Patent Description:
Electronic devices often include displays. For example, an electronic device may have a light-emitting diode (LED) display based on light-emitting diode pixels. In this type of display, each pixel includes a light-emitting diode and thin-film transistors for controlling application of a signal to the light-emitting diode to produce light. The light-emitting diodes may include OLED layers positioned between an anode and a cathode. To emit light from a given pixel in an light-emitting diode display, a voltage may be applied to the anode of the given pixel.

It is within this context that the embodiments herein arise.

Document <CIT> discloses a light-emitting device (LED) chip which includes a body having a light extraction surface. The body includes semiconductor layers including an n-type region and a p-type region. A plurality of micro-lenses is directly on the light extraction surface of the body.

According to the invention, there is disclosed a display as recited in claim <NUM> and a display as recited in claim <NUM>.

An electronic device may have a display that an includes an array of light-emitting diodes. Each light-emitting diode may be mounted on a substrate and may include an anode and a cathode.

To extract light from the light-emitting diode (and thereby improve efficiency of the display), a microlens stack may be formed over the light-emitting diode. The microlens stack may include an array of microlenses that is covered by an additional single microlens. Having stacked microlenses in this way increases lens power without increasing the thickness of the display.

The array of microlenses may be formed from an inorganic material having a high index of refraction such as <NUM>. The additional single microlens may be formed from an organic material having an index of refraction lower than that of the array of microlenses (e.g., <NUM>). The additional single microlens may conform to the upper surfaces of the array of microlenses.

An additional low-index layer may be interposed between the light-emitting diode and the array of microlenses. The low-index layer may increase the lens power of the microlens stack and may improve recycling efficiency for the display. A low-index overcoat may be formed over the microlens stack. A diffusive layer may be formed around the light-emitting diode to capture light emitted from the light-emitting diode sidewalls. An overcoat layer may also be formed between the microlens layers.

An illustrative electronic device of the type that may be provided with a display is shown in <FIG>. Electronic device <NUM> may be a computing device such as a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, a device embedded in eyeglasses or other equipment worn on a user's head, or other wearable or miniature device, a display, a computer display that contains an embedded computer, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an audio device (e.g., a speaker), an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, or other electronic equipment. Electronic device <NUM> may have the shape of a pair of eyeglasses (e.g., supporting frames), may form a housing having a helmet shape, or may have other configurations to help in mounting and securing the components of one or more displays on the head or near the eye of a user.

As shown in <FIG>, electronic device <NUM> may include control circuitry <NUM> for supporting the operation of device <NUM>. Control circuitry <NUM> may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access memory), etc. Processing circuitry in control circuitry <NUM> may be used to control the operation of device <NUM>. The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application-specific integrated circuits, etc..

Input-output circuitry in device <NUM> such as input-output devices <NUM> may be used to allow data to be supplied to device <NUM> and to allow data to be provided from device <NUM> to external devices. Input-output devices <NUM> may include buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device <NUM> by supplying commands through input resources of input-output devices <NUM> and may receive status information and other output from device <NUM> using the output resources of input-output devices <NUM>.

Input-output devices <NUM> may include one or more displays such as display <NUM>. Display <NUM> may be a touch screen display that includes a touch sensor for gathering touch input from a user or display <NUM> may be insensitive to touch. A touch sensor for display <NUM> may be based on an array of capacitive touch sensor electrodes, acoustic touch sensor structures, resistive touch components, force-based touch sensor structures, a light-based touch sensor, or other suitable touch sensor arrangements. A touch sensor for display <NUM> may be formed from electrodes formed on a common display substrate with the display pixels of display <NUM> or may be formed from a separate touch sensor panel that overlaps the pixels of display <NUM>. If desired, display <NUM> may be insensitive to touch (i.e., the touch sensor may be omitted). Display <NUM> in electronic device <NUM> may be a head-up display that can be viewed without requiring users to look away from a typical viewpoint or may be a head-mounted display that is incorporated into a device that is worn on a user's head. If desired, display <NUM> may also be a holographic display used to display holograms.

Control circuitry <NUM> may be used to run software on device <NUM> such as operating system code and applications. During operation of device <NUM>, the software running on control circuitry <NUM> may display images on display <NUM>.

