KR20150115607A - Apparatus and method for tft fingerprint sensor - Google Patents

Abstract

A low-cost two-dimensional fingerprint sensor includes a pixel array, and each pixel includes 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 selection lines, and by multiplexing sensed column data. Differential sensing may be used to improve common mode noise removal. The fingerprint sensor may be conveniently incorporated within a conventional touchpad LCD panel, and can mimic the performance of lower-density touchpad pixels.

Description

TECHNICAL FIELD [0001] The present invention relates to a TFT fingerprint sensor,

Cross reference to related applications

This application claims the benefit of priority filing date of U.S. Provisional Patent Application No. 61 / 820,477, filed on May 7, 2013, entitled " Apparatus and Method for TFT Fingerprint Sensor, "

Field of invention

FIELD OF THE INVENTION The present invention relates generally to electronic fingerprint sensors, and more particularly to a fingerprint sensor that capacitively senses a user ' s fingerprint using a thin film transistor ("TFT") array.

Conventional fingerprint sensors currently available on the commercial market utilize different methods for detecting the user's fingerprint. One type of fingerprint sensor includes a CMOS silicon chip with circuitry that provides a plurality of arrayed "pixels ". The CMOS silicon chip is then coated with a protective coating, which may be formed from a simple chemical coating, a flex substrate, or other thin materials. This type of fingerprint sensor requires that the silicon chip be at least as large as the pixel array.

A second type of commercially available fingerprint sensor includes metal lines formed on a substrate to form a pixel array, while a remote-positioned silicon chip of a smaller dimension than the pixel array is electrically connected thereto. The second type of fingerprint sensor may be used in a variety of different packaging configurations such as a ball grid array (BGA), wafer level fan-out (WLFO), or film substrate fitted around or on a plastic hump / stiffener Lt; / RTI >

Fingerprints are characterized by patterns of ridges and valleys present on the skin of the user's fingers. Most of the current commercial fingerprint sensors are capacitive touch sensors, because the circuitry used to derive the fingerprint image is derived from the capacitance induced by the finger "ridge" or "valley" It is necessary to be able to distinguish small changes in the received signal. These capacitive sensing elements are laid out in an array of X rows x Y columns, commonly referred to as "pixel arrays ". The intersection of each row and each column is referred to as "pixel ". These pixel arrays may be formed by CMOS devices formed in the semiconductor integrated circuit chip itself, such as in the finger sensor of the first type described above. Alternatively, the pixel array may be formed by metal lines formed on the non-semiconductor substrate material, such as in the fingerprint sensor of the second type described above.

The first type of fingerprint sensor described above is a much more expensive product because the CMOS silicon chip in which the pixel array is formed must be at least the size of the required fingerprint image. In the case of a touch sensor or a 2D sensor, this can require a relatively large area of silicon whose dimensions are three quarters of a square inch or more, which is relatively costly.

On the other hand, the aforementioned second type of fingerprint sensor, in which metal traces are formed on a non-semiconductor substrate, often has a low quality signal due to the restriction on the width of the lines used to transmit and receive the signal from which the fingerprint image is derived . Smaller sizes of transmitters and receivers, especially transmitters, can also seriously limit the material thickness on the sensor.

The proposed third type of fingerprint sensor uses a liquid crystal display (LCD), which is usually used to display rather than to sense information. In this third type of sensor, the LCD display itself is used to capture and capture fingerprints by providing a single device that is both a display and a fingerprint sensor. The method suggests the use of "column drivers" of the display to have an input mode that not only allows information to be output, but also can detect a change in capacitance on the pixels in the display. This method is extremely limited in terms of signal strength because the column lines must be used as both transmit (Tx) lines and receiver (Rx) lines. For example, it is possible to use the "pre-charge" state on each pixel before the user's finger is applied and then detect the voltage change on each such pixel in the presence of the user's finger, It has been proposed to monitor the capacitance provided by ridges or valleys of a finger. The use of column lines as both Tx (precharge) and Rx (receive or read) severely limits the signal-to-noise capabilities that this method can produce. In addition, this method is costly because all of the column drivers must be designed to function as both an output device (for general display) and a high-sensitivity input device (for fingerprint sensor).

In order for the aforementioned sensors to properly distinguish between "ridge" and "valley" signal delta, the fingers must be located as close as possible to the receiver plate (s) of the capacitor. Thus, the suppliers of known fingerprint sensors try to minimize the thickness of the receiver plate overlying the capacitive plate of each pixel. However, as the receiver plate thickness is reduced, such fingerprint sensors are more easily damaged physically or mechanically due to the close proximity of the sensor surface to the underlying electrical circuit, thereby reducing the durability and / or reliability of the sensor. For example, not only conventional BGA-style fingerprint sensors, but also newer and more advanced "flexible " (" flexible "fingerprint sensors are both sensitive to this type of damage.

As described above, current fingerprint sensors require the user's fingertip to be very close to the fingerprint sensor circuitry to sufficiently distinguish between ridges and valleys of the fingertip. Therefore, in the case of the second type of fingerprint sensor described above, the thickness and material type used to protect the fingerprint sensor are seriously limited. Protective coatings presently used to cover fingerprint sensors should be non-conductive, have a thickness of less than about 200 μm, and meet customer aesthetic requirements. For example, a simple fall of the pen that hits the exposed portion of the fingerprint sensor can damage the thin polyimide surface of the flexible fingerprint sensor, thereby creating aesthetic defects and potentially causing the sensor circuit located directly below the surface It can be damaged. The ability to place thicker materials on the sensor to increase the reliability of the fingerprint sensor is highly desirable. However, thicker protective coatings / surfaces introduce at least two new challenges: 1) signal strength from the signal transmitter to the fingers, and then to the receiver array, is typically increased by a square of the increased distance, (I.e., doubling the cover thickness reduces the signal strength by a factor of 4); And 2) - depending on how the transmitter signal is generated, the transmitter signal can be significantly defocused as it moves from the transmitter to the receiver.

Currently available fingerprint sensors include "Glass Cap Sensor " supplied by Silicon Display, Inc. of South Korea and having model number GCS-2. The device provides polysilicon thin film transistor (TFT) capacitive pixel arrays of 256 rows x 360 columns corresponding to 92 and 160 sensor cells. The pixel density corresponds to 508 dpi and is provided in a sensing area with a dimension of 12.8 mm x 18 mm. The pitch between successive pixels in the array is 350 micrometers. A gate / low shift register is formed on the integrated circuit and is used to select the row of active pixels to be sensed. Similarly, a column shift register is formed on the integrated circuit to select the columns to be sensed in the selected row. Four analog output sensing signals are provided at any given point in time. A multiplexer is also formed on the integrated circuit and is used to select the column output sense signals that are selected at any given point in time. Applicants have discovered that the above-described glass cap sensor essentially eliminates any signal generating electrodes for emitting a high frequency signal close to the pixel array to detect the effective capacitance formed between each of the pixels of the array and the fingertip of the user It is considered to be an active element which does not include the active element.

U.S. Patent No. 6,055,324 to Fujieda discloses a fingerprint imaging device including a two-dimensional array of thin film transistors (TFTs) formed in a substrate, a dielectric layer formed on such a substrate, and signal sensing electrodes formed on the dielectric layer Device. The signal sensing electrodes are connected to the source terminals of the thin film transistors. The gate electrodes of the TFTs lying in the same row of the array are connected to the common gate electrode lead. The gate electrode leads are connected to the output terminals of a shift register used to select a row that is active among the rows of the array. The drain electrodes of the TFTs placed in the same column are connected to the common drain electrode lead. The drain electrode leads are connected to the input terminals of the signal detection circuit. The signal generating electrodes are provided in the form of a mesh or comb to surround the pixels of the two-dimensional array and emit high-frequency signals toward the fingers resting on the array. The signal sensing electrodes of the array form electrostatic capacitances between the signal sensing electrodes and the user ' s fingers. Signals received by each of the signal sensing electrodes are detected row by row to provide an image of the fingerprint. However, at the fuji, the signal generating electrode is too close to each of the signal sensing electrodes of the array so that the critical components of the emitted high-frequency signal are capacitively coupled directly to the signal sensing electrodes without first passing the user's finger. As a result, the difference in signal strength between the first signal sensing electrode lying below the ridge of the user's fingertip and the second signal sensing electrode located below the valley of the user's fingertip is not so clear. Moreover, as the thickness of the protective layer separating the user's finger from the lower signal sensing electrodes increases, the direct capacitive coupling of the high frequency signal emitted from the signal generating electrode to the array of signal sensing electrodes causes the user 'Lt; RTI ID = 0.0 > high-frequency < / RTI >

As demonstrated by the acquisition of Authentec by Apple Inc., fingerprint sensors are biosecurity systems that have great potential in cell phones, notebooks, and laptops. Thus, the ability to embed a fingerprint sensor in an LCD panel, or to design a component common to most of such media, such as a fingerprint sensor on a button, is highly desirable.

It is therefore an object of the present invention to provide a fingerprint sensor for imaging a person's fingerprint without requiring the use of an integrated circuit semiconductor chip of the same dimensions as the pixel array used to capture the image of the fingerprint.

It is another object of the present invention to provide such a fingerprint sensor that more easily distinguishes between ridges and valleys of a fingertip applied to a cover plate overlying a pixel array used to image the fingerprint.

Yet another object of the present invention is to provide a method of forming a pixel array in which the pixel array is constructed with a thickness sufficient to adequately protect the pixel array or the cover layer or coating portion overlying the pixel array while still allowing easy discrimination between ridges and valleys of the applied fingertip And to provide such a fingerprint sensor.

It is a further object of the present invention to provide such a fingerprint sensor that can be manufactured at a relatively low cost.

It is a further object of the present invention to provide such a fingerprint sensor that more efficiently transmits such a carrier signal into the fingertip of a person without concurrently directly coupling the carrier electrical signal into the pixel array.

It is a still further object of the present invention to provide such a fingerprint sensor that reduces the number of electrical lines between the pixel array and the associated integrated circuit used to process fingerprint images captured by the pixel array.

It is a further object of the present invention to provide such a fingerprint sensor in which the signal components monitored by each pixel in the pixel array can be differentially sensed to eliminate common mode noise signals.

It is another object of the present invention to provide such a fingerprint sensor in which the pixel array may be included as part of a conventional touch-sensitive pad.

Yet another object of the present invention is to provide a fingerprint sensor that easily transmits a signal that can be sensed by a pixel array into a user's finger but the transmitted signal is not significantly and directly coupled to the pixel array through the fingerprint sensor itself will be.

It is a further object of the present invention to provide a fingerprint sensor that can be easily combined with a conventional touchpad to capture a fingerprint of a user and provide a single device that can detect that a user is touching a specific position of the touchpad within the same sense layers Sensor.

These and other objects of the present invention will become more apparent to those skilled in the art as the description of the invention proceeds.

Briefly, and in accordance with a preferred embodiment of the present invention, the present invention relates to a fingerprint sensor comprising a first substrate having a two-dimensional array of pixels arranged in R rows and N columns. The first substrate may be rigid or may be relatively flexible. Each pixel includes a switching device, preferably a TFT, and a capacitive plate proximate the top surface of the first substrate. A series of R row addressing electrodes are provided, each row addressing electrode coupled to switching devices of the pixels in the corresponding row of the pixel array to selectively enable switching devices in the corresponding pixel row . A series of N data electrodes are also provided, each data electrode having a corresponding pixel column for sensing a signal provided by a capacitive plate of a pixel located at a selected pixel row of the pixel array and at the intersection of the corresponding column Lt; RTI ID = 0.0 > of pixels in < / RTI >

The one or more transmitter electrodes are formed proximate an upper surface of the first substrate to transmit a varying amplitude electrical signal. In one embodiment, the transmitter electrodes are spaced laterally from the pixel array, and preferably extend substantially all around the periphery of the pixel array. The cover layer resting on an upper surface of the first substrate for receiving a fingertip of the user; If desired, the cover layer may be formed integrally with the first substrate. The variable amplitude electrical signal transmitted by the transmitter electrode is coupled into the user's finger that puts his or her fingertip on the cover layer and the electrical signal coupled into the user's finger causes the ridge of the user's fingertip And are further coupled to greater or lesser extent through the capacitive plates in the pixel array depending on whether they are laid or valleys.

