FINGERPRINT SENSORS
A sensor for detecting fingerprints is provided having first and second substrates, a two-dimensional array of sensing elements formed on the first substrate, and a plurality of thin-film transistors or TFTs for controlling the sensing elements at pixel location along the array. Each of the sensing elements detects one of electrical signals (e.g., capacitance, resistance, or impedance), temperature, or light via one of the first or second substrates representative of one or more fingerprints. The top of the second substrate or the bottom of the first substrate may provide a platen upon which one or more fingers can be disposed. The sensor may be utilized in a fingerprint scanner having one or more processors driving sensing elements or reading from sensing elements analog signals representative of one or more fingerprints, and generating an image representative of the one or more fingerprints from the analog signals.
This application claims the benefit of priority to U.S. Provisional Patent Application No. 61/486,766, filed May 17, 2011, which is herein incorporated by reference.
FIELD OF THE INVENTIONThe present invention relates to sensors, methods, and systems for detecting one or more fingerprints, and particularly a sensor for detecting one or more fingerprints utilizing thin-film transistors (TFT). The present invention is particularly useful in providing a fingerprint sensor having sensing element(s) at each pixel location of a two-dimension array where sensing element(s) are coupled to one a TFT at the pixel location for use in a fingerprint scanner to provide a two-dimension fingerprint image of one or more fingers. At each pixel location, a single sensing element of desired type or characteristic (e.g., light, electrical, or thermal sensing) may be coupled to a TFT enabling driving and readout of the sensing element, or multiple sensing elements of the same or different type may be coupled to a TFT.
BACKGROUND ON THE INVENTIONA thin-film transistor (TFT) is a particular kind of field-effect transistor. The most common applications of TFTs are displays such as LCD TVs and monitors. Less common is the use of TFTs as sensors, with the one exception being the use of TFT sensor arrays (with a scintillation layer) for the purposes of digital radiography (see for example DPIX, Inc., Palo Alto, Calif.). Whether for use in a display or a sensor application, each of these applications employ an array of pixels in a two-dimensional (2D) grid where within each pixel, layers of thin films (metals, oxides and amorphous silicon, for example) are deposited onto a substrate that is typically glass of 1.0 mm or thinner thickness. TFTs are created at each pixel (typically two or three per pixel) to facilitate the addressing of individual pixels whether for driving or readout purposes.
Present commercial optical fingerprint scanners capture images of reflected light representing an image of a fingerprint onto complementary metal-oxide semiconductor (CMOS) or charge-coupled device (CCD) two dimensional sensors. Such CMOS and CCD sensors are similar and sometimes identical to those used in commercial digital cameras. Free-space optics such as refractive lenses that comprise a multi-element objective lens are used to image the reflected light off of the finger and onto the 2D sensors. Because of the presence of free-space optics, a relatively large distance must be between the finger and the sensor, resulting in a fingerprint scanner that is larger and bulkier than would be desired for certain applications (in particular mobile, hand-held applications). It would be desirable to avoid free-space optics so as to provide significantly more compact and potentially lighter weight scanners than are presently utilized.
SUMMARY OF THE INVENTIONAccordingly, it is a feature of the present invention is to provide a fingerprint sensor having arrays of sensing elements controlled by TFTs for detecting one of more fingerprints, and thereby provide a TFT fingerprint sensor, which avoids free-space optics of conventional fingerprint scanners.
Briefly described, the present invention embodies a sensor having first (base) and second (cover) substrates, a two-dimensional array of sensing elements formed at pixel locations on the first substrate, and thin-film transistors for controlling the sensing elements at each of the pixel locations. Each of the sensing elements detects one of electrical signals (e.g., capacitance, resistance, or impedance), temperature, or light via one of the first or second substrates representative of one or more fingerprints.