<FIG> is a diagram of an illustrative display <NUM>. As shown in <FIG>, display <NUM> may include layers such as substrate layer <NUM>. Substrate layers such as layer <NUM> may be formed from rectangular planar layers of material or layers of material with other shapes (e.g., circular shapes or other shapes with one or more curved and/or straight edges). The substrate layers of display <NUM> may include glass layers, polymer layers, silicon layers, composite films that include polymer and inorganic materials, metallic foils, etc..

Display <NUM> may have an array of pixels <NUM> for displaying images for a user such as pixel array <NUM>. Pixels <NUM> in array <NUM> may be arranged in rows and columns. The edges of array <NUM> may be straight or curved (i.e., each row of pixels <NUM> and/or each column of pixels <NUM> in array <NUM> may have the same length or may have a different length). There may be any suitable number of rows and columns in array <NUM> (e.g., ten or more, one hundred or more, or one thousand or more, etc.). Display <NUM> may include pixels <NUM> of different colors. As an example, display <NUM> may include red pixels, green pixels, and blue pixels. Pixels of other colors such as cyan, magenta, and yellow might also be used.

Display driver circuitry <NUM> may be used to control the operation of pixels <NUM>. Display driver circuitry <NUM> may be formed from integrated circuits, thin-film transistor circuits, and/or other suitable circuitry. Illustrative display driver circuitry <NUM> of <FIG> includes display driver circuitry 20A and additional display driver circuitry such as gate driver circuitry 20B. Gate driver circuitry 20B may be formed along one or more edges of display <NUM>. For example, gate driver circuitry 20B may be arranged along the left and right sides of display <NUM> as shown in <FIG>.

As shown in <FIG>, display driver circuitry 20A (e.g., one or more display driver integrated circuits, thin-film transistor circuitry, etc.) may contain communications circuitry for communicating with system control circuitry over signal path <NUM>. Path <NUM> may be formed from traces on a flexible printed circuit or other cable. The control circuitry may be located on one or more printed circuits in electronic device <NUM>. During operation, control circuitry (e.g., control circuitry <NUM> of <FIG>) may supply circuitry such as a display driver integrated circuit in circuitry <NUM> with image data for images to be displayed on display <NUM>. Display driver circuitry 20A of <FIG> is located at the top of display <NUM>. This is merely illustrative. Display driver circuitry 20A may be located at both the top and bottom of display <NUM> or in other portions of device <NUM>.

To display the images on pixels <NUM>, display driver circuitry 20A may supply corresponding image data to data lines D while issuing control signals to supporting display driver circuitry such as gate driver circuitry 20B over signal paths <NUM>. With the illustrative arrangement of <FIG>, data lines D run vertically through display <NUM> and are associated with respective columns of pixels <NUM>.

Gate driver circuitry 20B (sometimes referred to as gate line driver circuitry or horizontal control signal circuitry) may be implemented using one or more integrated circuits and/or may be implemented using thin-film transistor circuitry on substrate <NUM>. Horizontal control lines G (sometimes referred to as gate lines, scan lines, emission control lines, etc.) run horizontally across display <NUM>. Each gate line G is associated with a respective row of pixels <NUM>. If desired, there may be multiple horizontal control lines such as gate lines G associated with each row of pixels. Individually controlled and/or global signal paths in display <NUM> may also be used to distribute other signals (e.g., power supply signals, etc.).

Gate driver circuitry 20B may assert control signals on the gate lines G in display <NUM>. For example, gate driver circuitry 20B may receive clock signals and other control signals from circuitry 20A on paths <NUM> and may, in response to the received signals, assert a gate line signal on gate lines G in sequence, starting with the gate line signal G in the first row of pixels <NUM> in array <NUM>. As each gate line is asserted, data from data lines D may be loaded into a corresponding row of pixels. In this way, control circuitry such as display driver circuitry 20A and 20B may provide pixels <NUM> with signals that direct pixels <NUM> to display a desired image on display <NUM>. Each pixel <NUM> may have a light-emitting diode and circuitry (e.g., thin-film circuitry on substrate <NUM>) that responds to the control and data signals from display driver circuitry <NUM>.