According to another embodiment of the present invention, a plurality of transmitter electrodes are located within the boundary of the pixel array, and preferably are interposed between successive pixel rows. The selectively-enabled transmitting electrodes transmit the carrier signal for transmission into the user's finger. The transmission electrodes adjacent to the selected row of the pixel array are disabled while the transmission electrodes at a greater distance from the selected row of the pixel array are enabled and transmit the desired carrier signal. This allows effective transmission of the carrier signal into the fingertip of the user without any significant direct coupling to the pixels of the carrier signal within the currently selected row. Each time a new row is selected, the enabling and disabling of the transmitting electrodes ensures that the transmitting electrodes neighboring the selected row are disabled and that transmitting electrodes at a greater distance are actively transmitting the carrier signal Updated.

According to an alternative embodiment of the present invention, the fingerprint sensor is included in a touchpad comprising a substrate. An array of sensor pixels is formed in the substrate and is arranged along the intersecting rows and columns to sense the presence and position of a finger, stylus, or other "pointer" that is proximate to the upper surface of the substrate. Adjacent sensor pixels are spaced apart from each other by a first predetermined distance corresponding to the first pitch. Each sensor pixel provides a signal indicating whether the pointer is being applied close to such a sensor pixel.

The touchpad includes a series of row address lines supported by the substrate. Each row address line is associated with a row of sensor pixels in the array to selectively enable and address the sensor pixels in such a row. The touchpad also includes a series of column sensing lines supported by the substrate. Each column sensing line is associated with a column of sensor pixels for sensing the signal provided by the sensor pixel in the row of sensor pixels selected by the enabled row address line.

A fingerprint sensor region is formed on the touchpad substrate. The fingerprint sensor region includes a series of fine pitch pixels arranged along rows and columns that intersect to form an array of fine pitch pixels. Each fine pitch pixel includes a switching device and a capacitive plate. Each fine pitch pixel is spaced a second predetermined distance from adjacent fine pitch pixels and a second predetermined distance is less than one third of a first predetermined distance spacing the second pixels of the touch pad.

To detect an image of a user ' s fingerprint within the fingerprint sensor region, a series of fine pitch row address lines are provided. Each fine pitch row address line is associated with a row of fine pitch pixels in a fine pitch pixel array, and each fine pitch row address line is selectively enabled to address fine pitch pixels associated therewith. Similarly, a series of fine pitch column sensing lines are provided, each fine pitch column sensing line being associated with a column of fine pitch pixels. The fine pitch column sensing lines serve to sense the signal provided by the capacitive plate of fine pitch pixels in the enabled row of fine pitch pixels.

The fingerprint sensor area of the touchpad is bounded by touchpad row address lines and touchpad column sensing lines. Ideally, at least one of the touch pad row address lines and / or the touch pad column sensing lines, which border the fingerprint sensor region, transmits a variable amplitude electrical signal when the fingerprint sensor region is being used to sense a fingerprint of the user And serves as a transmitter electrode for the transmission. The variable amplitude electrical signal transmitted by the transmitter electrode is coupled into the finger of the user placing the user's fingertip over the fingerprint sensor area. The electrical signals coupled into the user's fingers can be added to the larger or lesser extent through the capacitive plates in the fine pitch pixel array, depending on whether the ridge of the user's fingertip is over a particular pixel in the pixel array, .

In yet another embodiment of the present invention, the aforementioned fingerprint sensor region may mimic the operation of the touchpad sensors during a time when a fingerprint image is not required. As before, the touchpad includes an array of sensor pixels arranged along intersecting rows and columns and spaced apart from each other by a first predetermined distance. The touchpad also includes a series of row address lines, each row address line associated with a row of sensor pixels in the array. Each row address line is selectively enabled to address the sensor pixels associated with each such row. The touchpad further includes a series of column sensing lines, each column sensing line being associated with a sensor pixel of the column that is adapted to sense a signal provided by the sensor pixel in the addressed row of sensor pixels.

As before, the touchpad includes a fingerprint sensor area having an array of fine pitch pixels arranged along intersecting rows and columns. Each such fine pitch pixel includes a switching device and a capacitive plate. Each fine pitch pixel is spaced a second predetermined distance from adjacent fine pitch pixels and a second predetermined distance is less than one third of a first predetermined distance separating the sensor pixels of the touch pad.

As in the case of the immediately preceding embodiment, a series of fine pitch row address lines are provided. Each fine pitch row address line is associated with a row of fine pitch pixels in a fine pitch pixel array, and each fine pitch row address line is selectively enabled to address fine pitch pixels associated therewith. Similarly, a series of fine pitch column sensing lines are provided, each fine pitch column sensing line being associated with a column of fine pitch pixels. The fine pitch column sensing lines serve to sense the signal provided by the capacitive plate of fine pitch pixels in the enabled row of fine pitch pixels.

A control circuit is also provided responsive to a mode signal for determining whether the fine pitch pixels will function as fingerprint sensing pixels of the touchpad or as conventional sensor pixels. The control circuit enables the fine pitch pixels individually in each fine pitch row. When functioning as a fingerprint sensor, the signals provided by each fine pitch pixel are individually sensed. On the other hand, when the mode signal indicates that the fine pitch pixels will function as conventional sensor pixels of the touchpad, the control circuit simultaneously enables the fine pitch pixels in the plurality of adjacent fine pitch rows, and simultaneously enables the fine pitch Collectively sensing signals provided by the fine pitch pixels in the rows to simulate or mimic the operation of the conventional sensor pixels of the touchpad.

Another aspect of the invention relates to a fingerprint sensor comprising a demultiplexer for reducing the number of conductors that must extend between a pixel array and an associated integrated circuit. In this regard, the fingerprint sensor may be rigid or relatively flexible, and includes a first substrate on which a two-dimensional array of pixels arranged in R rows and N columns is formed. Each such pixel preferably includes a thin film transistor and a switching device (e.g., a TFT) that is a capacitive plate. A series of R row addressing electrodes extend across the pixel array and each row addressing electrode is coupled to switching devices in a corresponding row of the pixel array to selectively enable switching devices in such rows. Similarly, a series of N data electrodes are provided, and each data electrode is connected to the switching devices of the pixels in the corresponding column of the pixel array. Each data electrode senses a signal provided by a capacitive plate of a pixel located at the intersection of a selected pixel row and a corresponding column of the pixel array. The cover layer resting on a first substrate for receiving a fingertip of a user; This cover layer may be formed integrally with the first substrate if desired.

The fingerprint sensor of this embodiment of the present invention also includes a second substrate that is different from the first substrate and comprises a semiconductor material for forming an integrated circuit. The integrated circuit generates a set of S row addressing signals for addressing one of the R row addressing electrodes. The demultiplexer is coupled between the integrated circuit and the pixel array. The demultiplexer includes at least S input terminals for receiving a first set of S addressing signals provided by the integrated circuit and at least R output terminals. Each of the R output terminals of the demultiplexer is coupled to one of the R row addressing electrodes. The demultiplexer thereby selects one of the R row addressing electrodes based on the received S row addressing signals. The integrated circuit is also selectively coupled to the N data electrodes to receive signals provided by the capacitive plates in the pixel array. Preferably, the demultiplexer is constructed from a series of switching devices similar to those provided in the pixel array. The switching devices used to form the demultiplexer may be thin film transistors formed on the first substrate.

Apart from including a low-address demultiplexer, the fingerprint sensor described above may also include a multiplexer coupled between the integrated circuit and the column electrodes of the pixel array. In this regard, the integrated circuit generates a set of M column select signals to address one of a plurality of N data electrodes. The multiplexer includes a first set of N input terminals, each input terminal coupled to a respective electrode of the N data electrodes to receive signals provided by the capacitive plates in the pixel array. The multiplexer also includes a second set of M input terminals for receiving the M column select signals provided by the integrated circuit. Based on the state of the M column select signals, the multiplexer selects at least one of the N data electrodes to detect the signal provided by the capacitive plate located at the intersection of the selected row and column of the pixel array. Preferably, the multiplexer also includes an output terminal coupled to the integrated circuit for providing the selected data signal thereto. As in the case of the row-address demultiplexer described above, the column electrode multiplexer may be constructed from switching devices (e.g., thin film transistors) formed on the first substrate.

Ideally, as described above, a fingerprint sensor with a row-address demultiplexer also includes at least one transmitter electrode for transmitting a signal of a predetermined frequency and amplitude, supported by the first substrate and proximate to the pixel array . The transmitted signal travels into the fingertip of the user through the cover layer underlying the pixel array and is coupled to the capacitive plates of the pixel array through ridges and valleys of the user's fingertips. As already mentioned above, the transmitter electrode may take the form of a ring surrounding the periphery of the pixel array.

Another aspect of the invention is a fingerprint sensor that assists in blocking differential signals in which signals that are capacitively coupled into a pixel array from a user's finger are sensed in a differential manner. As in the preferred embodiments described above, the fingerprint sensor comprises a first substrate having a two-dimensional array of pixels arranged in R rows and N columns. Each such pixel includes a switching device (e.g., a TFT) and a capacitive plate. Again, a series of R row addressing electrodes are provided, and each row addressing electrode is coupled to switching devices in the row of the pixel array to selectively enable switching devices in the corresponding pixel row. Similarly, N data electrodes are provided, each data electrode corresponding to a pixel array corresponding to a selected pixel row of the pixel array and a pixel array for sensing a signal provided by the capacitive plate of the pixel located at the intersection of the corresponding column To the switching devices in the column. The cover layer overlies the first substrate for receiving the fingertip of the user.

In one example, a common electrode is provided. The common electrode extends at least partially through the pixel array formed on the first substrate. A series of differential amplifiers are provided to differentially sense the signals carried by the capacitive plates of the pixel array. Each differential amplifier has a first input connected to one of the data electrodes and a second input connected to the common electrode. Each differential amplifier also has an output terminal for providing an output signal indicative of the difference between the signal provided by the data electrode and the signal provided by the common electrode.

In the second example, a separate common electrode is omitted, and one of the data electrodes provides a dual function as a reference electrode. Each differential amplifier has a first input connected to one of the data electrodes and a second input connected to the reference electrode. Each differential amplifier has an output terminal for providing an output signal indicative of the difference between the data signal provided by its corresponding data electrode and the signal provided by the reference electrode.

Whether the differential fingerprint sensor uses a common electrode or a reference electrode, it preferably includes a second substrate of semiconductive material. This second substrate is different from the first substrate, and the integrated circuit is preferably formed in the second substrate to provide the control logic.

As described above, a preferred type of fingerprint sensor includes a transmitter electrode having one or more metal traces for transmission of a high frequency signal. The transmitter may be a single trace, or it may be multiple traces of various patterns, including but not limited to rings; The traces used to transmit such signals at any given point in time are transverse to the capacitive plates in the pixel array being sensed at the same point in time to avoid direct signal coupling from the transmitter electrodes to the capacitive plate being sensed It is preferable to be spaced apart. The transmitter electrode is used to emit a signal that is transmitted into the body of the finger. Thus, the position of the transmitter electrode is preferably sufficiently close to the finger to allow the signal to penetrate the finger, but far enough away from the active capacitive plates in the pixel array to block unwanted receivers moving through the finger. At least in theory, such undesired receipts can be corrected by first transmitting the high frequency signal and recording the reference received energy without any finger present, but the imaging of the fingerprint is such that such unwanted receptions are avoided in the first example If it becomes more simple and more accurate. Since the signal is transmitted into the entire finger and the generated transmit energy is transmitted to the receiver array through the entire finger, the signal travels through the relatively thick cover plate material away from the ridges and valleys of the finger and into the capacitive plates And is floated in a relatively focused state.

