Micro light emitting diode, micro light emitting diode device, display and method thereof

Abstract

The invention relates to various aspects of a [mu]-LED or a [mu]-LED arrangement for augmented reality or light applications, in particular in the automotive field. The [mu]-LEDs are characterized by particularly small dimensions in the range of several [mu] m.

Description

[0001] This invention is a divisional application of the parent application, which is filed on January 29, 2020, with application number 202080023800.9 and invention title "Miniature Light Emitting Diode, Miniature Light Emitting Diode Device, Display and Method Thereof" (PCT International Application PCT / EP2020 / 052191 entered the Chinese National Phase).

[0002] This patent application claims priority to the following German patent applications: DE 10 2019 201114.4, dated January 29, 2019; DE 10 2019 111 766.6, dated May 7, 2019; DE 10 2019 112 124.8, dated May 9, 2019; DE 10 2019 116 313.7, dated June 14, 2019; DE 10 2019 131 506.9, dated November 21, 2019; DE 10 2019 118 251.4, dated July 5, 2019; DE 10 2019 118 082.1, dated July 4, 2019; and DE 10 2019, dated March 29, 2019. 108 260.9, DE 10 2019 on September 20, 2019 125 349.7, DE 10 2019 on May 13, 2019 112 490.5, DE 10 2019 on May 14, 2019 112 604.5, DE 10 2019 on May 14, 2019 112 609.6, DE 10 2019 on January 31, 2019 102 509.5, DE 10 2019 on June 7, 2019 115 479.0, DE 10 2019 on May 14, 2019 112 616.9, DE 10 2019 on May 23, 2019 113791.8, DE 10 2019 110 499.8 on April 23, 2019, DE 10 2019 110523.4 on April 23, 2019, DE 10 2019 130 934.4 on November 15, 2019, DE 10 2019 114321.7 on May 28, 2019, DE 10 2019 127 425.7 on October 11, 2019, DE 10 2019 112639.8 on May 14, 2019, DE 10 2019 112 605.3 on May 22, 2019 113636.9, DE 10 2019 103 365.9 on February 11, 2019, DE 10 2019 116312.9 on June 14, 2019, DE 10 2019 115 991.1 on June 12, 2019, DE 10 2019 125875.8 on September 25, 2019, DE 10 2019 127 424.9 on October 11, 2019, DE 10 2019 118085.6 on July 4, 2019, DE 10 2019 125 336 on September 20, 2019.5. DE 10 2019 113793.4 on May 23, 2019; DE 10 2019 110 500.5 on April 23, 2019; DE 10 2019 111 767.4 on May 7, 2019; DE 10 2019 121 672.9 on August 12, 2019; DE 10 2019 118 084.8 on July 4, 2019; DE 10 2019 113 768.3 on May 23, 2019; DE 10 2019 113 792.6 on May 23, 2019; DE 10 2019 110 on April 23, 2019. 497.1, DE 10 2019 114 442.6 dated May 29, 2019, DE 10 2019 129 209.3 dated October 29, 2019, DE 10 2019 130 821.6 dated November 14, 2019, and DE10 2019 130 866.6 dated November 15, 2019, the disclosures of which are incorporated herein by reference, and also claim Danish patent applications DK PA201970059, DK PA201970060, and DK, dated January 29, 2019. The patent claims priority to PA201970061, the disclosure of which is incorporated herein by reference, and also to U.S. patent application US 62 / 937,552, dated November 19, 2019, the disclosure of which is incorporated herein by reference. Technical Field

[0003] This invention relates to miniature light-emitting diodes, miniature light-emitting diode devices, and displays. Background Technology

[0004] The ongoing developments in the Internet of Things (IoT) and communications fields have opened doors to a variety of new applications and designs. These designs and applications offer greater effectiveness and efficiency for development, service, and manufacturing purposes.

[0005] One aspect of the new design involves augmented reality, or virtual reality. The general definition of “augmented reality” is: “an interactive experience of a real environment in which objects in the real world are extended by computer-generated perceptible information.”

[0006] Information is primarily conveyed through visualization, but not limited to visual perception. Sometimes, tactile or other sensory perceptions can be used to augment reality. In the case of visualization, the overlaid sensory visual information can be constructive—that is, supplementing the natural environment—or non-constructive, such as by covering a portion of the natural environment. In some applications, interaction with the overlaid sensory information may also occur in one or another manner. Thus, augmented reality enhances the user's continuous perception of the real environment.

[0007] In contrast, "virtual reality" replaces the user's real environment with a completely simulated one. In other words, while users can perceive the real world at least partially in an augmented reality environment, the environment in virtual reality is completely simulated and may differ significantly from reality.

[0008] Augmented reality (AR) can be used to improve natural environmental conditions, thereby enriching the user experience or supporting them in performing certain tasks. For example, users can use displays with AR capabilities to assist them in performing certain tasks. By overlaying information about real objects to provide clues to the user, it provides additional information, enabling them to act faster, safer, and more efficiently during manufacturing, repair tasks, or other services. In the medical field, AR technology can be used to guide and support doctors in diagnosing and treating patients. In development, engineers can directly experience their test results, making it easier to evaluate the outcomes. In the tourism or events industry, AR can provide users with additional information about attractions, history, and more. AR can also support learning activities or tasks. Summary of the Invention

[0009] The following introduction illustrates various aspects of μ (micro) displays in automotive and augmented reality applications. These aspects include devices, displays, controls, process techniques, and other suitable features for augmented reality and automotive applications. This includes aspects designed to generate light through indicators, displays, etc. Additionally, aspects of control circuitry, power supplies, and optical coupling outputs, light guiding, and light focusing are listed, along with applications of such devices, explained using various examples.

[0010] Because of the various limitations and challenges posed by the small size of the light-generating components, combining various aspects is not only advantageous but often necessary. For ease of handling, this disclosure is divided into several parts with similar topics. However, it should not be explicitly understood that features of one topic cannot be combined with other topics. Rather, aspects from different subject areas must be combined to create displays for augmented reality or other applications or in the automotive field.

[0011] To consider the following solutions, some terms and expressions should be explained to define common and shared understanding. For clarity, the listed terms are generally used herein. However, in individual cases, they may deviate from the intended interpretation, where such deviation is identifiable.

[0012] "Active Matrix Display"

[0013] The term "active matrix display" originally referred to liquid crystal screens containing a matrix of thin-film transistors controlled by LCD (liquid crystal display) pixels. Each individual pixel has a circuit with active components (mainly transistors) and power connections. However, this technology should not be limited to liquid crystals at present, but should specifically refer to the control of μ-LEDs (micro-light-emitting diodes) or μ displays.

[0014] "Active Matrix Carrier Substrate"

[0015] An "active matrix carrier substrate" or "active matrix backplane" refers to the driving device for the light-emitting diodes (LEDs) of a display with thin-film transistor (TFT) circuitry. Here, these circuits can be integrated into or applied to the backplane. The "active matrix carrier substrate" has one or more interface contacts that form an electrical connection with the μ-LED display structure. Therefore, the "active matrix carrier substrate" can be part of or carry an active matrix display.

[0016] "Active layer"

[0017] An active layer is a layer in an optoelectronic device or light-emitting diode (LED) where charge carriers recombine. In its simplest form, an active layer is characterized by regions of two adjacent semiconductor layers with different conductivity types. More complex active layers include quantum wells (see related description), multiple quantum wells, or other structures with additional properties. Structural and material systems can also be used to define the band gap in the active layer (see related description), which defines the wavelength and thus the color of light.

[0018] "Alvarez Lens Device"

[0019] The optical path of the video glasses can be adjusted by using Alvarez lens pairs. The adjustment optics include Alvarez lens devices, particularly rotatable variants with moiré lens devices. Here, beam deflection is determined by the first derivative of the individual phase plate morphologies, approximately z = ax² + by² + cx + dy + e for the radiation direction z and the transverse directions x and y, and is determined by the offset of the two phase plates arranged in pairs in the transverse directions x and y. For alternative designs, pivotable prisms are provided in the adjustment optics.

