WO2024020983A1

WO2024020983A1 - Display comprising an optical biometric imaging device

Info

Publication number: WO2024020983A1
Application number: PCT/CN2022/108828
Authority: WO
Inventors: Jun Liu; Hans Martinsson; Su LIU; Petter Ostlund; Erxiang Shinny CHEN
Original assignee: Fingerprint Cards Anacatum Ip Ab
Priority date: 2022-07-29
Filing date: 2022-07-29
Publication date: 2024-02-01

Abstract

A display arrangement (101) comprising an optical biometric imaging device (102), the display arrangement comprising a cover plate (104), an organic light-emitting diode, OLED, substrate (106) and an image sensor (108) located on a side of the OLED-substrate facing away from the cover plate, wherein the OLED-substrate comprises: a color filter layer (110) comprising an array of color filters (112), each color filter being separated from an adjacent color filter by a light-blocking region (114); a pixel layer (116) comprising an array of pixels (118) corresponding to the array of color filters, the pixel layer being arranged on a side of the color filter layer facing away from the cover plate, wherein the pixel layer further comprises a plurality of apertures (120), each aperture being at least partially aligned with a light-blocking region (114) of the color filter layer (110), and wherein each aperture is configured to project an image of at least a portion of an object (122) placed on the cover plate (104) onto the image sensor (108).

Description

DISPLAY COMPRISING AN OPTICAL BIOMETRIC IMAGING DEVICE

Field of the Invention

The present invention relates to an optical biometric imaging device integrated in a display panel. In particular, the invention relates to an optical biometric imaging device suitable for fingerprint sensing.

Background of the Invention

Biometric imaging systems are widely used as means for increasing the convenience and security of personal electronic devices, such as mobile phones etc. Fingerprint sensing systems in particular are now included in a large proportion of all newly released consumer electronic devices, such as mobile phones.

Optical fingerprint sensors have been known for some time and may be a feasible alternative to e.g. capacitive fingerprint sensors in certain applications such as for use as under-display sensors in smartphones, tablet computers, presentation screens, access systems and the like. Optical fingerprint sensors may for example be based on the pinhole imaging principle and/or may employ micro-structures, such as collimators or microlenses to collect and steer incoming light towards an image sensor.

As the technological development progresses in for example OLED touch panel displays, new display models with increased resolution (i.e. LED pixel density) are constantly introduced to the market.

However, with an increasing pixel density in the display, the light transmittivity is similarly decreasing, meaning that less light reaches an optical biometric sensor located underneath the display panel. Thereby, with increasing resolution of the display, it becomes more difficult to acquire high quality biometric images using an optical sensor located under the display.

Moreover, in order to reduce the thickness of AMOLED displays, and to reduce the display power consumption, a partially opaque layer (black matrix layer) comprising color filters is introduced to replace the common polarizer. Such displays have almost negligible light transmittivity through the display panel.

Accordingly, it is desirable to find solutions to optical biometric imaging under displays with low light transmission.

Summary

In view of above-mentioned and other drawbacks of the prior art, it is an object of the present invention to provide an improved biometric imaging device suitable for integration in a display in an electronic user device.

According to a first aspect of the invention, there is provided a display arrangement comprising an optical biometric imaging device. The display arrangement comprises a cover plate, an organic light-emitting diode, OLED, substrate and an image sensor located on a side of the OLED-substrate facing away from the cover plate. The OLED-substrate comprises: a color filter layer comprising an array of color filters, each color filter being separated from an adjacent color filter by a light-blocking region; a pixel layer comprising an array of pixels corresponding to the array of color filters, the pixel layer being arranged on a side of the color filter layer facing away from the cover plate, wherein the pixel layer further comprises a plurality of apertures, each aperture being at least partially aligned with a light-blocking region of the color filter layer, and wherein each aperture is configured to project an image of at least a portion of an object placed on the cover plate onto the image sensor.

In the present context, the image sensor is configured to receive light having been reflected by a biometric object such as a fingertip, to thereby capture a fingerprint image. Accordingly, a light source is available for illuminating the finger to ensure that a sufficient amount of light reaches the image sensor. The light source may for example be the pixels of the OLED display panel with which the imaging device is integrated as will be exemplified in the following, but the light source may also be one or more controllable LEDs suitably arranged in relation to the imaging device and the object to be imaged.

