Patent Application
20050178827
The present invention relates, in general, to biometric print scanning devices. In particular, the present invention is a fingerprint sensor constructed in an array configuration.
Computer security systems use biometric data, such as fingerprints, to authenticate the identity of the users attempting to gain access to a computer system. These computer systems include, but are not limited to, general-purpose computers such as desktop and portable personal computers, peripheral devices that connect to a general-purpose computer, and mobile devices such as credit cards, smart cards, cellular telephones, satellite telephones, and portable digital assistants (PDAs). A fingerprint scan in combination with a conventional means of identification, such as a password, makes a computing device that relies on these computer security systems more reliable.
The most common fingerprint sensors used on a mobile computing device are made from thin silicon chips. These silicon-based capacitive arrays are very brittle and break easily if bent. Structures to support the chip and restrict bending of the sensor contribute most of the thickness of the sensor. Pad sensors can be easily broken if bent in either the X or Y directions. Newer swipe sensors greatly reduce the possibility of bending in the X direction, but are still easily broken if bent in the Y direction.
To obtain an image of a finger, a fingerprint scanner needs to determine whether the pattern of ridges and valleys in one image matches the pattern of ridges and valleys in another image. The two most common methods for obtaining a fingerprint are optical scanning and capacitance scanning. Optical scanning uses a charge coupled device to record light and dark pixels and form an image of the fingerprint. Capacitance scanning uses electrical current to sense the image of the fingerprint. The capacitance scanner includes a number of sensors. Each sensor includes one or more semiconductor chips that contain an array of cells. Each cell includes two conductor plates covered with an insulating layer. The sensor is connected to an integrator, an electrical circuit built around an inverting operational amplifier. The conductor plates form a basic capacitor and the finger acts as a third capacitor plate. Since a variance in the distance between the capacitor plates changes the total capacitance, the capacitor in a cell under a ridge will have a greater capacitance than the capacitor in a cell under a valley.
The two most common types of capacitance scanning fingerprint sensors are pad sensors and swipe sensors. A fingerprint pad sensor is typically a small square, usually one-half inch by one-half inch in size. When a person places their finger on the pad, a form of camera or imaging devices takes a single image of the complete fingerprint. The captured image is typically digitized and stored as a digital image that can be compared to other stored images of fingerprints.
A fingerprint swipe sensor is a more recent technological development. The fingerprint swipe sensor is typically a thin, rectangular shaped device measuring approximately one-half inch by one-sixteenth inch in size. The fingerprint swipe sensor obtains a number of small images, or snapshots, as a person passes, or swipes, their finger across the sensor. The fingerprint swipe sensor obtains a complete fingerprint by processing and combining each of the individual images to form a composite image. The compiling of the smaller images into a complete fingerprint is typically referred to as “stitching” the images.
A smart card is a computing device with a size and shape that resembles a credit card. The credit card stores data on the magnetic strip affixed to the back of the credit card. In contrast, a microprocessor is embedded in the smart card and connected to a memory that can store more information than the magnetic strip affixed to the back of a credit card. The microprocessor also enables the smart card to communicate with another computer system to change and update the data stored in the memory. For example, a smart card can store a prepaid amount of money. To pay for an item at a store, the card holder presents the smart card to the merchant, scans the smart card using a reader device to determine the balance on the card, deducts the cost of the item from the balance, and stores the new balance on the smart card. However, such an exemplary smart card cannot authenticate the card holder's identity. Incorporating an authentication mechanism, such as a fingerprint scan, into this exemplary smart card would increase the reliability of smart card, but at present would significantly increase the size of the card.
Thus, there is a need for a fingerprint sensor constructed in an array configuration that reduces the possibility of breakage due to bending of the medium holding the fingerprint sensor. The present invention addresses this need.
The present invention provides a print sensor, computing device, and method comprising a swipe sensor array that includes a number of sensor elements arranged in at least two columns with a gap separating each adjacent column and each sensor element in each adjacent column. Each sensor element generates signals related to a portion of a print when the print is positioned adjacent a top portion of the sensor element. When scanning, a user swipes a print perpendicular to said at least two columns, wherein each gap in a first column is overlapped by the sensor elements in the adjacent column.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description, examples, and figures which follow, all of which are intended to be for illustrative purposes only, and not intended in any way to limit the invention, and in part will become apparent to the skilled in the art on examination of the following, or may be learned by practice of the invention.
The accompanying figures illustrate details of the fingerprint sensor constructed in an array configuration. Reference numbers and designations that are alike in the accompanying figures refer to like elements.