Gate driver circuitry 20B may include blocks of gate driver circuitry such as gate driver row blocks. Each gate driver row block may include circuitry such output buffers and other output driver circuitry, register circuits (e.g., registers that can be chained together to form a shift register), and signal lines, power lines, and other interconnects. Each gate driver row block may supply one or more gate signals to one or more respective gate lines in a corresponding row of the pixels of the array of pixels in the active area of display <NUM>.

A schematic diagram of an illustrative pixel circuit of the type that may be used for each pixel <NUM> in array <NUM> is shown in <FIG>. As shown in <FIG>, display pixel <NUM> may include light-emitting diode <NUM>. A positive power supply voltage ELVDD may be supplied to positive power supply terminal <NUM> and a ground power supply voltage ELVSS may be supplied to ground power supply terminal <NUM>. Diode <NUM> has an anode (terminal AN) and a cathode (terminal CD). The state of drive transistor <NUM> controls the amount of current flowing through diode <NUM> and therefore the amount of emitted light <NUM> from display pixel <NUM>. Cathode CD of diode <NUM> is coupled to ground terminal <NUM>, so cathode terminal CD of diode <NUM> may sometimes be referred to as the ground terminal for diode <NUM>.

To ensure that transistor <NUM> is held in a desired state between successive frames of data, display pixel <NUM> may include a storage capacitor such as storage capacitor Cst. The voltage on storage capacitor Cst is applied to the gate of transistor <NUM> at node A to control transistor <NUM>. Data can be loaded into storage capacitor Cst using one or more switching transistors such as switching transistor <NUM>. When switching transistor <NUM> is off, data line D is isolated from storage capacitor Cst and the gate voltage on terminal A is equal to the data value stored in storage capacitor Cst (i.e., the data value from the previous frame of display data being displayed on display <NUM>). When gate line G (sometimes referred to as a scan line) in the row associated with display pixel <NUM> is asserted, switching transistor <NUM> will be turned on and a new data signal on data line D will be loaded into storage capacitor Cst. The new signal on capacitor Cst is applied to the gate of transistor <NUM> at node A, thereby adjusting the state of transistor <NUM> and adjusting the corresponding amount of light <NUM> that is emitted by light-emitting diode <NUM>. If desired, the circuitry for controlling the operation of light-emitting diodes for display pixels in display <NUM> (e.g., transistors, capacitors, etc. in display pixel circuits such as the display pixel circuit of <FIG>) may be formed using other configurations (e.g., configurations that include circuitry for compensating for threshold voltage variations in drive transistor <NUM>, etc.). The display pixel may include additional switching transistors, emission transistors in series with the drive transistor, etc. Capacitor Cst may be positioned at other desired locations within the pixel (e.g., between the source and gate of the drive transistor). The display pixel circuit of <FIG> is merely illustrative.

To extract light from a light-emitting diode, one or more microlenses may be incorporated over a light-emitting diode in the display. The one or more microlenses may be used to collimate light from the light-emitting diode and ensure that the light is directed vertically towards the viewer. In one embodiment, a single microlens may be formed over each light-emitting diode to extract light from that light-emitting diode. However, optimal light extraction may require the microlens to be spaced from the light-emitting diode by a large distance (undesirably increasing the thickness of the display). Therefore, each pixel may be covered by both an array of microlenses and a single microlens that is formed over the array of microlenses.

<FIG> is a cross-sectional side view of an illustrative display pixel that is covered by at least two microlenses. As shown, a light-emitting diode <NUM> is formed on a substrate such as substrate <NUM>. Substrate <NUM> may include glass layers, polymer layers, silicon layers, composite films that include polymer and inorganic materials, metallic foils, etc. The light-emitting diode <NUM> may be a micro-light-emitting diode (e.g., a light-emitting diode semiconductor die having a footprint of about <NUM> microns x <NUM> microns, more than <NUM> microns x <NUM> microns, less than <NUM> microns x <NUM> microns, less than <NUM> microns x <NUM> microns, less than <NUM> microns x <NUM> microns, or other desired size). This example is merely illustrative, and light-emitting diode <NUM> may also be an organic light-emitting diode (OLED) that includes a plurality of OLED layers. The light-emitting diode may be electrically connected to thin-film circuitry within substrate <NUM>. In one example, the light-emitting diode may be soldered to the substrate.