At each pixel location in the array, the sensing elements may be of the same types, such as light sensing, in which illumination is provide from below or within the sensor, or of two or more different types coupled to a common TFT at the pixel location, so that different characteristics (electrical, light, or temperature) of from fingers may be detected. The first or second substrate may provide a platen surface for placement of one or more fingers, or where light sensing elements are present in the array the platen surface of the sensor may be provided by the surface of optical prism element, which is disposed upon the sensor. Optionally, the optical prism element may provide the second substrate.
Optionally, the sensing elements represent different groups of multiple light sensing elements of different light sensing types or characteristics distributed uniformly or non-uniformly at pixel location along the array. For example, the sensing elements may have a first group of light sensing elements and a second group of electrical or temperature sensing elements, where the first group is used for imaging fingerprint(s) and the second group may also be used for imaging fingerprint(s) or parts thereof, or detecting liveliness of finger(s).
The first or second substrate may provide a platen surface for placement of one or more fingers, or a platen surface may be provided by the surface of optical prism element, which is disposed upon the sensor. Optionally, the optical prism element may provide the second substrate.
The present invention further comprises a system or scanner having the above sensor for detecting one or more fingerprints, and one or more processors, where each of the thin-film transistors controls the one or more of the sensing elements responsive to the processor(s) to enable the processor(s) to one or more of driving the one or more of the sensing elements or reading from the one or more sensing elements analog signals representative of one or more fingerprints, and generates an image representative of the one or more fingerprints responsive to the analog signals. One or more (or all) of the processor(s) may be part of a computer system. When the sensing elements of the array are at least optical sensing elements, illumination may be provided to the first and second substrates or from between the two substrates, such that the optical sensing elements detect a reflected part of illumination representative of one or more fingerprints.
Preferably, the arrays of TFT and coupled sensor(s) thereto are in 2D orthogonal grids. As the sensor of the present invention avoids the need for free-space optics described earlier, the magnification of the fingerprint(s) detected when light sensing elements are present is typically 1:1, but may be a slightly higher magnification in one axis due to the presence of a tilted platen as in the case of a prism element. For systems that have 1:1 magnification, the maximum pixel size desired for AFIS (Automatic Fingerprint Identification Systems) corresponds to 50.8×50.8 μm which translates to 500 points-per-inch (ppi). For a system that incorporates a 45 deg prism, the maximum pixel size is 50.8*sin(45)=35.9 μm.
In each pixel element of the array is a TFT to allow for individual driving and/or enabling reading of an analog value by the processor(s). Such may be enabled by drive/read electronics to the TFTs. Each pixel element may contain one or more of the following sensing elements: a light sensor, light source, capacitance sensor, resistance sensor, impedance sensor, and thermal sensor. For the optical measurement of a fingerprint pressed in contact with a platen surface, at a minimum a light sensor per pixel is needed for where the sensing element detect light. For optically sensitive TFT pixels, illumination by the fingerprint scanner may come from a light source external to the TFT sensor array such as from a light panel or light guide underneath the sensor (since it is printed on top of the first substrate and a portion of each pixel may be transmissive to allow light to transmit from underneath the array and illuminate a fingerprint that is above the first substrate of the sensor). Alternatively, the light source may be provided at each pixel of the array. By way of example, for a light sensing element may be a PIN photodiode, a LED (light-emitting diode) or an OLED (organic light-emitting diode). Additionally or in place of, other modes of detection by the sensing element may be used for measuring the electrical characteristics of the skin (resistance, capacitance, impedance) or temperature may be incorporated into each pixel. The electrical characteristics of the fingerprint may be the primary method for extracting the minutia detail required for enrollment, identification, and/or verification, or may be a complementary method used in order to determine that a fingerprint presented to the scanner system is an actual live finger and not a spoof or a dead finger. By incorporating electrical and/or temperature measurement systems, the scanner becomes more difficult to fool or spoof. By way of example, the array of the sensor may have at each pixel an optical sensing element and an electrical sensing element and in this manner be able to image a subject's fingerprint both optically and electrically. Alternatively, a TFT-based array may have predominantly one type of sensing elements for the purposes of imaging the fingerprint and a very low percentage of sensors of another technology that samples the fingerprint sparsely for the purposes of spoof detection or detection of the presence of the fingerprint. By way of example, consider an array that has 50.8 μm pixels wherein every area of 20×20 pixels (roughly 1×1 mm2) contains a pixel with an electrical sensor. One mode of operation for such an array is to only read out the sparse electrical sensor array by the processor(s) and when the analog signals received falls within the expected values for a finger (for example impedance values at certain AC frequencies), the optical sensor array is turned on to read the actual fingerprint by the processor(s).