The transmitter electrode may be formed using any metal layer already available in the fingerprint sensor region, or it may be an additional layer or component. The transmitter electrode may be part of a liquid crystal display (LCD) or external to it. The amplitude and frequency of the signal being transmitted by the transmitter electrode can be changed to best suit a particular environment. The transmitter driving circuit may be located inside the IC or outside the IC.

As described above, fingerprint sensors of the type described above may be included in a touch-sensitive LCD panel or on a flexible plastic substrate using standard TFT technology if desired, wherein the TFTs are arranged in a two-dimensional array. The TFT / capacitive plate array is initially used to acquire signals transmitted from a user's fingertip, and these signals are then transferred onto a separate IC chip for processing to form an image of the user's fingerprint. The pixel array may be provided in various sizes and configurations, including, but not limited to, circular, square, and rectangular.

Another aspect of the present invention relates to a method of operating a touch pad that generates a fingerprint sensor for sensing a fingerprint of a user at a substantially arbitrary position of the touchpad. In this regard, a substrate having an upper substrate is provided. An array of fine pitch pixels is formed on the substrate and arranged along the intersecting rows and columns. Each such fine pitch pixel comprises a switching device and a capacitive plate, wherein each fine pitch pixel is spaced from a first fine pitch pixel by a first predetermined distance. A series of fine pitch row address lines are provided to address the rows of fine pitch pixels, with each fine pitch row address line being associated with a row of fine pixels within the array. Each fine pitch row address line may be used to selectively address fine pitch pixels associated with each such fine pitch row address line. A series of fine pitch column sensing lines are also provided, each fine pitch column sensing line having a fine pitch for sensing a signal provided by a capacitive plate of fine pitch pixels in an enabled row of arrays of fine pitch pixels It is associated with a column of pixels.

The method described above further comprises subdividing fine pitch pixels into smaller arrays of "touchpad pixels ". The array of touchpad pixels is "smaller" in that it has fewer rows and fewer columns, even though it occupies the same two-dimensional space. The smaller array of touchpad pixels is also arranged in rows and columns. Each touchpad pixel comprises fine pixels located in at least two different rows of fine pitch pixels and also includes fine pitch pixels located in at least two different columns of fine pitch pixels. Each such "touchpad pixel" is spaced from a neighboring touchpad pixel by a second predetermined distance that is at least twice the first predetermined distance.

In the first mode of operation, the above-described method allows simultaneous enabling of such fine pitch pixels subdivided into common touchpad pixels for collective operation, and a signal provided by capacitive plates of fine pitch pixels clustered within the same touchpad pixel As a whole. In this manner, each such touchpad pixel functions as a conventional sensor pixel in a typical touchpad. Using the sensed signals provided by the touchpad pixels, a detection step is performed to detect whether a pointer (e.g., a user's fingertip) is being applied to the upper surface of the substrate; In such a case, a position that is relatively approximate to the substrate to which such a pointer is applied is also detected.

In a second mode of operation corresponding to fingerprint sensing, the method includes determining touchpad pixels that are located near the detected pointer position. The fine pixels in each touchpad pixels placed near the pointer position are selectively switched from the general operation to the separate operation mode. During discrete operating modes, the fine pitch pixels in each fine pitch row are individually enabled rather than being enabled at the same time, and the signals provided by the capacitive plate of each fine pitch pixel will be matched to each fine pitch row Are individually sensed as being enabled by the fine pitch row address lines. In this manner, the fine pitch pixels in the touchpad pixels located near the pointer position form a fingerprint sensor area for sensing the fingerprint image of the user's fingertip.

1A is a cross-sectional view illustrating a prior art fingerprint sensor of a first type that allows a pixel array to be formed on the surface of a silicon semiconductor chip to consume a large silicon area.
1B is a cross-sectional view of a fingerprint sensor of the prior art shown in FIG. 1A, showing how the increase in pixel count directly increases the silicon size.
2A is a cross-sectional view illustrating another type of prior art fingerprint sensor in which signal transmitting electrodes and signal receiving plates are formed by narrow metal traces located in close proximity to each other.
FIG. 2B is a top view of the prior art fingerprint sensor shown in FIG. 2A, wherein the use of an integrated circuit spaced from the pixel array requires a plurality of interconnect metal traces that consume a relatively large area between the IC and the pixel array .
FIG. 3A is a cross-sectional view illustrating one preferred embodiment of the present invention, including a transmitter electrode ring surrounding a periphery of a two-dimensional TFT / capacitive plate array formed on a flex substrate with a separate IC for signal processing.
FIG. 3B is a larger partial view of the structure shown in FIG. 3A.
4A is a cross-sectional view illustrating one of the TFT / capacitive plate pixels in a pixel array.
4B is a top view of four pixels in the pixel array.
4C is a cut-away plan view of the entire pixel array further illustrating the location of the transmit electrode ring, the row-address demultiplexer, and the column decode multiplexer.
5 is a schematic electrical circuit diagram of three rows and four columns of a fingerprint sensor pixel array.
6 is a partial schematic diagram illustrating the manner in which the number of external signal paths to the IC is reduced, combining the sensing devices of FIG. 5 with associated components of the fingerprint sensor.
7A is a top view of a fingerprint sensor illustrating a metal transmission ring disposed around a sensor pixel array with metal paths between the pixel array, the transmitter electrode, and the IC.
7B is a partial plan view of the upper left corner of Fig. 7A, but showing a detachable connector between the IC and the fingerprint sensor array.
FIG. 8 is an enlarged cross-sectional view similar to FIG. 3A, illustrating how the signal emitted by the transmitting electrode is coupled into the pixel array through the layers of the user's fingers behind ridges and valleys of the user's fingertip.
9 is a block diagram illustrating an alternative embodiment of the present invention in which the transmitting electrodes are interposed between the row addressing electrodes of the pixel array.
Figure 10 is a more detailed block diagram similar to Figure 9 but further illustrating a demultiplexing technique for driving row addressing electrodes.
11 is a block diagram illustrating a portion of a column decode multiplexer as well as a row addressing electrode demultiplexer.
FIG. 12 is a timing diagram showing timing waveforms for the signals shown in FIGS. 9-11. FIG.
13 is a plan view of a fingerprint sensor area surrounded by a transmitting electrode ring and adapted to be included as part of a touch-sensitive LCD panel.
14 is a plan view of a rectangular touch-sensitive LCD panel in which the fingerprint sensor area of FIG. 13 is included in the bottom left corner of the touch-sensitive LCD panel.
15A is a plan view of a touch-sensitive LCD panel formed of high density pixels subdivided into touchpad pixels generally similar to those shown in FIG. 14 but generally lower density.
Fig. 15B is an enlarged view of a portion of the touch-sensitive LCD panel shown in Fig. 15A where the area touched by the user's finger is re-configured as a fingerprint sensor area of higher pixel density.
16 is a simplified schematic electrical circuit diagram depicting how the signals received by the TFT / capacitive plates of the pixel array are differentially sensed by the differential amplifiers.
Figure 17A illustrates the more dense pixels of the fingerprint sensor region of the touch-sensitive LCD panel of Figure 14 adjacent to the lower density pixel cells.
FIG. 17B is a diagram illustrating a manner similar to that of FIG. 17A, but with higher density pixels being grouped together to simulate or mimic the function of adjacent, lower density pixel cells.
18 is an enlarged view of four grouped pixel cells formed by the upper four conventional pixel cells and the lower, higher density pixel cells with the corresponding metal electrodes.
19 is a timing diagram showing timing waveforms for the signals conducted by the electrodes shown in Fig.
20A is a plan view of a fingerprint sensor constructed in accordance with the present invention and embedded as a button.
FIG. 20B is a side view of the fingerprint sensor button shown in FIG. 20A. FIG.

The following detailed description is to be read with reference to the drawings, wherein like elements in different drawings have like reference numerals. The drawings are not necessarily to scale, but rather illustrate selected embodiments and are not intended to limit the scope of the invention.

1A and 1B illustrate a known fingerprint sensor 30 that utilizes an entire silicon chip 32 as a receiver for signals derived from a user's fingertip 34. Various methods of transmitting signals into the user's fingers on both the silicon chip itself and outside the silicon chip have been described; In either case, the pixels 40 used to receive signals from the user's fingertips are formed directly on the silicon chip. The signal is received at each pixel in the silicon chip. Signal detection may be performed by other methods for detecting differences between signals passing through the valley 38 of the fingertip 34 versus signals passing through the voltage amplitude, signal phase shift, or ridge 36 of the fingertip It may be based. The main disadvantage posed by this approach is the cost due to the size and complexity required of the silicon chip 32. Since the receiver pixels 40 are located in the silicon chip 32 itself, a relatively large silicon area is consumed, and any increase in pixel count directly increases the required size of the silicon chip. As the size of the silicon chip 32 increases, the likelihood of defects also increases; In some cases, even a single defect will render the entire silicon chip 32 useless. In addition, this approach lacks flexibility in packaging methods due to the need to protect the surface of the silicon chip 32, which is similar to fragile glass.

Figures 2a and 2b illustrate another known fingerprint sensor 50 in which an array of metal lines is arranged in an array of X rows 52 x Y columns 54. A series of X row lines 52 serve as receiver traces ("Rx"), and a series of Y column lines 54 serve as transmitter traces ("Tx"). The intersection of the Tx transmitter line and the Rx receiver line forms a single pixel region, denoted by 56 in Figure 2b. Typically, each receiver line 52 extends somewhat at each location where it intersects the transmitter line 54 to form a "receiver plate ". Theoretically, the source signal travels from the TX transmission line in the same position up into the user's fingertip 34 and down to the Rx receiver line. The individual IC chip 58 is connected to TX transmitter lines 54 and Rx receiver lines 52 by additional metal traces 60 and 62, respectively, to process the image received by the fingerprint sensor 50, Respectively.

The known approach illustrated in Figs. 2A and 2B suffers from serious signal-to-noise problems for a number of reasons as now described. Both the Tx transmitter lines 54 and receiver "plates" provided at each intersection of the Tx line 54 and the receiver line 52 are formed in the patterned metal layers. Because of the relatively tight spacing in the pixel array, each of the series of Tx lines 54 is relatively narrow, and each receiver plate formed on the receiver lines 52 is very small. The effective width of the Tx line is limited by the spacing between adjacent pixels. Moreover, the size of each receiver plate is also limited because Tx lines 54 and Rx lines 52 must be formed on individual metal layers (to avoid electrical disconnection), and accordingly Tx Since none of the receiver plates of line 54 or Rx line 52 can cover the entire pixel area; Otherwise, the metal forming the Tx line 54 will block the transmitted signal from reaching the receiver plate located below the Tx line 54. Alternatively, if receiver plates were formed in the upper layer of metal and Tx lines 54 were formed in the lower layer of metal, the receiver plates would block the transmitted signal from reaching the fingertip of the user. As a result, this approach suffers from large signal losses, de-focusing of the transmitted signal, and hence poor image quality. In addition, the IC chip 58 requires a relatively large number of I / O pads directly related to the number of Tx transmit and Rx receive lines required. The routing of these signals between the IC chip 58 and the pixel array consumes a fairly large area.