The light-emitting diode may be surrounded by diffusive layer <NUM>. The diffusive layer <NUM> may be used to increase the efficiency of the display. Light-emitting diode <NUM> has an upper surface <NUM>-U and sidewall surfaces <NUM>-S. Ideally, light-emitting diode <NUM> would emit light from upper surface <NUM>-U vertically (e.g., parallel to the Z-axis). However, in practice light-emitting diode <NUM> may emit some light from sidewalls <NUM>-S (e.g., parallel to the X-axis). The diffusive layer <NUM> may recapture some of that light by redirecting light vertically.

Diffusive layer <NUM> (sometimes referred to as diffuser layer <NUM>, diffuser <NUM>, light redirecting layer <NUM>, light scattering layer <NUM>, etc.) includes a plurality of light scattering particles <NUM>-P distributed throughout a host material <NUM>-H. The host material <NUM>-H may be a transparent polymer (e.g., a siloxane). Light scattering particles <NUM>-P may be formed from metal oxide (e.g., titanium dioxide) or another desired material. Light scattering particles <NUM>-P may have a different index of refraction than host material <NUM>-H. Light incident upon the light scattering particles may be scattered in a random direction. This scattering causes some of the light to ultimately be redirected towards the viewer, increasing the efficiency of the display in comparison to embodiments where the diffusive layer is omitted (and little to no light from the LED sidewall ends up visible to the viewer).

It should be noted that a diffusive layer may additionally or instead be incorporated above lens <NUM> within the display (e.g., a top diffuser). For example, a diffusive layer may be formed directly on lens <NUM> between lens <NUM> and overcoat layer <NUM>, overcoat layer <NUM> may itself be a diffusive layer, a diffusive layer may be formed on overcoat layer <NUM> between overcoat layer <NUM> and polarizer <NUM>, etc. These examples are merely illustrative. In general, one or more diffusive layers may be incorporated at any desired location within the display stackup.

A cathode layer <NUM> may be formed over the light-emitting diode and may serve as the cathode terminal (e.g., cathode terminal CD in <FIG>) for light-emitting diode <NUM>. The cathode layer may serve as the cathode for multiple light-emitting diodes and is therefore formed as a blanket layer across the display. The cathode layer may be formed from a transparent conductive material (e.g., indium tin oxide).

An opaque masking layer <NUM> (sometimes referred to as black masking layer <NUM>, black mask <NUM>, opaque mask <NUM>, etc.) is formed over the substrate <NUM>. The opaque masking layer <NUM> may have an opening that overlaps light-emitting diode <NUM>. The opening in opaque masking layer <NUM> over the light-emitting diode allows light from the light-emitting diode to pass through the opaque masking layer towards the viewer (e.g., in the positive Z-direction). Elsewhere (e.g., over portions of diffuser layer <NUM> between pixels), the opaque masking layer may block light (e.g., to prevent cross-talk between adjacent pixels). The opaque masking layer <NUM> may transmit less than <NUM>% of incident light (at a wavelength associated with light emitted from LED <NUM>), less than <NUM>% of incident light, less than <NUM>% of incident light, less than <NUM>% of incident light, etc. The opaque masking layer may be formed from any desired material (e.g., an organic or inorganic opaque material).

Microlenses <NUM> and <NUM> are included to collimate light that passes through the opening in opaque masking layer <NUM>. Microlenses <NUM> and <NUM> may collectively be referred to as microlens stack. First, a microlens array <NUM> is formed in the opening in opaque masking layer <NUM>. Microlens array <NUM> includes a plurality of microlenses <NUM> (e.g., arranged in a plurality of rows and columns, as one example). Additionally, a single microlens <NUM> is formed over microlens array <NUM>. An overcoat layer <NUM> is formed over microlens <NUM>. Including microlens array <NUM> in addition to microlens <NUM> allows for more collimating of light from LED <NUM> (e.g., by providing additional lens power) without increasing the thickness of the display.

