Apparatus and Method for TFT Fingerprint Sensor

• US 20140333328A1
• Filed: 04/03/2014
• Published: 11/13/2014
• Est. Priority Date: 05/07/2013
• Status: Active Grant

• Current Assignee: Egis Technology Inc.
• Original Assignee: Egis Technology Inc.
• Inventors: Nelson, Richard B., Erhart, Richard A.
• Granted Patent: US 10,203,816 B2
• Time in Patent Office: Days
• US Class Current: 324/663
• CPC Class Codes: G06F 3/041 Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
• CPC Class Codes: G06F 3/0416 Control or interface arrangements specially adapted for digitisers
• CPC Class Codes: G06F 3/041661 using detection at multiple resolutions, e.g. coarse and fine scanning; using detection within a limited area, e.g. object tracking window
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing

Abstract

A low cost, two-dimensional, fingerprint sensor includes a pixel array, each pixel including a switch and a pixel electrode for forming a capacitance with a fingertip. One or more active transmission electrodes are spaced from a selected row of the pixel array, and transmit a carrier signal into the finger without direct coupling into the selected pixels. Signals sensed by the pixel array are coupled to an independent integrated circuit, and connections between the IC and the pixel array are reduced by demultiplexing row select lines, and by multiplexing sensed column data. Differential sensing may be used to improve common mode noise rejection. The fingerprint sensor may be conveniently incorporated within a conventional touchpad LCD panel, and can mimic the performance of lower density touchpad pixels.

Claims

1. A fingerprint sensor comprising in combination:

a) a first substrate having a plurality of pixels formed therein, the first substrate including an upper surface, the pixels being arranged in a pixel array of R rows and N columns, each pixel including a switching device and further including a capacitive plate proximate the upper surface of the first substrate;

b) a plurality of R row addressing electrodes, each such row addressing electrode being coupled to the switching devices of the pixels in a corresponding row of the pixel array for selectively enabling the switching devices in the corresponding pixel row;

c) a plurality of N data electrodes, each such data electrode being coupled to the switching devices of the pixels in a corresponding column of the pixel array for sensing a signal provided by the capacitive plate of the pixel located at an intersection of a selected pixel row and the corresponding column of the pixel array;

d) a cover layer overlying the upper surface of the first substrate for receiving a fingertip of a user;

e) at least one transmitter electrode formed proximate to the upper surface of the first substrate and laterally spaced apart from the pixel array for transmitting a varying amplitude electrical signal;

f) whereby the varying amplitude electrical signal transmitted by the at least one transmitter electrode is coupled into a finger of a user who places his or her fingertip over the cover layer, and wherein the electrical signal coupled into the user'"'"'s finger is further coupled through the capacitive plates in the pixel array to a greater or lesser extent, depending upon whether a ridge or valley of the user'"'"'s fingertip overlies a particular pixel in the pixel array.

2. The fingerprint sensor recited by claim 1 wherein the switching devices included in the pixel array are thin-film-transistors (TFTs).

3. The fingerprint sensor recited by claim 1 wherein the at least one transmitter electrode extends substantially entirely around the pixel array.

4. The fingerprint sensor recited by claim 1 wherein the first substrate and cover layer are integrally formed.

5. The fingerprint sensor recited by claim 1 wherein the first substrate is relatively flexible.

6. A touchpad incorporating a fingerprint sensor for sensing a user'"'"'s fingerprint, comprising in combination:

a) a substrate having an upper surface;

b) an array of sensor pixels formed in said substrate and arranged along intersecting rows and columns for sensing the presence and location of a pointer applied proximate to said upper surface of the substrate, adjacent sensor pixels being spaced apart from each other by a first predetermined distance, each sensor pixel providing a signal indicative of whether a pointer is being applied proximate to such sensor pixel;

c) a plurality of row address lines supported by the substrate, each row address line being associated with a row of sensor pixels in the array of sensor pixels, and each row address line being selectively enabled for addressing the sensor pixels associated with each such row address line;

d) a plurality of column sensing lines supported by the substrate, each column sensing line being associated with a column of sensor pixels for sensing a signal provided by a sensor pixel in a row of sensor pixels selected by an enabled row address line;

e) a fingerprint sensor area formed upon the substrate, the fingerprint sensor area including;

i) a plurality of finer-pitch pixels arranged along intersecting rows and columns to form an array of finer-pitch pixels, each finer-pitch pixel including a switching device and further including a capacitive plate, each finer-pitch pixel being spaced apart from adjacent finer-pitch pixels by a second predetermined distance, the second predetermined distance being less than one-third the first predetermined distance;