Also, the signals transmitted from the Tx line 54 into the fingertip 34 and into the receiver plates formed on the road Rx line 52 can not be effectively separated for the exact pixel region where such lines intersect with each other. This is because, at any given time, the entire Tx line 54 is active and the entire Rx line is being detected. This can result in unwanted signals that can vary depending on the image being requested. For example, if a wide finger ridge 36 is positioned over the entire Tx line 54 or over the entire Rx line 52, the received signal may be from a similar pixel having ridges only over the correct area of that one pixel anywhere Which is the case even if it is desirable to detect the same signals from both pixels. This can lead to large image distortion problems and complicate post-processing requirements that attempt to reconstruct the proper image.

3A and 3B show a fingerprint sensor 70 according to a first embodiment of the present invention. The pixel array 72 includes an array of thin film transistors ("TFT") or similar low cost switching devices as an alternative to silicon integrated circuit devices. The TFTs may be formed on the flexible substrate 73. The pixel array 72 is shown in more detail in Figures 3B, 4A, 4B, 4C and 5, described below. Each pixel of the array includes one TFT device. In addition, relatively large metal capacitors, or more precisely, "capacitive plates" are formed in each pixel in the array. A protective dielectric layer 78 is formed over the pixel array 72 and includes an uppermost surface 80 for receiving a user's fingertip 34. The capacitive plates are formed below the dielectric layer 78 in the flexible substrate 73 but are formed as close to the fingertip of the user as possible (generally close to the top surface on which the user has placed his or her fingertip) . Relatively large Tx transmission traces 74 and 76 extend along both sides of the pixel array 72 as indicated by arrows 82 and 84 to provide a high frequency signal to the fingerprint sensor 70, To the fingertip 34 of the user. As will be described in greater detail below, Tx transmit traces 74 and 76 may in fact be part of a single Tx transmit ring surrounding pixel array 72. Transmitter traces 74 and 76 may be formed on the lowermost surface of the flexible substrate 73. An individual integrated circuit silicon chip 86 is bonded to the lowermost surface of the flexible substrate 73 and conductive traces extend along and / or through the flexible substrate 73 to form an IC chip 86 and pixel array 72, Respectively. Although the flexible substrate 73 is illustrated, the structure described can be easily fabricated on glass or other stiffer substrates as needed.

As best shown in Figures 4A and 5, each TFT 90 has a gate electrode 92 connected to a row address line 94. 5 is a schematic diagram of the first three rows and the first four columns of the pixel array 72. FIG. 5, the TFT 90 is located in the first row of the pixel array and its gate electrode 92 is connected to the row address line 94 for the first row ("row 1") of the pixel array 72, Lt; / RTI > 5, each row of pixel arrays 72 (i.e., row 1, row 2, row 3, ...) may be individually addressed one at a time. This is accomplished by having a TFT (e.g., 90) at each pixel location within the pixel array 72. [ Apart from the gate electrode 92, the TFT 90 also includes a drain electrode 96 and a source electrode 98 which are separated from each other by the semiconductor region 100. In addition, the gate electrode 92 is spaced from the semiconductor region 100 by the gate dielectric layer 102 from the drain electrode 96 and the source electrode 98. When the row line 94 to which the gate electrode 92 is connected is selected, the gate 92 makes the semiconductor region 100 conductive and the drain electrode 96 and the source electrode 98 are electrically connected to each other do. On the other hand, when the row line 94 is not selected, the semiconductor region 100 electrically isolates the drain electrode 96 and the source electrode 98. The above-described configuration of the TFT 90 is entirely consistent with known methods currently used to create TFTs on flexible substrates.

4A and 5, a pixel electrode or a capacitive plate 104 is formed on the TFT 90. The pixel electrode 104 is substantially parallel to the flexible substrate 73 and parallel to the surface on which the user ultimately presses his or her fingertip against. The pixel electrode 104 is supported on the uppermost surface of the interlayer dielectric layer 106 and this interlayer dielectric layer electrically isolates the pixel electrode 104 from the gate electrode 92 and the row line 94. A via 108 is formed to penetrate the gate dielectric layer 102 and the interlayer dielectric layer 106 to electrically connect the pixel electrode 104 to the drain electrode 96 of the TFT 90. 3B, when the fabrication of the fingerprint sensor 70 is completed, the pixel electrodes 104, 110, 112, 114, and 116 of the pixel array 72 are protected by the protective layer, Lt; RTI ID = 0.0 > fingertip < / RTI > The source and drain lines of the TFT 90 are located significantly below the pixel electrode 104 and do not enter into significant direct capacitive coupling with the user's fingertip 34, It should be noted that it reduces any introduction of stray signals. When manufactured as described above, the row lines are connected to the gates of the TFTs and the column lines are connected to the sources of the TFTs. Each pixel electrode 104 forms a capacitor from the drain of each TFT to the fingertip of the user.

Figure 3b illustrates pixel electrodes 104, 110, 112, 114, and 116 all of which lie in a common row of pixel arrays. In practice, there are many rows of pixel electrodes. 4B, the pixel electrodes 104 and 110 are placed adjacent to each other in row 1, and the gate electrodes of both the TFT 90 and the TFT 124 are common to the row line 94 Lt; / RTI > Two additional pixel electrodes 118, 120 are also shown in Figure 4b as being located in the row that follows. The TFTs 126 and 128, respectively associated with the pixel electrodes 118 and 120, each have their gate electrodes connected to the row line 130 corresponding to row 2 of the pixel array. Each pixel electrode essentially forms a capacitor with the protective dielectric layer and the fingertip of the user that electrically isolates the pixel electrode from the fingertip of the user. The signal transmitted into the fingertip of the user is coupled into the pixel array 72 through each such capacitor. The plates of such effective capacitors are closer together if the ridge of the user's fingertips is directly above the pixel, but the plates of such effective capacitors are farther apart if the valleys of the user's fingertips are directly above the pixels. Due to variations in such capacitance from pixel to pixel, the transmitted signal coupled through the TFT of each pixel will change accordingly, and these variations can be used to form an image of the fingerprint. In addition, by forming the wide metal capacitors or "pixel electrodes" close to the top of the material stack while the column lines are further underneath, external signals from other locations in the array can be read from the data being detected by the column lines More effectively separated. On the other hand, the IC chip 86 can be mounted on the lower surface of the flexible substrate 73 to drive the row lines and process the data signals provided by the column lines.

4C is a simplified plan view of the fingerprint sensor 70. FIG. Pixel array 72 includes pixels of X rows and Y columns, and each such pixel is fabricated in the manner described above with respect to FIGS. 4A, 4B, and 5. FIG. The pixel array 72 is surrounded by a transmission ring 74 'for transmitting a high frequency signal into the fingertip of the user around its periphery. The transmit ring 74 'is located outside the area of the pixel array 72. The transmitting ring 74 'effectively transmits a high frequency signal into the body of the user's fingertip 34. This emitted signal is conducted by the fingertip of the user and passes through the ridges and valleys of the fingertip surface through the protective interstitial material in the customer's system (e.g., cell phone cover glass) Lt; RTI ID = 0.0 > metal plates or pixel electrodes.

The demultiplexer 140 extends along one side of the pixel array 72. The demultiplexer 140 receives control signals from the IC 86 to indicate the row to be selected at a point in time among the rows in the pixel array. The demultiplexer 140 decodes such control signals and drives the row lines 94, 130, ..., 142 to enable only one row at any given time. The demultiplexer 140 reduces the number of conductive traces that need to be extended between the IC 86 and the pixel array 72. For example, if pixel array 72 includes 256 rows of pixels, then pixel array 72 includes 256 rows. On the other hand, only eight binary control lines need to be present between the IC 86 and the demultiplexer 140 to select one of the 256 rows.

4B and 5, a series of Y column electrodes, including column electrodes 146, 148, 150, 152, are coupled to a pixel array (not shown) to detect a signal derived from a pixel located in a corresponding column of a selected row. (72). For example, when the row 94 is selected, the column electrode 146 connected to the source electrode of the TFT 90 senses the signal provided by the pixel electrode 104; Likewise, the column electrode 148 connected to the source electrode of the TFT 124 senses the signal provided by the pixel electrode 110. Thus, the gate of each TFT is connected to a corresponding row driver, the drain of each TFT is connected to a pixel electrode (which forms a capacitor with the user's fingertip), and the source terminal of each TFT is connected to a column line To the "data line", to the IC 86 for signal processing. The illustrated row lines 94 and 130 and the column lines 146, 148, 150 and 152 may be formed of any conductive metal including indium tin oxide (ITO), which is a transparent metal used to create LCDs. have. Other metals such as aluminum or copper may be utilized where transparency is not required.

4C, the column decode circuit block 144 is electrically connected to all the column electrodes including the column electrodes 146, 148, 150, and 152 shown in FIG. Whereby the column decode circuit block 144 detects the signal levels at each pixel in the selected row. By moving sequentially through the X rows of the pixel array, an image of the user ' s fingerprint with X x Y pixels may be derived. The capacitive plates or pixel electrodes may have a signal amplitude from the user's fingertip 34 as long as the characteristics of the detected signal change as the transmitted signal passes through the ridges of the user's fingertip or through the valleys, Signal phase shift, or other methods. In preferred cases, the characteristics (frequency, amplitude, etc.) of the transmitted Tx signal can be changed from one detection pass through the pixel array to the next, and multiple samples are taken to produce a more accurate image Can be highly averaged.

In use, a single row driver will be turned on to activate the pixels of that particular row. The transmitting ring 74 'is used to transmit a known signal at a predetermined frequency. The signal contents of the pixels in the selected row are transferred onto the column lines for detection, sensing, and processing in the external IC chip 86. [ This approach allows the IC chip 86 to be physically displaced from the pixel array and the use of demultiplexing / multiplexing schemes to select between the IC chip 86 and the pixel array the row select lines and the sensed signal data lines . Each pixel electrode 104, 110, etc., forms a capacitor with the fingertip, and the value of that capacitor will depend on the surface (ridge or valley) of the finger above each pixel location. Each pixel electrode receives a signal from the fingertip and is turned on when the associated TFT is in the "on" state (i.e., when the row driver for this particular row is enabled to turn on the & Will be conducted through the TFT and will be provided on the "data line" or column electrode of the pixel array.

A column decode circuit block 144 is electrically coupled to the IC 86, which processes the signals detected at each pixel of the array to form an image of the fingerprint. The detected signals may be transmitted in block units from the column decode circuit block 144 to the IC chip 86 to minimize the number of conductive traces between the column decode circuit block 144 and the IC chip 86. [ For example, if pixel array 72 includes 256 columns of pixels, column decode circuit block 144 may transmit blocks of 16 signals at a time to generate 16 such transmissions for each row of the array . Apart from the 16 conductive traces between the column decode circuit block 144 and the IC chip 86 for transmitting the signal data block there are only four additional control lines to represent the blocks being transmitted among the 16 data blocks, May only be needed. This multiplexing technique significantly reduces the number of metal traces that must extend between the column decode circuit block 144 and the IC chip 86. [

6 illustrates a further illustration of how demultiplexer 140 and column decode circuit block 144 reduce the number of conductive traces that need to extend between IC 86 and pixel array 72 It is possible. The low lines 94, 130, etc. are driven by the demultiplexer 140. The demultiplexer 140 has a number of output terminals equal to the number of row lines, and only one such row is selected at any given time. In contrast, the number of selection lines 154 extending between the IC 86 and the demultiplexer 140 decreases exponentially. Also, if there are 256 rows of pixels in the array, select lines 154 require only 8 conductive traces to uniquely identify one of the 256 rows. Thus, the demultiplexer 140 can take multiple (x) selection lines and address 2 ^x rows through simple digital logic. Alternatively, the demultiplexer 140 may simply be a digital shift register, where a logic "1" output signal is sequentially routed from the low 1 output terminal to the low 2 output terminal, etc. until all the rows are enabled To enable one row at a time.

