Patent Application
20200403186
Organic light emitting diode (OLED) displays often include a circular or linear polarizer in order to reduce reflection of ambient light from reflective components within the display, such as various layers of the integrated circuits that form pixel drivers. Circular polarizers can contain absorbing materials that substantially absorb one polarization state of incident light, while substantially transmitting the orthogonal state. Thus, the polarizer absorbs approximately half of unpolarized light incident thereon. While other components of the display also reduce overall transmission of light through the display, the polarizer is generally a substantial contributor to this transmission loss.
A common design goal for mobile devices such as smartphones is to reduce the size of the bezel that frames the device's display. However, sensors such as front-facing cameras are often located in the device's bezel. Locating a sensor behind the display is one pathway to reducing the bezel's size while maintaining the front facing sensors. However, many displays currently used in mobile devices exhibit very low transmission of light incident thereon. As a result, achieving satisfactory signal-to-noise ratios using a sensor behind a display presents challenges.
The transmission loss through an OLED display can be reduced in front of a sensor by reducing the absorption of the polarizer at that location, providing a high transmission window for the sensor. This however also can result in an increased reflectance in that region and thus a visual artifact, especially where there is a sharp transition between the low and high absorption regions of the polarizer. This visual impact of the high transmission window can be mitigated by including a region between the conventional polarizing area and the high transmission window having a gradual change in transmission from the one region to the other.
In general, in one aspect, the invention features a device that includes a display panel including an array of pixels extending in a plane of the display panel, each pixel having an organic light emitting diode (OLED) arranged to emit light to a front side of the display panel, and an absorptive polarizing layer arranged between the array of pixels and the front side of the display panel, the absorptive polarizing layer including a first area that transmits substantially all (e.g., about 98% or more, about 99% or more) of a first polarization state of visible light incident thereon in a direction normal to the plane of the display and absorbs substantially all of a second polarization state of the visible light, the first and second polarization states being orthogonal polarization states, the absorptive polarizing layer further including a second area that transmits more than 50% (e.g., about 60% or more, about 70% or more, about 80% or more, about 90% or more) of unpolarized visible light incident thereon in the direction normal to the plane of the display, and a third area located between the first area and the second where the polarizing layer's transmission decreases monotonically from the second area to the first area. The device also includes a sensor arranged on a back side of the display panel, the sensor configured to receive light transmitted through the second area of the polarizing layer.
Examples can include one or more of the following features and/or features of other aspects. For instance, the absorptive polarizing layer can be a linearly polarizing layer.
The device can include a retarder (e.g., a quarter wave retarder) forming a circular polarizer with the linearly polarizing layer. In some embodiments, the polarizing layer is a layer of a linear polarizer.
The second area can correspond to an area of the sensor in the plane of the display. For example, the second area can have the same or a similar footprint to the sensor and/or be located in line with the sensor.
The sensor can be an image sensor (e.g., for visible and/or IR light).
The second area can be surrounded by the third area, and the third area can be surrounded by the first area. In some examples, the second area extends across a width of the display.
The third area can have a minimum dimension of 0.2 mm or less (e.g., 1 mm or less, 0.5 mm or less) along one or more directions in the plane of the display.
The device can be a mobile device, such as a smart phone, a tablet computer, or a wearable device.
The mobile device can have a bezel surrounding the display, the bezel having a maximum width of 0.2 mm or less (e.g., 1 mm or less, 0.5 mm or less).
In general, in another aspect, the invention features a method that includes (i) locally bleaching an absorptive polarizer to provide a first area that transmits substantially all of a first polarization state of visible light incident thereon in a direction normal to a plane of the absorptive polarizer and absorbs substantially all of a second polarization state of the visible light, the first and second polarization states being orthogonal polarization states, the absorptive polarizer further including a second area that transmits more than 50% of unpolarized visible light incident thereon in the direction normal to the plane, and a third area located between the first area and the second where the absorptive polarizer's transmission decreases monotonically from the second area to the first area; (ii) disposing the bleached absorptive polarizer on an OLED display panel; and (iii) arranging the display panel in front of an image sensor so that the sensor receives light transmitted through the second area of the polarizing layer.