RFID functions may be incorporated into the scanner and the sensor of the present invention in order to interact with badge or other form of identification in addition to that provided by the presented fingerprint.
TFTs, since they use amorphous silicon rather than crystalline silicon, can be printed on flexible substrates. Flexible substrates can be advantageous since they can allow more compact fingerprint scanners wherein folds or rolls up when not in use. Alternately or in addition to, these flexible substrates can be fabricated in a “sling-like” configuration suitable for capture of rolled print equivalents. Flexible TFT-based arrays can be made very thin in order to accommodate “smart ID card” applications.
A surface of the second substrate facing the first substrate may be the top of the substrate in the sandwich light assembly of the first and second substrates and the array disposed there between. Alternatively, the surface of the first substrate opposite the array formed thereupon may be the top of the substrate, in this case the sensor may be considered “up-side-down”, in which case a metal (like steel or aluminum) plate or substrate may be provided as part of the assembly. Thus, the array may be printed where the second substrate is considered the bottom of the sensor. The TFT is printed on top of the first substrate and the light to be collected comes from above the sensor. However, if the TFT needs to be encapsulated with a gel or epoxy, trapped air bubbles will hinder light coming from the object and reach the TFT sensor. By printing the sensor “upside-down” one avoids this potential issue. In other words, the sensor is made such that light is expected to be collected from the bottom on of first substrate. This way, if any encapsulating is required, trapped air bubbles will only affect the illumination light (and not even this if LEDs or OLEDs are present at each pixel in the array. This and can thus increase optical resolution of a scanner utilizing the sensor. The metal plate may encapsulate the “upside down” sensor, and strengthen the sensor as well as to act as a heat sink for temperature stabilization.
In addition to a fingerprint scanner, the sensor of the present invention may also be used to image other object(s) such as a document in the case of a document scanner, signature to provide a signature/text reader, or a barcode to provide a barcode reader.
The foregoing and other objects, features and advantages of the invention will become more apparent from a reading of the following description in connection with the accompanying drawings in which:
Referring to
Referring to
In
Optionally, the array 17 may having multiple groups of sensing elements 17 of different types, such as one group having light sensing elements and another having electrical sensing elements (or thermal sensing elements). By selection for readout of the sensing elements 17 of each group different types of two-dimensional images can be obtained, or the light sensing group can provide an image of fingerprints and the information from readout of the electrical (or thermal) sensing group can be used for other purposes, such as to determine if the signals read are in the range of a live finger so as for spoof detection. For example, a uniform distribution may be provided where every N pixels has a sensing element of a different group along x and y axes, where N may be 1 or other number depending of desired resolution by each group of pixels. For example, a non-uniform distribution may be provided have pixels of one group of electrical sensing pixels for liveliness detection of finger(s) present but outside expected fingerprint regions along the array where light sensing pixels are provided.
