GB2612819A

GB2612819A - Apparatus

Info

Publication number: GB2612819A
Application number: GB2116352.2A
Authority: GB
Inventors: Derckx Henricus; Cowin Michael; Van Lier Wilhelmus; Sakai Toru
Original assignee: Touch Biometrix Ltd
Current assignee: Touch Biometrix Ltd
Priority date: 2021-11-12
Filing date: 2021-11-12
Publication date: 2023-05-17
Also published as: GB202116352D0

Abstract

A cover glass comprising: an optically transparent substrate 202; a capacitive biometric fingerprint (skin) sensor 203, 204 array whose pixels (120, Fig.1) comprise capacitive electrodes (124, Fig.1) and thin film transistor (TFT) elements (130, 140, 150, 160, Fig.1); and an optically transparent protective cover layer 205 attached to the capacitive sensor via an optically transparent adhesive. The substrate and cover layer may be made of a glass or polyimide material. The cover layer 205 may be tempered glass and have: a thickness of less than 50 microns; a dielectric constant of at least 5; and a hardness of at least 6H. The capacitive sensing electrode may be made of an optically transparent material (e.g. indium tin oxide). The cover glass may be attached (laminated or adhered) to a surface of a mobile phone display 201. Alignment marks (indicia) may facilitate correct alignment of the cover glass onto the display. The optically transparent substrate 202 may be omitted and the sensor 203, 204 be applied directly to a display surface 201 (Fig. 2C)

Description

Apparatus

Technical Field

The present disclosure relates to cover glasses and devices. In particular, the present disclosure relates to biometric skin contact sensors installed on cover glasses or devices.

Background

Secure, verifiable authentication, of user identity is an increasingly important part of all technology. To give just a few examples, it plays a part in: * user equipment (UE) used for communication and consumer access to media content, * computer devices and systems which store and provide access to sensitive data, * devices and systems used for financial transactions, access control for buildings, and * access control for vehicles.

Biometric measurement of the user is now prevalent in all of these contexts and others. Biometric measures such as iris scanning, and facial recognition are dependent on lighting and field of view of a camera. It may also be possible to circumvent such security measures by presenting a video or photo of the user to the camera. Fingerprint sensors have been thought of as being more secure, but it is possible also to overcome the security they provide, and the manufacturing requirements of such sensors makes it difficult to integrate them into other electronic devices such as mobile telephones and other UEs. In particular, fingerprint sensing demands very high resolution -at least hundreds of pixels per inch.

One example of such a sensor is Apple Inc's Touch ID (RTM). This sensor is based on a laser-cut sapphire crystal. It uses a detection ring around the sensor to detect the presence of the user's finger. The Touch ID (RTM) sensor uses capacitive touch sensing to detect the fingerprint, and has a 500 pixel per inch (PPI) resolution.

Capacitance sensors such as these use capacitive effects associated with the surface contours of the fingerprint. The sensor array pixels each include an electrode which acts as one plate of a capacitor, the dermal layer (which is electrically conductive) acts as the other plate, and the nonconductive epidermal layer acts as a dielectric. The capacitance is greater where the dermis is closer to the pixel electrode, and so the surface contours of the skin can be sensed by measuring the capacitance of each pixel (e.g. based on the charge accumulated on the pixel electrode) and assembling an image from those pixels.

Both passive matrix and active-matrix capacitive touch sensors have been proposed. Most so-called passive capacitive touch sensing systems use an external driving circuit (such as an integrated circuit, IC) to drive a matrix of passive electrodes, and a separate readout circuit (e.g. an IC) to readout charge stored on these electrodes during the drive cycle. The stored charge varies dependent on the tiny capacitance changes due to touch events. Passive electrode systems are sensitive to environmental noise and interference.

Active-matrix capacitive touch sensors include a switching element in each pixel. The switching element may control a conduction path between the capacitive sensing electrode in the pixel, and an input channel to an analogue to digital converter (ADC) in a read-out circuit. Typically, each column of pixels in an active array is connected to one such input channel. The charge stored in the array can thus be read from the active matrix by controlling the switching elements to connect each row of pixels, one-by-one, to the ADC.

Each pixel needs to be connected to the read-out circuit, and all of the pixels of each column are effectively connected in parallel. The parasitic capacitance associated with each pixel therefore combines additively. This places an inherent limit on the number of pixels that can be combined together in any one column. This in turn limits the size and/or resolution of a capacitive touch sensor. There thus remains a significant unmet commercial need for large area high resolution touch sensors.

Summary

Aspects of the disclosure are set out in the independent claims and optional features are set out in the dependent claims. Aspects of the disclosure may be provided in conjunction with each other, and features of one aspect may be applied to other aspects.

In an aspect, there is provided a cover glass comprising: an optically transparent substrate; a capacitive biometric skin contact sensor provided on the optically transparent substrate; an optically transparent cover layer provided on the capacitive biometric skin contact sensor on the opposite side to the optically transparent substrate; wherein the capacitive biometric skin contact sensor comprises a sensor array of sensor pixels, wherein each sensor pixel comprises capacitive sensing electrode and at least one thin film transistor, TFT; and wherein the optically transparent cover layer is attached to the capacitive biometric skin contact sensor via an optically coupled adhesive layer.

At least one of the substrate and the cover layer may be made of glass. The adhesive may have a thickness of 5 microns or less. The cover layer may have a thickness of 50 microns or less. The cover layer may have a thickness of 35 microns or less. The cover layer may have a hardness of 6H or more, e.g. 9H or more. The cover layer may be made of tempered glass. At least a portion of the sensor may be provided by an at least partially optically transparent electrical conductor. The capacitive sensing electrode of each sensor pixel may be made of an optically transparent material. The cover layer may have a minimum bend radius of under 2 mm. The substrate and/or the cover layer may be made of a polyimide material. The cover glass may be configured for installation on a display of a device. The optically coupled adhesive layer may be optically tuned to the display of the device and/or optical properties of the cover glass.