ii) a plurality of finer-pitch row address lines, each finer-pitch row address line being associated with a row of finer-pitch pixels in the array, and each finer-pitch row address line being selectively enabled for addressing the finer-pitch pixels associated with each such finer-pitch row address line;

iii) a plurality of finer-pitch column sensing lines, each finer-pitch column sensing line being associated with a column of finer-pitch pixels for sensing a signal provided by the capacitive plate of a finer-pitch pixel in a row of finer-pitch pixels selected by an enabled finer-pitch row address line; and

f) at least one of the i) touchpad row address lines, or ii) touchpad column sensing lines, bordering the fingerprint sensor area also serving as a transmitter electrode for transmitting a varying amplitude electrical signal when the fingerprint sensor area is being used to sense a user'"'"'s fingerprint;

g) whereby the varying amplitude electrical signal transmitted by the transmitter electrode is coupled into a finger of a user who places his or her fingertip over the fingerprint sensor area, and wherein the electrical signal coupled into the user'"'"'s finger is further coupled through the capacitive plates in the finer-pitch pixel array to a greater or lesser extent, depending upon whether a ridge or valley of the user'"'"'s fingertip overlies a particular pixel in the finer-pitch pixel array.

7. A touchpad incorporating a fingerprint sensor, comprising in combination:

a) a touchpad for sensing the presence and location of a pointer applied to such touchpad, the touchpad including;

an array of sensor pixels arranged along intersecting rows and columns, adjacent sensor pixels being spaced apart from each other by a first predetermined distance, each sensor pixel providing a signal indicative of whether a pointer is being applied to such touchpad proximate to such sensor pixel;

a plurality of row address lines, each row address line being associated with a row of sensor pixels in the array, and each row address line being selectively enabled for addressing the sensor pixels associated with each such row address line;

a plurality of column sensing lines, each column sensing line being associated with a column of sensor pixels for sensing a signal provided by a sensor pixel in a row of sensor pixels selected by an enabled row address line;

b) the touchpad including a fingerprint sensor area, the fingerprint sensor area including a portion of the array of sensor pixels, the fingerprint sensor area further including;

a plurality of finer-pitch pixels arranged along intersecting rows and columns, adjacent finer pitch pixels being spaced apart from each other by a second predetermined distance, the second predetermined distance being less than one-third the first predetermined distance;

a plurality of finer-pitch row address lines, each finer-pitch row address line being associated with a row of finer-pitch pixels in the array, and each finer-pitch row address line being selectively enabled for addressing the finer-pitch pixels associated with each such finer-pitch row address line;

a plurality of finer-pitch column sensing lines, each finer-pitch column sensing line being associated with a column of finer-pitch pixels for sensing a signal provided by a finer-pitch pixel in a row of finer-pitch pixels selected by an enabled finer-pitch row address line;

c) a control circuit responsive to a mode signal for determining whether the finer-pitch pixels function as fingerprint sensing pixels or conventional sensor pixels of the touchpad, and wherein;

the control circuit individually enabling the finer-pitch pixels in each finer-pitch row, and individually sensing a signal provided by each finer-pitch pixel in such enabled finer-pitch row, when the mode signal indicates that the finer-pitch pixels are to function as fingerprint sensing pixels; and

the control circuit simultaneously enables the finer-pitch pixels in a plurality of adjacent finer-pitch rows, and collectively senses the signals provided by the finer-pitch pixels in the simultaneously enabled finer-pitch rows, when the mode signal indicates that the finer-pitch pixels are to function as conventional sensor pixels of the touchpad.

8. A fingerprint sensor comprising in combination:

a) a first substrate having a plurality of pixels formed therein, the pixels being arranged in a pixel array of R rows and N columns, each pixel including a switching device and a capacitive plate;

b) a plurality of R row addressing electrodes, each such row addressing electrode being coupled to the switching devices of the pixels in a corresponding row of the pixel array for selectively enabling the switching devices in the corresponding pixel row;

c) a plurality of N data electrodes, each such data electrode being coupled to the switching devices of the pixels in a corresponding column of the pixel array for sensing a signal provided by the capacitive plate of the pixel located at an intersection of a selected pixel row and the corresponding column of the pixel array;

d) a cover layer overlying the first substrate for receiving a fingertip of a user;

e) a second substrate being different from the first substrate, the second substrate including a semiconductive material;

f) an integrated circuit formed within the second substrate, the integrated circuit generating a set of S row addressing signals to address one of the plurality of R row addressing electrodes, the integrated circuit also being selectively coupled to the plurality of N data electrodes to receive the signals provided by the capacitive plates in the pixel array; and

f) a demultiplexer coupled between the integrated circuit and the pixel array, the demultiplexer including at least S input terminals for receiving the first set of S row addressing signals, the demultiplexer including at least R output terminals, each of the R output terminals being coupled to one of the plurality of R row addressing electrodes, the demultiplexer selecting one of the plurality of R addressing electrodes based upon the S row addressing signals received thereby.