Implementations can include one or more of the following features and/or features of other aspects. For example, the absorptive polarizer can be bleached by exposing a polarizing layer of the absorptive polarizer to light having an energy sufficient to reduce the absorption of a light absorbing material in the polarizing layer. The exposure light can be UV light. A dose of the exposure can be varied to form the first, second, and third areas of the absorptive polarizer.
The absorptive polarizer can be bleached by exposing a polarizing layer of the absorptive polarizer to a bleaching agent.
Among other advantages, embodiments feature devices that incorporate sensors behind an OLED display without substantial sacrifices in performance of the sensor due to high absorption of light by the OLED display stack layers. Moreover, this performance can be achieved without substantial degradation of the display's appearance in the region above the sensor. For example, improved light transmission through the display can be achieved by providing a high light transmission window in the polarizer of the OLED display. The window can be made less conspicuous to a user by incorporating a transition zone where the polarizer's absorption gradually decreases from an area where the degree of polarization is high and transmission is low to the high transmission window.
Other advantages and features will be apparent from the description below and from the claims.
Like labels indicate like elements.
Referring to
Referring also to
In general, polarizer 112 is configured to substantially transmit visible light have one circularly polarized state while substantially absorbing visible light having the orthogonal state of polarization. Ideally, for normally incident unpolarized incident light, this means that polarizer 112 will transmit approximately 50% of the light, while absorbing approximately 50%.
While most of the area of polarizer 112 is a conventional circular polarizer (i.e., transmitting close to 50% of light (e.g., about 42% to 45%), corresponding to transmission of substantially one polarization state while substantially blocking the other), polarizer 112 includes an area 145 having higher overall transmission for normally incident unpolarized visible light. Correspondingly, the degree of polarization provided in area 145 is lower than outside area 145 (i.e., in area 115, shown in the inset in
Area 145 is composed of a high transmission window 140 and a transition zone 150. High transmission window 140 is positioned adjacent (i.e., in front of) sensor 192, increasing the transmission of light through the display to sensor 192 compared to light transmission through the other parts of the display. Generally, window 140 is sized and shaped to provide high light transmission to the entire optically-sensitive area of sensor 192, and can vary according to the size and shape of the sensor. In some embodiments, window 140 has a lateral dimension (i.e., in the plane of the display) in a range from about 0.5 mm to about 5 mm (e.g., about 1 mm or more, about 2 mm or more, about 4 mm or less, about 3 mm or less) in at least one direction. Window 140 is depicted in
Generally, the transmission level of window 140 can be selected to provide a desired level of performance of the display versus a desired level of performance of the underlying sensor. For instance, where a greater signal-to-noise ratio of the sensor is desired, a window with a higher level of transmission can be selected compared to a device where reduced reflection from the display is desired. In some embodiments, window 140 transmits about 60% or more of normally incident unpolarized visible light (e.g., about 70% or more, about 80% or more). In certain cases, window 140 can transmit close to 100% of incident light (e.g., about 95% or more).
In transition zone 150, light transmission decreases from the edge of window 140 radially outward to the conventional polarizer area 115 (which transmits about 50% or less of normally incident unpolarized visible light). In general, the size of transition zone 150 can vary. In some embodiments, transition zone 150 extends radially at least 0.2 mm or more (e.g., 0.3 mm or more, 0.4 mm or more, 0.5 mm or more, 0.8 mm or more, 1 mm or more) than window 140, e.g., about 5 mm or less (e.g., 4 mm or less, 3 mm or less, 2 mm or less). As discussed further below, the size and brightness gradient of transition zone 150 can be selected to reduce the contrast between window 140 and area 115 perceived by a user.