[0020] Augmented Reality (AR)

[0021] This is an interactive experience of a real-world environment, where the filmed project is located in the real world and enhanced by computer-generated perceptible information. Augmented reality is understood as a computer-aided extension of the perception of reality through such computer-generated perceptible information. This information can appeal to all human senses. However, augmented reality often refers only to the visual representation of information, i.e., images or videos with computer-generated additional information or virtual objects added through fade-in / overlay. Applications and explanations of how augmented reality works can be found in the introduction to the examples and below.

[0022] "car"

[0023] "Automotive" generally refers to motor vehicles or the automotive industry. Therefore, the term is intended to include this branch, but also all other industry branches, including microdisplays or general luminous indicators with very high resolution and μ-LEDs.

[0024] "band gap"

[0025] The energy gap between the valence band and conduction band of a solid is called the band gap, also known as the band gap or band exclusion zone. Its electrical and optical properties depend largely on the size of the band gap. The size of the band gap is usually expressed in electron volts (eV). The band gap is used to distinguish metals, semiconductors, and insulators. The band gap can be tuned (i.e., changed) by various measures such as spatial doping to detune the crystal structure or by altering the material system. Material systems with a so-called direct band gap, where the maximum value of the valence band and the minimum value of the conduction band are superimposed in momentum space, allow electron-hole pairs to recombine with emitted light.

[0026] "Prague Grating"

[0027] A Bragg fiber grating is a special optical interference filter etched into an optical waveguide. Wavelengths within the filter bandwidth near λB are reflected. Various methods are used to generate periodic modulation of the refractive index within the fiber core of the waveguide. This creates regions with high and low refractive indices that reflect light of specific wavelengths (bandstop). The center wavelength of the filter bandwidth in a single-mode fiber is determined by the Bragg condition.

[0028] "Directionality"

[0029] Directivity, or directionality, is used to describe the radiation characteristics of μ-LEDs or other light-emitting components. High directionality corresponds to highly directional radiation or a low-radiation cone. Typically, the goal is to achieve a high level of directional radiation to minimize crosstalk between light and adjacent pixels. Consequently, the brightness of the light-emitting component varies depending on the viewing angle, thus differing from a Lambertian emitter.

[0030] Directionality can be altered, for example, by mechanical or other means on the side used for emission. Besides lenses, this includes photonic crystals or columnar structures (pillar structures) arranged on the emission surface of the pixelated array or, in particular, on an arrangement of μ-LEDs. These create a virtual bandgap that reduces or prevents the light vector from diffusing along the emission surface.

[0031] "Far field"

[0032] The terms near field and far field describe the spatial regions surrounding components that emit electromagnetic waves and have distinct characteristics. Typically, these spatial regions are divided into three areas: the reactive near field, the transition field, and the far field. In the far field, electromagnetic waves propagate as plane waves, independent of the radiating element.

[0033] "Screen window effect"

[0034] The screen-door effect (SDE) is a permanently visible image artifact in digital video projectors. The term describes an undesirable, technically relevant dark distance between individual pixels or their projected information, taking the form of a screen. This distance originates from the construction, as the conductive circuitry used for control runs between the individual LCD segments, where light is swallowed up and cannot reach the screen. If small photoelectric light-emitting devices are used, particularly μ-LEDs, or the distance between individual LEDs is too large, the low packing density produced when viewing a single LED can result in a visible difference in pixel areas between bright and dark spots. This so-called screen-door effect is particularly noticeable when viewed from a smaller distance, especially in applications such as VR (virtual reality) glasses. When the illumination differences within a pixel persist periodically across the entire matrix arrangement, the sub-pixel structure is often perceived and annoying. Therefore, the screen-door effect should be avoided as much as possible in automotive and augmented reality applications.

[0035] "Flip Chip"

[0036] Flip chip assembly is a method of fabrication and connection technology used to contact unpackaged semiconductor chips via contact bumps known as "bumps." With flip chip assembly, the chip can be directly mounted without additional interconnects, with its effective contact surface facing down (towards the substrate / circuit carrier) above the bumps. This results in a particularly small housing size and shorter conductor length. Therefore, flip chips are especially suitable for electronic semiconductor components that contact on their back side. Such components may also require special transfer techniques, such as using an auxiliary carrier. In the case of flip chips, the radiation direction is typically opposite to the side of the contact surface.

[0037] "trigger"

[0038] A flip-flop, also commonly known as a bistable switching stage or bistable switching element, is an electronic circuit with two stable output signal states. The current state depends not only on the currently available input signal but also on the state that existed prior to the point in time being considered. There is no time correlation, only event correlation. Due to its bistable nature, a flip-flop can store one bit of data indefinitely. However, unlike other types of memory, a voltage supply must always be guaranteed. Flip-flops are a fundamental component of sequential circuits and an essential part of digital technology, thus forming a basic element in many electronic circuits, from quartz clocks to microprocessors. In particular, as a basic one-bit memory, it is a fundamental element of the static memory module used in computers. Some embodiments may use different types of flip-flops or other buffer circuits to store state information. Their respective input and output signals are digital, meaning they alternate between logical "false" and logical "true". These values ​​are also referred to as "low" 0 and "high" 1.

[0039] Head-up display

[0040] A head-up display (HUD) is a display system or projection device in which a user maintains a certain head posture or gaze as information is projected into the user's field of view. HUDs are augmented reality systems. In some cases, HUDs incorporate sensors that determine the direction or orientation of the user's gaze in space.

[0041] Horizontal LED

[0042] In the case of horizontal LEDs, the electrical connection is located on the common side of the LED. This is typically the back side of the LED, away from the light-emitting surface. Therefore, horizontal LEDs have contacts formed only on the surface side.

[0043] "Interference filter"

[0044] An interference color filter is an optical component that uses the interference effect to filter light in a frequency-dependent manner (i.e., in a color-dependent manner for visible light).

[0045] "Collimation"

[0046] In optics, collimation refers to the parallel direction of diverging rays. The associated lens is called a collimator or condenser. A collimated beam contains mostly parallel rays and therefore has minimal scattering during propagation. Its use in this sense relates to the scattering of light emitted from a light source. A collimated beam emitted from a surface is highly dependent on the angle of radiation. In other words, the radiance (unit power per unit angle of a projected light source area) of a collimated light source varies with increasing angle. Light can be collimated in various ways, such as by using a special lens placed in front of the light source. Therefore, collimated light can also be considered as light with a high degree of directional dependence.

[0047] "Converter Materials"

[0048] Converter materials are materials suitable for converting light of a first wavelength into light of a second wavelength, shorter than the second. These include various permanent inorganic and organic dyes as well as quantum dots. Converter materials can be applied and constructed in a variety of processes.

[0049] "Lambert Launcher"

[0050] The so-called Lambertian radiation characteristic is required in many applications. This means that the luminescent surface ideally has a uniform radiation density on its surface, resulting in a vertically circular distribution of radiation intensity. Since humans can only assess brightness with their eyes (brightness is the luminous equivalent of illuminance), such Lambertian materials appear equally bright regardless of the viewing direction. This uniform, angle-independent brightness can be an important quality factor, especially for curved and flexible display surfaces, which is sometimes difficult to achieve with currently available displays due to their structure and LED technology.

[0051] LEDs and μ-LEDs are similar to Lambertian emitters and emit light at a large spatial angle. Depending on the application, further steps can be taken to improve radiation characteristics, or greater directionality can be attempted (see related notes).

[0052] "Conductivity type"

[0053] The term "conductivity type" refers to the majority (n- or p-type) charge carriers in a given semiconductor material. That is, a semiconductor material doped with n (negative) type is considered to be of n conductivity type. Similarly, if a semiconductor material is n-type, then it is n-type doped. The term "active" region in a semiconductor refers to the boundary region between an n-type doped layer and a p (positive)-type doped layer. Radiative recombination of p-type and n-type charge carriers occurs in this region. In some embodiments, the active region is further constructed and includes, for example, a quantum well or quantum dot structure.

[0054] "Light field display"

[0055] A display technology that projects raster images directly onto the retina of the eye is called a Virtual Retinal Display (VNA) or Light Field Display. The user gains the impression of a canvas floating in front of them. Light Field Displays can be provided as glasses, projecting raster images directly onto the user's retina. Using a Virtual Retinal Display, an image is created within the user's eye through direct projection of the retina. Light Field Displays are augmented reality systems.

