OLED DISPLAY MODULE STRUCTURE FOR MITIGATING DARK SPOT VISIBILITY IN BACK COVER OPEN REGIONS

A mobile computing device includes an emissive display panel configured to emit light from a front surface of the display panel, with the display panel having a plurality of transparent layers and an opaque back cover layer. The mobile computing device also includes a light sensor located behind the opaque back cover layer, and the opaque back cover layer includes an opening through which light from outside the display that is transmitted through the transparent layers of the display can pass to reach the sensor. An air gap separates the light sensor from the transparent layers of the display panel. The plurality of transparent layers includes a reflection attenuating layer on a back side of the display panel configured to attenuate the reflection of light from an interface between a transparent layer of the display panel and the air gap.

FIELD OF THE DISCLOSURE

The present disclosure relates to flat panel displays and more specifically to displays that include a through-the-display optical components (e.g., optical sensors/emitters).

BACKGROUND

Expanding a display to cover more area of a mobile device (e.g., mobile phone, tablet, etc.) may be desirable from, at least, a user experience standpoint. However, electro-optical devices positioned on a side of the mobile device that also includes the display (e.g., a front-facing camera, a light sensor, a proximity sensor, etc.) may compete for real estate on the side of the device that includes the display. Thus, a sensor on display side of the device may be located under the display, such that light passes through the display to reach the sensor. However, the presence of the sensor under the display may cause undesirable distortions to the appearance of the display.

SUMMARY

In a first general aspect, a mobile computing device includes an emissive display panel configured to emit light from a front surface of the display panel, with the display panel having a plurality of transparent layers and an opaque back cover layer. The mobile computing device also includes a light sensor located behind the opaque back cover layer, and the opaque back cover layer includes an opening through which light from outside the display that is transmitted through the transparent layers of the display can pass to reach the sensor. An air gap separates the light sensor from the transparent layers of the display panel. The plurality of transparent layers includes a reflection attenuating layer on a back side of the display panel configured to attenuate the reflection of light from an interface between a transparent layer of the display panel and the air gap.

Implementations can include one or more of the following features, alone, or in any combination with each other.

In an example, the display panel can include an active matrix organic light emitting diode (AMOLED) display.

In another example, the opaque back cover layer can include a metal layer configured to spread heat through the metal layer.

In another example, the reflection attenuating layer can include a first quarter wave plate, a linear polarizer, and a second quarter wave plate, wherein the linear polarizer is located between the first and second quarter wave plates.

In another example, the first quarter wave plate, the linear polarizer, and the second quarter wave plate can be located within the opening of the opaque back cover layer.

In another example, the first quarter wave plate, the linear polarizer, and the second quarter wave plate can be located above the opaque back cover layer, between the back cover layer and the front surface of the display panel.

In another example, the linear polarizer, and the second quarter wave plate can be located within the opening of the opaque back cover layer, and the first quarter wave plate can be located above the opaque back cover layer, between the back cover layer and the front surface of the display panel.

In another example, the first quarter wave plate can include a PET film layer.

In another example, the first quarter wave plate can include a combination of a PET film layer and a birefringent, non-PET, film layer.

In another example, one or more of the first quarter wave plate, the linear polarizer, or the second quarter wave plate can include a partially-transmissive, partially-opaque layer.

In another example, the reflection attenuating layer can include a partially-transmissive, partially-opaque layer that attenuates an intensity of light that passes through the layer.

In another example, the partially-transmissive, partially-opaque layer can be located within the opening of the opaque back cover layer.

In another example, the partially-transmissive, partially-opaque layer can be located above the opaque back cover layer, between the back cover layer and the front surface of the display panel.

In another example, the display panel can include a polarization layer that receives randomly-polarized light from outside the display panel and circularly polarizes the light as a result of the light propagating through the polarization layer.

In another example, the display panel can include OLED emitters and semiconductor circuit elements configured to control a luminance of light emitted from the OLED emitters, where the semiconductor circuit elements are shielded from direct light received from outside the display panel by at least some opaque structures in the display panel.

The components in the drawings are not necessarily drawn to scale and may not be in scale relative to each other. Like reference numerals designate corresponding parts throughout the several views.