Display panel 152, in turn, is composed of a top layer 141, a cathode layer 142, a pixel layer 160, a pixel circuit layer 162, and a lower substrate 172. Top substrate 141 provides mechanical support and protection to the display panel and can be formed from a transparent material such as a transparent polymer (e.g., trifluoroethylene) or glass. Layer 141 can be a substrate or a thin film encapsulent. Cathode layer 142 is generally formed from a translucent thin metal layer. Pixel layer 160 is composed of an array of OLED pixels formulated to emit light within an appropriate wavelength band (e.g., red, green, or blue light, or cyan, magenta, or yellow light). Pixel circuit layer 162 includes integrated circuit elements (e.g., thin film transistors, capacitors, and the like) that control the delivery of electrical current to each pixel in pixel layer 160. Lower substrate 172 provides mechanical support and protection for the pixel circuits and OLED pixels and can include layers of one or more material to provide these functions. In some embodiments, lower substrate 172 is composed of polymer, e.g., a polyimide, and can support one or more additional layers, such as a poly-ethyl terephthalate layer.
A sensor module 190 is arranged on the opposite side of display panel 152 from touch panel 132. Sensor module includes sensor 130 that can include a radiation transmitter and/or receiver, depending on the embodiment. In some embodiments, for example, sensor 192 is a camera sensor (e.g., a front facing camera). In certain embodiments, sensor 192 is a facial recognition sensor and includes a transmitter (e.g., an IR radiation source, such as an IR laser) and a receiver for detecting radiation from the transmitter that is reflected from an object (e.g., the device user's face). For an IR sensor, the module can include an optical filter to block certain light, e.g., visible wavelengths, from the sensor.
An interfacial layer 180 connects sensor module 190 to the back surface of display panel 152. Interfacial layer includes a light transparent aperture 182 and other regions 184 that facilitate the attachment (e.g., physical and/or electrical) of sensor module 192 to the display panel. Light transparent aperture 182 is positioned in front of sensor 130, providing an optical path from the sensor to the back surface of display panel 152. In some embodiments, sensor module 190 can simply be assembled behind the display without an interfacial layer.
During operation, an electronic controller (e.g., including a CPU and/or GPU and/or other integrated circuits and electronic components) sends drive signals to the pixel circuits, which in turn control electrical current delivery to the OLED pixels causing them to emit unpolarized light towards touch panel 132. This light is transmitted through the touch panel to circular polarizer 112. For region 115 and at least partly for region 150, the circular polarizer absorbs one polarization state of the emitted light and transmits the other, which exits the display and forms an image for the user.
In some embodiments, the electronic controller is programmed so that the pixel circuits drive the OLED pixels at different current levels to account for the different amount of absorption provided by polarizer 112. For example, the OLED pixels adjacent window 140 can be driven at a lower current level than the pixels adjacent conventional polarizer area 115 so that the brightness level of pixels in both region is the same. Pixels adjacent transition zone 150 can be driven at intermediate current levels. In this way, pixels in window 140 do not appear brighter than pixels elsewhere on the display. The current levels can be established during a calibration procedure. For example, the display can be set to show white across the full screen and a look up table can be generated to record relative pixel currents that provide uniform luminance across the display.
Referring to
Without wishing to be bound by theory, it is believed that including transition zone 150 between the conventional polarizing area 115 and high transmission window 140 can advantageously make window 140 less conspicuous to a viewer. This is due to the Mach bands effect, which occurs where the human visual system exaggerates the perceived contrast at an interface when there are sudden changes in gray levels. See, e.g., https://en.wikipedia.org/wiki/Mach_bands. Accordingly, in general, the dimensions and transmission gradient of transition zone 150 can be selected to reduce (i.e., minimize) any Mach band effect due to the difference in contrast between area 115 and window 140.