Similarly, if the pixel array includes 256 column electrodes including column electrodes 146, 148, 150 and 152, and the columns are subdivided into 16 blocks each of 16 columns, then the column decode circuit block 144, May transmit each data block through the sixteen conductive traces represented by bus 156 in FIG. The four additional conductive traces represented by select lines 158 in Figure 6 are sufficient in this example to uniquely address one of the sixteen data blocks for any given row of pixels. For column drivers, the signals will be analog and de-muxed through analogue muxes. As an example, it may be from the 2 ^Y columns to one final analog input "M" using Y selection lines. Depending on the configuration, M may be 1 or even a larger number. This simply depends on the required signals and the reduction in timing allowed for such a process. For example, if the system chooses to address one pixel (M = 1) at a time, all X x Y pixels must be individually addressed.

Figure 7a illustrates the position of the Tx transmit ring 74 'relative to the pixel array 72 better. The Tx transmit ring 74 'can be a simple metal structure and can be formed on either the gate dielectric layer 102 (see FIG. 4A) or under the gate dielectric layer 102. The Tx transmit ring 74 'may be driven by a signal supplied by either IC chip 86 or by an external driver. The Tx transmit ring 74 'is disposed sufficiently far away from the pixel array 72 to avoid direct signal injection from the transmit ring 74' to the pixel electrodes; More precisely, the high frequency signal emitted from the transmitting ring 74 'must first be moved into the fingertip 34 of the user before being coupled to the pixel electrodes. 7A, the connector 160 extends between the pixel array 72 and the IC chip 86 to move electrical signals therebetween. If desired, the connector 160 may be formed as a detachable connection 160 'as shown in FIG. 7B.

Figure 8 is similar to Figure 3a previously described above, except that the signals emitted by the transmitting electrodes 74, 76 pass through the layers of the user's finger to ridges and valleys of the road user's fingertips and into the pixel array Better illustrate how it is combined. In Figure 8, the user's fingertip is generally indicated by reference numeral 170. [ The outer layer of the user ' s fingertip including ridges and valleys is denoted 172. Above the outer layer 172 is the inner conductive layer of the tissue 174. The high frequency signals emitted from the transmitting electrodes 74 and 76 pass through the protective dielectric layer 78 and through the outer layer 172 of the user's fingertip into the larger conductive layers of the tissue 174, 82 and 84 in the upward direction. The signal conducted by layer 174 passes through the ridges and valleys of outer layer 172 along the path represented by arrows 176 for reception by the pixel electrodes (labeled 178 in FIG. 8) And is emitted downward through the protective dielectric layer 78 toward the pixel array 72. 8, the metal layer 180 disposed under the pixel array 72 represents the routing of row address lines used to select, for example, the active row in the pixel array. Again, the IC chip 86 may be mounted on the bottom of the substrate supporting the pixel array 72.

Within Figure 9, an alternate embodiment of the present invention is illustrated in block diagram form wherein the transmission electrodes are interposed between the row addressing electrodes of the pixel array. In this example, the pixel array 72 is a matrix of 96 rows and 96 columns. As in the previous embodiment, the pixel array 72 is formed by a matrix of pixel cells, each pixel cell comprising a TFT and a pixel electrode. In Figure 9, block 190 represents the logic used to address row lines 192 (row G0), 194 (row G1) through 196 (row G95). The row line 192 (G0) is connected to the gate electrodes of the TFTs lying in the common first row (in Figure 9, the array is rotated 90 degrees and the rows actually extend vertically). Similarly, row line 194 (G1) is connected to the gate electrodes of the TFTs in a common second row. The row lines 196 (G95) are connected to the gate electrodes of the TFTs located in the common last row of the pixel array 72. [

As in the case of the above-described embodiments, the column or data electrodes including the lines 198 (C0), 200 (C1) to 202 (C95)) receive the signals received by the pixel electrodes in the pixels of the addressed row Are connected to the source terminals of the TFTs laid along the common column for sensing. The column electrode lines 198 (C0), 200 (C1) through 202 (C95)) are coupled to the column decode circuit block 144 to detect signals received by each pixel electrode in the pixels of the selected row .

In the embodiment shown in FIG. 9, TX0 line 204, TX1 line, ... , TX10 line 206 through TX95 line 208 which also extend from the TFT row logic block 190 and include row addressing lines 192 (row G0), 194 G1) to 196 (row G95)). These TX lines can be used to transmit high frequency signals into the fingertip of a user on behalf of the transmitting ring 74 'shown in FIG. 7A. Initially, it is the purpose of the applicant to keep the transmitting electrodes transversely spaced from the pixel array to prevent direct capacitive coupling from the transmitting electrodes to the pixel electrodes (i.e., bypassing the user's fingertip) May seem contradictory. However, by carefully choosing to be active at any of the transmit electrodes at certain times, and by keeping the active transmit electrodes away from the selected row of the pixel array, a direct capacitive couple from the transmit electrodes to the pixel electrode The ring problem can be largely avoided. In addition, by placing the transmitting electrodes within the pixel array rather than around it, it avoids the need to devote extra areas on the substrate for the transmitting electrodes surrounding the pixel array.

Figure 10 shows the row addressing lines 192 (row G0), 194 (row G1) through 196 (row G95) and TX0 line 204, TX1 line 206, ..., Level functional diagram of the logic components formed in the TFT row logic block 190 to generate drive signals used to control the TX10 line 207 to the TX95 line 208. [ The operation of the TFT low logic block 190 will be better understood by reference to the timing waveforms shown in FIG. The IC chip 86 initiates a read cycle of the pixel array 72 and transmits the start signal 220 to the TFT row logic block 190 to erase / reset the logic elements. A pulsed clock signal 222 is also provided to the TFT low logic block 190 by an IC chip 86 to provide a timing reference. IC chip 86 also transmits a pulse GD on line 224 indicating that the sequence of enabling row addressing lines is to begin. In the first clock cycle C where pulse GD is active, row address line 192 (G0) is activated to enable the gate electrodes of the TFTs in the pixels of the first row. In the next consecutive clock cycle C, the row address line 192 (G0) is switched to the road low state, while the next row address line 194 (G1) is active. This process continues until the row address line 196 (G95) is active in the 96th clock cycle.

9, 10, and 12, the Tx signal 226 represents the high frequency signal to be transmitted into the fingertip of the user. As described above, the Tx signal 226 may be provided by the IC chip 86 or from an external source. An additional signal TD is provided on line 228 as an input to the first flip-flop register 230. The output of the flip-flop register 230 is connected to the AND gate 232. When the output of the flip-flop register 230 is low, the AND gate 232 blocks the signal TX on the line 226 from being transmitted to the TXO line 204. The output of the flip-flop register 230 also functions as a data input to the next successive flip-flop register, which in turn controls the AND gate driving the TX1 line 206, and so on.

With reference to Figures 9 and 10, Applicant has found that it is sufficient to have inactive transmitter lines of about ten rows on each side of the active row of the pixel array being sensed at any given time. Thus, if the pixels of the first row are selected by the gate electrode 192, it is desirable to disable the first 10 transmit electrodes 204 (TX0), 206 (TX1), ..., TX9). Initially, the first eleven flip-flops including the first flip-flop 230 are reset by an initialization (I) signal 220 while the remaining flip-flops are reset by an initialization (I) signal 220 Is set. Thus, when the pixels of the first row are selected, the first eleven transmit electrodes 204 (TX0), 206 (TX1), ..., TX10) include their respective AND gates (including the AND gate 232) While TX11 through TX96 are enabled for the first 85 total active transmit electrodes.

For each successive clock cycle, the other transmit electrodes are disabled until the number of active transmit electrodes decreases to 76. During the first 10 clock cycles (C) of the clock signal 222, the TD input signal 228 provided by the IC chip 86 is maintained at a logic low level ("0 & The transmission electrodes 204 (TX0), 206 (TX1), ..., TX10) are kept disabled by their respective AND gates while one additional transmission electrode on the right is disabled do. After 10 such clock cycles, the TD input signal 228 is switched to a logic high level ("1 ") and remains high for the remaining clock cycles used to terminate reading of the pixels of each row. Thus, as pixels in the eleventh row are selected by the row address line G10, the transmitting electrode 204 (TXO) is enabled to transmit a high frequency signal into the user's finger while the neighboring transmitting electrodes TX1 to TX20 Is disabled. This pattern continues in each clock cycle, effectively providing ten inactive TX rows on either side of the selected row being sensed. As the active sense row moves across the pixel array in each clock cycle, the "inactive range" of the TX transmit electrodes also shifts. As the last 20 rows are selected for sensing, the number of inactive transmit electrodes begins to decrease from 20 to 10. In the illustrated example, the maximum number of TX transmit electrodes disabled at one time is 20, but in that example, at least 76 other TX transmit electrodes are enabled simultaneously to reliably transmit the high frequency TX signal into the user ' do.

12, the transmission lines 204 (TX0), 206 (TX1) to 207 (TX10)) are low or disabled during the time that the row address line 192 (G0) . Meanwhile, the transmission lines 234 (TX11) to 208 (TX95)) are actively driven with a high frequency TX signal to help transmit the TX signal into the fingertip of the user. Similarly, when row address line / gate electrode G10 is selected, the transmit electrodes for TX1 through TX10 and TX11 through TX20 are disabled, while all other TX lines (i.e., TX0 and TX21 through TX95) And is enabled to help transmit the signal into the fingertip of the user. In this manner, the pixel electrodes being sensed receive TX signals only as a result of capacitive coupling between the pixel electrodes and the fingertip of the user, rather than directly receiving TX signals from nearby TX lines. 10 may be formed on the same flexible substrate on which the pixel array 72 is formed, using the same type of TFTs used to form the pixel array, for the TFT row logic block 190 have.

Fig. 11 is a schematic diagram of a column decoder circuit 144 (see Figs. 9 and 10), along with the waveform of Fig. 12, configured as a multiplexer to reduce the number of conductive lines connected between the pixel array 72 and the IC chip 86 It can be seen that The three binary select signals represented by bus 250 are received by a three-to-eight decoder 252, which provides eight output lines including lines 254 through 256. [ The first multiplexer, shown as dashed box 258, includes a series of eight TFTs. The first such TFT extends between the column electrode 260 (c95) and the output port 264 (Cout11). The last one of such TFTs in dashed box 258 extends between column electrode 262 (c88) and output port 264 (Cout11). Thus, at any given time, one of the eight column electrodes c95 to c88 is connected to the output port Cout11.

11, there are eleven such multiplexers, including those shown at 266 and 268, which are used to provide data signals on output ports 270 (Cout0) through 272 (Cout10) in the same manner will be. Thus, at any given time, twelve output signals are provided through output ports 270 through 264 (Cout0 through Cout11). By circulating the select bus signals 250 through each of their eight possible states, data in all 96 columns can be sensed and communicated to the IC chip 86. As shown in FIG. 12, the select bus signals 250 are cycled through their eight possible states during each row address period so that all columns in the selected row can be sensed. Thus, in FIG. 12, when the selection bus signals 250 are in the first state (= 0), the column c0 is sensed and the TX signal waveform transmitted is placed on the corresponding pixel electrode, (C0) to a greater or lesser extent depending on whether the valley is laid down or not. Similarly, when the selection bus signals 250 are in the second state (= 1), the column c1 is sensed and the TX signal waveform transmitted is either a ridge of the user's fingertip over the corresponding pixel electrode, Lt; / RTI > is reproduced to a greater or lesser extent on line 200 (c1) depending on whether it is placed.

Those skilled in the art will recognize that the fingerprint sensors described above may be included within a conventional LCD touchpad of the type used in computers, computer tablets, or cell phones with a touch screen monitor. For example, FIG. 13 illustrates a generic type of fingerprint sensor 300 including a transmit electrode ring 302 surrounding a pixel array 304, as described above with respect to FIGS. 3-8. Referring to FIG. 14, the cell phone LCD touch pad display panel 310 includes the fingerprint sensor 300 of FIG. 13 in the lower left corner.