The cover glass may have one or more reference features thereon arranged to facilitate correct alignment of the cover glass onto the display. The reference features of the cover glass may be configured to be aligned with corresponding reference features of the display screen such that the cover glass will be arranged on the display in the correct alignment if the reference features of the cover glass are correctly aligned with the reference features of the display. The reference features on the cover glass may comprise indicia. The cover glass may comprise at least one reference feature, and wherein the sensor array of sensor pixels of the biometric skin contact sensor may be arranged at a selected offset from said at least one reference feature. The tolerance for the selected offset of the sensor array from the at least one reference feature may be less than a pixel pitch for the sensor pixels of the sensor array. The tolerance for the selected offset of the sensor array from the at least one reference feature may be less than a pixel pitch for the pixels and/or sub-pixels of the display screen. The tolerance may be less, e.g. under 10 microns, such as under 5 microns, e.g. under 4 microns, e.g. under 3 microns, e.g. under 2 microns, e.g. between 1 to 3 microns. The cover layer may have a dielectric constant of 5 or more. The cover glass may be configured to be attached, optionally laminated, onto the display. The sensor may be laminated onto the substrate.

The cover glass may be a user equipment ('UE') cover glass arranged for use with a selected type of UE. A UE may comprise any digital device having a display. For example, the UE may comprise a mobile telecommunications device, such as a mobile phone (cellular phone), a tablet, a laptop, a desktop computer, a smart watch, a display screen (e.g. a TV) or any other digital technology with a display screen and a processor. For example, aspects of the present disclosure may provide a mobile phone cover glass (e.g. cover glasses disclosed herein may be mobile phone cover glasses). For example, aspects may provide a mobile phone cover glass configured to overlie a display screen of a mobile phone.

The capacitive sensing electrode may be provided in a user-facing layer of the sensor pixel. The capacitive sensing electrode of each sensing pixel may cover the majority of the area of the sensor pixel. Each capacitive sensing electrode may have an area selected based on a capacitance associated with that electrode. For example, the area of the electrode may have an increased area when the layer separating the electrode from the user is thicker, and vice-versa. In other words, the capacitive sensing electrode may have an area selected to provide a desired capacitive response from user interaction with the device. Where the layer separating the capacitive sensing electrode from the user is thinner, the electrode may take up less of the cross-sectional area of each sensor pixel. The capacitive sensing electrode may have an area which is as large as it can be for each sensor pixel (e.g. to maximise measurement sensitivity).

Each sensor pixel may comprise a reference capacitor, and wherein for each sensor pixel, the reference capacitor and the capacitive sensing electrode may be connected to a gate region of the thin film transistor. For each sensor pixel: the reference capacitor may be connected in series with the capacitive sensing electrode so that, in response to a control voltage, an indicator voltage is provided at the connection between the reference capacitor and the capacitive sensing electrode to indicate a proximity to the capacitive sensing electrode of a conductive object to be sensed; and the thin film transistor may comprise a sense voltage-controlled impedance having a control terminal connected so that the impedance of the sense voltage-controlled impedance is controlled by the indicator voltage. Each sensor pixel may comprise a reset circuit for setting the control terminal of the sense voltage controlled impedance to a reset voltage selected to tune the sensitivity of the pixels.

In an aspect, there is provided a device comprising: a display; a capacitive biometric skin contact sensor arranged on a user-facing side of the display, the capacitive biometric skin contact sensor comprising a sensor array of sensor pixels, wherein each sensor pixel comprises a capacitive sensing electrode and at least one thin film transistor, TFT; and an optically transparent cover layer arranged on a user-facing side of the sensor; wherein the cover layer is attached to the capacitive biometric skin contact sensor via an optically coupled adhesive layer. The device may further comprise a first protective layer arranged on a user-facing surface of the display. The sensor may be arranged on a user-facing surface of the first protective layer, e.g. so that the first protective layer separates the sensor from the display (and e.g. the optically transparent cover layer separates the sensor from the user interacting with the sensor).

Aspects of the present disclosure may comprise one or more computer program products comprising computer program instructions configured to program a computer to perform any of the methods disclosed herein.

Figures Some examples of the present disclosure will now be described, by way of example only, with reference to the figures, in which: Figs. la to 1c each show a schematic diagram of an exemplary sensor pixel for a capacitive biometric skin contact sensor.

Fig. 2a is a schematic diagram illustrating a cross-sectional view of an exemplary approach for providing a capacitive biometric skin contact sensor on a display screen.

Figs 2b and 2c are schematic diagrams illustrating a cross-sectional view of two examples of a capacitive biometric skin contact sensor arranged on a display screen.

In the drawings like reference numerals are used to indicate like elements.

Specific Description

Embodiments of the present disclosure relate to a cover glass having a capacitive biometric skin contact sensor provided on an optically transparent substrate, with an optically transparent cover layer on the sensor (on the opposite side to the substrate). The cover layer is attached to the sensor via an optically coupled adhesive layer.

Firstly, three different sensor pixel designs for such a capacitive biometric skin contact sensor will now be described with reference to Figs. la to lc.

Fig. la shows a sensor pixel 120 for a capacitive biometric skin contact sensor. The sensor pixel 120 includes a capacitive sensing electrode 124 and a voltage-controlled impedance shown as a thin film transistor (TFT') and referred to hereon in as 'sense TFT 130'. The capacitive sensing electrode 124 is shown with a variable capacitor symbol. It will be appreciated that the capacitive sensing electrode 124 is formed of one electrode (e.g. a plate), and the variable capacitance for this will effectively be provided by a user interacting with that one electrode (e.g. due to the proximity of a portion of the user's skin proximal to the electrode). As will be appreciated, the capacitance associated with this capacitive sensing electrode 124 will vary in dependence on the proximity of the user's skin to the capacitive sensing electrode 124. The sensor pixel 120 also includes a reference capacitor 122. Also shown is a first gate drive channel 101 and a first readout channel 111.

In the pixel 120 of Fig. la, a first region of the sense TFT 130 is coupled to the first gate drive channel 101. A second region (e.g. a control terminal) of the sense TFT 130 is coupled to the capacitive sensing electrode 124. A third region of the sense TFT 130 is coupled to the first readout channel 111. The second region of the sense TFT 130 may be a gate region. The first region of the sense TFT 130 may be a drain region and the third region of the TFT 130 may be a source region. A first electrode of the reference capacitor 122 is coupled to the first gate drive channel 101. A second electrode of the reference capacitor 122 is coupled to the capacitive sensing electrode 124 and the second region of the sense TFT 130. As such, a connection between the second region of the sense TFT 130 and the capacitive sensing electrode 124 is also connected to the second electrode of the reference capacitor 122. Likewise, a connection between the first gate drive channel 101 and the first electrode of the reference capacitor 122 is also connected to the first region of the sense TEl 130.