The plots in
The lower plot in
Note that while the upper plot in
In contrast to
While the foregoing discussion features a front facing image sensor behind the high transmission window in the polarizer, the disclosed principles can be applied more generally. For example, mobile devices can include other types of sensor beneath the display panel and a high transmission window can be positioned in front of those sensors too. For instance, certain smartphones can include facial recognition sensors for three-dimensional facial recognition beneath the display panel. High transmission windows can be placed in front of these sensors too. Furthermore, emitters, such as IR emitters for 3D facial recognition, can be placed beneath a display panel behind a high transmission window.
Moreover, while
Generally, polarizers can include more than one high transmission window where more than one sensor and/or transmitter is located beneath the display (e.g., two or more high transmission windows). Alternatively, or additionally, in some embodiments, a polarizer can include a high transmission window sufficiently large to span more than one sensor and/or emitter. For example, referring to
A front facing image sensor 492 and a facial recognition module 495 are located behind the display panel in line with window 440. Facial recognition module 495 includes a sensor 496 and a transmitter 497. Accordingly, the window provides a region of relatively high light transmission through touch display 410 for light to and from sensor 492 and module 495.
Generally, a high transmission window can be formed in a polarizer using a variety of techniques. For example, the absorptive layer of the polarizer (e.g., layer 220 in the example shown in
In some embodiments, UV radiation can be delivered locally by focusing UV light from a light source (e.g., a UV laser or an incoherent source that includes UV radiation) and moving the focused beam relative to the surface of the polarizer (e.g., using a scanning mirror and/or moving the polarizer while holding the focused beam still).
Alternatively, or additionally, in some embodiments a polarizer can be subjected to a blanket exposure of UV radiation, while the masking the polarizer so that only the appropriate locations are exposed. The mask can have regions of intermediate UV transmission levels to provide intermediate doses for transition zone creation.
Other bleaching methods can be used. Chemical bleaching is possible, for instance, by exposing the polarizer to a chemical compound that reduced the polarizer's absorption. For example, the absorption of a stained PVA layer (e.g., layer 220 in
Polarizer bleaching can be performed as part of a roll-to-roll process when the polarizer film is being made. For example, referring to
The manufacturing process works as follows: first, a web is unwound from PVA roll 510. The PVA is stretched to form a highly oriented layer 501 at 511, which is then submerged in bath 518. The bath stains PVA layer 501 with iodine, forming stained layer 502 at 512. After staining, a layer of CTA 503 from roll 520 is laminated to one side of stained PVA layer 502 forming a laminate 521. Next, a second layer of CTA 504 is laminated to the top surface of stained PVA layer 502 forming polarizer 531 that is then rolled up into a roll 540.
Additional layers can be included. For example, in some embodiments, a pressure sensitive adhesive (and a release layer) can be coated on one or both sides of the polarizer 531 before the polarizer is would into roll 540, Alternatively, or additionally, a retarder (e.g., a quarter wave retarder) can be laminated to the polarizer during this process.
Bleaching can be introduced into this process in a number of ways. For example, referring to
Alternatively, in some embodiments, the bleaching agent is deposited onto a surface of CTA layer 503 prior to the layer being laminated to stained PVA layer 502. For example, as shown in
Subsequently, individual sheets of polarizer can be die cut out of the roll of polarizing film 540. Accurate registration of the bleached portions of the polarizer film to the correct location of the display can be facilitated by carefully aligning the die for cutting out polarizer sheets from the roll during the manufacturing process. For example, in some embodiments, the process can include printing alignment marks on one or more of the layers of the polarizer, such as CTA layers 503 and 504. The alignment marks can be registered with the location of the bleached areas, for example, using machine vision.
Referring to
In general, the amount of transmission of a bleached high transmission region can be controlled in a bleaching process, for example, by controlling the concentration of the bleaching agent in the solution. For example,
A number of embodiments are disclosed. Other embodiments are in the following claims.