9. The fingerprint sensor recited by claim 8 wherein the first substrate and cover layer are integrally formed.

10. The fingerprint sensor recited by claim 8 wherein the first substrate is relatively flexible.

11. The fingerprint sensor recited by claim 8 wherein the switching devices included in the pixel array are thin-film-transistors (TFTs).

12. The fingerprint sensor recited by claim 8 wherein the demultiplexer is formed by a plurality of switching devices.

13. The fingerprint sensor recited by claim 12 wherein the plurality of switching devices forming the demultiplexer are thin-film-transistors formed upon the first substrate.

14. The fingerprint sensor recited by claim 8 wherein:

a) the integrated circuit generates a set of M column selection signals to address one of the plurality of N data electrodes; and

b) the fingerprint sensor further includes a multiplexer coupled between the integrated circuit and the pixel array, the multiplexer including a first set of N input terminals, each of the first set of N input terminals being coupled to one of the plurality of N data electrodes to receive the signals stored on the capacitors in the pixel array, the multiplexer including a second set of M input terminals for receiving the M column selection signals from the integrated circuit for selecting one of the N data electrodes based upon the M column selection signals received thereby.

15. The fingerprint sensor recited by claim 14 wherein the multiplexer further includes an output terminal coupled to the integrated circuit for providing a selected data signal thereto.

16. The fingerprint sensor recited by claim 14 wherein the multiplexer is formed by a plurality of switching devices.

17. The fingerprint sensor recited by claim 16 wherein the plurality of switching devices forming the multiplexer are thin-film-transistors formed upon the first substrate.

18. The fingerprint sensor recited by claim 8 further including at least one transmitter electrode supported by the first substrate for transmitting a signal of predetermined frequency and amplitude proximate to the pixel array, the transmitted signal passing through the cover layer into the fingertip of the user.

19. The fingerprint sensor recited by claim 18 wherein the at least one transmitter electrode forms a ring encircling the pixel array.

20. A fingerprint sensor comprising in combination:

a) a first substrate having a plurality of pixels formed therein, the pixels being arranged in a pixel array of R rows and N columns, each pixel including a switching device and a capacitive plate;

b) a plurality of R row addressing electrodes, each such row addressing electrode being coupled to the switching devices of the pixels in a corresponding row of the pixel array for selectively enabling the switching devices in the corresponding pixel row;

c) a plurality of N data electrodes, each such data electrode being coupled to the switching devices of the pixels in a corresponding column of the pixel array for sensing a signal provided by the capacitive plate of the pixel located at an intersection of a selected pixel row and the corresponding column of the pixel array;

d) a common electrode extending at least partially through the pixel array on the first substrate;

e) a cover layer overlying the first substrate for receiving a fingertip of a user;

f) a plurality of differential amplifiers, each differential amplifier having a first input coupled to one of the plurality of data electrodes and having a second input coupled to the common electrode, each differential amplifier having an output terminal for providing an output signal, the output signal being representative of the difference between a signal provided by a data electrode and a signal provided by the common electrode.

21. A fingerprint sensor comprising in combination:

a) a first substrate having a plurality of pixels formed therein, the pixels being arranged in a pixel array of R rows and N columns, each pixel including a switching device and a capacitive plate;

b) a plurality of R row addressing electrodes, each such row addressing electrode being coupled to the switching devices of the pixels in a corresponding row of the pixel array for selectively enabling the switching devices in the corresponding pixel row;

c) a plurality of N data electrodes, each such data electrode being coupled to the switching devices of the pixels in a corresponding column of the pixel array for sensing a signal provided by the capacitive plate of the pixel located at an intersection of a selected pixel row and the corresponding column of the pixel array;

d) a cover layer overlying the first substrate for receiving a fingertip of a user;

e) a plurality of differential amplifiers, each differential amplifier having a first input coupled to a corresponding one of the plurality of data electrodes and having a second input coupled to a selected one of the plurality of data electrodes serving as a reference electrode, each differential amplifier having an output terminal for providing an output signal, the output signal provided by each differential amplifier being representative of the difference between the data signal provided by its corresponding data electrode and a signal provided by the reference electrode.

22. The fingerprint sensor recited by claim 21 including:

a) a second substrate being different from the first substrate, the second substrate including a semiconductive material;

b) an integrated circuit formed within the second substrate; and

c) the plurality of differential amplifiers being formed within the integrated circuit.