To operate the sensor pixel 120 shown in Fig. la, a scanning signal is applied to the sensor pixel 120 through the first gate drive channel 101. As such, current may flow to the first electrode of the reference capacitor 122 and also to the drain region of the sense TFT 130. As a result, some of the current may flow through the sense TFT 130 from drain to source, wherein the amount of current flowing through will depend on the voltage division to the gate region of the sense TFT 130. This gate voltage will vary depending on the capacitive potential division between the reference capacitor 122 and the capacitive sensing electrode 124, which in turn will be representative of the capacitance of the capacitive sensing electrode 124 due to proximity of a conducting body (e.g. a portion of the user's body in proximity to that capacitive sensing electrode 124). As such, a magnitude of the current output from the sensor pixel 120 to the first read-out channel 111 will vary in dependence on the proximity to the capacitive sensing electrode 124 of the conducting body.

Fig. lb shows a sensor pixel 120 for a capacitive biometric skin contact sensor. As with the sensor pixel 120 of Fig. la, the sensor pixel 120 of Fig. lb includes a reference capacitor 122, a capacitive sensing electrode 124, and a sense TFT 130. A first gate drive channel 101 is shown in Fig. lb, as is a first read-out channel 111. The sensor pixel 120 of Fig. lb also includes a select TFT 140, a select reference connection 142, a reset TFT 150, a first reset reference connection 152, and a second reset reference connection 154.

The select TFT 140 is coupled to the sense TFT 130 to selectively inhibit the sense TFT 130 from outputting a read-out signal to the first read-out channel 111. The select TFT 140 has a conductive channel connected in series between a reference signal supply and the sense TFT 130. A first region of the select TFT 140 is arranged to receive the reference signal supply (via the select reference connection 142). The second region of the select TFT 140 is coupled to the first gate drive channel 101, and a third region of the select TFT 140 is coupled to the first region of the sense TFT 130. As with Fig. la, the third region of the sense TFT 130 is coupled to the first read-out channel 111. Likewise, a first electrode of the reference capacitor 122 is coupled to the first gate drive channel 101, and a second electrode of the reference capacitor 122 is coupled to both the capacitive sensing electrode 124 and the second region of the sense TFT 130.

Additionally, reset circuitry is also coupled to the second electrode of the reference capacitor 122 (and thus also the second region of the sense TFT 130 and the capacitive sensing electrode 124). The reset circuitry is configured to selectively tune the second region of the sense TFT 130 to a reference voltage (e.g. to provide a selected sensitivity for the pixel 20). A first region of the reset TFT 150 is coupled to the second electrode of the reference capacitor 122, the capacitive sensing electrode 124, and the second region of the sense TFT 130. A second region of the reset TFT 150 is arranged to receive a reset voltage (e.g. via the first reset reference connection 152). The first reset reference connection 152 may be connected to a preceding gate drive channel of the sensor. The reset circuitry is arranged so that, in response to the second region of the reset TFT receiving the reset voltage, a conductive channel is opened between the first and third regions of the reset TFT 150. Current may flow either way through this channel (e.g. it could be arranged to permit current flow in either direction). For example, current may flow into the pixel 120 to charge the second region of the sense TFT 130 to a selected voltage (e.g. to tune its sensitivity).

Alternatively, current may flow away from the pixel to discharge the second region of the sense TFT 130. The second reset reference connection 154 thus connects the reset TFT 150 to provide relevant current flow (e.g. it is either connected to a reset reference voltage, or to distribute current elsewhere away from the pixel 120).

To operate the sensor pixel 120 shown in Fig. 1 b, a preceding scanning signal is applied to the sensor. That is, a scanning signal is applied to a preceding row of gate-drive channels (hereinafter referred to as N-1). The N-1 scanning signal is applied to the second region of the reset TFT 150, which opens up the conductive channel therethrough and thus sets the second region of the sense TFT 130 to the reference voltage. The N-1 scanning signal is then stopped, and thus the conductive channel of the reset TFT 150 is closed. A subsequent scanning signal ('N scanning signal') is then applied to the first gate drive channel 101. As with Fig. 1a, this causes a capacitive potential division between the reference capacitor 122, the capacitive sensing electrode 124, and the sense TFT 130, which can be used to determine the proximity to the capacitive sensing electrode of a conductive body to be sensed. Additionally, however, in Fig. 1 b, the N scanning signal is also applied to the second region of the select TFT 140, which acts to connect the first region of the sense TFT 130 to the reference signal supply, so that the sense TFT 130 may output a current through its third region to the first read-out channel 111 (as described above). Thus, once the N scanning signal is stopped, the sense TFT 130 may no longer output a current to the first read-out channel 111 (as the conductive channel of the select TFT 150 will be closed).

Fig. 1c shows a sensor pixel 120 for a capacitive biometric skin contact sensor. As with Fig. 1b, the sensor pixel 120 includes a reference capacitor 122, a capacitive sensing electrode 124, a sense TFT 130, a select TFT 140, a select reference connection 142, a reset TFT 150, and a first reset reference connection 152. As shown, the pixel 120 is connected to a first gate drive channel 101 and a first read-out channel 111. Also, the pixel 120 of Fig. lc includes biasing circuitry comprising a bias TFT 160, and a bias reference connection 162.

The sensor pixel 120 shown in Fig. lc is described in more detail in the Applicant's pending application GB 2013864.0. The structural arrangement of this sensor, the function of the sensor and the individual components of the sensor, and the method of operation as described in GB2013864.0 is incorporated herein by reference for all purposes.