Each pixel 15 may have in addition to a sensing element 17 (e.g., photodetector) for light sensing, but a second sensing element 17a for electrical sensing, e.g., capacitance, (or temperature sensing) which are both coupled to the same TFT 16 of a pixel, as shown for example in
Further, instead of each pixel 15 having a single TFT and one sensing element (
The top surface of cover 14 provides a platen or platen surface 18 upon which one or more fingers 20 (with or without thumb) may be pressed against so that the sensing element 17 of array 15 can detect detects one of electrical signals, temperature, or light representative of fingerprint(s) 21 in accordance with the type of sensing element. The sensor 10 (sandwich of substrates or layers 13 and 14, and array 11) may be flat to provide a flat platen 18, or have curvature as shown for example in
One or more processors 22 control operation of the scanner 8, including at least the sensor 10, as well as the illumination source 12a (e.g., illuminator 12) if present, by cables or wires shown in
In the case of array having a pixel 15 with two or more different types of sensing elements one light sensing element 17 and the other electrical or temperature sensing 17a element coupled to a common TFT 16 for drive and readout. The illuminator 12 is turned on by processor(s) 22 and at each pixel an analog signal is read out representing the combine analog signal from both sensing elements 17 and 17a at each x,y pixel location and converted into a digital signal and stored at a first location in memory of the processor or other memory coupled thereto. The illuminator 12 is then turned off by processor(s) 22 and at each pixel location an analog signal is read out representing the analog signal from sensing elements 17a (or at least substantially so where ambient light is limited by hood over the platen or other means) at each x,y pixel location and converted into a digital signal for stored in a second location in memory of the processor or other memory coupled thereto. By the processor(s) 22 subtracting at each pixel location the digital signals at the first and second memory locations, the result is a digital signal at each pixel location representative (or at least substantially so) of sensing elements 17 and hence representative of fingerprint(s). Alternatively, depending on each different sensing element in a pixel, the analog signal readout may be performed simultaneous in which each of the sensing element have distinguishable signal characteristics, such as AC or DC.
The scanner 8 may be coupled by power and communication cable or wirelessly to computer system or other microprocessor based system 24 having other processor(s) for processing of image(s) captured by the scanner from processor(s) 22, and/or such processing may be carried out by processor(s) in housing of scanner 8. Optionally, computer system 24 may be in the same housing as scanner 8. The computer system 24 and/or processor(s) 22 may store fingerprint images segmented from images captured by apparatus in memory (e.g., memory of processor(s) (or separate memory accessible to the processors, and/or computer system) for later use for fingerprint enrollment, verification, or identification as typical of a biometric-based security systems.
Referring to
In one mode of operation of sensor 10 of
Referring to
Referring to
Referring to
Referring to
Although surface 32a is at a right angle (perpendicular) to prism's surface 32c attached to surface 14a of cover 14, prism 32 may similarly be attached to surface 13b of base 13 in the case of the sensor 10 of
Referring to
Surface 38a of prism 38 may be rectangular (right angle), obtuse (as shown) with respect to its surface 38c attached to surface 14a of cover 14, or at another angle, so long as light 40 is directed at a TIR angle with respect to surface 38a from a light source so that light 43 is reflected from platen 18 onto array 11. The dashed line 42 indicates that little light is reflected due to rough index match between skin of finger 20 and surface 38b of prism 38. Although surface 38c of the prism 38 is attached to surface 14a of cover 14, prism 38 may similarly be attached to surface 13b of base 13 in the case of the sensor of
The sensor 10 of
Optionally, polarized light may be used in sensor 10. Incident light can be polarized and a polarizer be placed directly over array 11 or upon a part of the sensor 10 through with light from illuminator 12 passes prior to platen 18. Illuminator 12 (or 33
The sensor 10 may use TIR as described above, or ambient Light Rejection TIR may be used, in which platen 18 may have an ALRF film, such that most of ambient light is reflected by platen and the array 11 sees primarily desired illumination light and not outside light.
As stated earlier, although the figures are shown directed to an array 11 utilizing sensing elements 17 for detecting light, other types of sensing elements may be used for electrical (capacitance, resistance, or inductance) or temperature sensing without any sensing element for detecting light, in which case the sensor 10 is the same as shown in
From the foregoing description, it will be apparent that there has been provided an improved finger print sensors and systems utilizing same. Variations and modifications in the herein described sensors, methods, and systems will undoubtedly suggest themselves to those skilled in the art. Accordingly, the foregoing description should be taken as illustrative and not in a limiting sense.