23. A fingerprint sensor comprising in combination:

a) a first substrate having a plurality of pixels formed therein, the first substrate including an upper surface, the pixels being arranged in a pixel array of R rows and N columns, each pixel including a switching device and further including a capacitive plate proximate the upper surface of the first substrate;

b) a plurality of R row addressing electrodes, each such row addressing electrode being coupled to the switching devices of the pixels in a corresponding row of the pixel array for selectively enabling the switching devices in the corresponding pixel row;

c) a plurality of N data electrodes, each such data electrode being coupled to the switching devices of the pixels in a corresponding column of the pixel array for sensing a signal provided by the capacitive plate of the pixel located at an intersection of a selected pixel row and the corresponding column of the pixel array;

d) a cover layer overlying the upper surface of the first substrate for receiving a fingertip of a user;

e) a plurality of transmitter electrodes formed proximate to the upper surface of the first substrate, each of said plurality of transmitter electrodes extending generally parallel to, and closely proximate to, a corresponding one of said plurality of row addressing electrodes, each of said plurality of transmitter electrodes selectively transmitting a varying amplitude electrical signal;

f) said plurality of transmitter electrodes including a first set of transmitter electrodes located generally proximate to a selected row addressing electrode, and including a second set of transmitter electrodes located more distant from the selected row addressing electrode, the first set of transmitter electrodes being disabled while the selected row addressing electrode is selectively enabling the switching devices in the corresponding pixel row, and the second set of transmitter electrodes being enabled to transmit the varying amplitude electrical signal while the selected row addressing electrode is selectively enabling the switching devices in the corresponding pixel row;

g) whereby the varying amplitude electrical signal transmitted by the second set of transmitter electrodes is coupled into a finger of a user who places his or her fingertip over the cover layer, and wherein the electrical signal coupled into the user'"'"'s finger is further coupled through the capacitive plates in the pixel array to a greater or lesser extent, depending upon whether a ridge or valley of the user'"'"'s fingertip overlies a particular pixel in the pixel array.

24. A method of operating a touch pad to create a fingerprint sensor for sensing a user'"'"'s fingerprint at substantially any location of the touch pad, comprising the steps of:

a) providing a substrate having an upper surface;

b) providing a plurality of finer-pitch pixels arranged along intersecting rows and columns to form an array of finer-pitch pixels, each finer-pitch pixel including a switching device and further including a capacitive plate, each finer-pitch pixel being spaced apart from adjacent finer-pitch pixels by a first predetermined distance;

c) providing a plurality of finer-pitch row address lines, each finer-pitch row address line being associated with a row of finer-pitch pixels in the array, and each finer-pitch row address line selectively addressing the finer-pitch pixels associated with each such finer-pitch row address line;

d) providing a plurality of finer-pitch column sensing lines, each finer-pitch column sensing line being associated with a column of finer-pitch pixels for sensing a signal provided by the capacitive plate of a finer-pitch pixel in a row of finer-pitch pixels selected by an enabled finer-pitch row address line;

e) sub-dividing the plurality of finer pitch pixels into a smaller array of touch pad pixels, the smaller array of touch pad pixels being arranged in rows and columns, each such touch pad pixel including finer-pitch pixels located in at least two different rows of the finer-pitch pixels, and each of such touch pad pixels including finer-pitch pixels located in at least two different columns of the finer pitch pixels, each touch pad pixel being spaced apart from an adjacent touch pad pixel by a second predetermined distance, the second predetermined distance being at least twice as large as the first predetermined distance;

e) in a first mode of operation, simultaneously enabling those finer-pitch pixels that are sub-divided into a same touch pad pixel for collective operation, and collectively sensing signals provided by the finer-pitch pixels sub-divided into the same touch pad pixel, to cause each such touch pad pixel to function as a conventional sensor pixel of a conventional touch pad;

f) using sensed signals provided by the touch pad pixels to detect whether a pointer is being applied proximate to the upper surface of the substrate, and detecting a pointer location above the substrate where such pointer is being applied;

h) in a second mode of operation, determining which touch pad pixels lie proximate to the pointer location; and

selectively switching the finer-pitch pixels within each of the touch pad pixels that lie proximate to the pointer location from collective operation to an individual operation mode wherein;

i) the finer-pitch pixels in each finer-pitch row are individually enabled; and

ii) the signals provided by the capacitive plate of a finer-pitch pixel are individually sensed as each finer-pitch row is enabled by a corresponding finer-pitch row address line; and

whereby the finer-pitch pixels within the touch pad pixels that lie proximate to the pointer location form a fingerprint sensor area for sensing a fingerprint image of a user'"'"'s fingertip.