The sensor pixel 120 of Fig. lc is similar to that of Fig. lb in that it receives a scanning signal from a gate drive channel which in turn gives rise to a capacitive potential divider arrangement involving the capacitive sensing electrode 124 and the reference capacitor 122. Likewise, this capacitive potential division controls operation of a TFT (sense TFT 130) to regulate the current output from the pixel in dependence on the proximity to the capacitive sensing electrode 124 of a conductive body to be sensed.

The sensor pixel 120 of Fig. lc includes biasing circuitry comprising a one-way conduction path from a bias voltage connection to a control terminal of the sense TFT 130 so that current flows from the bias voltage towards the control terminal of the sense TFT 130 in response to the control terminal voltage of the sense TFT 130 dropping below a floor value. In other words, the biasing circuitry of the sensor pixel 120 is arranged to ensure that prior to making a measurement, the voltage at the control terminal (e.g. gate region) of the sense TFT 160 is at a selected value (e.g. a predefined voltage). The bias voltage may be varied to provide a selected voltage at the gate region of the sense TFT 130 (e.g. to provide a selected level of sensitivity for the sensor, or a define operation point for starting operation of the pixel). As shown in Fig. lc, the biasing circuitry comprises a connection to the bias voltage (via bias reference connection 162) and the bias TFT 160. The bias TFT 160 is connected in diode configuration to provide the one-way conduction path. The drain of the bias TFT 160 is coupled to each of the second electrode of the reference capacitor 122, the capacitive sensing electrode 124 and the gate region of the sense TFT 130.

As with Fig. lb, the sensor pixel 120 of Fig. lc includes reset circuitry selectively operable to provide a reference voltage on the reference capacitor 122. The reset circuity includes the reset TFT 150. The reset TFT 150 is selectively operable to provide a conductive path between the two electrodes of the reference capacitor 122 (e.g. to short the capacitor to zero voltage). A gate region of the reset TFT 150 is coupled to receive a reset voltage in order to open the conductive channel through the reset TFT 150 and short the reference capacitor 122. The gate region of the reset TFT 150 is arranged to receive a reference voltage to selectively open a conductive path through the reset TFT 150. The first reset reference connection 152 couples the second region of the reset TFT 150 to receive this reference voltage. As shown, this may comprise connecting the second region of the reset TFT 150 to a preceding gate drive channel in the sensor array (e.g. an N-1 gate drive channel). A first region of the reset TFT 150 is coupled to the first electrode of the reference capacitor 122 and the third region of the reset TFT 150 is coupled to the second electrode of the reference capacitor. Thus, a voltage for the reference capacitor 122 will be reset to zero in response to application of an N-1 scanning signal to the relevant preceding gate drive channel.

As with Fig. lb, the sensor pixel 120 of Fig. lc may include select circuitry to selectively couple the sense TFT 130 to the supply voltage. The select circuitry includes the select TFT 140, which is arranged to function in a similar manner to the select TFT 140 of Fig. lb. To operate the sensor pixel 120 of Fig. lc to obtain a measurement, a reset signal is first applied to the reset circuitry. This may comprise a signal from a preceding gate drive channel (e.g. an N- 1 scanning signal) being applied to the gate region of the reset TFT 150. In turn, this will cause the reference capacitor 122 to be shorted, and its voltage returned to zero. Then, the biasing circuitry will operate to charge the control terminal of the sense TFT 130 to its floor value. This may comprise the bias voltage being applied to the (diode-connected) bias TFT 160 so that current flows through the bias TFT 160 and charges the gate region of the sense TFT 130 being charged to a selected voltage (the floor value). After the sense TFT 130 has been charged to the floor value, a scanning signal is then applied to the sensor pixel 120 (e.g. an N scanning signal). The scanning signal may act to charge up the first electrode of the reference capacitor 122 and also to apply a voltage to the gate region of the select TFT 140. Current may then flow from the supply voltage through the select TFT 140 and to the sense TFT 130 for obtaining a read-out current therefrom (as described above with reference to Fig. lb).

The biometric skin contact sensor may be formed of an array of sensor pixels (e.g. of any of the types disclosed herein). The sensor pixels of the sensor are arranged in a grid-like array. The sensor pixels are arranged in a regular repeating pattern. In other words, the sensor pixels may form a series of adjacent rectangles (e.g. squares). The sensor pixels are arranged in a series of rows and columns. Each sensor pixel 120 in a row is aligned with the other sensor pixels in that row. Each sensor pixel 120 in a column is aligned with the other sensor pixels in that column. The sensor array may be designed to span across some, or all, of the display screen (e.g. it may cover a majority of the screen and/or may be located over a region of the screen with which a user will predominantly interact). Each sensor pixel 120 is arranged closely enough to its neighbouring sensor pixel 120 to enable the sensor pixels to resolve the difference between ridges and valleys in a user's skin. The sensor spans a surface area large enough to enable sufficient biometric data to be obtained for a user interacting with the display.

The sensor may include a plurality of gate drive channels, and a plurality of read-out channels. Each gate drive channel may be coupled to a plurality of sensor pixels (e.g. to each sensor pixel in a row). Each read-out channel may be coupled to a plurality of sensor pixels (e.g. to each sensor pixel in a column). Each sensor pixel 120 has an associated gate drive channel and read-out channel. The read-out channels run perpendicular to the gate drive channels. The read-out channels and gate drive channels are arranged in an active-matrix pattern (e.g. which forms a criss-cross pattern across the sensor).

The sensor comprises gate drive circuitry and read-out conversion circuitry. The gate drive circuitry is arranged to selectively apply scanning signals to the gate drive channels, e.g. as described above for activating sensor pixels. The conversion circuitry is arranged to receive readout signals from the read-out channels and to process the read-out signals to obtain biometric skin contact data therefrom. For example, the conversion circuitry is configured to receive a read-out current from a read-out channel, and to determine therefrom an indication of proximity. For example, this may comprise analogue to digital conversion, such as by using an integrator to integrate the received current. By sensing from a number of different sensor pixels, data may be obtained for a sufficiently large enough region to provide biometric identification (e.g. to identify biometric markers, such as ridges and valleys, on a subject's skin in contact with the sensor). The sensor may also include one or more reference voltage providers, such as for use with the sensor pixels of Figs. lb and 1c. For example, to provide a reference voltage to the select TFT 140 and/or bias TFT 160.