Claims
1. A sensor for detecting one or more fingerprints comprising:
- a first substrate and a second substrate;
- a two-dimensional array of sensing elements formed at pixel locations on said first substrate; and
- a plurality of thin-film transistors for controlling said sensing elements at each of said pixel locations, wherein each of said sensing elements detects one of electrical signals, temperature, or light via one of said first substrate or said second substrate representative of one or more fingerprints.
2. The sensor according to claim 1 wherein said second substrate has a surface opposite said first substrate, and said second surface provides a platen surface for placement of one or more fingers, and said two-dimensional array of sensing elements receive said one of electrical signals, temperature, or light via said second substrate representative of one or more fingerprints.
3. The sensor according to claim 1 wherein said first substrate has a first surface and a second surface, and said sensing elements are formed on a first surface, and said second surface provides a platen surface for placement of one or more fingers, and said two-dimensional array of sensing elements receives said one of electrical signals, temperature, or light via said second surface representative of one or more fingerprints.
4. The sensor according to claim 1 wherein said sensing elements of said array are at least light sensing elements, and said sensor further comprises an illuminator providing light to said first and second substrates, and a plurality of said light sensing elements detect reflected light representative of one or more fingerprints.
5. The sensor according to claim 4 further comprising a prism array for receiving light from said illuminator and one or more of refracting or diffracting said light received to said first and second substrates.
6. The sensor according to claim 1 wherein said sensing elements of said array are at least light sensing elements, and said sensor further comprises an array of light sources between said first substrate and said second substrate for transmitting light via said second substrate, and a plurality of said light sensing elements detect reflected light representative of one or more fingerprints via said second substrate.
7. The sensor according to claim 1 further comprising one or more processors, each of said thin-film transistors controls said one or more of said sensing elements responsive to said one or more processors to enable said one or more processor to one or more of driving said one or more of said sensing elements or reading from said one or more sensing elements analog signals representative of one or more fingerprints, and generates an image representative of said one or more fingerprints responsive to said analog signals.
8. The sensor according to claim 7 wherein at least one of said one or more of said processors is part of a computer system.
9. The sensor according to claim 1 wherein said electrical signals are one of capacitance, resistance, or impedance.
10. The sensor according to claim 1 wherein said sensing elements of said array are at least light sensing elements, and said first substrate has a first surface and a second surface, and said sensing elements are formed on a first surface, and said second substrate has a third surface opposite said first substrate, and said sensor further comprises an optical element disposed upon one of said second surface or said third surface, in which said optical element has a fourth surface and a fifth surface, said fourth surface provides a platen surface for placement of one or more fingers, and light when received by said optical element via said fifth surface is directed to said fourth surface, and said plurality of said light sensing elements detect reflected light representative of one or more fingerprints via said disposed upon one of said second surface or said third surface upon which said optical element is disposed.
11. The sensor according to claim 10 wherein said optical element is a prism.
12. The sensor according to claim 11 wherein said prism is a right angle prism and said fifth surface is perpendicular to said second surface or said third surface upon which said optical element is disposed.
13. The sensor according to claim 11 wherein said fourth surface of said prism providing said platen is along a plane parallel to the plane of said sensing elements of said array.
14. The sensor according to claim 10 said optical element provides said second substrate.
15. The sensor according to claim 1 wherein said sensing elements of said array are only light sensing elements for receiving light via one of said first substrate or said second substrate representative of one or more fingerprints.
16. The sensor according to claim 1 wherein said sensing elements of said array are only electrical sensing elements for receiving electrical signals via one of said first substrate or said second substrate representative of one or more fingerprints.
17. The sensor according to claim 1 wherein said sensing elements of said array are only temperature sensing elements for receiving temperature signals via one of said first substrate or said second substrate representative of one or more fingerprints.
18. The sensor according to claim 1 wherein said sensing elements of said array represent a first plurality of light sensing elements for detecting light representative of one or more fingerprints, and a second plurality of electrical sensing elements for receiving electrical signals representative of one or more fingerprints or for detecting liveliness of said one or more fingers.