DETAILED DESCRIPTION

The present disclosure describes a flat panel display (i.e., display) that can be used with a computing device (e.g., mobile phone, tablet, etc.). The front surface of a mobile device includes a display typically operating as a graphic user interface (GUI) and one or more optical devices operating as sensors/emitters in areas below the display and facing the front surface. The one or more optical devices can be configured for a variety of functions, including (but not limited to) sensing lighting conditions (e.g. an ambient light sensor), sensing proximity of objects near the display (e.g., electromagnetic sensor), capturing images (e.g., a fingerprint sensor).

A proximity sensor may include a transmitter and a receiver of electromagnetic radiation, which are used to determine proximity of the display to an object that reflects electromagnetic radiation transmitted by the transmitter, which radiation is then reflected by the object and received by the receiver. For example, when a percentage of the transmitted radiation intensity received at the receiver, after being reflected by an object, exceeds a threshold value, a signal from the proximity sensor may determine that the display is closer to the object than a threshold distance.

A fingerprint sensor also may include a transmitter and a receiver of electromagnetic radiation, which are used to image a fingerprint on a finger pressed to the display. For example, radiation can be transmitted from a transmitter of the fingerprint sensor, reflected off the finger, and then detected by the receiver. A fingerprint pattern can be determined based on the reflected light received at the receiver and may be compared to a stored data associated with a fingerprint.

An ambient light sensor may include a receiver of light and may determine an amount of ambient light received by the sensor.

Light sensors are used in many mobile devices. Recent advances in emissive display technology (e.g., active matrix organic light emitting diode (AMOLED)) facilitate extending the emissive (i.e., active) area of the display towards (e.g., to) the edges of the mobile device. By extending the active area of the display towards the edges of the mobile device, a user may experience the benefits of a larger display without the drawbacks of a larger device. However, this may leave insufficient space for light sensors or other optical devices outside the area of the emissive display on the front side of the mobile device.

The emissive display disclosed herein is configured to share the front surface of a mobile device with one or more sensors so that the active area of the display can be extended to the edges, without the need for leaving a gap in the display, or space around the display, for the light sensor(s). Accordingly, one or more portions of the disclosed display covering the light sensors can be configured so that the light sensor(s), positioned behind the display, can transmit and receive electromagnetic radiation through the display. Generally, an air gap separates the back side of the display panel from the light sensor(s).

Ideally, when a light sensor is located under the display panel light would pass unimpeded through the display panel to the sensor. However, in reality, light is scattered, absorbed, and reflected by elements within the display panel. Some the reflected and/or scattered light may interfere with the operation of the pixel circuits in the display panel, causing unintended operation of at least some of the pixel circuits. In particular, light (e.g., ambient light that passes through the display) can reflect off an interface between a back side of the display panel and an air gap between the panel and a light sensor and then strike semiconductor circuits that control the pixel luminance of OLEDs above the air gap. This reflected light can interfere with the intended luminance of the OLEDs, such that the OLEDs may have a different intensity and/or color than they are programmed to produce.

To mitigate this effect, structures are disclosed herein that reduce the amount of light reflected from the interface between a back side of the display panel and an air gap between the panel and a light sensor. For example, an antireflection polarizer or an attenuator can be placed at the interface to reduce reflections.

Traditionally, the display and the optical devices located on a surface of the device that includes the display have occupied separate areas of the front surface. For example,FIG.1Adepicts a mobile device101having a display110and a light sensor (e.g., ambient light sensor, proximity sensor, etc.)111that occupy different portions of the front surface.

FIG.1Billustrates a mobile device102with a display112that extends towards the edges of the device and that occupies a larger portion of the surface of the device102than does the display110of device101. Unlike mobile devices in which the display is excluded from an area reserved for optical devices, the light-emitting (i.e., active) area of the display112extends over substantially the entire front surface. Accordingly, nearly the entire front surface of the mobile device102may be used to present color, black-and-white, or gray-scale images, graphics, and/or characters. In some implementations, the display112can include one or more areas120behind which (i.e., below which) a light sensor or emitter may be disposed.