[0056] "Plate printing" or "photolithography"

[0057] Photolithography is one of the core methods in semiconductor and microsystems technology, used to manufacture integrated circuits and other products. In this process, the image of a photomask is transferred onto a photosensitive photoresist through exposure. Subsequently, the exposed areas of the photoresist are dissolved (or the unexposed areas can also be dissolved when the photoresist cures under light). This forms a lithographic mask, which can be further processed through chemical and physical processes, such as applying material to the open areas or etching recesses in the open areas. The remaining photoresist can then be removed.

[0058] “μ-LED”

[0059] μ-LEDs are optoelectronic devices with edge lengths less than 70 μm, particularly less than 20 μm, and especially in the range of 1 μm to 10 μm. Another range is between 10 and 30 μm. This results in a range of several hundred μm. 2 Up to tens of μm 2 The area of ​​a μ-LED is approximately 60 μm², with an edge length of approximately 8 μm. In some cases, the edge length of a μ-LED is 5 μm or less, resulting in a size less than 30 μm². For example, the typical height of such a μ-LED is between 1.5 μm and 10 μm.

[0060] Besides classic lighting applications, μ-LEDs are primarily used in displays. Here, μ-LEDs form pixels or subpixels and emit light of a specified color. Due to their small pixel size and high density at close range, μ-LEDs are also suitable for small, monolithic displays used in AR applications.

[0061] Due to the extremely small size of μ-LEDs, their production and processing are significantly more difficult compared to previous large LEDs. This also applies to other components such as contact lenses, packaging, and lenses. Some aspects feasible in large optoelectronic components cannot be achieved in μ-LEDs, or must be achieved in different ways. In this respect, μ-LEDs are therefore significantly different from traditional LEDs, i.e., light-emitting elements with an edge length of 200 μm or more.

[0062] μ-LED array

[0063] See Microdisplay

[0064] "Miniature display"

[0065] A microdisplay, or μ-LED array, is a matrix with a large number of pixels arranged in prescribed rows and columns. Functionally, a μ-LED array typically forms a matrix primarily composed of μ-LEDs of the same type and color. Therefore, it provides a larger surface area for illumination. On the other hand, the purpose of a μ-display is to transmit information, which often also necessitates different colors or positional control for each individual pixel or subpixel. A microdisplay can consist of multiple μ-LED arrays, formed together on a backplane or other carrier. However, μ-LED arrays can also be used to form microdisplays.

[0066] Each pixel is on the order of a few μm, similar to a μ-LED. Therefore, a μ-display with 1920×1080 pixels, each with a 5μm μ-LED, and directly adjacent pixels has an overall size of 10 mm². In other words, a microdisplay or μ-LED array is a small-scale device implemented using μ-LEDs.

[0067] Microdisplays or μ-LED arrays can be formed from a single, identical component. The μ-LEDs in a μ-LED array can be formed monolithically. Such microdisplays or μ-LED arrays are called monolithic μ-LED arrays or microdisplays.

[0068] Alternatively, both components can be formed by growing μ-LEDs individually on a substrate and then arranging them individually or in groups on a carrier using a so-called pick-and-place process, maintaining a certain distance between them. Such a microdisplay or μ-LED array is referred to as non-monolithic. In a non-monolithic microdisplay or μ-LED array, other distances between individual μ-LEDs are also possible. These distances can be flexibly chosen depending on the application and implementation. Therefore, such a microdisplay or μ-LED array can also be referred to as a pitch-extended component. In a pitch-extended microdisplay or μ-LED array, the μ-LEDs are arranged at greater distances when delivered to the carrier than they are on the growth substrate. In a non-monolithic microdisplay or μ-LED array, each individual pixel may each include a blue-emitting μ-LED, a green-emitting μ-LED, and a red-emitting μ-LED.

[0069] To leverage the advantages of both monolithic and non-monolithic μ-LED arrays within a single module, monolithic μ-LED arrays can be combined with non-monolithic μ-LED arrays in a microdisplay. This allows the microdisplay to be used for different functions or applications. Such a display is called a hybrid display.

[0070] "μ-LED nanopillars"

[0071] μ-LED nanopillars are typically a stack of semiconductor layers with an active layer, thus forming a μ-LED. The edge length of a μ-LED nanopillar is less than its height. For example, the edge length of a μ-LED nanopillar is approximately 10 nm to 300 nm, while the height of the device may be 200 nm to 1 μm or higher.

[0072] "μ column"

[0073] μ-pillars or pillars specifically refer to a geometric structure, particularly a rod or bar, or generally a slender, cylindrical structure. The spatial dimensions of manufactured μ-pillars range from μm to nm. Therefore, nanopillars are also included herein.

[0074] "Nanopillars"

[0075] In nanotechnology, nanopillars are a design concept for nanoscale objects. Each of them ranges in size from approximately 10 nm to 500 nm. They can be synthesized from metallic or semiconducting materials. The aspect ratio (length divided by width) is 3 to 5. Nanopillars are made through direct chemical synthesis. A combination of ligands acts as a shape control agent and attaches to different faces of the nanopillar with varying strengths. This allows for different designs of nanopillars with different growth rates to produce an elongated object. μLED nanopillars are such nanopillars.

[0076] Miniature LED

[0077] Its size ranges from 100μm to 750μm, especially in the range greater than 150μm.

[0078] Moiré effect and Moiré lens array

[0079] The moiré effect refers to the noticeably coarser gratings produced by the superposition of regular, finer gratings. The resulting pattern, resembling a pattern from interference, is a special case of aliasing caused by undersampling. In signal analysis, aliasing occurs when the signal being sampled contains frequency components higher than half the sampling frequency. In image processing and computer graphics, aliasing occurs when an image is sampled, resulting in patterns not present in the original image. A moiré lens array is a special case of an Alvarez lens array.

[0080] "Single component"

[0081] A single-unit component refers to a component made from a single part. A typical example of such a component is a single-pixel array, where the array is made from a single part, and the array's μ-LEDs are fabricated together on a carrier.

[0082] "Optical mode"

[0083] A mode is a description of a wave's specific time-static properties. The wave is described as a sum of different modes. These modes differ in their spatial distribution of intensity. The shape of a mode is determined by the boundary conditions of wave propagation. Analysis based on vibration modes can be applied to both standing waves and continuous waves. For electromagnetic waves such as light, lasers, and radio waves, the following types of modes are distinguished: TEM (transverse electromagnetic) mode, TE (transverse electric) or H (magnetic) mode, TM (transverse magnetic) or E (electric) mode. TEM (transverse electromagnetic) mode: Both the electric and magnetic fields are always perpendicular to the direction of propagation. This mode can only propagate when there are two isolated conductors (equipotential surfaces) in a coaxial cable or when there are no electrical conductors in a gas laser or optical waveguide. TE or H mode: Only the electric field component is perpendicular to the direction of propagation, while the magnetic field component points in the direction of propagation. TM or E mode: Only the magnetic field component is perpendicular to the direction of propagation, while the electric field component points in the direction of propagation.

[0084] "Optoelectronic components"

[0085] An optoelectronic component is a semiconductor substrate that generates light through recombination of charge carriers during operation, and then emits light. The emitted light can range from infrared to ultraviolet, with the wavelength depending on various parameters, the material system used, and the doping. Optoelectronic components are also known as light-emitting diodes (LEDs).

[0086] For the purposes of this disclosure, the terms optoelectronic component and light-emitting component are used synonymously. Therefore, in terms of its geometry, a μ-LED (see related description) is a specific type of optoelectronic component. In displays, optoelectronic components are typically monolithic or single components placed on a matrix.

[0087] "Passive matrix backplane" or "passive matrix carrier substrate"

[0088] A passive matrix display is a matrix display in which individual pixels are passively controlled (without additional electronic components for each pixel). The light-emitting diodes (LEDs) of the display can be controlled by the circuitry of an integrated circuit (IC). In contrast, a screen with active pixels controlled by transistors is called an active matrix display. A passive matrix carrier substrate is part of and supports the passive matrix display.