Microlenses <NUM> and <NUM> may be formed from any desired material. Microlens <NUM> may be formed from an organic material such as an acrylate based material. Microlenses <NUM> may be formed from an inorganic material such as silicon nitride. These examples are merely illustrative. In general, both microlenses <NUM> and <NUM> may be formed from any desired organic or inorganic material.

There may be a difference in index of refraction between microlenses <NUM> and <NUM>. The index of refraction difference between microlenses <NUM> and <NUM> may be greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, less than <NUM>, between <NUM> and <NUM>, or any other desired magnitude. Microlenses <NUM> may have an index of refraction that is greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, between <NUM> and <NUM>, between <NUM> and <NUM>, or any other desired magnitude. Microlens <NUM> may have an index of refraction that is greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, less than <NUM>, less than <NUM>, between <NUM> and <NUM>, between <NUM> and <NUM>, or any other desired magnitude. In one example, microlenses <NUM> are formed from an inorganic material (a silicon nitride) having an index of refraction of <NUM> and microlens <NUM> is formed from an organic material (an acrylate based material) having an index of refraction of <NUM>.

Microlens <NUM> may conform to (and directly contact) the upper surfaces of microlenses <NUM>. Microlens <NUM> is in turn covered by overcoat layer <NUM>, with overcoat layer <NUM> conforming to (and directly contacting) the surface of microlens <NUM>. Overcoat layer <NUM> may have a lower index of refraction than microlens <NUM> and therefore may sometimes be referred to as a low-index overcoat layer, a low-index layer, etc. Overcoat layer <NUM> may be formed from an acrylate based organic material or an epoxy based organic material. These examples are merely illustrative and in general any desired organic or inorganic material may be used for low-index overcoat layer <NUM>. The difference in refractive index between microlens <NUM> and overcoat layer <NUM> may be greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, less than <NUM>, between <NUM> and <NUM>, or any other desired magnitude. Overcoat layer <NUM> may have an index of refraction that is greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, between <NUM> and <NUM>, between <NUM> and <NUM>, or any other desired magnitude. In one example, overcoat layer <NUM> is formed from an epoxy based material having an index of refraction of <NUM>.

Additional layers may be formed over low-index overcoat <NUM>. As shown in <FIG>, a polarizer <NUM> and transparent cover layer <NUM> may be formed over the low-index overcoat layer. Polarizer <NUM> may be a linear polarizer or a circular polarizer. Transparent cover layer <NUM> may be a transparent layer (e.g., formed from glass or plastic) that protects the display. One or more additional layers may be included in the display if desired (e.g., between overcoat layer <NUM> and transparent cover layer <NUM> or above transparent cover layer <NUM>).

As shown in <FIG>, according to the invention, layer <NUM> is interposed between light-emitting diode <NUM> and microlenses <NUM>. Layer <NUM> (sometimes referred to as transparent layer <NUM>, low-index layer <NUM>, low-index overcoat layer <NUM>, overcoat layer <NUM>, etc.) may be formed from an organic material (e.g., an epoxy based or acrylate based material) or an inorganic material (e.g., silicon dioxide). Layer <NUM> may have a transparency that is greater than <NUM>%, greater than <NUM>%, greater than <NUM>%, greater than <NUM>%, or any other desired transparency. Low-index layer <NUM> may offer numerous performance advantages for the display. First, the presence of low-index layer <NUM> increases the distance between microlenses <NUM> and <NUM> and light-emitting diode <NUM> (due to the thickness <NUM> of layer <NUM>). This increased distance results in microlenses <NUM> and <NUM> having increased lens power, resulting in light from LED <NUM> being better collimated. The specific thickness <NUM> of layer <NUM> may be selected to optimize the microlens performance. Thickness <NUM> may be less than <NUM> microns, less than <NUM> microns, less than <NUM> microns, less than <NUM> micron, greater than <NUM> micron, greater than <NUM> micron, between <NUM> and <NUM> microns, between <NUM> and <NUM> microns, or any other desired magnitude.

The difference in refractive index between microlens <NUM> and overcoat layer <NUM> may be greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, less than <NUM>, between <NUM> and <NUM>, or any other desired magnitude. The difference in refractive index between microlenses <NUM> and overcoat layer <NUM> may be greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, less than <NUM>, between <NUM> and <NUM>, or any other desired magnitude. Overcoat layer <NUM> may have an index of refraction that is greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, between <NUM> and <NUM>, less than <NUM>, less than <NUM>, between <NUM> and <NUM>, or any other desired magnitude.