The size, shape, and/or position of the area120may be implemented variously. For example, the area120shown inFIG.1Bhas a rounded (e.g., circular) shape and is positioned apart from edges of the display112, but this need not be the case. For example, the area120can have rectangular in shape and can be positioned along an edge of the display112.

FIG.2Adepicts a side, cross-sectional view of a mobile device having a display112with areas120A,120B through which electromagnetic radiation can be transmitted to an underlying optical device, for example, a fingerprint sensor, an ambient light sensor, or a proximity sensor. The mobile device can include multiple optical devices140A,140B, each positioned behind a different area120A,120B.FIG.2Bdepicts a side, cross-sectional view of a mobile device having a display112with a single region120C for use by the multiple optical devices140A,140B. The optical devices140A,140B may transmit and/or receive electromagnetic radiation125through the areas120A,120B,120C.

FIG.3illustrates a side, cross-sectional view of an emissive display (e.g., an AMOLED display) suitable for use with the mobile device ofFIG.1. While the principles of the disclosure may be applied to display technologies other than AMOLED displays, the implementation of an AMOLED display will be considered throughout the disclosure.

As shown inFIG.3, the AMOLED display300includes a plurality of layers that make up a display panel360. The layers include a cover glass layer310that can form the front surface of the mobile device102. In a possible implementation, the display300can include a polarizer film layer315. The display300can also include a touch sensor layer320that includes touch sensor electrodes322. Pixels337for the display are formed from a cathode layer330, an OLED emitter stack335, and separate elements of an anode layer336. Elements of the anode layer336may be reflective so that light emitted from the OLED emitter stack335is directed in a vertical (z) direction from the anode layer336. An element of the anode layer336can be coupled to a thin film transistor (TFT) semiconductor structure340that includes a source, a gate, and a drain, which can be controlled by electrical signals transmitted over signal lines342. The display300can further include a transparent barrier layer345that includes, for example, SiNx or SiONx and a transparent substrate layer350that includes, for example, polyimide (PI) and/or polyethylene terephthalate (PET). An opaque layer/film370for mechanical support, heat spreading, and electrical shielding can be located below the display panel360to protect the display from localized hot spots due to heat-generating elements in the mobile device, such as, for example, a CPU, a GPU, etc., as well as from electrical signals/electrical noise from electrical components in the device located below the display300.

The layers of the display300may include transparent and non-transparent circuit elements. For example, the TFT structure340, the pixels337, the signal lines342, and/or touch sensor electrodes322may all block light from propagating through the display300. Light can be either reflected or absorbed by the non-transparent (i.e., opaque) circuit elements.

FIG.4is a schematic diagram of mobile device400that includes a light sensor (e.g., a proximity sensor)402located under a display panel404interacting with an object406that is a distance, D, away from a front surface of the display panel404. The light sensor402can include a transmitter408and a receiver410of electromagnetic radiation (e.g., infrared light). An opaque layer412for heat spreading and/or electrical shielding can be disposed between the display panel404, and the proximity sensor402and/or an opaque layer412can be disposed between a layer that includes OLED emitters of the display and the proximity sensor402. The opaque layer412can include one or more openings through which electromagnetic radiation can pass when transmitted to the object406and when received from the object. In some implementations, the electromagnetic radiation transmitted to the object406and received from the object can pass through different openings in the opaque layer412that are spatially separated from each other, and in some implementations, the electromagnetic radiation transmitted to the object406and received from the object can pass through the same opening, The proximity sensor402can operate by determining an amount of electromagnetic radiation (e.g., an intensity) that is emitted from the transmitter408, reflected off the object406, and then is received by the receiver410. The amount of light received by the receiver410can be used as a signal for how close the front surface of the display panel404is to an object406under the assumption that the amount of light received by the intensity of received light increases monotonically with decreasing distance, D, between the display panel404and the object406. The amount of light received at the receiver can be correlated with a distance between the object and the display panel, where the correlation is based on either an empirical calibration between received intensity and distance, or is based on a theoretical model of the propagation of light from the transmitter408to the object406and from the object406to the receiver410, or a combination of the two.