[0089] "Photonic crystal" or "photonic structure"

[0090] A photonic structure can be a photonic crystal, a quasi-periodic, or a deterministic aperiodic photonic structure. A photonic structure generates a band structure for photons through periodic variations in the optical refractive index. This band structure can have a band gap within a specific frequency range. This means that photons cannot propagate through the photonic structure in all spatial directions. In particular, propagation parallel to the surface is generally blocked, but propagation perpendicular to the surface is possible. In this way, the photonic structure or photonic crystal determines propagation in a specific direction. It blocks or reduces the radiation along one direction and thus produces a radiation or a beam of radiation, directed as needed to a spatial region or emission region provided for this purpose.

[0091] Photonic crystals are photonic structures that appear or are generated in transparent solids. Photonic crystals are not necessarily crystals; their name comes from the diffraction and reflection effects of X-rays in crystals, due to their lattice constant. The structural size is equal to or greater than one-quarter of the photon's wavelength, meaning they range from 1 μm to several μm. They are generated using classical photolithography or through self-organizing processes.

[0092] Alternatively, similar or identical properties of photonic crystals can also be produced with aperiodic but still ordered structures. Such structures are in particular quasi-periodic or well-defined aperiodic structures. For example, this could be a helical arrangement of photons.

[0093] In particular, the so-called two-dimensional photonic crystal is mentioned here by way of example, which has a periodic variation of optical refractive index in two spatial directions that are perpendicular to each other, especially in two spatial directions that are parallel to the light emitting surface and perpendicular to each other.

[0094] However, one-dimensional photonic structures, particularly one-dimensional photonic crystals, also exist. One-dimensional photonic crystals exhibit a periodic change in refractive index along a single direction. This direction can extend parallel to the light exit surface. The one-dimensional structure allows beam shaping to occur in a first spatial direction. In a photonic structure, the photonic effect can be achieved in just a few cycles. The photonic structure can be designed, for example, to ensure that electromagnetic radiation is at least approximately collimated relative to the first spatial direction. Therefore, a collimated beam can be generated at least relative to the first spatial direction.

[0095] "Pixel"

[0096] The individual color values ​​of a digital raster graphic, and the surface elements required to record or display these color values ​​in an image sensor or screen with raster control, are called pixels, image points, image cells, or image dots. Therefore, a pixel is a positionable element in a display device and has at least one light-emitting device. Pixels have a definite size, and adjacent pixels are separated by a defined spacing or pixel space. In displays, especially μ displays, three (or several with added redundancy) subpixels of different colors are typically combined into one pixel.

[0097] "planar array"

[0098] A planar array is a substantially flat surface. It is typically smooth and has no protruding structures. Generally, surface roughness is undesirable and does not provide the desired functionality. A planar array is, for example, a monolithic planar array with multiple optoelectronic components.

[0099] Pulse width modulation

[0100] Pulse Width Modulation (PWM) is a type of modulation used to control components, particularly μ-LEDs. A PWM signal controls a switch configured to turn on and off the current flowing through the corresponding μ-LED, thus causing the μ-LED to light up or not. When using PWM, the output provides a square wave signal with a fixed frequency f. During each cycle T (= 1 / f), the relative amount of on-time compared to the off-time determines the brightness of the light emitted by the μ-LED. The longer the on-time, the brighter the light.

[0101] "Quantum trap"

[0102] A quantum well is understood as a potential line in a strip structure within one or more semiconductor materials, which restricts the degree of freedom of a particle to move in one spatial dimension (typically the z-direction). Thus, a charge carrier can only occupy a planar region (the xy-plane). The width of the quantum well determines the quantum mechanical states that the particle can adopt, resulting in the formation of energy levels (sub-bands), meaning the particle can only have discrete (potential) values.

[0103] "complex"

[0104] There is generally a distinction between radiative and nonradiative recombination. The latter produces a photon that can leave the component. Nonradiative recombination results in the generation of acoustic quanta, which heat the component. The ratio of radiative to nonradiative recombination is an important parameter that depends on the component size, among other factors. Typically, the smaller the component, the smaller the ratio, thus increasing nonradiative recombination relative to radiative recombination.

[0105] Refresh time

[0106] The refresh time is the time after which units such as displays must be rewritten to prevent information loss or premature refresh by external factors.

[0107] "Rohchip" or "light-emitting element"

[0108] A light emitter, or virgin chip, is a semiconductor structure fabricated on a wafer and then separated from it. This semiconductor structure is adapted to generate light after electrical contact during operation. Therefore, in this context, a virgin chip is a semiconductor structure containing active layers for generating light. Virgin chips are typically separated after contact, but can also be further processed in array form.

[0109] "Slot antenna"

[0110] A slot antenna is a special type of antenna in which, instead of surrounding the metallic structure with air (as a non-conductor) in space, an interruption is provided in the metallic structure (e.g., a metal plate, waveguide, etc.). This interruption causes the reflection of electromagnetic waves, the wavelength of which depends on the geometry of the interruption. Typically, the interruption follows the dipole principle, but theoretically it can have any other geometry. Therefore, a slot antenna comprises a metallic structure with a cavity resonator whose length is on the order of the visible light wavelength. The metallic structure can be arranged in or surrounded by an insulating material. The metallic structure is typically grounded to establish a certain potential.

[0111] Field of view

[0112] The field of view (FOV) refers to the area within the field of view of an optical device, solar sensor, camera's image surface (film or recording sensor), or perspective display where events or changes can be perceived and recorded. The field of view is specifically the area that a person can see without moving their eyes. Regarding augmented reality and prominent objects placed in front of the eyes, the field of view includes the area specified as multiple angles of view during stable eye fixation.

[0113] "Subpixel"

[0114] A subpixel describes the internal structure of a pixel. Generally, the term "subpixel" is associated with a higher resolution than that expected from a single pixel. A pixel can also contain several smaller subpixels, each emitting a different color. The overall color impression of a pixel is produced by the mixing of the individual subpixels. Therefore, a subpixel is the smallest locatable unit in a display device. Similarly, a subpixel has a specific size, smaller than the size of the pixel to which it belongs.

[0115] Vertical LED

[0116] Compared to horizontal LEDs, vertical LEDs have electrical connections on both the front and back sides. One of the two sides also forms a light-emitting surface. Therefore, a vertical LED has contacts formed on two opposing main surface sides. Consequently, a conductive yet transparent material must be deposited to ensure electrical contact while allowing light to pass through.

[0117] Virtual Reality

[0118] Virtual reality (VR) refers to the representation and simultaneous perception of reality and its physical properties in a real-time, computer-generated, interactive virtual environment. Virtual reality can replace the operator's real environment with a completely simulated environment.

[0119] On the other hand, it involves the control of the light-emitting elements in the μ-LED display. Currently, the available space under the matrix element pixels is limited, requiring further consideration of how to handle and control each pixel. Due to space constraints, conventional methods and techniques cannot be used. This also applies to designs where the current is controlled by each pixel. Since the space required for μ-LEDs as sub-pixels is significantly smaller than that of ordinary pixels, a more advanced design is needed.

[0120] Furthermore, the driver circuitry should be suitable for providing the current frame rate of 60 Hz to 240 Hz. In this case, it is also necessary, or at least should, to achieve a large luminance dynamic range (1:100,000) or 100 dB per individual pixel. This area is essential for obtaining sufficient contrast and image brightness, even in automotive or augmented reality applications where various external lighting conditions exist.

[0121] Given the already mentioned size of individual μ-LEDs, digitally generated pulse-width modulation (PWM) appears advantageous in both pixelated displays and monolithic arrays. Therefore, this technique should be scalable in terms of both pixel array size and CMOS (Complementary Metal-Oxide-Semiconductor) processing nodes. Digitally generated PWM also allows for calibration of non-uniformity in the pixel array and the desired pixel current.

[0122] Digital nonlinear PWM can process digital codes, thus generating pulse widths through a nonlinear transfer function of the code over the pulse width. Below, various designs suitable for implementation in monolithic displays or pixelated arrays with μ-LEDs are presented due to their unique size and scalability.

[0123] Small display devices with high resolution are particularly ideal for AR systems, such as heads-up displays or glasses with light field displays that project raster images directly onto the retina.

