.g., the point) of a conductive structure in order to stimulate corona discharge and dielectric breakdown into the conductive structure. 
     An additional enhancement to the ESD structure disclosed herein is to create an actively charged frame  400  by connecting the frame  400  to a voltage supply. The voltage applied by the voltage supply may be alternating current (“AC”) or direct current (“DC”) and is sufficient to cause free charges to emanate from the tips of the conductive structures via corona discharge. Using a DC voltage supply will produce either positively or negatively charged particles, depending on the polarity of the voltage supply. Using an AC voltage supply will produce both positively and negatively charged particles. In such an embodiment, as the finger approaches the vicinity of the charged pointed conductive structures, appropriately charged particles generated by the high electric fields at the points of the conductive structure will be attracted to a charged finger thereby canceling or counteracting the electric charge. If, for example, the finger is negatively charged, the free positive charges will be attracted to it, thereby canceling the negative charge on the finger, and the free negative charges will be repelled. In such an embodiment, the structure  100  surrounding the charged frame  400  may possess a number of ports or other openings or a grill or louvers in order to allow the charged particles to emanate from the frame&#39;s conductive structures through structure  100  and into the air in the vicinity of the approaching finger and near the surface of the platen. The number of conductive structures of the frame  400  may also be larger and the conductive structures may be more closely packed in a charged frame  400  embodiment as compared to non-charged frame embodiments as a larger number of charged conductive structures placed in a closely packed array increases the number of charged particles that may emanate from the tips of the conductive structures. In such an embodiment, the structure  100  may also serve a protective purpose by preventing or reducing the chance that a user receives an electric shock from the charged frame and conductive structures. As such, the conductive structures may be located a sufficient distance behind or under the walls of the protective structure  100  in order to eliminate or otherwise reduce the possibility of shock or arcing from the charged conductive structures to the user&#39;s approaching finger. 
     Although the present invention has been described with reference to the alternative embodiments, those of ordinary skill in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of this disclosure. Terminology used in the foregoing descriptions is for the purpose of describing the particular versions or embodiments only, and is not intended to limit the scope of the present invention which will be limited only by the appended claims. For example, the present disclosure generally relates to providing systems for protecting a sensor from electrostatic energy from an object proximate to the sensor. While the term “sensor” is used throughout the disclosure, it is not meant to limit the disclosure to any particular type of sensor, such as a fingerprint sensor or an area sensor. A sensor could refer generally to any device that retrieves information. For example and without limitation, as depicted in  FIG. 7 , a swipe sensor may also include an electrostatic discharge structure as taught herein. The swipe sensor  700  may have a raised structure, as in the sensors described above in reference to  FIGS. 1 through 5 . However, rather than having the raised structure surround the platen on all sides, as in the area sensor embodiments used in  FIGS. 1 to 5 , an embodiment for a swipe sensor  700  may include only raised lateral side walls  705  formed as vanes on the sides of the platen  710  of the swipe sensor (the “swipe strip”) that parallel the motion of a swiping finger. Each side wall  705  may include one or more conductive structures, such as  715  and  720 . In addition, one or more conductive structures, such as  725  and  730 , may be located within areas on either side of the swipe strip  710 . During operation, a finger may be received in an area on one side of the swipe strip  710 , drawn over the swipe strip and continue onto an area on the other side. An alternative swipe sensor embodiment, depicted in  FIG. 8 , may utilize small, raised and rounded conductive hemispheres  805  located in the molding surrounding the swipe stripe directly within the path of a swiping finger. In such an embodiment, as the finger approaches the swipe strip, the finger comes into direct contact with the conductive structures  805 , thereby encouraging any charges present in the finger to flow into the conductive structures. The conductive structures  805  may be retractable. As such, as a finger contacts each conductive structure  805 , the pressure from the finger presses the conductive structure into the molding, as depicted in  810 , such that the top of the hemisphere is substantially flush and level to the surface of the sensor. When the finger no longer presses against a conductive structure  805 , the structure may return to a raised position (i.e., slightly above the surface of the level swipe sensor), as depicted in  815 . Similarly, an alternative swipe sensor embodiment may utilise slightly raised conductive strips  820  that are affixed to the surface of the swipe sensor and positioned directly in the path of a swiping finger. Such strips  820  may additionally assist in guiding the finger through the swipe strip. 
     As used herein and in the appended claims, the singular forms “a,” “an” and “the” include plural references unless the context clearly dictates otherwise. Similarly, the words “include,” “includes” and “including” when used herein shall be deemed in each case to be followed by the words “without limitation.” Unless defined otherwise herein, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. All publications mentioned herein are incorporated by reference. Nothing herein is to be construed as an admission that the embodiments disclosed herein are not entitled to antedate such disclosure by virtue of prior invention. Thus, various modifications, additions, substitutions and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the following claims.