FIG.5is a schematic diagram of an implementation of a display panel500and a sensor502located under the display panel500illustrating light propagating through the display panel to the sensor. The sensor502can be coupled to a sensor module503containing control electronics for operating the sensor.

The display panel can include multiple layers. For example, the display panel500can include a cover glass layer506, a polarizer layer that can include a linear polarizer508aand a quarter-waveplate508bthat can reduce the amount of light reflected off of an OLED layer in the panel that exits the front surface of the display, an encapsulation/touch sensor layer510containing touch sensor electrodes, a cathode layer,512, an OLED layer514, a pixel circuit layer516containing anodes518for supplying current to the OLEDs and semiconductor circuit elements520for controlling the current provided to the anodes, a PI layer522, a PET layer524, and an opaque back cover layer526. An opening in the back cover layer526allows light from outside the display panel to pass through the panel and through the opening528to reach the sensor.

Two paths530,532of light passing through the display panel500are shown inFIG.5, with each path showing a possible reflection of light within the panel. In one path532, light can traverse the transparent elements of the display panel and be reflected by a top surface of the back cover526, such that the light is then directed back into the panel500. However, the amount of light reflected from beam path532from the top surface of the back cover526can be relatively small due to the low reflectivity of the back cover526(e.g. 0.1% of the light in the incoming light). In another path530, light can traverse the transparent elements of the display panel and be reflected by an the interface between a transparent layer (e.g., PET layer524) and an air gap between the panel and a light sensor located below an opening528in the back cover526(i.e., as a result of a mismatch in the indices of refraction between air and the transparent layer), which also results in the reflection of light from the interface back into the panel500. The reflection from the interface of the light path530can be appreciably higher (e.g. 4% of the incoming light) than the reflection of light along path532from the top surface of the back cover layer526, and the difference results in higher exposure of the reflected light to the bottom surface of the semiconductor layer of the display pixel circuits than the rest of the display areas that are covered by the back cover526.

In some cases, reflected light that strikes semiconductor circuit elements520can cause reduction in light emission from pixels, in turn resulting in unintended dark spots in the display. For example, although semiconductor circuit elements520are shielded from direct light that enters the front surface of the panel through the cover window layer506(e.g., by the anodes518or the OLEDs themselves), reflected light (e.g., high-intensity, short wavelength light) that strikes semiconductor circuit elements520can increase the TFT leakage current of a circuit that controls the emission of light from a pixel. In some cases, the increased leakage current can be due to the photelectric effect caused by the reflected light on the circuit. The increased TFT leakage current for a circuit can cause a pixel controlled by the circuit to appear darker than intended. Because the semiconductor layer and the associated pixel circuits located over the opening528in the back cover526are struck by higher intensity reflected light, as compared with the rest of the display regions that are covered by the back cover526, the display panel500may appear to have odd dark spots above the locations of under-the-display light sensors.

FIG.6is a schematic diagram another implementation of a display panel600and a sensor602located under the display panel600illustrating light propagating through the display panel to the sensor. The sensor602can be coupled to a sensor module603containing control electronics for operating the sensor.

The display panel can include multiple layers. For example, the display panel600can include a cover glass layer606, a polarizer layer that can include a linear polarizer608aand a quarter wave plate608b, an encapsulation/touch sensor layer610containing touch sensor electrodes, a cathode layer,612, an OLED layer614, a pixel circuit layer616containing anodes618for supplying current to the OLEDs and semiconductor circuit elements620for controlling the current provided to the anodes, a PI layer622, a PET layer624, and an opaque back cover layer626. An opening628in the back cover layer626allows light from outside the display panel to pass through the panel and through the opening628to reach the sensor. A reflection attenuating layer on the back side of the display panel including a first film layer630, a linear polarizer632, and another quarter wave plate layer634can be included in the opening628.