Each sensor pixel 120 may be defined by the region circumscribed by two adjacent gate drive channels and two adjacent read-out channels. At least one of the two adjacent gate drive channels is configured to supply a scanning signal to the sensor pixel 120. At least one of the two adjacent read-out channels is configured to transmit a read-out signal from the sensor pixel 120 to conversion circuitry of the sensor. Additionally, each sensor pixel 120 may be coupled to one or more other gate drive channel (e.g. for receiving a N-1 scanning signal therefrom).

The area of each capacitive sensing electrode 124 may be selected based on a desired capacitive response for that electrode 124. For example, where the area of the electrode 124 may be selected based on the thickness of any cover layer separating that electrode 124 from a user interacting with the electrode. The thicker the cover layer, the larger the area of the electrode 124 (e.g. so that the resulting capacitance may exceed a selected threshold in response to proximity to the electrode 124 of the user's skin, such as when a user is touching the cover layer above the electrode 124).

Such sensors described above may therefore obtain biometric skin contact data.

Each of the sensor pixels 120 may be provided by a layered stack of components. The capacitive sensing electrode 124 may be provided on a higher layer than the TFTs, reference capacitor 122 or conductors. That way, the capacitive sensing electrode 124 may be closer to the skin of the user touching the display (and there will be fewer components/layers separating the electrode 124 from the skin). The remaining components of the sensor pixel 120 may be provided on lower layers. For example, the capacitive sensing electrode 124 may be provided on a top metallisation layer of the sensor. For this, the sensor pixel 120 may also include a capacitive sensing electrode connector 126, which may be in the form of a conductive via. The connector 126 may be arranged to electrically connect the capacitive sensing electrode 124 to other components of the sensor pixel 120.

Beneath the top metallisation layer, there may be two or more other layers (e.g. other metallisation layers). The remaining sensor components may span across these layers. For example, the reference capacitor 122 may have one electrode (e.g. plate) on each layer. Likewise, each TFT may span across two layers, such as with its second (gate) region on one layer, and its first and third (drain and source) layers on another layer. For example, the second plate of the reference capacitor 122 and the second region of the sense TFT 130 may be provided on a second layer of the sensor pixel 120. The first plate of the reference capacitor 122 and the first and third regions of the sense TFT 130 may be provided on a first layer of the sensor pixel 120. The select TFT 140 may be distributed across layers in the same way as the sense TFT 150.

Such exemplary sensor pixels may be used in a sensor array of a capacitive biometric skin contact sensor, and such sensors may be used to provide a cover glass. Fig. 2a shows method steps for preparing a cover glass, and installing that cover glass on a display screen of a user equipment device. A display 201 is shown as the bottommost layer. Other components are then installed on top of the display 201. A cover layer 205 is provided to protect the components underneath it (e.g. sensor/display 201).

It is to be appreciated that a capacitive biometric skin contact sensor of the present disclosure may be provided over multiple layers. For example, a gate region of a TFT of the sensor may be provided in a different layer to source and drain regions of that TFT. The capacitive sensing electrode may be provided on a separate (e.g. upper) layer. To illustrate there being different layers, in Figs. 2a to 2c, the sensor is shown over two layers: a display facing layer 203 and a user facing layer 204 (although it will be appreciated that this is just to illustrate the principle, and that further layers may be provided). The display facing layer 203 may comprise parts of the one or more TFTs and/or one or more electrodes of a reference capacitor. The user facing layer 204 may comprise the capacitive sensing electrode. A protective cover layer 205 is provided on the user facing side of the user facing layer 204 of the sensor (e.g. on top of the sensor so that the protective cover layer 205 will be between the sensor and the user).

In Fig. 2a, a cover glass is provided for installation. The cover glass is arranged to provide a means for installing the sensor onto the display screen. The cover glass may also provide structural integrity and/or protection to the sensor, and it may also provide protection to the display screen. The cover glass may be arranged so that, once installed on the display 201, the cover glass can protect the display 201 and the sensor installed on the display 201 (e.g. from damage due to impact with the user-facing side of the assembled device).

The cover glass includes a substrate (first protective layer 202), a capacitive biometric skin contact sensor (of the type described above -sensor 203 and 204), and a cover layer (second protective layer 205). To provide the cover glass, the sensor may be built onto the first protective layer 202. The sensor will be arranged on a user-facing side of the substrate (first protective layer 202) when installed on the display. An additional protective layer (second protective layer 205) is then provided on the user-facing side of the sensor. For example, the cover glass may be arranged to enable one or more substrates to overlie the display screen for protecting the display screen and/or to overlie the sensor for protecting the sensor. Building the sensor may comprise depositing a plurality of conductive layers to build up the sensor pixels.

The cover glass of Fig. 2a thus includes a sensor sandwiched between two protective layers. The display-facing layer 203 of the sensor is adjacent to the first protective layer 202 (the user-facing side of the first protective layer 202), and the user-facing layer 204 of the sensor will be closer to the user. The second protective layer 205 is provided to protect the sensor. The first protective layer 202 may provide protection to the display 201, as well as providing a uniform and consistent surface on which to build the sensor. This cover glass may then be installed on the display screen. Such installation may comprise laminating the cover glass onto the display 201, or affixing in some other means, such as using adhesive etc. (e.g. an optically coupled adhesive).

The cover glass shown in Fig. 2a could be built in several ways. The sensor could be built onto either protective layer. The other protective layer may then be applied to the sensor (e.g. deposited on top of it), or the combined sensor and protective layer may then be coupled to the other protective layer (e.g. laminated on to that other protective layer). Wien coupling different components of the cover glass to each other, an optically coupled adhesive may be used.

For example, the sensor could be built on to the first protective layer 202. This may comprise first building the display-facing layer of the sensor on the using-facing surface of the first protective layer 202. The display-facing layer 203 of the sensor may include a portion of one or more of the TFTs, an electrode of the reference capacitor, and/or some of the conductors of the sensor circuitry. Subsequent sensor layers may then be built on top of the display-facing layer 203. A final user-facing layer 204 may then be built to provide the top of the sensor (e.g. containing the capacitive sensing electrodes). This assembled sensor and first protective layer 202 may then be coupled with the second protective layer 205. For example, the second protective layer 205 may then be attached on top (on the user-facing side) of the sensor -e.g. by laminating the second protective layer 205 onto the sensor. Providing the second protective layer 205 on the user-facing surface 204 of the sensor may be performed before or after the first protective layer 202 and sensor have been installed on the display screen. In other words, the sensor installed on the user-facing surface of the first protective layer 202 may form the cover glass, or the sensor installed on the user-facing surface of the first protective layer 202 with the second protective layer 205 installed thereon may form the cover glass.