19. The sensor according to claim 1 wherein at each said pixel location along said array has a plurality of sensing elements for sensing different types and each of said plurality of sensing elements is coupled to a same one of said TFT at the pixel location
20. The sensor according to claim 1 wherein a plurality of said sensing elements for sensing different types of characteristics are uniformly distributed at different pixel locations along said array.
21. The sensor according to claim 1 wherein a plurality of said sensing elements for sensing different types of characteristics are non-uniformly distributed at different pixel locations along said array.
22. The sensor according to claim 1 wherein said sensing elements of said array are of different groups, in which each group of sensing elements has a different mode of operation.
23. The sensor according to claim 1 wherein said sensing elements of said array are at least light sensing elements, and said sensor further comprising means for providing illumination of collimated or nearly collimated light illumination, in which a plurality of said light sensing elements detect reflected part of said collimated or nearly collimated light illumination representative of one or more fingerprints.
24. The sensor according to claim 1 wherein said sensing elements of said array are at least light sensing elements, and said sensor further comprising means for providing illumination, in which a plurality of said optical sensing elements detect reflected part of said illumination representative of one or more fingerprints via said second substrate, and said illumination of one or more wavelength which reduce diffraction in said light received by said plurality of said optical sensing elements.
25. The sensor according to claim 1 wherein said second substrate represents a cover formed upon the first substrate.
26. The sensor according to claim 1 wherein said sensing elements of said array are at least light sensing elements, and said sensor further comprises means for providing polarized illumination to enable a plurality of said light sensing elements to detect reflected part of said illumination representative of one or more fingerprints.
27. The sensor according to claim 1 wherein said array has one or more other sensing elements for radio frequency sensing.
28. A method for detecting one or more fingerprints comprising:
- providing a two-dimensional array of sensing elements at pixel locations on said first substrate, in which each of said sensing elements detects one of electrical signals, temperature, or light via one of said first substrate or a second substrate facing said first surface representative of one or more fingerprints; and
- a plurality of thin-film transistors for controlling said sensing elements at each of said pixel locations.
29. A system for detecting one or more fingerprints comprising:
- a first substrate and a second substrate;
- a two-dimensional array of sensing elements formed at pixel locations on said first substrate;
- a plurality of thin-film transistors for controlling said sensing elements at each of said pixel locations, wherein each of said sensing elements detects one of electrical signals, temperature, or light via one of said first substrate or said second substrate representative of one or more fingerprints; and
- one or more processors, each of said thin-film transistors controls said one or more of said sensing elements responsive to said one or more processors to enable said one or more processor to one or more of driving said one or more of said sensing elements or reading from said one or more sensing elements analog signals representative of one or more fingerprints, and generates an image representative of said one or more fingerprints responsive to said analog signals.
30. The system according to claim 29 wherein said sensing elements of said array are at least light sensing elements, and said sensor further comprising means for providing illumination, in which a plurality of said optical sensing elements detect reflected part of said illumination representative of one or more fingerprints via one or said first or second substrates.
31. A device for capturing an image of an object comprising:
- a first substrate and a second substrate;
- a two dimensional array of photoreceptors and TFTs in which each photoreceptor is controlled by one of said TFTs, in which one of said first and second substrates provides a platen surface for capturing an image of an object when disposed upon said platen surface and illumination is provide from within said first and second substrates or below said first and second substrates to enable reflected light representing said object to be captured onto said two dimensional array of photoreceptors.
32. The device according to claim 31 wherein said object is a document, a signature, a bar code, or one or more fingers.
Type: Application
Filed: May 17, 2012
Publication Date: Dec 20, 2012
Inventors: JOHN F. CARVER (PALM CITY, FL), DANIEL H. RAGUIN (North Palm Beach, FL)
Application Number: 13/474,484
International Classification: G06K 9/00 (20060101);