The portion of the panel 310 of Fig. 14, which lies outside of the typical LCD touchpad, i.e. the fingerprint sensor area 300, is formed of a two-dimensional array of relatively low density pixels arranged at a pitch of approximately 500 microns, The distance from the center of one pixel cell to the center of the next pixel cell is approximately 500 microns. The pixel density may be relatively low because the panel is only needed to detect that the fingertip or stylus is in contact with the area of the display panel 310. In contrast, in order to function properly, the fingerprint sensor array portion 300 should have more densely packed pixels arranged in a finer pitch that is approximately 50 to 70 microns center-to-center. Thus, the fingerprint sensor region 300 may have as many pixels as there are ten rows of pixels for every pixel row in the touch panel 310. Likewise, the fingerprint sensor region 300 may have as many pixels as there are ten columns of pixels for every pixel column in the touch panel 310.

However, the technique used to fabricate the fingerprint sensor region 300 is very similar to that used to fabricate low-density touch-sensitive pixels throughout the remainder of the display panel 310. [ 14 that the fingerprint sensor area 300 is limited to the bottom left corner of the display panel 310, the fingerprint sensor area 300 may be formed on the entire bottom of the display panel 310, But may be enlarged to cover any other area within the panel 310. [

To further protect against external noise signals, the accuracy of sensing the signals detected by the pixel electrodes may be further improved by sensing the pixel electrode signals in the differential mode. This approach allows for the elimination of all types of common mode noise, whether from the human body itself or from other sources such as electronic equipment housed in a fingerprint sensor. 16, the TFT 400 and its associated pixel electrode 401 form a first pixel of the fingerprint sensor region; The TFT 402 and its associated pixel electrode 403 form a second pixel in the same row in the TFT 400; The TFT 404 and its associated pixel electrode 404 form a third pixel in the same column as the TFT 400. [ The TFT 400 and the TFT 402 are connected to the first row addressing line 406. The TFT 404 is connected to the second row addressing line 408. The source terminals of the TFT 400 and the TFT 404 are both connected to the first column electrode 410; The source terminal of the TFT 402 is connected to the second column electrode 412.

16, the first column electrode 410 is connected to the positive (non-inverting) input of the first differential amplifier 414. [ Similarly, the second column electrode 412 is connected to the positive (non-inverting) input of the second differential amplifier 416. In one example, similar differential amplifiers are provided on the remaining column electrodes of the pixel array, except that the number of such differential amplifiers may be one less than the number of column electrodes, as described below. The column electrode 418 is connected to the negative (inverting) terminal of each of the differential amplifiers 414, 416, and the like. The column electrode 418 extends the length of the pixel array to the same extent as the typical column electrodes 410, 412, and so on. Any floating interfering signals received by typical column electrodes (e.g., 410, 412) are also received by the column electrode 418. Thus, the differential amplifier 414 will effectively subtract the floating interfering signal provided by the column electrode 418 from the signal provided by the column electrode 410, and the generated output signal 420 will have an unwanted noise component Will include the signal sensed by the pixel electrode in the selected pixel row.

16, the column electrode 418 may be a "dummy" electrode that is not actually connected to any active pixels if desired. For best noise rejection of human body noise, such dummy columns should be located in areas that are equally close to the user ' s fingers as actual column electrodes. Alternatively, the column electrode 418 may be the actual column electrode associated with the pixels of that particular column in the array; In such a case, no data will be sensed for the column electrodes that are "sacrificed " to receive common mode noise. In order to regenerate the data signals for the missing columns of the pixel array, it should be realized that fingerprints are not arbitrary data. By definition, the fingerprint includes ridges (maxima) and valleys (minima), and the fingerprint image is in the range between the minimum and maximum signals. One relatively simple way to reconstruct the data in a missing column of a pixel array is to look at the values of neighboring pixels and calculate the missing data value by interpolating the values in each row of the missing column.

It has been described above with respect to Figs. 13 and 14 that the fingerprint sensor area 300 may be included in the conventional LCD touchpad panel 310. [ To further support the integration of the fingerprint sensor area 300 within a conventional LCD touchpad panel, the fingerprint sensor area 300 may be selectively operated in a mode that mimics the operation of surrounding, lower density sensing pixels .

17A, the fingerprint sensor area 500 is formed at the bottom left corner of the touchpad display panel 502. [ In this example, the surrounding transmission ring 302 of Fig. 13 is omitted for interleaved transmission electrodes operated in the general manner described above with respect to Figs. 9-12. The touchpad display panel 502 includes an array of low density sensing pixels 504-520. Each sensing pixel 504-520 functions to detect whether the fingertip of the user is positioned with respect to the cover glass just above such a sensing pixel, or whether a stylus is being placed. In the example shown in FIG. 17A, there are approximately seven high density pixels per linear length in the fingerprint sensor region 500 for every single low density pixel (e.g., 504). The area occupied by the fingerprint sensor area 500 replaces another 4 x 4 array of low density pixels. When the fingerprint sensor area 500 is being used in the "fingerprint mode" to generate a fingerprint image, each pixel electrode in the pixel array is individually addressed and sensed in the manner previously described.

17B, during the operation of the " mimic mode ", groups of seven unit pixels within the fingerprint sensor area 500 are grouped together to form virtual low density pixels, Density pixels 504 through 520 of FIG. As shown in FIG. 17B, a virtual low density pixel 522 is formed by a 7 x 7 array of high density pixels. When the FPS area 500 is configured to mimic the touchpad area 502, the rows of the FPS area 500 in the cluster mode are selected or de-selected. The number of rows in the FPS area 500 that are enabled / selected at any one time depends on the size of the denser touchpad pixels than the density of the more dense FPS pixels. In the example shown in FIGS. 17A and 17B, groups of seven rows of the FPS area 500 are clustered together. Apart from simultaneously selecting seven adjacent rows, seven adjacent column electrodes are also shorted together. In this manner, the signals collected on the pixel electrodes of 49 pixels (7 x 7) are averaged together to be compared to each other by each of the lower density pixels (e.g., 504, 506, etc.) of the touchpad display panel 502 And provides one output signal that imitates the generated signals. Those skilled in the art will appreciate that, in operation of this " mimic mode ", it is possible to connect the crowded / shorted column electrodes in the FPS area 500 to existing column lines of the touchpad panel, It will be desirable to do so.

As shown in FIG. 18, the four low density pixels of the touch pad 502 include 503, 504, 505 and 506. These low density sensor pixels are addressed by row lines 530, 532 and by column lines 534, 536. In Figure 18, the more dense pixels of the fingerprint sensor region are now shown to be clustered together at a higher density of 10 pixels x 10 pixels per hypothetical low density pixel. In this example, the touchpad pixels 503, 504, 505, and 506 are 500 um x 500 um, while the FPS pixels are 50 um x 50 um. In order to allow the FPS region to mimic the touch pad region, the FPS row 1 to the FPS row 10 are simultaneously switched to the "on" state and the FPS columns are shorted together for each group of 10 columns (i.e., 10 is short-circuited; FPS column 11 to FPS column 20 are short-circuited; In this way, the imaginary FPS pixel size can increase from 50 um x 50 um to 500 um x 500 um. Clustering together the FPS rows by simultaneously selecting multiple rows and shorting together the desired number of columns is accomplished using TFTs. This method allows fine pixel FPS to mimic large pixels of the touchpad.

The more dense pixels of the fingerprint sensor region 500 are addressed by row select lines 548 and the columns of the selected rows are sensed by the column electrode lines 550. The four hypothetical low density pixels are denoted by 540, 542, 544 and 546. The ten row address lines (FPS row 11 through FPS row 20) can individually address each of the ten rows 11-20 in the hypothetical low density pixel 540 when a fingerprint image is required, All 10 of the rows can be selected at the same time as they mimic the operation of the lower density pixels. Similarly, the ten column sensing electrodes (FPS column 1 through FPS column 10) can individually sense each of the ten columns 1 through 10 in the hypothetical low density pixel 540 when fingerprints are required, Or all ten of such columns may be shorted together when imitating the operation of the lower density pixels.

The timing waveform of FIG. 19 further illustrates the operation of the fingerprint sensor area (FPS) 500 and its denser pixels as it is being used to mimic the operation of lower density pixels. During the first clock cycle t0, FPS row 1 through FPS row 10 are all enabled such that the virtual pixels 544 and 546 can be selected. During the same clock cycle, FPS column 1 through FPS column 10 are short-circuited to sense virtual pixel 544, and FPS column 11 through FPS column 20 are short-circuited to sense virtual pixel 546. During the next clock cycle t1, FPS row 1 through FPS row 10 are all disabled again, while FPS row 11 through FPS row 20 are all disabled so that the virtual pixels 540 and 542 are all selected Is enabled. Again, during the clock cycle t1, the FPS column 1 through the FPS column 10 are short-circuited to sense the virtual pixel 540, and the FPS column 11 through the FPS column 20 are short-circuited to sense the virtual pixel 542. This process continues until all the virtual pixels are detected. Thereafter, a sufficient number of additional clock cycles follow, while the rows of the touch pad panel including the rows 530 and 532 (i.e., TP row 1; TP row 2; TP row 3; N) are individually selected and touchpad column lines (e.g., 534, 536) are used to determine whether any of the pixels in the selected touch pad row are being touched by the user's finger or stylus .

Now, these figures refer to Figs. 14 and 15B which illustrate an LCD touch-sensitive panel or touchpad that is formed of a high density TFT / capacitive plate pixel array, but is typically operated in a lower density touchpad mode. When operating in the touchpad mode, the pixels of higher density (finer pitch) mimic the behavior of the lower density touchpad pixels in the manner already described. 15A and 15B also serve to illustrate how to operate such a touchpad, wherein the fingerprint sensor area can be selectively provided at a location of the touchpad where the user is applying his or her finger at any location. 15A, the touchpad 702 includes an array of low density touchpad pixels including adjacent touchpad pixels 704, In Fig. 15A, the user's fingertip is applied to the area of the touchpad indicated by the "contact" area, that is, the ellipse 700 of dashed lines.

15B is an enlarged view of the lower half of the touch pad 702. The dotted ellipse 700 includes touch pads 704 and 706 which are disposed in the vicinity of the dashed ellipse 700 including the areas corresponding to the touch pad pixels 704 and 706, Are superimposed over a rectangular area of the touch pad 702 formed by the pixels. However, in FIG. 15B, the touchpad pixels 704 and 706, and other touchpad pixels that lie near the dotted ellipse 700 have been switched to the fingerprint sensor mode, where the fine pitch high density pixels are now generally To provide a higher resolution when operated in the touchpad pixel mode.

The ability of the touchpad 702 to mimic a less dense touchpad allows any portion of the entire touch panel area or touch panel area to be utilized as the fingerprint sensor area. A fingerprint image may be taken from any location on the touch panel 702 if desired. Initially, the touchpad 702 can be configured as a conventional touchpad by shorting the addressing rows together and shorting the column sensing lines together, as described above, to form larger and less dense pixels. Alternatively, the touch panel 702 can be used as one large high resolution fingerprint sensor, where one finger, multiple fingers, or even the palm parts of a person can be sensed. Finally, the touch panel 702 may be configured to first detect where the fingertip of a person is located, and then configure the detected position as a fingerprint sensor area according to the fingertip position to pick up a fingerprint of a person.

Whether the touch panel 702 is used as a touch pad or as a fingerprint sensor area, a general position in which a user is applying his or her fingertip can be detected. When the touch panel 702 imitates the operation of a conventional touch pad, the same methods currently used to determine the finger position and finger swipe direction for conventional touch pads may also be used for the same purpose, ). ≪ / RTI > Once the position of the fingertip is determined, the immediate surrounding area is converted to a high resolution fingerprint sensor area to allow high quality images of the fingerprint to be captured.