The present invention is based on the realization that in OLED display panels with low light transmission, the properties of an optical biometric imaging device comprising an image sensor below the display panel can be improved by forming apertures in the pixel layer of the OLED substrate. As discussed in the background section, an AMOLED-substrate comprising red, green and blue (RGB) pixels driven by TFT (thin film transistor) circuitry can have almost negligible light transmission. The apertures in the pixel layer thereby allows light transmission such that an image of a biometric object can be captured by the image sensor located below the display panel, thereby enabling optical in-display fingerprint detection.

The light-blocking regions in the color filter layer can be referred to as a “black matrix” (BM) , and the color filter (CF) layer with a black matrix replaces a polarizer to reduce the display total thickness which in turn increases the lifetime for foldable display panels. The light path from the object to the image sensor thereby goes through the color filter and through an aperture to reach the image sensor.

A further advantage of the claimed invention is that since the apertures are located in the pixel layer instead of in the color filter layer, there is no visual difference in the display panel as seen by a user.

According to one embodiment of the invention, the aperture is a pinhole aperture located between two adjacent pixels. Each pinhole aperture in the array of pinhole apertures will then project a part of the object onto the image sensor. A plurality of sub-images are thus captured by the image sensor, and the sub-images can be stitched together to acquire a full fingerprint image for biometric verification.

According to one embodiment of the invention, the pinhole apertures are arranged to be fully overlapping with the light-blocking region such that only light reaching the cover plate with an oblique incident angle reach the pinhole aperture. In other words, light reaching the color filter layer perpendicularly to the plane of the layer will not reach the image sensor. This also has the advantageous effect that the apertures are not visible in the display panel since they are fully covered by the light-blocking regions in the color filter layer.

According to one embodiment of the invention, a size of a pinhole aperture is in the range of 1 μm to 20 μm and a distance between adjacent pinhole apertures is in the range of 20 μm to 500 μm. The described size and distance ranges are based on current OLED manufacturing technology and the dimensions of the apertures can be adapted based on the requirements in a certain application. Moreover, the size of the aperture can refer to a diameter of a circular aperture or the side of a rectangular aperture. However, other shapes of the apertures are also feasible in which case the size can be seen as a general description of the size of the aperture.

According to one embodiment of the invention, the plurality of pinhole apertures can be sparsely arranged such that there are two or more pixels between adjacent pinhole apertures. The density of apertures required for achieving a fingerprint image with sufficient resolution depends on a range of parameters such as aperture size, distance between the apertures and the display surface, offset between apertures and color filters, display thickness etc. Accordingly, the configuration of the array of apertures can be selected based on other system parameters, for example by having two or more pixels between adjacent apertures in the array of apertures.

According to one embodiment of the invention, each aperture is arranged and configured to encircle a pixel. The aperture can thereby be formed as a ring-shaped aperture when the pixel is a circular pixel structure or as a rectangular aperture when the pixel is a rectangular pixel structure. An advantage of using a ring-shaped aperture is that light of the same incidence angle but coming from different radial directions (imaging lights pass through center of color filter but reaching different point on the ring) all can pass through the display. This will not break the radial symmetry of lens or pinhole imaging. Moreover, using a ring-shaped structure where the color filter is larger than the size of the pixel means that light which is perpendicular to the display can pass through the aperture.

According to one embodiment of the invention, the aperture is divided into a plurality of separate sections. It is thus not required that the aperture is a single continuous opening. An aperture encircling a pixel can for example be divided into several regions. In some applications, the electrical connection to the pixel is non-transparent meaning that a ring-shaped aperture will be intersected in at least one location by pixel wiring. A ring shaped aperture may thus be divided into sections by two or more connection wires or similar structures.

According to one embodiment of the invention, the apertures are arranged to encircle pixels of only one color. Apertures can for example be arranged to only encircle green pixels and since the green pixels are located underneath a green color filter, only green light will reach the aperture and subsequently the image sensor. An advantage of selecting reflection from the object within specific wavelength ranges is that contrast and liveness detection can be improved.