The fingerprint pad sensor 130 is a silicon-based capacitive semiconductor chip, a naturally brittle and easily breakable material. Since the material composition of the smart card 100 makes it bendable, especially when produced to confirm to credit card dimensions, the fingerprint pad sensor 130 will be susceptible to breakage in both the X and Y directions. An approach to prevent breakage of the fingerprint pad sensor 130 (i.e., reduce the bending moment) is to add (i.e., bond) a support structure layer to the back of the fingerprint pad sensor 130. The material composition of the support structure layer must be a rigid, reinforcing material, such as aluminum plate, stainless steel, or titanium. Since the fingerprint pad sensor 130 is very likely to be bent, the thickness of the reinforcing material is increased to reduce the bending moment. However, the thickness of the reinforcing material that will prevent breakage when added to the thickness of the fingerprint pad sensor 130 contributes to most of thickness of the smart card 100. Thus, this approach is not feasible in the prior art, particularly if credit card thickness is maintained.
The fingerprint swipe sensor 230 is a silicon-based capacitive semiconductor chip, a naturally brittle and easily breakable material. In contrast to the fingerprint pad sensor 130, the fingerprint swipe sensor 230 is significantly narrower in the X direction, but equivalent in size in the Y direction. Since the material composition of the smart card 200 makes it inherently bendable, the fingerprint swipe sensor 230 will be susceptible to breakage, in primarily the Y direction. An approach to prevent breakage of the fingerprint swipe sensor 230 (i.e., reduce the bending moment) is to add (i.e., bond) a support structure layer to the back of the fingerprint swipe sensor 230. The material composition of the support structure layer must be a rigid, reinforcing material, such as aluminum plate, stainless steel, titanium, or other rigid sheet-like material. However, for the reasons stated with regard to the print pad sensor 130, the fingerprint swipe sensor 230 is also very likely to bend. Consequently, in the prior art the thickness of the reinforcing material is increased to reduce the bending moment. Unfortunately, the thickness of the reinforcing material needed to prevent breakage of the fingerprint swipe sensor 230 contributes substantially to the thickness of the smart card 200, making this approach is not feasible if credit card thickness is maintained.
Each fingerprint swipe sensor element 331, 332, 333, 334, 335, 336, 337 is a silicon-based capacitive semiconductor chip, a naturally brittle and easily breakable material. In an exemplary embodiment, each element of measures approximately one-sixteenth inch by one-sixteenth inch in size. However, for the same reason the fingerprint swipe sensor 230 shown in
An approach to prevent breakage of each fingerprint swipe sensor element 331, 332, 333, 334, 335, 336, 337 (i.e., reduce the bending moment) is to add (i.e., bond) a support structure layer to the back of each fingerprint swipe sensor element 331, 332, 333, 334, 335, 336, 337. The material composition of the support structure layer must be a rigid, reinforcing material, such as aluminum plate, stainless steel, titanium, or other rigid sheet-like material. Since the length of each fingerprint swipe sensor element 331, 332, 333, 334, 335, 336, 337 is narrow in both the X and Y directions, each supported element is less likely to bend. Thus, the thickness of the reinforcing material to reduce the bending moment is significantly less than the thickness required for the fingerprint pad sensor 130 and the fingerprint swipe sensor 230.
Small silicon-based capacitive semiconductor chips used in fingerprint sensors are cut from very large silicon disks. A single flaw in a large chip will force rejection of the whole chip and reduce the yield of the wafer. Reducing the size of the chip will not reduce the number of flaws, but it will reduce the amount of rejected material and improve the overall yield of the wafer.
The fingerprint swipe sensor array 330 is constructed from a number of overlapping small chips, fingerprint swipe sensor elements 331, 332, 333, 334, 335, 336, 337, to reduce the possibility of breakage due to bending and to improve the yield in manufacturing the chips. This array of chips will require additional assembly, which will be easily offset by the production of thinner and more durable sensors. These sensors will be ideal for use in smart cards where a limited amount of bending of the card is permitted and is a requirement of the smart card specification. The array can be constructed, and software designed, such that damage to any chip in the array does not adversely affect the ability to obtain a workable fingerprint image. Another advantage of the fingerprint sensor array 330 is that most of the stress applied to the each small chip, fingerprint swipe sensor elements 331, 332, 333, 334, 335, 336, 337, due to card bending can be absorbed in the plastic matrix surrounding the chips.
Although the disclosed embodiments describe a fully functioning fingerprint sensor constructed in an array configuration, the reader should understand that other equivalent embodiments exist. Since numerous modifications and variations will occur to those reviewing this disclosure, the fingerprint sensor constructed in an array configuration is not limited to the exact construction and operation illustrated and disclosed. Accordingly, this disclosure intends all suitable modifications and equivalents to fall within the scope of the claims.
This application for letters patent is related to and incorporates by reference provisional application Ser. No. 60/544,556, titled “Flexible Fingerprint Sensor Arrays,” and filed in the United States Patent and Trademark Office on Feb. 13, 2004.
| Number | Date | Country | |
|---|---|---|---|
| 60544556 | Feb 2004 | US |