In implementing the method illustrated by Figs. 15A and 15B, the array of fine pitch pixels is arranged over the entire surface of the touch panel 702 along rows and columns that intersect essentially. As described earlier, each fine pitch pixel preferably includes a capacitive plate and a switching device (e.g., a TFT) for sensing a high frequency signal transmitted through a user's finger. A series of fine pitch row address lines are provided, and each fine pitch row address line is associated with a row of fine pitch pixels in the array. Each fine pitch row address line may selectively address fine pitch pixels associated with corresponding rows of the array. As before, a plurality of fine pitch column sensing lines are also provided, and each fine pitch column sensing line is associated with a column of fine pitch pixels in the fine pitch pixel array. Each such fine pitch column sensing line can sense a signal provided by a capacitive plate of fine pitch pixels in a selected row of fine pitch pixel arrays. Although not shown in FIG. 15A or 15B, those skilled in the art will appreciate that the high frequency signal transmitter electrodes as described above with respect to FIGS. 9 and 10 can be included in the pixel array and can be selectively enabled and disabled, &Quot; effectively " transmits into the fingertip of the user that is applied to the "contact"

As described above with respect to FIGS. 17A, 17B, and 18, fine pitch pixels may be arranged in rows and columns with an array of larger touchpad pixels, such as touchpad pixels 704 and 706 in FIG. ≪ / RTI > The array of touchpad pixels is a "smaller array" in that it includes fewer rows and columns, even though it covers the same basic two-dimensional space. Each such touchpad pixel includes at least two, and typically five or more, fine pitch pixels of different rows. Likewise, each such touchpad pixel includes at least two, and typically five or more, fine pitch pixels of different columns. The center-to-center distance from one such touchpad pixel to the next adjacent touchpad pixel is at least two times, and more typically five times greater, than the center-to-center distance from one fine pitch pixel to the next adjacent fine pitch pixel .

15A and 15B, the above-described method includes a first mode of operation in which all of the fine pitch pixels in touchpad 702 are configured to mimic the operation of lower density touchpad pixels, such as 704 and 706 . In this first mode of operation, the fine pitch pixels forming the overall touchpad pixel 704 are enabled at the same time, for example for general operation. In other words, all the row address lines for the fine pitch pixels located in the touchpad pixel 704 are enabled at the same time (i.e., the row addressing lines enabling the fine pitch pixels of the group are effectively shorted together). Similarly, the column sensing electrodes connected to the fine pitch pixels located at the touchpad pixel 704 also collectively detect signals provided by the capacitive plates of all the fine pitch pixels located within the touchpad pixel 704 Effectively shorted together. In this manner, each such touchpad pixel mimics the functionality of a conventional touchpad pixel of a conventional touchpad during a first mode of operation. During such a first mode of operation, the signals provided by the touchpad pixels are used to detect whether a pointer (fingertip, stylus, etc.) is being applied close to the top surface of the touchpad 702, , The position of such a pointer on the touch pad 702 is also detected.

Referring to Fig. 15B, the touch pad 702 may be changed to a second operation mode, for example, when an image of the user's fingertip is sensed. During this second mode of operation, it is determined which touchpad pixels lie close to the pointer position. For example, in FIG. 15B, it is determined that a group of twenty touchpad pixels (four touchpad pixels extending horizontally and five touchpad pixels vertically extending) are placed close to the pointer position; Among these twenty touchpad pixels are those labeled with 704 and 706 in Figures 15A. These twenty touchpad pixels are then reconfigured, i. E., Selectively switched to fine pitch pixels that can be individually addressed and sensed. During this separate mode of operation, the fine pitch pixels in each fine pitch row are enabled individually, and the signal provided by each of the capacitive plates of each such fine pitch pixel is such that each fine pitch row has a corresponding fine pitch row Are individually sensed as being enabled by the address lines. This is why, in FIG. 15B, the array or grid illustrated in the "touch" region 700 is depicted as being much denser than the touchpad pixels located outside the "touch" region 700. Accordingly, the individual fine pitch pixels in the "touch" area 700 are now configured to form a fingerprint sensor area for sensing a fingerprint image of the user's fingertip.

15A and 15B illustrate a manner in which a fingerprint sensor area can be provided anywhere in the touch panel 702 where the touchpad 702 is proximate to the touch area currently being touched by the user's finger. However, those skilled in the art will appreciate that the fingerprint sensor region can be extended to cover the entire surface of the touchpad 702, if desired. In other words, all of the touchpad pixels shown in FIG. 15A can be switched from its first (or "mimic") mode to its second (or "discrete") mode, Pixel mode. In this way, two or more fingerprints or even palm prints can be detected.

The fingerprint sensor of the above-described type in the first half may also be included in the button as illustrated in Figs. 20A and 20B. The button 600 may be a security feature in, for example, a protected doorway, an elevator, etc. In this case, the identity may be granted to those who have a fingerprint that matches the previously stored individual fingerprint Is limited. The button 600 includes a pixel array 602 covered by a protective layer 604 of glass. The pixel array is formed on the flexible substrate 606 mounted on the printed circuit board 608 by an adhesive 609. [ The integrated circuit chip 686 is mounted on the printed circuit board 608. The flexible electrical connector 610 extends between the flexible substrate 606 and the printed circuit board 608 to make an electrical connection between the pixel array 602 and the IC chip 686. 20A, the peripheral ring 612 may be provided to transmit a high frequency signal into the user's finger when the user presses the button with his or her fingertip. Alternatively, if desired, the external transmitting electrode may be omitted, and the transmitting electrodes may be selectively activated away from the particular row being sensed at a given instant in the manner already described above.

Those skilled in the art will appreciate that the fingerprint sensor described herein provides itself to applications for touch electronics and increases the ability of the sensor to read fingerprint images through thicker protective surfaces that provide greater protection to the lower pixel array Will recognize. Thus, for example, the fingerprint sensor of the present invention can be successfully used in thick cover glasses commonly provided in cell phone touch display panels. In addition, the device described herein can be used in relatively small integrated circuit chips regardless of the dimensions of the pixel array, which reduces manufacturing costs. The disclosed fingerprint sensor provides increased signal strength and improved signal-to-noise ratio through thicker materials and the ability to keep the signal "focused" through thicker materials, so that finger ridges and images of valleys So that the resolution is sufficiently high for detection. The invention described herein can be used in any application that uses touch sensitive surfaces such as cell phones, touch pads, notebooks, notepads, E-readers, and the like. The present invention can be used to embed biometric security technology in electronic products with minimal impact on product size, cost, and processing.

From the foregoing description of the preferred embodiments, those skilled in the art will appreciate that the present invention does not require the use of an integrated circuit semiconductor chip of the same dimensions as the pixel array used to capture the image of the fingerprint, The present invention provides a fingerprint sensor for capturing a fingerprint of a fingerprint. The fingerprint sensor of the present invention more easily distinguishes the ridges and valleys of the fingertips applied to the cover plate lying under the pixel array even when using relatively thick cover plates. The disclosed invention effectively transmits a high frequency carrier signal into the fingertip of a person without transmitting the carrier signal directly into the pixel array simultaneously, i.e., before the carrier signal is transmitted back into the pixel array, Lt; / RTI >

As described above, a fingerprint sensor constructed in accordance with the present invention is used to process fingerprint images captured by a pixel array and a pixel array, primarily by demultiplexing row address lines and / or demultiplexing column data lines But also significantly reduces the number of electrical lines that must extend between the associated integrated circuits. The present invention provides itself for differential sensing of signals detected by pixel electrodes, resulting in improved rejection of common mode noise signals. The fingerprint sensor of the present invention can be easily included in conventional touch-sensitive pads using the same sensing layers and the same fabrication techniques, and can even be used to mimic the lower density pixels of the touchpad when not used to form an image of the fingerprint can do.

While the invention has been described in terms of preferred embodiments, such description is for illustrative purposes only and is not to be construed as limiting the scope of the invention. Various modifications and changes may be made by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.

The present invention relates to a fingerprint sensor, and more particularly, to a fingerprint sensor having a pixel array and a flexible substrate.

Claims (24)