[0124] Micro-OLEDs have been proposed for use in μ-displays with active pixel-sized light sources. Their drawbacks include insufficient brightness and limited lifespan. An alternative to self-emissive light sources is the use of μ-LEDs arranged in a matrix, such as GaN- or InGaN-based μ-LEDs, which promise long lifespan, high efficiency, and fast response time. These are particularly well-suited for display devices with high packing density to form high-resolution μ-displays.

[0125] The starting point is a display device comprising an IC substrate and a monolithic pixelated optical chip mounted thereon. As used herein, the monolithic pixelated optical chip is understood as a matrix-shaped array of light-emitting photoelectric sources formed on a coherent chip substrate using a common fabrication process. Some of the structures disclosed herein can be fabricated in a matrix. These include, for example, antenna structures, vertical or horizontal μ-pillars, paired columnar structures with converter material between μ-LEDs, or μ-LEDs along a specific crystal orientation, to name a few non-limiting examples. These light sources are designed as μ-LEDs.

[0126] The IC substrate component has a monolithic integrated circuit, which is produced by a common manufacturing process. In addition, IC substrate contacts are arranged in a matrix on the top side of the IC substrate component facing the monolithic pixelated optical chip.

[0127] A monolithically pixelated optical chip includes a sequence of semiconductor layers having a first semiconductor layer and a second semiconductor layer, the first semiconductor layer having a first doping and the second semiconductor layer having a second doping, the polarity of the charge carriers in the first semiconductor layer being different from the polarity of the charge carriers in the second semiconductor layer. The first and second semiconductor layers preferably extend laterally throughout the monolithically pixelated optical chip. For one design, the first semiconductor layer may have p-type doping and the second semiconductor layer may have n-type doping. Reverse doping is possible, as with using several identically doped sublayers for at least one semiconductor layer, these sublayers differing in doping intensity and / or semiconductor material. In particular, the sequence of semiconductor layers can form a double heterostructure. Between the first and second semiconductor layers, there is a region with a junction, where a light-emitting active region is formed during display operation. For a feasible design, the active region is located in a doped or undoped active layer disposed between the first and second semiconductor layers and has, for example, one or more quantum well structures.

[0128] Each light-emitting photoelectric source in the pixelated optoelectronic chip is a μ-LED, arranged in a matrix. Each μ-LED has a back surface facing the IC substrate assembly and a first light source contact that is contactively adjacent to and conductively connected to one of the IC substrate contacts. In other words, each μ-LED in the pixelated optical chip is designed to include a region of one of the aforementioned active layers. Between adjacent μ-LEDs, the active layer or another of the aforementioned layers can be interrupted to avoid crosstalk.

[0129] The inventors have realized that a display device with high packing density and simplified manufacturing can be achieved if the projected area of ​​the first light source contact on the back of the μ-LED is at most half the area of ​​the back of the μ-LED, and the first light source contact is surrounded by the back absorber in the lateral direction. As used herein, the lateral direction is understood to be a direction perpendicular to the stacking direction determined by the surface normal of the average semiconductor layer sequence.

[0130] By applying a first light source contact with a small area, significantly smaller than the pixel area of ​​the allocated μ-LEDs, the lateral narrowing of the current path in the semiconductor stack is achieved. Therefore, the lateral extent of the active region is limited to a μm dimension, allowing individually controllable μ-LEDs to be separated from each other due to localized recombination regions in the semiconductor stack. Advantageously, the pixel size of each μ-LED, currently defined as the maximum face-to-face angle on the back side of the μ-LED, is selected to be <70 μm, preferably <20 μm, and particularly preferably <7 μm. Also significantly smaller is the preferred first light source contact, wherein, for advantageous designs, the projected area of ​​the first light source contact on the back side of the μ-LED occupies at most 25% of the back side area of ​​the μ-LED, preferably at most 10%.

[0131] To limit the lateral extent of the active region, the p- or n-type conductivity of the first and second semiconductor layers is preferably designed to be less than 10. 4 Sm -1 Preferably less than 3×10 3 Sm -1 or more preferably less than 10 3 Sm -1 This limits the lateral expansion of the current path. Additionally, it is advantageous that the thickness of the first semiconductor layer in the stacking direction is at most ten times, and preferably at most five times, the maximum diagonal of the first light source contact in the lateral direction.

[0132] In the improved design, the first light source contact on the monolithic pixelated optical chip is not directly adjacent to the assigned IC substrate contact. Instead, the actual optical chip contact element, whose cross-sectional area is larger than that of the first light source contact, is located below the first light source contact relative to the stacking direction. This measure simplifies the positioning and mutual contact of the monolithic pixelated optical chip on the IC substrate component without compromising the lateral demarcation of the current path.

[0133] According to the invention, a region surrounding the first light source contact of the smaller structure is used to arrange a back-side absorber, which reduces optical crosstalk between adjacent μ-LEDs. Specifically, downward electromagnetic radiation emitted from the active region at the angular location is absorbed as long as the limiting angle with respect to the stacking direction is exceeded. The preferred material for the back-side absorber is a structural layer having silicon, germanium, and gallium arsenide. It is also possible to incorporate graphene or carbon black particles into the back-side absorber.

[0134] The back-side absorber laterally surrounds and extends laterally from the first light source contact, wherein the back-side absorbers of adjacent μ-LEDs are adjacent to each other and preferably integrally constructed. In one design, the back-side absorber extends at least into the first semiconductor layer in the stacking direction. In another design, a portion of the back-side absorber extends within the correspondingly constructed first semiconductor layer and shields the boundary region between adjacent μ-LEDs. For this purpose, reflective radiation blockers can be additionally or alternatively used, such as structured elements made of reflective materials like aluminum, gold, or silver, or made of a dielectric material with a refractive index lower than that of the first semiconductor layer. In another design, the back-side absorber not only has optical functions but can also act as an electrical insulator, limiting current paths from the side.

[0135] The display device has a second light source contact for each μ-LED above the second semiconductor layer along the stacking direction. This second light source contact is made of a transparent material such as indium tin oxide (ITO) and is conductively connected to a large-area contact layer on the front side of the transparent pixelated optoelectronic chip. In an advantageous design, the second light source contact is formed by the large-area contact layer itself, allowing the entire second light source contact of the matrix-arranged μ-LEDs to be used as a common surface contact. In an alternative design to further reduce optical crosstalk, the second light source contacts are adjacent to the contact layer in a contact manner, wherein the second light source contacts of adjacent μ-LEDs are separated from each other in a lateral direction perpendicular to the stacking direction by a front absorber. The front absorber can be composed of a material that absorbs or reflects electromagnetic radiation emitted from the active region. Additionally or alternatively, the front absorber can act as an electrical insulator and contribute to the lateral confinement of the current path to position the recombination region within a μm area.

[0136] For feasible improvements, the front absorber extends in the opposite direction to the stacking direction at least in a portion of the second semiconductor layer. Furthermore, the lower and / or upper sides of the second light source contact and / or the contact layer of the second semiconductor layer and / or the upper side of the second semiconductor layer can have optically effective structures to improve light coupling output.

[0137] The proposed method for manufacturing a display device involves electrically connecting an IC substrate assembly having a monolithic integrated circuit and IC substrate contacts arranged in a matrix to a monolithic pixelated optoelectronic chip. For previously manufactured monolithic pixelated optical chips, a semiconductor layer sequence having a first semiconductor layer and a second semiconductor layer is preferably epitaxially grown. The first semiconductor layer has a first doping, and the second semiconductor layer has a second doping, wherein the polarity of the charge carriers in the first semiconductor layer differs from that in the second semiconductor layer, and the semiconductor layer sequence defines a stacking direction. Furthermore, μ-LEDs arranged in a matrix are applied in the pixelated optical chip, wherein each μ-LED has a back surface facing the IC substrate assembly and a first light source contact that is adjacent to the first semiconductor layer in a contact manner and electrically connected to one of the IC substrate contacts. According to the invention, the first light source contact is sized such that the surface whose normal to its projection surface is perpendicular to the stacking direction occupies at most half the area of ​​the back surface of the μ-LED. Additionally, the first light source contact is surrounded by a back-side absorber in a lateral direction perpendicular to the stacking direction. Attached Figure Description

[0138] The following sections use various design schemes and examples to illustrate some of the aspects mentioned above and summarized in more detail.