To affix the protective layer onto the sensor, an optically coupled adhesive may be used. The adhesive may be coupled to the display 201 such that it is effectively transparent to light output from the display 201. The adhesive applied may have a thickness of less than 10 microns, e.g. less than 5 microns, e.g. less than 4 microns. For example, the adhesive may have a thickness of about 3 microns.

As another example, the sensor could be built on to the display facing surface of the second protective layer 205. This may be performed by providing the sensor in a reverse stack configuration (e.g. by first depositing the capacitive sensing electrodes and then building up the lower components of the sensor in layers above those electrodes). This assembled sensor and second protective layer 205 may then be installed on (e.g. laminated onto) the first protective layer 202 to form the cover glass. Again, an optically coupled adhesive may be used to affix the sensor and second protective layer 205 onto the first protective layer 202.

The most user-facing layer may be arranged to provide a selected amount of optical transmission (e.g. it may be optically transparent). For example, the most user-facing layer may be formed of glass or any other suitable material. The most user-facing layer may be arranged to enable a selected amount of sensitivity to be provided for any capacitance between the capacitive sensing electrodes of the sensor and the conducting body of the user in proximity to the most user-facing layer. For example, the most user-facing layer may have a thickness of less than 100 microns, such as less than 75 microns, such as less than 60 microns, such as less than 50 microns. For example, the most user-facing layer may be provided by glass having a thickness of under 50 microns (e.g. under 40 microns, or under 35 microns, or under 30 microns, or under 25 microns, or under 20 microns). For example, the thickness may be in the range of 10 to 30 microns, such as 10 to 20 microns The cover glass may be configured for installation onto a selected display 201. For example, it may be a cover glass for a mobile phone, and the dimensions of the cover glass may be selected to correspond to those required for covering the display 201 on the relevant phone. The protective layer for the sensor (the most user-facing layer) may be applied onto the sensor as a foil or it may be laminated onto the sensor (e.g. for a glass cover layer). For example, the protective layer may be laminated onto the sensor (on to the user-facing side of the sensor). The protective layer may be laminated on to the sensor to provide a hard coating for the sensor. The protective layer, once applied, may form a thin laminate which protects the sensor. For example, this protective layer may be a thin substrate (e.g. glass under 50 microns in thickness, under 30 microns etc., or it may be applied as a covering foil and/or inorganic coating).

Examples of the present disclosure may provide a multi-layer optically transparent cover glass.

For this, a biometric skin contact sensor is provided on an optically transparent substrate. The sensor may either be built directly onto the optically transparent substrate or the sensor may be built elsewhere and then subsequently installed onto the sensor. An optically coupled adhesive may be used to couple the sensor to the optically transparent cover glass (if adhesive is needed for this). In one example, a layer of optically coupled adhesive may be coupled to the other side of the sensor to the substrate for installation of the sensor and the substrate onto another component (such as another protective substrate or a display). In another example, a second optically transparent substrate may be provided on the other side of the sensor to the first optically transparent substrate. The second optically transparent substrate may be coupled to the sensor using an optically couple adhesive. The multi-layer optically transparent cover glass may comprise the sensor coupled to one or both optically transparent substrates. The resulting cover glass may be coupled to a display using an optically coupled adhesive.

For example, an optically transparent substrate may be provided as a base layer. A biometric skin contact sensor may be provided on a user-facing side of the optically transparent substrate. A layer of optically coupled adhesive is provided on a user-facing side of the sensor. A transparent protective layer is provided on top of the optically coupled adhesive. The resulting stack may provide a multi-layer optically transparent cover glass capable of providing biometric skin contact sensing.

Examples described herein may utilise one or more protective layers. Each protective layer may be provided by a transparent substrate. The transparent substrate may comprise glass. The glass may have a hardness of 6H or more, e.g. 7H or more, e.g. 8H or more, e.g. 9H or more. The glass may be chemically tempered. For example, either or both of the first and second protective layers may be provided by a layer of 9H tempered glass, e.g. at a thickness of under 50 microns, e.g. about 10-35 microns (e.g. at 30 or less microns, e.g. 10-30 microns, e.g. 10-20 microns).

In examples described above, protective layers are provided such as the first and second protective layers. However, it will also be appreciated that such layers may be provided for additional or alternative reasons. For example, the substrate onto which the sensor is provided/built may provide a flat and consistent surface for the sensor. For example, a first or second protective layer, as relevant, and as described herein may be used to provide a suitable surface onto which the sensor is to be provided (rather than being provided to protect the display per se.). For example, the layer may provide a flat substrate with a low surface roughness to facilitate installation of the sensor (e.g. flatter and less rough than a display screen). Protective layers described herein may be configured to provide protection against dust and/or moisture (e.g. as per IP65), to provide hardness for scratch protection (e.g. 6H hardness or more, such as up to 9H hardness), and/or to provide any relevant filters, such as a UV filter.

In the examples described above, the optically transparent substrate may be made of glass. The glass substrate may have a thickness of 300 microns (e.g. where that substrate forms a protective layer for the display screen, such as for first protective layer 202 in Figs. 4a and 4b). As an alternative, a suitable polymer may be used, such as polyimide. A polyimide substrate may have a thickness of 20 microns. The optically coupled adhesive may have a thickness of 3 microns.

The transparent protective layer may be made of glass. For example, the glass protective layer may have a thickness of 30 microns (e.g. between 20 and 50). The glass protective layer may be even thinner, such as under 20 microns. Such a multi-layer optically transparent cover glass may be designed for coupling to a particular device (with a particular display 201). The assembled cover glass may include one or more reference features (e.g. on the optically transparent substrate), which are configured to facilitate correct alignment of the cover glass onto the display screen (by cooperating with corresponding reference features on the display screen).