In addition to increasing spacing between the microlenses and the LED, overcoat layer <NUM> may improve light recycling (and therefore efficiency) in the display. When overcoat layer <NUM> has a low index of refraction, more light will be recycled (due to a smaller escape cone caused by the low index of refraction). This example is merely illustrative. In another possible embodiment, overcoat <NUM> may be formed from the same material as microlenses <NUM> or another material having a higher refractive index. In this type of embodiment (where the index of refraction is high in layer <NUM>), there may be less recycling efficiency improvements but still improved lens power due to the additional separation provided by thickness <NUM>.

Each microlens may have any desired dimensions. Microlens <NUM> may have a height (sometimes referred to as thickness) <NUM> that is greater than <NUM> microns, greater than <NUM> microns, greater than <NUM> microns, greater than <NUM> microns, greater than <NUM> microns, less than <NUM> microns, less than <NUM> microns, between <NUM> and <NUM> microns, between <NUM> and <NUM> microns, between <NUM> and <NUM> microns, or any other desired magnitude. Microlens <NUM> may have a width (sometimes referred to as diameter) <NUM> that is greater than <NUM> microns, greater than <NUM> microns, greater than <NUM> microns, greater than <NUM> microns, less than <NUM> microns, less than <NUM> microns, between <NUM> and <NUM> microns, between <NUM> and <NUM> microns, or any other desired magnitude. Each microlens <NUM> may have a height (sometimes referred to as thickness) <NUM> that is greater than <NUM> micron, greater than <NUM> microns, greater than <NUM> microns, greater than <NUM> micron, greater than <NUM> microns, less than <NUM> microns, less than <NUM> microns, between <NUM> and <NUM> microns, between <NUM> and <NUM> micron, or any other desired magnitude. Each microlens <NUM> may have a width (sometimes referred to as diameter) <NUM> that is greater than greater than <NUM> microns, greater than <NUM> micron, greater than <NUM> microns, greater than <NUM> microns, greater than <NUM> microns, less than <NUM> microns, less than <NUM> microns, between <NUM> and <NUM> microns, or any other desired magnitude.

<FIG> is a top view showing an illustrative pixel with an array of microlenses covered by a single microlens such as the pixel of <FIG>. As shown, microlens array <NUM> includes a plurality of microlenses <NUM>. The microlenses <NUM> in <FIG> are arranged in uniform rows and columns. This example is merely illustrative. The microlenses may alternatively be arranged in other (regular or irregular) patterns. For example, the footprint of the microlens array may be circular or another desired shape. A single microlens <NUM> is then formed over the microlens array <NUM>. As shown, the entire microlens array <NUM> is overlapped by the microlens <NUM>. Microlens <NUM> may conform to and contact the upper surface of every microlens in microlens array <NUM>. Microlenses <NUM> in array <NUM> are coplanar.

The example in <FIG> of LED <NUM> being laterally surrounded (e.g., surrounded on all sides within the XY-plane) by diffusive layer <NUM> is merely illustrative. <FIG> shows an alternate configuration where light-emitting diode <NUM> is laterally surrounded by layer <NUM>. In some cases, layer <NUM> may be an optically clear passivation layer formed from a transparent polymer. In this case, layer <NUM> may have a transparency greater than <NUM>%, transparency greater than <NUM>%, transparency greater than <NUM>%, transparency greater than <NUM>%, etc. Alternatively, layer <NUM> may be an opaque layer (e.g., a black masking layer, black mask, opaque mask, etc.) that blocks incident light. In this case, layer <NUM> may have a transparency less than <NUM>%, transparency less than <NUM>%, transparency less than <NUM>%, transparency less than <NUM>%, etc. <FIG> also shows how opaque masking layer <NUM> from <FIG> may optionally be omitted.