[0139] Figure 1A The diagram illustrates some requirements for a so-called μ display or microdisplay device in terms of various dimensions of field of view and pixel spacing in a μ display; Figure 1B A diagram showing the spatial distribution of rod and cone cells in the human eye; Figure 1C A diagram showing the perceptual abilities of the human eye with assigned projection areas; Figure 1D A graph showing the sensitivity of rod and cone cells at different wavelengths is presented; Figure 2A The diagram illustrates some requirements for microdisplays of various sizes in terms of the field of view and collimation of pixels in a μ display; Figure 2B An exemplary design of a pixel array is shown to illustrate... Figure 1A and Figure 2A The parameters represented in the text; Figure 3 A graph showing the required number of pixels depends on the number of fields of view for a given resolution; Figure 4 A cross-sectional view illustrates an embodiment of a display device comprising a monolithic pixel array with a monolithic IC, based on some aspects of the proposed design; Figure 5 A previous embodiment of the proposed display device is shown in cross-section, with a plotted possible optical path. Figure 6 A second embodiment of the proposed display device, having a monolithic pixel array and an IC, is shown in cross-sectional view; Figure 7 A third embodiment of the proposed display device based on other aspects of the proposed principles is shown in cross-sectional view; Figure 8 A fourth embodiment of the proposed display device is shown in cross-section, which has an additional mechanism for light guidance; Figure 9 and Figure 10 Two alternative embodiments are shown for improving the positioning of charge carriers in one of the proposed display devices by utilizing other aspects of this disclosure. Detailed Implementation

[0140] Augmented reality is largely created by a dedicated display that overlays images onto reality. This display can be placed directly in the user's line of sight, i.e., directly in front of them. Alternatively, beam deflection elements can be used to direct light from the display toward the user's eyes.

[0141] In both cases, a display can be implemented, and the user can wear glasses or other visual augmentation devices as part of the device. Google's™ Glasses is an example of such a visual augmentation device, allowing users to overlay certain information about objects in the real world. With Google™ Glasses, the information is displayed on a small screen in front of the glasses. In this respect, the appearance of this add-on device is a key feature of the glasses, combining technological functionality with the design aspects of wearing glasses. Simultaneously, users need glasses that don't have such bulky or easily damaged devices to provide augmented reality functionality. Therefore, one concept is that the glasses themselves become a display or at least one screen, with information projected onto or into a projector.

[0142] In this type of situation, the user's field of view is limited to the size of the glasses. Therefore, the area on which augmented reality can be projected is approximately the size of the glasses lenses. The same but different information can be projected onto or onto both lenses of a pair of glasses.

[0143] In other words, the image experienced by a user while wearing augmented reality glasses should have a resolution that creates a seamless impression, so that the user doesn't perceive augmented reality as a pixelated object or a low-resolution element. Straight bevels, arrows, or similar elements appear as staircase-like outlines at low resolutions, which is distracting for the user.

[0144] To achieve an ideal visual impression, two display parameters are considered important, as they influence the visual impression for a given or known human eye. One is the pixel size itself, the geometry and dimensions of a single pixel, or the area of ​​three subpixels representing that pixel. The second parameter is the pixel pitch, the distance between two adjacent pixels or subpixels, which varies depending on the context. Sometimes, pixel pitch is also referred to as the space between pixels. Larger pixel gaps can be detected by the user and perceived as gaps between pixels, potentially leading to what is known as the "flying screen effect." Therefore, the gap should not exceed a certain limit.

[0145] The maximum angular resolution of the human eye is typically between 0.02 and 0.03 arcminutes, roughly equivalent to 1.2 to 1.8 arcminutes per line. This results in a pixel pitch of 0.6-0.9 arcminutes. Some current mobile phone displays have approximately 400 pixels per inch, resulting in a viewing angle of approximately 2.9° at a distance of 25 cm from the user's eyes, or approximately 70 pixels per degree. Therefore, the distance between two pixels in such a display is within the range of maximum angular resolution. Furthermore, the pixel size itself is approximately 56 μm.

[0146] Figure 1A The pixel spacing is shown, that is, the distance between two adjacent pixels that depends on the field of view. In this respect, the field of view is the extension of the observable world seen at a given moment. This is because human vision is defined as the angle of view in degrees during a stable fixation of the eye.

[0147] In particular, the forward horizontal curvature of the binocular visual field is slightly higher than 210°, while the vertical curvature of the human visual field is approximately 135°. However, the range of visual ability is not uniform across the entire visual field and may vary from person to person.

[0148] Human binocular vision covers approximately 114° horizontally (peripheral vision) and approximately 90° vertically. The remaining degrees on both sides do not constitute binocular vision, but can be considered part of the field of view.

[0149] Furthermore, color vision and the ability to perceive shape and motion further limit the horizontal and vertical fields of vision. The rods and cones responsible for color vision are unevenly distributed.

[0150] This viewpoint Figures 1B to 1DThis was explained in more detail. In the central visual domain, that is, directly in front of the eyes, as required by augmented reality applications, and partly in the automotive field, the eye's sensitivity is very high in terms of spatial resolution and color perception.

[0151] Figure 1B The spatial density of cones and rods per square millimeter is shown, which is related to the angle of the central concave region. Figure 1C The wavelength-dependent color sensitivity of cones and rods is described. In the central region of the fovea, increased cone density (L, S, and M) leads to better color perception. Sensitivity begins to decrease at a distance of approximately 25° around the fovea, as the density of visual cells decreases. Near the edges, color perception decreases further, but contrast vision through rods remains over a wider angular range. Overall, this creates a radially symmetrical visual pattern for the eye, rather than a Cartesian one. Therefore, high resolution of all primary colors is necessary, especially at the center. At the edges, working with an emitter adapted to the spectral sensitivity of rods may suffice (maximum sensitivity 498 nm, see...). Figure 1D And the sensitivity of the eyes).

[0152] Figure 1C The graph of angular resolution A relative to the angular deviation α from the optical axis of the eye illustrates the different perceptual abilities of the human eye. It can be seen that the highest angular resolution A exists within the interval of + / - 2.5° angular deviation α, where the fovea 7 is arranged on the retina 19 with a diameter of 1.5 mm. Furthermore, the location of the blind spot 22 on the retina 19 is plotted, which appears in the region of the optic disc 23, with an angular deviation α of approximately 15°.

[0153] The eye can compensate for this non-constant density, and it can also compensate for so-called blind spots through minute eye movements. This change in the direction or focus of the gaze can be counteracted through appropriate optical systems and eye tracking.

[0154] In addition, even when wearing glasses, the field of vision is further limited; for example, the field of vision of each lens can be within approximately 80°.

[0155] Figure 1AThe pixel pitch on the Y-axis, measured in μm, defines the distance between two adjacent pixels. Different curves, C1 to C7, define the diagonal dimensions of the corresponding displays, ranging from 5mm to approximately 35mm. For example, curve C1 corresponds to a display with a diagonal dimension of 5mm, meaning a side length of approximately 2.25mm. For a field of view of approximately 80°, the pixel pitch of a display with a 5mm diagonal dimension is within the range of 1μm. For larger displays, such as those using curve C7 and a 35mm diagonal dimension, the same field of view can be achieved with a pixel pitch of approximately 5μm.

[0156] However, Figure 1A The curves in the diagram illustrate that a larger field of view is preferred for augmented reality applications, while very high pixel density and small pixel pitch are required to avoid the well-known screen-flying effect. We can now calculate the pixel size for a given number of pixels, a given field of view, and a given diagonal size for a μ display.

[0157] Equation 1 shows the relationship between pixel size D, pixel pitch pp, number of pixels N, and display edge length d. The distance r between two adjacent pixels, calculated from their respective centers, is given by the following equation.

[0158] r = d / 2 + pp + d / 2.

[0159] D = d / N-pp (1)

[0160] N = d / (D + pp)

[0161] Assuming the distance between the monitor (e.g., glasses) and the eye is 2.54 cm (1 inch), then for the roughly estimated 1 arcminute angular resolution above, the distance r between two adjacent pixels is...

[0162] r = tan(1 / 60°) × 30mm

[0163] r = 8.7μm

[0164] Therefore, pixel size is less than 10 μm, especially when a certain space is required between two different pixels. Using the distance r between two pixels and a display with a size of 15 mm × 10 mm, 1720 × 1150 pixels can be arranged on the surface.