A path640of light passing through the display panel600is shown inFIG.6. The structure of the additional layers630,632,634in display panel600as compared with the panel500can be used to reduce the amount of light reflected from the interface between the panel and the air gap between the panel and the light sensor602. For example, when light enters the panel600through the cover window layer606the light can be randomly polarized. Then, after passing through the linear polarizer layer608a, which is polarized in a first direction in a plane of the layer608a, the light can be linearly polarized in the first direction. Then, after passing through the quarter wave plate610, the light can be circularly polarized with a first chirality (e.g., right circularly polarized).

In some implementations, the first film layer630can include birefringent material, such that the layer630functions as a quarter wave plate for light transmitted through the layer. Thus, after passing through the first film layer630in the opening628, the light can be linearly polarized in a second linear polarization direction, wherein the second linear polarization direction is orthogonal to the first linear polarization direction due to film608a. This second linear polarization direction of the light can be transmitted with close to zero attenuation by the linear polarization layer632, whose polarization axis is aligned with the second linear polarization direction of the light. Then, after passing through the second quarter wave plate layer634in the opening628, the light can be circularly polarized with a second chirality (e.g., left circularly polarized), opposite to the first chirality. When the light interacts with the interface between the interface between the bottom transparent layer634of the panel and the air gap between the panel and the light sensor602, a first portion642of the light is transmitted through the interface and a second portion644is reflected from the interface. The reflected portion of the light has the chirality of its polarization reversed, so that it is circularly polarized with the first chirality. Then, after again passing through the quarter wave plate634the reflected light is linearly polarized in the first direction. Because the first linear polarization direction is orthogonal to the polarization axis of the linear polarization layer632, the reflected light is sharply attenuated by the layer632, and very little light646is transmitted though the layer632in a direction from the back side of the panel toward the front side of the panel. Therefore, very little reflected light reaches the pixel circuit layer616containing semiconductor circuit elements620for controlling the current provided to the anodes618of the OLEDs. Therefore, the TFT leakage current of the pixels circuits does not increase, and the OLEDs emit their designed amounts of light, so that a dark spot in the display over the opening628for the sensor602can be avoided.

In some implementations, the transparent PET layer624of the display panel can introduce some polarization rotation to light passing through the layer624. Therefore, the thickness, composition, and other material properties of the first film layer630can be selected, such that the combination of the PET layer630and the first film layer630, which can include birefringent PET or non-PET material acts as a quarter wave plate to light passing through the combination of layers. In some implementations, one or more of layers630,632,634can be applied as coatings to the display panel600.

FIG.7is a schematic diagram another implementation of a display panel700and a sensor702located under the display panel700illustrating light propagating through the display panel to the sensor. The sensor702can be coupled to a sensor module703containing control electronics for operating the sensor.

The display panel can include multiple layers. For example, the display panel700can include a cover glass layer706, a polarizer layer that can include a linear polarizer708aand a quarter wave plate708b, an encapsulation/touch sensor layer710containing touch sensor electrodes, a cathode layer,712, an OLED layer714, a pixel circuit layer716containing anodes718for supplying current to the OLEDs and semiconductor circuit elements720for controlling the current provided to the anodes, a PI layer722, a first film layer (e.g., a PET film layer)724, and an opaque back cover layer726. An opening728in the back cover layer726allows light from outside the display panel to pass through the panel and through the opening728to reach the sensor. A reflection attenuating layer on the back side of the display panel including the first film layer724, a linear polarizer730, and a quarter wave plate layer732, with at least some of the layers of the reflection attenuating layer being included in the opening728. In some implementations, one or more of layers724,730,732can be applied as coatings to the display panel700.

A path740of light passing through the display panel700is shown inFIG.7. The reflection attenuating layer in display panel700can be used to reduce the amount of light reflected from the interface between the panel and the air gap between the panel and the light sensor702. For example, when light enters the panel700through the cover window layer706the light can be randomly polarized. Then, after passing through the linear polarizer layer708a, which is polarized in a first direction in a plane of the layer708a, the light can be linearly polarized in the first direction. Then, after passing through the quarter wave plate710, the light can be circularly polarized with a first chirality (e.g., right circularly polarized).