According to one embodiment of the invention, the apertures are arranged to encircle pixels of a first color in a first sub-area of the display and to encircle pixels of a second color in a second sub-area of the display, wherein the first color is different from the second color and wherein the first sub-area is non-overlapping with the second sub-area.

Color information of the finger comes from diffusive reflection. Diffusive reflection of finger is stronger with red light comparing to blue and green light. As color information is used for anti-spoofing, the use of red light at an edge of a sensing area can improve anti-spoofing. Red light is preferably not used in a central portion of the sensing area so that contrast in the center is not reduced since the center portion is critical to biometric matching.

According to one embodiment of the invention a pixel size may be smaller than or equal to a size of a color filter. This provides a flexibility in the design of the imaging device since the size of pixels, color filters and apertures can be tailored individually to fit a specific application.

According to one embodiment of the invention, the pixel layer comprises apertures in a sub-area of a total display area, thereby providing an active sensing area in part of the display. The active sensing area can also be referred to as a hot-zone.

According to one embodiment of the invention, the image sensor comprises a camera lens arranged to focus light having passed through the plurality of pinholes onto an active sensing area of the image sensor. By using a focusing camera lens, the size of the image sensor can be reduced to be smaller than a total sensing area.

According to one embodiment of the invention, the image sensor comprises a plurality of microlens structures arranged to focus light having passed through the plurality of pinholes onto an active sensing area of the image sensor.

According to one embodiment of the invention, the image sensor comprises a collimating structure configured to collimate light having passed through the plurality of pinholes before reaching an active sensing area of the image sensor. An advantage of using a collimator structure between the object and the image sensor is that the combined thickness of the image sensor and collimator is lower than for example when using a camera lens. However, a collimator solution requires that the area of the collimator and image sensor correspond to the total active sensing area. There are thus different advantages associated with the different alternatives and it is possible to select the solution which is most suitable for a given application.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person will realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.

Brief Description of the Drawings

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing an example embodiment of the invention, wherein:

Fig. 1 schematically illustrates an electronic consumer device comprising a display arrangement according to an embodiment of the invention;

Fig. 2 schematically illustrates details of a display arrangement according to an embodiment of the invention;

Figs. 3A-B schematically illustrate details of a display arrangement according to an embodiment of the invention;

Figs. 4A-C schematically illustrates details of a display arrangement according to an embodiment of the invention;

Fig. 5 schematically illustrates a display arrangement according to an embodiment of the invention; and

Fig. 6 schematically illustrates a display arrangement according to an embodiment of the invention.

Detailed Description of Example Embodiments

In the present detailed description, various embodiments of the display arrangement comprising an optical biometric imaging device according to the present invention are mainly described with reference to a fingerprint imaging sensor suitable for use in a display panel of a consumer device such as a smartphone, tablet computer and the like. However, other implementations of the imaging device are also possible.

Fig. 1 schematically illustrates a smartphone 100 equipped with a display arrangement 101 comprising an integrated optical biometric imaging device 102 according to example embodiments. In particular, the biometric imaging device 102 is located in an active display area of the display panel 104. The biometric imaging device 102 is arranged to capture an image of a finger 122 placed on the display panel. In the following description, a display arrangement having a biometric imaging device 102 in a sub-area of the total display area will be described. However, it would equally well be possible to configure the display arrangement so that fingerprint sensing is possible over the full display area. Moreover, the biometric imaging device 102 may also capture palmprints.

Fig. 2 is a schematic cross section view of the display arrangement 101 which comprises a cover plate 104, an organic light-emitting diode, OLED, substrate 106 and an image sensor 108 located on a side of the OLED-substrate facing away from the cover plate 104. The cover plate can be any type of cover structure used in display panels, such as a glass plate or the like. Moreover, the image sensor can be a CMOS based image sensor (CIS) . Furthermore, the display panel may contain one or more transparent layers, such as adhesive layers (e.g. optically clear adhesives) and/or spacer layers. Such layers can be used as suitable for a specific application and will not be discussed in detail in the present disclosure.