[0165] Figure 2BAn arrangement with a carrier 21 is shown, on which a plurality of pixels 20 and 20a to 20c are arranged. Pixels 20 arranged adjacent to each other have a pixel pitch pp, while pixels 20a to 20c are placed on the carrier 21 with a larger pixel pitch pp. The distance between two pixels is given by the sum of the pixel pitch and half the size of each adjacent pixel. Each pixel 20 is configured such that its illumination characteristics, or emission vector 22, are substantially perpendicular to the emission surface of the corresponding LED.

[0166] The angle between the vertical axis on the emitting surface of the LED and the beam vector is defined as the collimation angle. In the example of emission vector 22, the collimation angle of LED 20 is approximately zero. LED 20 emits collinear light and does not expand significantly.

[0167] Conversely, the collimation angle of the emission vector 23 of LED pixels 20a to 20c is very large, and is in the range of approximately 45°. As a result, a portion of the light emitted by LED 20a overlaps with the emission of the adjacent LED 20b.

[0168] The emission of LEDs 20a to 20c partially overlaps, resulting in the superposition of their respective light emissions. If the LEDs emit different colors of light, the result will be a mixture or combination of colors. A similar effect occurs between high-contrast areas, i.e., when LED 20a is dark while LED 20b emits some kind of light. Due to the overlap, the contrast is reduced, and the information at each individual location corresponding to the pixel position is also reduced.

[0169] For displays with a small distance from the user's eyes, such as those mentioned above, a large collimation angle can be quite annoying due to the aforementioned effects and other drawbacks. Users can perceive a large collimation angle and may experience a slight difference in the color of depicted objects, a blurriness, or reduced contrast.

[0170] in this regard, Figure 2A This illustrates the collimation angle in degrees relative to the field of view in degrees, which is independent of a specific display size. For smaller display sizes, such as those in curve C1 (approximately 5mm diagonally), the collimation angle increases significantly depending on the field of view.

[0171] As monitor sizes increase, the requirements for collimation change dramatically. Therefore, even with large monitor geometries, as shown by curve C7, the collimation angle reaches approximately 10° within a 100° field of view. In other words, the collimation requirements increase for larger monitors and larger fields of view. In such monitors, the light emitted from the pixels must be highly collimated to avoid or reduce the aforementioned effects. Therefore, when providing users with monitors that offer large fields of view, even if the monitor's geometry is relatively large, robust collimation capabilities are necessary.

[0172] Based on the above charts and equations, it can be deduced that as the geometry and field of view of a display increase, the requirements regarding pixel pitch and collimation become increasingly challenging. As Equation 1 shows, the size of a display increases dramatically with the number of pixels. Conversely, a large field of view requires a large number of pixels to achieve sufficient resolution and avoid screen flickering or other interference effects.

[0173] Figure 3 The diagram illustrates the number of pixels required to achieve an angular resolution of 1.3 armes. For a field of view of approximately 80°, the number of pixels exceeds 5 million. It can be quickly estimated that the pixel size for QHD resolution is far less than 10μm, even with a display size of 15mm × 10mm. In total, an augmented reality display with resolutions in the HD range (i.e., 1080p) requires a total of 2,073,600 pixels. This would cover a field of view of approximately 50°. The number of pixels arranged in a 10 × 10mm display with a pixel spacing of 1μm would result in a pixel size of approximately 4μm.

[0174] The above considerations make it clear that the challenges in terms of resolution, collimation, and field of view suitable for augmented reality applications are considerable. Therefore, the technical implementation of such displays also places very high demands on them.

[0175] Traditionally used technologies were designed for manufacturing displays with LED edge lengths in the range of 100 μm or even longer. However, they cannot automatically scale to the 70 μm and below dimensions required here. Pixel sizes of a few μm and distances of a few μm or even smaller, closer to the order of magnitude of the generated light wavelength, require new processing technologies.

[0176] Furthermore, new challenges have emerged in light collimation and guidance. For example, optical lenses that can be easily structured into larger LEDs and calculated using classical optics cannot be directly scaled down to such small sizes without using Maxwell's equations. In addition, it is nearly impossible to manufacture small lenses without large errors or deviations. In some variants, quantum effects affect the behavior of pixels of these sizes and must be taken into account. Tolerance requirements in the production or transmission techniques of pixels on auxiliary carriers or matrix structures are becoming increasingly stringent. Pixels must also be contactable and individually controllable. Conventional circuitry has space requirements that, in some cases, exceed the pixel area, creating placement and space issues.

[0177] Therefore, new designs for controlling and accessing pixels of this size may be entirely different from traditional technologies. Finally, a key focus is on the power consumption of such displays and controls. Low power consumption is particularly desirable for mobile applications.

[0178] In summary, many designs suitable for larger pixel sizes require extensive modifications before successful scaling down. While a design suitable for producing 200 μm LEDs can be easily scaled up to 2000 μm LEDs, scaling down to 20 μm is much more difficult. Many documents and literature disclosing such designs do not account for the various effects and increased requirements of extremely small sizes, and therefore are not directly applicable to or limited to pixel sizes significantly larger than 70 μm.

[0179] The following sections present various aspects of the structure and fabrication of μ-LED semiconductors, including processing, optical coupling output and light guidance, display, and control. These are suitable for designing displays with pixel sizes of 70 μm and below. Some designs are specifically designed for the production, optical coupling output, and control of μ-LEDs with edge lengths less than 20 μm, particularly less than 10 μm. It goes without saying that the designs presented here regarding these aspects can and should be combined with each other. For example, this relates to the design of μ-LEDs with designs for producing coupled output light. Specifically, μ-LEDs implemented, for example, by methods to avoid edge defects or by current conduction or current contraction, can provide optical coupling output structures based on photonic crystal structures. Special control can also be implemented for displays with variable pixel sizes. Light guidance with piezoelectric mirrors can be implemented in μ-LED displays based on slot antennas or conventional monolithic pixel matrices.

[0180] In some of the design options and aspects described below, additional examples of various design options or combinations of their aspects are indicated. These are intended to clearly show that those skilled in the art can combine the aspects, design options, or parts thereof with each other. Some applications require specially modified designs, while others have lower technical requirements. Automotive applications and displays, for example, typically have larger pixel edge lengths due to the greater distance from the user. In particular, there are classic pixel applications or virtual reality applications, in addition to augmented reality applications. In the context of this disclosure, this is also clearly desirable for realizing μ-LED displays with pixel edge lengths below 70 μm.

[0181] For displays, the control of each pixel is implemented independently and separately from the next pixel to provide the appropriate flexibility to visualize any type of information. In short, it requires individual control of a 1920×1080 pixel matrix, much like in a regular television or a monitor with approximately 2 million pixels. Besides the challenge of handling so many pixels individually, displays in augmented reality and automotive applications are also extremely small, with pixel sizes (as mentioned at the beginning) of only a few μm.

[0182] In conventional drivers used for larger pixel sizes and displays, analog drivers and digital circuitry can be easily placed below the corresponding pixels.

[0183] In this pixel size, for example, 200μm 2 In conventional displays, the available space "below" the pixel is on the same order of magnitude. The driver circuitry can be easily implemented within this available space, and the size of the pixel itself is not a limiting factor. However, as pixel sizes decrease, the available space becomes insufficient for conventional circuitry techniques. Similar problems arise when using digital circuitry techniques with the material systems used to date. Silicon technology offers the possibility of further reducing circuit size, but this material system cannot be simply combined with existing materials to produce blue or green light.

[0184] Therefore, new designs are needed, which can be broadly divided into two areas. The first area involves new designs for transistors, capacitors, or other components. These designs may exist for entirely different applications or technical fields, but cannot be combined with the material system used for μ-LEDs, nor with μ-LEDs themselves. The second area involves circuitry and the principles of controlling μ-LED pixels. In short, the digital transmission paths used to locate pixels in rows and columns, and the corresponding row and column decoding, all occupy space. The same applies to the implementation of current sources or buffers to apply the necessary current to each μ-LED. The construction of μ-LEDs in monolithic and individually assembled configurations allows for different designs, thus enabling the use of new methods to position μ-LEDs in displays for optimal visual effects.