A cover glass may be designed to protect the entire display onto which it is to be installed. For example, the cover glass may be sized and shaped according to the form factor for the device having the display 201 onto which the cover glass is to be installed. For example, where the device is a mobile phone, the cover glass may be sized based on the mobile phone screen (e.g. so that it covers the entire screen). To aid this process, one or more reference features may be used. Reference features may be used when providing the sensor on the substrate (to provide the cover glass). The substrate may be of a selected size and shape so that it will fit the display screen. The sensor may therefore be provided in a selected arrangement relative to the substrate. Reference features may also be used when providing the cover glass onto the display. Reference features (e.g. alignment markers) may be provided on the substrate against which the sensor may be aligned (e.g. when providing the sensor on the substrate). The sensor itself may comprise one or more corresponding reference features to align with the reference features of the substrate. Additionally, or alternatively, properties of the structural arrangement of the sensor may provide a reference feature (e.g. which may be aligned with a reference feature on the substrate). For example, read-out channels and gate drive channels of the sensor may be arranged in a grid-like structure. This grid-like structure (e.g. edges thereof) may be used when aligning the sensor on the substrate (e.g. the grid-like structure itself may effectively form a reference feature of the sensor which may then be aligned with the substrate to ensure the correct alignment is provided). For example, this may comprise aligning the edge of the grid-like structure with a fixed spatial offset to an edge of the cover glass.

As another example, the reference features may comprise some form of corresponding indicia which are designed to overlap with each other in a known manner when installed correctly. Such indicia may comprise one or more markings on e.g. the substrate, the sensor and/or the display screen, wherein the markings are designed to have a known appearance if overlapped correctly (e.g. in response to correct alignment). Examples of this include a circle arranged to fit with in an annulus, two crosses designed to overlap centrally and/or a cross inside a circle. Another example includes a cross on one component and four rectangles on another component. If overlaid correctly, the four rectangles will align with the cross so that the four rectangles are separated from each other by the cross. Such reference features may be provided to enable the sensor to be installed in a correct arrangement on the substrate (e.g. reference features on at least one of the sensor and substrate). Such reference features may be provided to enable the assembled cover glass (substrate and sensor) to be installed in a correct arrangement on the display 201. For example, the reference features may be provided on the cover glass (as part of the sensor and/or on the substrate) and/or on the display screen onto which the cover glass is to be installed.

Examples of devices with sensors installed thereon will now be described with reference to Figs. 2b and 2c.

Fig. 2b shows an assembled device having a display 201 with a sensor installed thereon. The assembled device includes two protective layers: a first protective layer 202 arranged between the display 201 and the display-facing side 203 of the sensor, and a second protective layer 205 arranged on a user-facing side of the user-facing side 204 of the sensor. Although not shown, the display-facing side 203 of the sensor may be coupled to the first protective layer 202 via an optically coupled adhesive layer, and/or the user-facing side 204 of the sensor may be coupled to the second protective layer 205 via an optically coupled adhesive layer, and/or the first protective layer 202 may be coupled to the display 201 via an optically coupled adhesive layer.

Fig. 2c shows an assembled device having a display 201 with a sensor installed thereon. Unlike with Fig. 2b, the device of Fig. 2c has only one protective layer (shown as "202/205"). The device has a sensor provided on a user-facing surface of the display 201. The display-facing surface 203 of the sensor is adjacent to the display. A protective layer (202/205) is provided on a user-facing surface 204 of the sensor. The user-facing surface 204 of the sensor is adjacent to a display-facing surface of the protective layer 202/205. Although not shown, the display-facing side 203 of the sensor may be coupled to the display 201 via an optically coupled adhesive layer and/or the user-facing side 204 of the sensor may be coupled to the protective layer 202/205 via an optically coupled adhesive layer.

Cover glasses of the present disclosure may be designed to interact with a particular display/device. That is, a cover glass may be arranged for installation on a particular display screen (e.g. that of a selected electronic device). Such a cover glass may be arranged (sized and shaped) so that it may be affixed onto the device to cover the display. It is to be appreciated in the context of the present disclosure that the particular type of device or display need not be considered limiting. Examples of suitable devices may include any device which has a display screen on it, such as a mobile phone, a tablet, a computer/laptop, a TV, a camera etc. Likewise, the particular type of display should not be considered limiting.

The sensor may comprise at least some optically transparent components. For instance, one or more components of the sensor pixel 120 may be at least partially optically transparent. In particular, one or more of the electrically conductive components of the sensor may be provided by an optically transparent electrically conductive material. Optical transparency may comprise enabling the majority of the light incident on the optically transparent material to pass through that material; it may comprise allowing at least 80%, such as at least 90%, such as at least 95%, such as at least 99%, of light to pass through that material.

The optically transparent components may be provided by any suitable transparent conductors. A transparent conductor may comprise any suitable material with simultaneous high electrical DC conductivity and high transmission of light. For instance, indium tin-oxide may be used to provide a transparent electrically conductive material. Other examples include transparent conducting films (e.g. a thin film of optically transparent and electrically conductive material). Examples of such transparent conducting films include transparent conductive oxides (ITCOs'), conductive polymers, metal grids/random metallic networks, carbon nanotubes, graphene, nanowire meshes and/or ultra-thin metal films. As one particular example, an indium tin oxide-based component (e.g. a component made of indium tin oxide) may be used to provide transparent conduction.

As described herein, to provide optical transparency to components of the sensor pixels, an optically transparent electrical conductor may be used, such as indium fin oxide. This may be used to provide any of the relevant electrically conducting components as transparent (e.g. the capacitive sensing electrode, conductors of the sensor, electrodes of the capacitor). Other transparent materials could also be used, such as to use transparent semi-conductor material, e.g. indium gallium zinc oxide ('IGZO), and/or to use transparent insulator layer(s) through use of e.g. inorganic silicon nitride (SiNk), silicon dioxide (SiO2') or organic polymers such as organic polyimide.