In some implementations, the first film layer724, which in some implementations can include PET film, can include birefringent material, such that the layer724functions as a quarter wave plate for light transmitted through the layer. Thus, after passing through the first film layer724, the light can be linearly polarized in a second linear polarization direction, wherein the second linear polarization direction is perpendicular to the first linear polarization direction. This second linear polarization direction of the light can be transmitted with close to zero attenuation by the linear polarization layer730, whose polarization axis is aligned with the second linear polarization direction of the light. Then, after passing through the quarter wave plate layer732in the opening728, the light can be circularly polarized with a second chirality (e.g., left circularly polarized), opposite to the first chirality. When the light interacts with the interface between the interface between the bottom transparent layer732of the panel and the air gap between the panel and the light sensor702, a first portion742of the light is transmitted through the interface and a second portion744is reflected from the interface. The reflected portion of the light has the chirality of its polarization reversed, so that it is circularly polarized with the first chirality. Then, after again passing through the quarter wave plate732the reflected light is linearly polarized in the first direction. Because the first linear polarization direction is orthogonal to the polarization axis of the linear polarization layer730, the reflected light is sharply attenuated by the layer730, and very little light746is transmitted though the layer730in a direction from the back side of the panel toward the front side of the panel. Therefore, very little reflected light reaches the pixel circuit layer716containing semiconductor circuit elements720for controlling the current provided to the anodes718of the OLEDs. Therefore, the TFT leakage current of the pixels circuits does not increase, and the OLEDs emit their designed amounts of light, so that a dark spot in the display over the opening728for the sensor702can be avoided.

FIG.8is a schematic diagram another implementation of a display panel800and a sensor802located under the display panel800illustrating light propagating through the display panel to the sensor. The sensor802can be coupled to a sensor module803containing control electronics for operating the sensor. Like the display panels ofFIGS.6and7, the display panel800can include a reflection attenuating layer on the back side of the panel, but, unlike the display panels ofFIGS.6and7, the reflection attenuating layer in panel800can be located above the opaque back cover layer826.

Thus, the display panel can include multiple layers, such as a cover glass layer806, a polarizer layer that can include a linear polarizer808aand a quarter wave plate808b, an encapsulation/touch sensor layer810containing touch sensor electrodes, a cathode layer,812, an OLED layer814, a pixel circuit layer816containing anodes818for supplying current to the OLEDs and semiconductor circuit elements820for controlling the current provided to the anodes, a PI layer822, a first film layer (e.g., a PET film layer)824, a linear polarizer layer830, a quarter wave plate layer832, and an opaque back cover layer826. An opening828in the back cover layer826allows light from outside the display panel to pass through the panel and through the opening828to reach the sensor. A reflection attenuating layer on the back side of the display panel800above the opaque back cover layer826can include the first film layer824, the linear polarizer layer830, and the quarter wave plate layer832. In some implementations, one or more of layers824,830,832can be applied as coatings to the display panel800.

In the implementation shown inFIG.8, the first film layer824, which in some implementations can include PET film, can include birefringent material, such that the layer824functions as a quarter wave plate for light transmitted through the layer. Thus, after passing through the first film layer824, the light can be linearly polarized in a second linear polarization direction, wherein the second linear polarization direction is perpendicular to the first linear polarization direction. This second linear polarization direction of the light can be transmitted with close to zero attenuation by the linear polarization layer830, whose polarization axis is aligned with the second linear polarization direction of the light. Then, after passing through the quarter wave plate layer832, the light can be circularly polarized with a second chirality (e.g., left circularly polarized), opposite to the first chirality. When the light interacts with the interface between the interface between the bottom transparent layer832of the panel and the air gap between the panel and the light sensor802, a first portion842of the light is transmitted through the interface and a second portion844is reflected from the interface. The reflected portion of the light has the chirality of its polarization reversed, so that it is circularly polarized with the first chirality. Then, after again passing through the quarter wave plate832the reflected light is linearly polarized in the first direction. Because the first linear polarization direction is orthogonal to the polarization axis of the linear polarization layer830, the reflected light is sharply attenuated by the layer830, and very little light846is transmitted though the layer830in a direction from the back side of the panel toward the front side of the panel. Therefore, very little reflected light reaches the pixel circuit layer816containing semiconductor circuit elements820for controlling the current provided to the anodes818of the OLEDs. Therefore, the TFT leakage current of the pixels circuits does not increase, and the OLEDs emit their designed amounts of light, so that a dark spot in the display over the opening828for the sensor802can be avoided.