A passivation layer (sometimes referred to as an overcoat layer) <NUM> may optionally be included between each adjacent microlens layer if desired. The passivation layer may have any desired refractive index (e.g., greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, between <NUM> and <NUM>, between <NUM> and <NUM>, less than <NUM>, less than <NUM>, between <NUM> and <NUM>, between <NUM> and <NUM>, between <NUM> and <NUM>, between <NUM> and <NUM>, etc.). This example is merely illustrative. In general, a passivation layer may optionally be included on the upper and/or lower surface of each microlens layer (e.g., in direct contact with the upper and/or lower surface of each microlens layer). The passivation layer <NUM> in <FIG> conforms to the upper surface of the microlenses <NUM> of microlens array <NUM>. The lower surface of microlens <NUM> in turn conforms to the upper surface of passivation layer <NUM>.

The opaque masking layer arrangements depicted thus far (e.g., in <FIG> and <FIG>) are merely illustrative. In addition to simply being included (as in <FIG>) or omitted (as in <FIG>), the opaque masking layer may have different footprints in embodiments where the opaque masking layer is included in the pixel.

As shown in <FIG>, the footprint of microlens array <NUM> may have a width <NUM>. In <FIG> and <FIG>, the width <NUM> of array <NUM> is approximately equal to the width of microlens <NUM>. In other words, width <NUM> may be within <NUM>%, within <NUM>%, within <NUM>%, or within <NUM>% of the width of microlens <NUM> (width <NUM> in <FIG>). In contrast, in <FIG> width <NUM> differs from the width of microlens <NUM> by a greater amount (e.g., more than <NUM>%, more than <NUM>%, more than <NUM>%, etc.). Said another way, the width of microlens <NUM> may be greater than array width <NUM> by a factor of <NUM> or more, <NUM> or more, between <NUM> and <NUM>, etc..

In <FIG> and <FIG>, opaque masking layer <NUM> defines an opening that is entirely occupied by microlens array <NUM>. In other words, there is no gap between microlenses <NUM> and opaque masking layer <NUM>. This example is merely illustrative. If desired, there may be a gap between the opaque masking layer <NUM> and the edges of microlens array <NUM>. In <FIG>, microlens <NUM> vertically overlaps and directly contacts a portion of opaque masking layer <NUM> in addition to the entire microlens array <NUM>. <FIG> also shows how low-index overcoat <NUM> between LED <NUM> and microlens array <NUM> may optionally be omitted.

<FIG> shows an alternative arrangement where the width <NUM> of microlens array <NUM> is greater than the width <NUM> of microlens <NUM>. In this case, microlens array <NUM> is partially covered by microlens <NUM> (instead of completely covered as in <FIG>, <FIG>, and <FIG>). Microlens <NUM> is still the only microlens formed over array <NUM> in this embodiment. In <FIG>, width <NUM> may differ from width <NUM> by more than <NUM>%, more than <NUM>%, more than <NUM>%, etc. Said another way, the width <NUM> may be greater than width <NUM> by a factor of <NUM> or more, <NUM> or more, between <NUM> and <NUM>, etc..

In <FIG> and <FIG>, an example is depicted where a larger single microlens is formed over a plurality of smaller microlenses. This example is merely illustrative. If desired, the position of the microlenses may be switched (e.g., with an array of smaller microlenses formed over a larger microlens). In general, two or more layers of microlenses may be included with each microlens layer including one or more microlenses of any desired size.

In <FIG> and <FIG>, microlenses <NUM> of array <NUM> are depicted as having curved upper surfaces. An arrangement of this type is shown in detail in <FIG>. As shown, each microlens has a curved upper surface <NUM>. Each curved upper surface may have a uniform radius of curvature or a non-uniform radius of curvature. The width, height, center-to-center spacing between microlenses (pitch), radius of curvature, and contact angle (e.g., the angle at which the curved upper surface of a given microlens meets a curved upper surface of an adjacent microlens) of the microlenses may be tuned to optimize the display performance.