A number of exemplary pixel designs have been described above. However, it is to be appreciated that these are not to be considered limiting -other pixel designs could be used. For example, where TFTs have been used, these could be provided by alternative components, e.g. other types of transistors. Likewise, although reference capacitors have been described, these may be optional. Exemplary pixel structures include one or more TFTs. A first (e.g. sense) TFT may be included so that the read-out current from that pixel has a value proportional to capacitance associated with the reference capacitor. A second (e.g. select) TFT may be included to select whether the first TFT can output a read-out current (e.g. to control current supplied to that first TFT). A third (e.g. reset) TFT may be included to reset the pixel circuit to a reference value. A fourth (e.g. bias) TFT may be included to ensure the pixel is charged to a reference value.

It will be appreciated from the discussion above that the examples shown in the figures are merely exemplary, and include features which may be generalised, removed or replaced as described herein and as set out in the claims. As will be appreciated by the skilled reader in the context of the present disclosure, each of the examples described herein may be implemented in a variety of different ways. Any feature of any aspects of the disclosure may be combined with any of the other aspects of the disclosure. For example, method aspects may be combined with apparatus aspects, and features described with reference to the operation of particular elements of apparatus may be provided in methods which do not use those particular types of apparatus. In addition, each of the features of each of the examples is intended to be separable from the features which it is described in combination with, unless it is expressly stated that some other feature is essential to its operation. Each of these separable features may of course be combined with any of the other features of the examples in which it is described, or with any of the other features or combination of features of any of the other examples described herein. Furthermore, equivalents and modifications not described above may also be employed without departing from the invention.

Certain features of the methods described herein may be implemented in hardware, and one or more functions of the apparatus may be implemented in method steps. It will also be appreciated in the context of the present disclosure that the methods described herein need not be performed in the order in which they are described, nor necessarily in the order in which they are depicted in the drawings. Accordingly, aspects of the disclosure which are described with reference to products or apparatus are also intended to be implemented as methods and vice versa. The methods described herein may be implemented in computer programs, or in hardware or in any combination thereof. Computer programs include software, middleware, firmware, and any combination thereof. Such programs may be provided as signals or network messages and may be recorded on computer readable media such as tangible computer readable media which may store the computer programs in non-transitory form. Hardware includes computers, handheld devices, programmable processors, general purpose processors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and arrays of logic gates.

Other examples and variations of the disclosure will be apparent to the skilled addressee in the context of the present disclosure.

Claims

Claims 1. A cover glass comprising: an optically transparent substrate; a capacitive biometric skin contact sensor provided on the optically transparent substrate; an optically transparent cover layer provided on the capacitive biometric skin contact sensor on the opposite side to the optically transparent substrate; wherein the capacitive biometric skin contact sensor comprises a sensor array of sensor pixels, wherein each sensor pixel comprises a capacitive sensing electrode and at least one thin film transistor, TFT; and wherein the optically transparent cover layer is attached to the capacitive biometric skin contact sensor via an optically coupled adhesive layer.
2. The cover glass of claim 1, wherein at least one of the substrate and the cover layer is made of glass
3. The cover glass of any preceding claim, wherein the adhesive has a thickness of 5 microns or less.
4. The cover glass of any preceding claims, wherein the cover layer has a thickness of 50 microns or less.
5. The cover glass of claim 4, wherein the cover layer has a thickness of 35 microns or less.
6. The cover glass of any preceding claim, wherein the cover layer has a dielectric constant of 5 or more.
7. The cover glass of any preceding claim, wherein the cover layer has a hardness of 6H or more.
8. The cover glass of any preceding claim, wherein the cover layer is made of tempered glass.
9. The cover glass of any preceding claim, wherein at least a portion of the sensor is provided by an at least partially optically transparent electrical conductor.
10. The cover glass of any preceding claim, wherein the capacitive sensing electrode of each sensor pixel is made of an optically transparent material.
11. The cover glass of any preceding claim, wherein the cover layer has a minimum bend radius of under 2 mm.
12. The cover glass of any preceding claim, wherein the substrate and/or the cover layer are made of a polyimide material.
13. The cover glass of any preceding claim, wherein the cover glass is configured for installation on a display of a device.
14. The cover glass of claim 13, wherein the cover glass is configured to be attached, optionally laminated, onto the display.
15. The cover glass of claim 13 or 14, wherein the optically coupled adhesive layer is optically tuned to the display of the device.
16. The cover glass of any of claims 13 to 15, wherein the cover glass has one or more reference features thereon arranged to facilitate correct alignment of the cover glass onto the 20 display.
17. The cover glass of claim 16, wherein the reference features of the cover glass are configured to be aligned with corresponding reference features of the display screen such that the cover glass will be arranged on the display in the correct alignment if the reference features of the cover glass are correctly aligned with the reference features of the display.
18. The cover glass of claim 16 or 17, wherein the reference features on the cover glass comprise indicia.
19. The cover glass of any preceding claim, wherein the cover glass is a mobile phone cover glass configured for installation on a display of the mobile phone.
20. The cover glass of any preceding claim, wherein the sensor is laminated onto the substrate.
21. The cover glass of any preceding claim, wherein the cover glass comprises at least one reference feature, and wherein the sensor array of sensor pixels of the biometric skin contact sensor is arranged at a selected offset from said at least one reference feature.
22. The cover glass of claim 21, wherein a tolerance for the selected offset of the sensor array from the at least one reference feature is less than a pixel pitch for the sensor pixels of the sensor array.
23. The cover glass of claim 22, as dependent on claim 17, or any claim dependent thereon, wherein the tolerance for the selected offset of the sensor array from the at least one reference feature is less than a pixel pitch for the pixels and/or sub-pixels of the display screen.
24. A device comprising: a display; a capacitive biometric skin contact sensor arranged on a user-facing side of the display, the capacitive biometric skin contact sensor comprising a sensor array of sensor pixels, wherein each sensor pixel comprises a capacitive sensing electrode and at least one thin film transistor, TFT; and an optically transparent cover layer arranged on a user-facing side of the sensor; wherein the cover layer is attached to the capacitive biometric skin contact sensor via an optically coupled adhesive layer.
25. The device of claim 24, wherein the device further comprises a first protective layer arranged on a user-facing surface of the display; and wherein the sensor is arranged on a user-facing surface of the first protective layer.