In some cases, the implementation ofFIG.8, in which the reflection attenuating layer is located above the opening828, rather than at least partially within the opening, can be easier to manufacture than an implementation with part of the reflection attenuating layer be located in the opening828, but the cost of the materials (e.g., for polarization layers824,830,832that span the width of the display) may be higher.

FIG.9Ais a schematic diagram another implementation of a display panel900and a sensor902located under the display panel900illustrating light propagating through the display panel to the sensor. The sensor902can be coupled to a sensor module903containing control electronics for operating the sensor. The display panel900can include a reflection attenuating layer on the back side of the panel, where the reflection attenuating layer includes a partially-transmissive, partially-opaque layer or coating that attenuates the intensity of light that passes through the layer.

The display panel900can include multiple layers, such as a cover glass layer906, a polarizer layer that can include a linear polarizer908aand a quarter wave plate908b, an encapsulation/touch sensor layer910containing touch sensor electrodes, a cathode layer,912, an OLED layer914, a pixel circuit layer916containing anodes918for supplying current to the OLEDs and semiconductor circuit elements920for controlling the current provided to the anodes, a PI layer922, and a clear PET film layer924. An opening928in the back cover layer926allows light from outside the display panel900to pass through the panel and through the opening928to reach the sensor902. A reflection attenuating layer on the back side of the display panel900within the opening928in the opaque back cover layer926can include partially-transmissive, partially-opaque material layer930(e.g., a neutral density filter) that attenuates the light passing through the layer.

In the implementation shown inFIG.9A, the transmissivity of the partially-transmissive, partially-opaque material layer930can be selected such that enough transmitted light942passes through the layer930for the sensor902to function as designed, but such that when light is transmitted through the layer twice (i.e., once in a direction toward the sensor902and once, after reflection from the interface with the air gap, in a direction away from the sensor902), that the intensity of light944reflected from the air gap is attenuated enough that reflected light944does not interfere significantly with the operation of the semiconductor circuit elements920for controlling the current provided to the anodes918of the OLED emitters.

FIG.9Bis a schematic diagram another implementation of a display panel and a sensor located under the display panel illustrating light propagating through the display panel to the sensor, wherein the implementation is similar to that ofFIG.9A, except that the partially-transmissive, partially-opaque material layer930is located above the opaque back cover layer926. In some implementations, the layer930can be applied as a coating to the display panel900.

In some implementations, one or more layers of the reflection attenuating layers of display panels600,700, or800can include a partially-transmissive, partially-opaque layer that attenuates the intensity of light that passes through the layer. For example, quarter wave plate layer or a linear polarizer layer of the reflection attenuating layers of display panels600,700, or800can include a partially-transmissive, partially-opaque layer.

The disclosed displays have been presented in the context of a mobile device, such as a tablet or a smart phone. The principles and techniques disclosed, however, may be applied more generally to any display in which it is desirable to position a sensor behind the display. For example, a virtual agent home terminal, a television, or an automatic teller machine (ATM) are a non-limiting set of alternative applications that could utilize a light sensor positioned behind an active area of a display. Further, the motivation for placing a light sensor behind a display is not limited to an expansion of the display to the edges of a device. For example, it may be desirable to place the light sensor behind a display for aesthetic or stealth reasons.

In the specification and/or figures, typical embodiments have been disclosed. The present disclosure is not limited to such exemplary embodiments. The use of the term “and/or” includes any and all combinations of one or more of the associated listed items. Unless otherwise noted, specific terms have been used in a generic and descriptive sense and not for purposes of limitation. As used in this specification, spatial relative terms (e.g., in front of, behind, above, below, and so forth) are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, a “front surface” of a mobile computing device may be a surface facing a user, in which case the phrase “in front of” implies closer to the user. Additionally, a “top surface” of a display may be the surface facing a user, in which case the phrase “below” implies deeper into an interior of the mobile computing device.