As a fingerprint sensor,
a) a first substrate on which a plurality of pixels are formed, the first substrate comprising an upper surface, the pixels being arranged in a pixel array of R rows and N columns, Wherein the pixel further comprises a capacitive plate including a switching device and proximate to the upper surface of the first substrate;
b) a plurality of R row addressing electrodes, each row addressing electrode being connected to switching devices of pixels in corresponding rows of the pixel array to select the switching devices in the corresponding pixel row ;
c) a plurality of N data electrodes, each data electrode comprising a selected pixel row of the pixel array and a corresponding counter of the pixel array sensing a signal provided by the capacitive plate of the pixel located at the intersection of the corresponding column To the switching devices of the pixels in the column;
d) a cover layer overlying the upper surface of the first substrate to receive a user's fingertip; And
e) at least one transmitter electrode proximate to the upper surface of the first substrate and spaced apart from the pixel array to transmit a varying amplitude electrical signal,
f) whereby the variable amplitude electrical signal transmitted by the at least one transmitter electrode is coupled into a user ' s finger that places its fingertip on the cover layer, and wherein the electrical signal coupled into the user ' Is coupled further to a greater or lesser extent through the capacitive plates in the pixel array depending on whether a ridge of the user's fingertip or a valley lies over a particular pixel in the array ,
Fingerprint sensor. The method according to claim 1,
Wherein the switching devices included in the pixel array are thin film transistors (TFT)
Fingerprint sensor. The method according to claim 1,
Wherein the at least one transmitter electrode extends substantially entirely around the pixel array,
Fingerprint sensor The method according to claim 1,
Wherein the first substrate and the cover layer are integrally formed,
Fingerprint sensor. The method according to claim 1,
The first substrate is relatively flexible,
Fingerprint sensor. 1. A touch pad comprising a fingerprint sensor for sensing a fingerprint of a user,
a) a substrate having an upper surface;
b) an array of sensor pixels formed on the substrate and arranged along the intersecting rows and columns to sense the presence and position of a pointer proximate to the upper surface of the substrate-adjacent sensor pixels are arranged at a first predetermined distance Wherein each sensor pixel provides a signal indicating whether a pointer is being applied proximate the 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, each row address line being associated with a respective row address line Selectively enabled to address sensor pixels;
d) a plurality of column sensing lines supported by the substrate, each column sensing line sensing a signal provided by a sensor pixel in a row of sensor pixels selected by an enabled row address line Associated with a column of sensor pixels;
e) a fingerprint sensor region formed on the substrate,
i) a plurality of fine pitch pixels arranged along intersecting rows and columns to form an array of fine pitch pixels, each fine pitch pixel comprising a switching device and further comprising a capacitive plate, Pixels are spaced from adjacent fine pitch pixels by a second predetermined distance that is less than one-third of the first predetermined distance,
ii) a plurality of fine pitch row address lines, each fine pitch row address line being associated with a row of fine pitch pixels in the array, each fine pitch row address line being associated with a respective corresponding fine pitch row address line Selectively enabled to address fine pitch pixels, and
iii) a plurality of fine pitch column sensing lines, each fine pitch column sensing line having a signal provided by a capacitive plate of fine pitch pixels in rows of fine pitch pixels selected by an enabled fine pitch row address line, Associated with a column of fine pitch pixels to be sensed; And
i) touch pad row address lines that border the fingerprint sensor region, which also serves as a transmitter electrode to transmit a variable amplitude electrical signal when the fingerprint sensor region is being used to sense a fingerprint of a user, or ii) At least one of the pad column sensing lines,
g) whereby the variable amplitude electrical signal transmitted by the transmitter electrode is coupled into a user ' s finger putting his or her fingertip on the fingerprint sensor area, and the electrical signal coupled into the user ' Pitch pixel array is further coupled to greater or less extent through capacitive plates within the fine pitch pixel array depending on whether a ridge of the user's fingertip is laid over a particular pixel in the pixel array,
Touchpad. A touch pad including a fingerprint sensor,
a) a touch pad for sensing the presence and position of an applied pointer,
Arrays of sensor pixels arranged along intersecting rows and columns-adjacent sensor pixels are spaced apart from each other by a first predetermined distance, and each sensor pixel determines whether the pointer is being applied to a corresponding touch pad proximate to the sensor pixel Provide a signal to indicate -
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 to address sensor pixels associated with respective respective row address lines -, and
A plurality of column sensing lines, each column sensing line associated with a column of sensor pixels sensing a signal provided by a sensor pixel in a row of sensor pixels selected by an enabled row address line; Touchpad;
b) a fingerprint sensor area comprising a portion of the array of sensor pixels,
A plurality of fine pitch pixels arranged along intersecting rows and columns, adjacent fine pitch pixels being spaced apart from each other by a second predetermined distance less than one third of the first predetermined distance,
A plurality of fine pitch row address lines, each fine pitch row address line being associated with a row of fine pitch pixels in the array, each fine pitch row address line having a fine pitch associated with each corresponding fine pitch row address line, Selectively enabled to address the pixels, and
A plurality of fine pitch column sensing lines, each fine pitch column sensing line having a plurality of fine pitch column sensing lines, each fine pitch column sensing line having a plurality of fine pitch column sensing lines, And a column associated with the touch pad; And
c) a control circuit responsive to a mode signal determining whether the fine pitch pixels function as fingerprint sense pixels of the touchpad or as conventional sensor pixels,
Wherein the control circuit is operable to individually enable fine pitch pixels in each fine pitch row when the mode signal indicates that the fine pitch pixels are functioning as fingerprint sensing pixels and to enable each fine Individually senses the signal provided by the pitch pixel,
Wherein the control circuit is configured to simultaneously enable fine pitch pixels in a plurality of adjacent fine pitch rows when the mode signal indicates that the fine pitch pixels function as conventional sensor pixels of the touchpad, Said control circuit collectively sensing signals provided by fine pitch pixels in pitch rows;
Touchpad As a fingerprint sensor,
a) a first substrate on which a plurality of pixels are formed, the pixels arranged in a pixel array of R rows and N columns, each pixel comprising a switching device and a capacitive plate;
b) a plurality of R row addressing electrodes, each row addressing electrode coupled to switching devices of pixels in corresponding rows of the pixel array to selectively enable switching devices in the corresponding row;
c) a plurality of N data electrodes, each data electrode comprising a plurality of N data electrodes, each of said data electrodes comprising a plurality of N data electrodes, Connected to the switching devices of the pixels in the corresponding column;
d) a cover layer overlying the first substrate to receive a user's fingertip;
e) a second substrate different from the first substrate and comprising a semiconductor material;
f) forming a set of S row addressing signals, formed in the second substrate, for addressing one of the plurality of R row addressing electrodes, and selectively connected to the plurality of N data electrodes, An integrated circuit for receiving signals provided by capacitive plates in the array; And
g) at least S input terminals coupled between the integrated circuit and the pixel array for receiving the first set of S row addressing signals, each connected to one of the plurality of R row addressing electrodes And a demultiplexer for selecting one of the plurality of R addressing electrodes based on the S row addressing signals received thereby,
Fingerprint sensor. 9. The method of claim 8,
Wherein the first substrate and the cover layer are integrally formed,
Fingerprint sensor. 9. The method of claim 8,
The first substrate is relatively flexible,
Fingerprint sensor. 9. The method of claim 8,
Wherein the switching devices included in the pixel array are thin film transistors (TFT)
Fingerprint sensor. 9. The method of claim 8,
Wherein the demultiplexer is formed by a plurality of switching devices,
Fingerprint sensor. 13. The method of claim 12,
Wherein the plurality of switching devices forming the demultiplexer are thin film transistors formed on the first substrate,
Fingerprint sensor. 9. The method of claim 8,
a) the integrated circuit generates a set of M column select signals for addressing one of the plurality of N data electrodes,
b) the fingerprint sensor further comprises a multiplexer coupled between the integrated circuit and the pixel array, the multiplexer comprising a first set of N input terminals, each of the N input terminals of the first set Receiving signals stored in capacitive plates in the pixel array coupled to one of the plurality of N data electrodes, wherein the multiplexer receives the M column select signals, thereby receiving the M column select signals And a second set of M input terminals receiving from the integrated circuit selecting one of the N data electrodes based on the second set of M input terminals.
Fingerprint sensor. 15. The method of claim 14,
Wherein the multiplexer further comprises an output terminal coupled to the integrated circuit for providing a selected data signal to the integrated circuit,
Fingerprint sensor. 15. The method of claim 14,
Wherein the multiplexer is formed by a plurality of switching devices,
Fingerprint sensor. 17. The method of claim 16,
Wherein the plurality of switching devices forming the multiplexer are thin film transistors formed on the first substrate,
Fingerprint sensor. 9. The method of claim 8,
Further comprising: at least one transmitter electrode supported by the first substrate and transmitting a signal of a predetermined frequency and amplitude proximate the pixel array, wherein the transmitted signal passes through the cover layer, Moving into the end,
Fingerprint sensor. 19. The method of claim 18,
Wherein the at least one transmitter electrode forms a ring surrounding the pixel array,
Fingerprint sensor. As a fingerprint sensor,
a) a first substrate on which a plurality of pixels are formed, the pixels arranged in a pixel array of R rows and N columns, each pixel comprising a switching device and a capacitive plate;
b) a plurality of R row addressing electrodes, each row addressing electrode being coupled to switching devices of pixels in a corresponding row of the pixel array to selectively enable switching devices in the corresponding pixel row;
c) a plurality of N data electrodes, each data electrode comprising a plurality of N data electrodes, each of said data electrodes comprising a plurality of N data electrodes, Connected to the switching devices of the pixels in the corresponding column;
d) a common electrode extending over the first substrate at least partially through the pixel array;
e) a cover layer overlying the first substrate to receive a user's fingertip; And
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 providing an output signal Wherein the output signal represents a difference between a signal provided by the data electrode and a signal provided by the common electrode,
Fingerprint sensor. As a fingerprint sensor,
a) a first substrate on which a plurality of pixels are formed, the pixels arranged in a pixel array of R rows and N columns, each pixel comprising a switching device and a capacitive plate;
b) a plurality of R row addressing electrodes, each row addressing electrode being coupled to switching devices of pixels in a corresponding row of the pixel array to selectively enable switching devices in the corresponding pixel row;
c) a plurality of N data electrodes, each data electrode comprising a plurality of N data electrodes, each of said data electrodes comprising a plurality of N data electrodes, Connected to the switching devices of the pixels in the corresponding column;
d) a cover layer overlying the first substrate to receive a user's fingertip; And
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 a second input coupled to a selected one of the plurality of data electrodes, Each differential amplifier having an output terminal providing an output signal, the output signal representing a difference between a data signal provided by a corresponding data electrode and a signal provided by the reference electrode; Included in combination,
Fingerprint sensor. 22. The method of claim 21,
a) a second substrate different from the first substrate and comprising a semiconductor material;
b) an integrated circuit formed in the second substrate; And
c) a plurality of differential amplifiers formed in the integrated circuit,
Fingerprint sensor. As a fingerprint sensor,
a) a first substrate on which a plurality of pixels are formed, the first substrate comprising an upper surface, the pixels being arranged in a pixel array of R rows and N columns, each pixel comprising a switching device And a capacitive plate proximate to the upper surface of the first substrate;
b) a plurality of R row addressing electrodes, each row addressing electrode being coupled to switching devices of pixels in a corresponding row of the pixel array to selectively enable switching devices in the corresponding pixel row;
c) a plurality of N data electrodes, each data electrode comprising a selected pixel row of the pixel array and a corresponding counter of the pixel array sensing a signal provided by the capacitive plate of the pixel located at the intersection of the corresponding column To the switching devices of the pixels in the column;
d) a cover layer overlying the upper surface of the first substrate to receive a user's fingertip;
e) a plurality of transmitter electrodes formed proximate to the upper surface of the first substrate, each of the plurality of transmitter electrodes being substantially parallel and extending very close to a corresponding one of the plurality of row addressing electrodes Each of the plurality of transmitter electrodes selectively transmitting a variable amplitude electrical signal; And
f) a plurality of transmitter electrodes comprising a first set of transmitter electrodes located generally proximate to selected row addressing electrodes and a second set of transmitter electrodes located further away from the selected row addressing electrode, The first set of transmitter electrodes being disabled while the selected row addressing electrode is selectively enabling switching devices in the corresponding pixel row and the second set of transmitter electrodes being disabled when the selected row addressing electrode And to transmit the variable amplitude electrical signal while selectively enabling switching devices in a pixel row;
g) whereby the variable amplitude electrical signal transmitted by the second set of transmitter electrodes is coupled into the finger of a user putting his or her finger tip over the cover layer, and the electrical signal coupled into the user ' Further comprising a plurality of capacitive plates coupled to the capacitive plates in the pixel array to a greater or lesser extent depending on whether a ridge of the user's fingertip is laid over a particular pixel in the pixel array,
Fingerprint sensor. A method of operating a touch pad to generate a fingerprint sensor that senses a fingerprint of a user at substantially all locations of the touchpad,
a) providing a substrate having an upper surface;
b) providing a plurality of fine pitch pixels arranged along intersecting rows and columns to form an array of fine pitch pixels, each fine pitch pixel comprising a switching device and further comprising a capacitive plate, Wherein the fine pitch pixels of the fine pitch pixels are spaced from the adjacent fine pitch pixels by a first predetermined distance;
c) providing a plurality of fine pitch row address lines, each fine pitch row address line being associated with a row of fine pitch pixels in the array, each fine pitch row address line being associated with a respective fine pitch row address line Selectively address fine pitch pixels associated with the pixel;
d) providing a plurality of fine pitch column sensing lines, each fine pitch column sensing line being provided by a capacitive plate of fine pitch pixels in a row of fine pitch pixels selected by an enabled fine pitch row address line Associated with a column of fine pitch pixels for sensing a signal to be detected;
e) subdividing the plurality of fine pitch pixels into smaller array of touchpad pixels, wherein the smaller array of touchpad pixels is arranged in rows and columns, each corresponding touchpad pixel is a fine pitch pixel Wherein each of the touchpad pixels comprises fine pitch pixels located in at least two different columns of fine pitch pixels, each of the touchpad pixels being located in at least two different rows of fine pitch pixels, Spaced from a neighboring touchpad pixel by a second predetermined distance that is at least twice as large as the first predetermined distance;
f) in a first mode of operation, simultaneously enabling fine pitch pixels subdivided by the same touchpad pixel for collective operation and collectively sensing signals provided by said fine pitch pixels subdivided by said same touchpad pixel Causing each respective touchpad pixel to function as a conventional sensor pixel of a conventional touchpad;
g) detecting using the sensed signals provided by the touchpad pixels to detect whether a pointer is being applied close to the upper surface of the substrate, and detecting the position of the pointer on the substrate to which the pointer is applied step; And
h) in a second mode of operation, determining a touchpad pixel positioned proximate to the pointer position, and selecting fine pitch pixels within each of the touchpad pixels positioned proximate to the pointer position from a general mode of operation to a separate mode of operation , ≪ / RTI >
i) Fine pitch pixels in each fine pitch row are individually enabled,
ii) determining and switching the signals provided by the capacitive plate of fine pitch pixels are sensed individually as each fine pitch row is enabled by a corresponding fine pitch row address line,
Wherein the fine pitch pixels in the touchpad pixels positioned proximate to the pointer position form a fingerprint sensor area that senses a fingerprint image of the user's fingertip,
Way.

Images