The OLED-substrate 106 comprises a color filter layer 110 comprising an array of color filters 112, each color filter being separated from an adjacent color filter by a light-blocking region 114 and a pixel layer 116 comprising an array of pixels 118 corresponding to the array of color filters 114, the pixel layer 116 being arranged on a side of the color filter layer 110 facing away from the cover plate 104 such that the color filter layer 110 is located between the pixel layer 116 and the cover plate 104. The color filter layer 110 comprises red, green and blue (RGB) color filters 112a-c configured to be transparent to light in the respective wavelength ranges. The light-blocking region 114 is made from an opaque material which is configured to block light in at least the visible wavelength ranges and/or in the wavelength ranges detectable by the image sensor 108. Moreover, the light-blocking region 114 can be seen as a contiguous region in the color filter layer 110 comprising openings only at the locations of the color filters 112.

The pixel layer 116 further comprises a plurality of apertures 120, each aperture being at least partially aligned with a light-blocking region 114 of the color filter layer 110, and wherein each aperture 120 is configured to project an image of at least a portion of a finger 122 placed on the cover plate 104 onto the image sensor 108. That the aperture 120 is aligned with a light blocking region 114 means that the light-blocking region 114 overlaps the aperture 120 so that light reaching the light blocking region 114 in a direction perpendicular to the plane of the color filter layer 110 will not reach the aperture. Accordingly, an aperture being partially aligned with a light blocking region allows some of the light reaching the color filter layer perpendicular to the plane of the layer to also reach the aperture. The image sensor 108 will thereby capture an image comprising a plurality of sub-images, where each sub-image corresponds to the light received through one aperture 120. The sub-images are subsequently stitched together to form a complete fingerprint image.

Fig. 3A is schematic illustration of an example embodiment where the apertures 120 are pinhole apertures 120 located between two adjacent pixels 118 in the pixel layer 116. The color filter layer 110 separated from the pixel layer 116 by a transparent spacer layer 130 which defines the distance between the two

layers

110, 116. Accordingly, the optical properties of the imaging device can be tailored by selecting the appropriate thickness of the transparent spacer layer 130. Furthermore, the pinhole aperture 120 can in principle have an arbitrary shape such as circular, square, rectangular or the like. For simplicity, the aperture 120 will be assumed to be circular in the following description. The plurality of apertures can typically be aligned with the pixels in the pixel array, so that if pixels are arranged in a square array, the apertures follow the square alignment of the pixels. However, it would equally well be possible to use other alignments for the plurality of apertures, for example along the diagonals of a square pixel array.

In a high-resolution display having a pixel density of 500 ppi or above, pixels can be sparsely arranged with a pinhole aperture size in the range of 1 μm to 20 μm and a separation distance in the range of 20 μm to 500 μm.

In Fig. 3A, the pinhole aperture 120 is smaller than the light blocking region 114 and also arranged to be fully overlapping with the light-blocking region 114 such that only light reaching the cover plate 104 with an oblique incident angle reach the pinhole aperture 120. This is illustrated by the angles θ ₁ and θ ₂ defining the angle range θ ₁ to θ ₂ of light reaching the pinhole aperture 120 and which can subsequently reach the image sensor. The magnitude of the angles θ ₁ and θ ₂ can be controlled by tailoring the size of the apertures 120, the distance between the color filter layer 110 and the pixel layer 116, the offset between the aperture 120 and the color filter 112 and also the optical properties of the materials used. Accordingly, the optical properties of the biometric imaging device can be tailored to suit the properties of the display panel with which the device is integrated.

Fig. 3B illustrates an example embodiment of the biometric imaging device where the size of the aperture 120 is larger than the distance between adjacent pixels 118 so that there is a partial overlap between the color filter 122 and the aperture 120. This has the effect that light reaching the cover plate at an oblique angle can reach the pinhole aperture and subsequently the image sensor which has the effect that more light is allowed to reach the image sensor. The angle range is here defined by the angles θ ₃ and θ ₄.

Figs. 4A-C schematically illustrate an example embodiment of the biometric imaging device where each aperture 120 is arranged and configured to encircle a pixel 118. Fig. 4A schematically illustrates that light having an incident angle in the range ±θ ₅ will pass through the aperture 120. The aperture can be a ring-shaped aperture 402 where the pixel 118 is a circular pixel structure as illustrated in Fig. 4B or the aperture can be a rectangular aperture 404 where the pixel 118 is a rectangular pixel structure as illustrated in Fig. 4C. The ring-shaped aperture 402 can also be described as an annulus or as being donut-shaped.