The example of <FIG> is merely illustrative. In general, each microlens <NUM> may have any desired shape. As shown in <FIG>, each microlens <NUM> (sometimes referred to as a light focusing feature <NUM>) may have a triangular cross-sectional shape (e.g., associated with a pyramidal shape, triangular prism shape, etc.). Each microlens may have surfaces that meet at an angle <NUM> and may be at an angle <NUM> relative to adjacent microlenses. The width, height, center-to-center spacing between microlenses, angle <NUM>, and angle <NUM> of the microlenses may be tuned to optimize the display performance. In the example of <FIG>, each microlens has an isosceles triangular cross-section. This example is merely illustrative. If desired, the microlens may have any other type of triangular cross-sectional shape.

<FIG> shows another example of a microlens shape that may be used in the pixels <NUM>. In <FIG>, each microlens has a planar upper surface <NUM> that is parallel to lower surface <NUM>. This may be referred to as a pillar-shaped microlens. The width of upper surface <NUM>, the width of lower surface <NUM>, the center-to-center spacing between microlenses, the height of the microlens, and the contact angle between adjacent microlenses may be tuned to optimize the display performance.

Another possible arrangement for microlens array <NUM> is shown in <FIG> shows an example where microlenses having different cross-sectional shapes are incorporated in a single display. As shown, microlenses <NUM>-<NUM> and <NUM>-<NUM> may have cross-sectional shapes that are right triangles. These cross-sectional shapes may be symmetric about a vertical axis. Additionally, microlens array <NUM> includes microlenses <NUM>-<NUM> and <NUM>-<NUM> that have cross-sectional shapes that are right trapezoids (trapezoids that have at least two right angles). The cross sectional shapes of microlenses <NUM>-<NUM> and <NUM>-<NUM> may also be symmetric about a vertical axis (e.g., the same vertical axis as microlenses <NUM>-<NUM> and <NUM>-<NUM>).

The microlens shapes shown in <FIG> (or any other desired microlens shape) may be used in any of the aforementioned embodiments if desired. Each pixel in the display may be covered by one or more microlenses as shown in in any of <FIG> and <FIG>. The microlens arrangement for each pixel may be the same across the display or different pixels may have different microlens arrangements. The features of <FIG> and <FIG> may be used in any combination. For example, any pixel may optionally include or omit low-index layer <NUM>, may use a diffusive layer, opaque layer, or transparent polymer around LED <NUM>, may optionally include or omit the opaque masking layer <NUM>, may have stacked microlenses of any desired widths and heights, may include microlenses and overcoats formed from any desired materials, may include an overcoat layer between microlens layers, etc. Similarly, any of these combinations may use microlenses <NUM> of any shape (e.g., as in <FIG>, or <FIG>).

In one illustrative example, the microlens stack over each pixel may be optimized based on the wavelength of light emitted by each pixel. Consider an example where the display includes red, blue, and green light-emitting diodes. Instead of all of the pixels in the display having the same microlens stack, each color of LED may be covered by the same microlens stack. In this case, all of the red pixels would have the same, first microlens stack, all of the green pixels would have the same, second microlens stack, and all of the blue pixels would have the same, third microlens stack. In another example, two colors may use the same stack and a third color may use a different stack. For example, all of the blue and green pixels may have the same, first microlens stack, and all of the red pixels may have the same, second microlens stack.

Additionally, herein examples are shown of at least two stacked microlens layers. In other possible arrangements, three microlens layers or more than three microlens layers may be included in the microlens stack for additional lens power. In these types of arrangements, three or more microlens may be vertically overlapping.

Claim 1:
A display (<NUM>) comprising;
a substrate (<NUM>);
a light-emitting diode (<NUM>) formed on the substrate (<NUM>);
a microlens array (<NUM>) that is formed over the light-emitting diode (<NUM>), wherein
the microlens array (<NUM>) comprises a plurality of first microlenses (<NUM>) and wherein the microlens
array (<NUM>) has a first width (<NUM>); and a second microlens (<NUM>) that conforms to and covers the microlens array (<NUM>),
wherein the second microlens has a second width (<NUM>) that is greater than the first width, wherein
each one of the first microlenses is formed from a first material having a first index of refraction and wherein the second microlens is formed from a second material having a second index of refraction that is less than the first index of refraction;
characterised by
a low-index layer (<NUM>) that is interposed between the light-emitting diode (<NUM>) and the microlens array (<NUM>), wherein the low-index layer (<NUM>) has a third index of refraction that is less than the second index of refraction and the first index of refraction.