In Fig. 5 the illustrated biometric imaging device 102 further comprises a lens arrangement 500 comprising at least one lens 502 configured to focus light reflected by a biometric object 122 onto the image sensor 108, where the lens 500 is located between the apertures 120 and the image sensor 108.

Fig. 6 schematically illustrates a biometric imaging device comprising a collimator structure 600 located between the OLED-substrate 106 and the image sensor 108.

Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Also, it should be noted that parts of the device may be omitted, interchanged or arranged in various ways, the device yet being able to perform the functionality of the present invention.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

A display arrangement (101) comprising an optical biometric imaging device (102) , the display arrangement comprising a cover plate (104) , an organic light-emitting diode, OLED, substrate (106) and an image sensor (108) located on a side of the OLED-substrate facing away from the cover plate, wherein the OLED-substrate comprises:

a color filter layer (110) comprising an array of color filters (112) , each color filter being separated from an adjacent color filter by a light-blocking region (114) ;

a pixel layer (116) comprising an array of pixels (118) corresponding to the array of color filters, the pixel layer being arranged on a side of the color filter layer facing away from the cover plate, wherein the pixel layer further comprises a plurality of apertures (120) , each aperture being at least partially aligned with a light-blocking region (114) of the color filter layer (110) , and wherein each aperture is configured to project an image of at least a portion of an object (122) placed on the cover plate (104) onto the image sensor (108) .
The display arrangement according to claim 1, wherein the aperture is a pinhole aperture located between two adjacent pixels.
The display arrangement according to claim 1 or 2, wherein the pinhole apertures are arranged to be fully overlapping with the light-blocking region such that only light reaching the cover plate with an oblique incident angle reach the pinhole aperture.
The display arrangement according to any one of the preceding claims, wherein a size of a pinhole aperture is in the range of 1 μm to 20 μm.
The display arrangement according to any one of the preceding claims, wherein a distance between adjacent pinhole apertures is in the range of 20 μm to 500 μm.
The display arrangement according to any one of the preceding claims, wherein the plurality of pinhole apertures are sparsely arranged such that there are two or more pixels between adjacent pinhole apertures.
The display arrangement according to claim 1, wherein each aperture is arranged and configured to encircle a pixel.
The display arrangement according to claim 7, wherein the aperture is a ring-shaped aperture and the pixel is a circular pixel structure.
The display arrangement according to claim 7, wherein the aperture is rectangular aperture and the pixel is a rectangular pixel structure.
The display arrangement according to any one of claims 7 to 9, wherein a width of the aperture is in the range of 1 μm to 10 μm.
The display arrangement according to any one of claims 7 to 10, wherein the aperture is divided into a plurality of separate sections.
The display arrangement according to any one of claims 7 to 11, wherein the apertures are arranged to encircle pixels of one color.
The display arrangement according to any one of claims 7 to 12, wherein the apertures are arranged to encircle pixels of a first color in a first sub-area of the display and to encircle pixels of a second color in a second sub-area of the display, wherein the first color is different form the second color and wherein the first sub-area is non-overlapping with the second sub-area.
The display arrangement according to any one of the preceding claims, wherein a pixel size is smaller than or equal to a size of a color filter.
The display arrangement according to any one of the preceding claims, wherein the pixel layer comprises apertures in a sub-area of a total display area.
The display arrangement according to any one of the preceding claims, wherein the image sensor comprises a camera lens (500) arranged to focus light having passed through the plurality of pinholes onto an active sensing area of the image sensor.
The display arrangement according to any one of claims 1 to 15, wherein the image sensor comprises a plurality of microlens structures (600) arranged to focus light having passed through the plurality of pinholes onto an active sensing area of the image sensor.
The display arrangement according to any one of claims 1 to 15, wherein the image sensor comprises a collimating structure (700) configured to collimate light having passed through the plurality of pinholes before reaching an active sensing area of the image sensor.