[0185] Small, high-resolution displays are particularly ideal for AR systems, such as head-up displays or glasses with light field displays that project raster images directly onto the retina. For μ displays with pixel-sized light sources, matrix-based μ displays based on GaN or InGaN have been proposed.

[0186] Figure 4 A display device comprising an IC substrate component and a monolithic pixelated optoelectronic chip disposed thereon is illustrated as a first embodiment. An IC substrate component 1 is shown, having monolithic integrated circuits 2.1, 2.1, 2.3 and IC substrate contacts 3.1, 3.2, 3.3 controlled by them. The IC substrate component 1 may have other components for control, power supply, and signal exchange with peripheral devices, wherein an interface 23 is exemplarily depicted. In this context, reference should be made to other different designs in this application, which describe digital and analog circuit components in more detail.

[0187] IC substrate contacts 3.1, 3.2, and 3.3 are designed to be metallic, and each is separated by an insulating layer. A monolithically pixelated optical chip 4 is arranged on the IC substrate component 1 and electrically and mechanically connected to the IC substrate contacts 3.1, 3.2, and 3.3. More precisely, contacts 22.1m, 22.2, and 22.3 are mounted on the surface of the pixelated optoelectronic chip 4 in such a way that they are opposite to the IC substrate contacts 3.1, 3.2, and 3.3 when precisely positioned on the IC. As shown, the contacts each have the same dimensions; therefore, even a small offset will not have any negative impact, and short circuits are avoided. Various techniques for this type of connection are disclosed in this application.

[0188] The monolithically pixelated optical chip 4 includes a semiconductor layer sequence 5 having a first semiconductor layer 6 and a second semiconductor layer 7, wherein the first semiconductor layer 6 is p-type doped and the second semiconductor layer 7 is n-type doped. The first semiconductor layer 6 and the second semiconductor layer 7 are placed over a large area and extend substantially over the entire monolithically pixelated optoelectronic chip 4 in a lateral direction perpendicular to the stacking direction 8. Design variations of the semiconductor layers 6, 7 with different doping intensities or made of different semiconductor materials are not shown in detail. Between the first semiconductor layer 6 and the second semiconductor layer 7 is an active layer (not shown in detail) having a quantum well, in the region of which an active region 24 emitting electromagnetic radiation is formed when current flows through the semiconductor layer sequence 5 in the stacking direction 8.

[0189] A transparent contact layer 16, for example made of indium tin oxide (ITO), is applied planarly on the front side 17 above the semiconductor layer sequence 5. To achieve a small pixel size P, in this embodiment, the μ-LED 9 has a diagonal size of 2 μm to 5 μm, and the first light source contacts 10.1, 10.2, and 10.3 on the underside of the first semiconductor layer 6 facing the IC substrate assembly 1 are substantially smaller than the pixel size P. For this embodiment, the maximum diagonal MD of the first light source contacts 10.1, 10.2, and 10.3 (300 nm) is selected to satisfy this feature, thereby ensuring that the projection surface 13 of the first light source contacts 10.1, 10.2, and 10.3 on the back side 12 of the μ-LED corresponds to at most half the area of ​​the back side 12 of the μ-LED. For this embodiment, in the case of a diagonal of 4 μm, the projection surface 13 has approximately 5% of the area of ​​the back side of the μ-LED back side 12. This results in a laterally defined current path 25 within the μ-LED 9 between the first light source contact 10.2 and the second light source contact 11 formed by a segment of the transparent contact layer 16, wherein this current path leads to the active region 24 defined in the lateral direction. Furthermore, nonradiative recombination at the edges of the active region 24 is suppressed. To improve the lateral demarcation of the current path 25, the first semiconductor layer 6 and the second semiconductor layer 7 are preferably doped such that their p- or n-type conductivity is less than 10. 4 Sm -1 Preferably less than 3×10 3 Sm -1 Further preference is given to those with a value of less than 10. 3 Sm -1 Furthermore, it is advantageous to select a smaller layer thickness SD for the first semiconductor layer 6. Preferably, the layer thickness SD of the first semiconductor layer 6 in the stacking direction 8 is at most ten times, and more preferably at most five times, the maximum diagonal MD of the first light source contacts 10.1, 10.2, and 10.3 in the lateral direction.

[0190] According to the present invention, the first light source contact 10.2 is surrounded by back-side absorbers 15.1 and 15.2 with light-blocking function in a transverse direction perpendicular to the stacking direction 8, wherein the back-side absorbers 15.1 and 15.2 are preferably composed of silicon, germanium, or gallium and / or have interlayers containing graphene or carbon black particles. (From the first embodiment) Figure 5 As can be seen from the optical path 26 shown, this measure reduces crosstalk from the controlled μ-LED 9 to adjacent pixels.

[0191] for Figure 6The second embodiment shown uses the same reference numerals for components corresponding to those in the first embodiment. A three-dimensional structure on the upper side of the second semiconductor layer 7 is shown, which improves the coupling output of light to the front side 17. It can be seen that the degree of total internal reflection is reduced and the coupling output cone is enlarged. For alternative design variants not shown in detail, 17 Fresnel lensing sections are provided on the front side. In another alternative, a photonic crystal structure is arranged on the surface. This measure is described in detail in this application. In some designs, some structures are arranged there above the μ-LED and also extend at least partially into the active layer. This type of combination is also possible to produce a contraction and localization of the recombination region.

[0192] Figure 7 A third embodiment with back-side absorbers 15.2, 15.2 is shown, which have sub-segments 27.1, 27.2 extending into the semiconductor layer sequence 5. These sub-regions further shield the boundary regions between adjacent μ-LEDs 9. For sub-segments 27.1, 27.2, structured elements made of reflective materials such as aluminum, gold, or silver, or of dielectric materials, with a refractive index lower than that of the first semiconductor layers 6, 7, can be used. For improved design, sub-segments 27.1, 27.2 additionally improve the lateral delimitation of the current path.

[0193] exist Figure 8 The fourth embodiment shown further reduces optical crosstalk between adjacent μ-LEDs 9 through front absorbers 21.1, 21.2, 21.3, and 21.4, which laterally surround the second light source contacts 11.1, 11.2, and 11.3. If the front absorbers 21.1, 21.2, 21.3, and 21.4 are designed to be electrically insulated, the lateral confinement of the current path used for localization of the active region 24 can be further improved.

[0194] In the embodiment shown in the figure, optical chip contact elements 22.1, 22.2, and 22.3 are arranged between the first light source contacts 10.1, 10.2, and 10.3 and the corresponding IC substrate contacts 3.1, 3.2, and 3.3. The cross-sectional area of ​​the photoelectric chip contact elements 22.1, 22.2, and 22.3 is larger than that of the first light source contacts 10.1, 10.2, and 10.3, so the monolithically pixelated photoelectric chip 4 can be contacted on the IC substrate assembly 1 in a simplified manner.

[0195] Figure 9 It shows that it is basically based on Figure 4This is an alternative design to the previous example. However, additional measures are taken to limit current and prevent optical and electrical crosstalk. In particular, after applying layer 6 and the active layer, a trench 20 is created between the middle and right μ-LEDs. This trench has optically reflective but also insulating material (at least on the trench walls). The latter prevents short circuits between pixels, while the former prevents optical crosstalk. A larger trench is created between the left-hand pixel and the middle pixel, which essentially extends through layers 6 and 7. It forms not only an optical barrier between the pixels or μ-LEDs but also an electrical barrier. Other aspects of this design can be found in the accompanying drawings and elsewhere in this application.

[0196] Figure 10 Another design based on the previous example is shown. The same components again have the same reference numerals. In this design, doping 32 is introduced into layer 6 between the individual μ-LEDs. Doping alters the band structure in this region and causes an increase in the band gap. The injected charge carriers thus experience a field and move away from this region. Therefore, together with the light source contact 10.2, in Figure 10 The reorganization area shown also achieved effective positioning.

[0197] On the other hand, there is a photonic structure 32 applied to the surface of layer 16. Here, a transparent material 31a with a high refractive index (e.g., Nb₂O₅) is directly applied as rods or pillars on the recombination region. The light generated in region 24 is bundled and thus directed by the rods, which act as waveguides. In this design, another rod made of the same material 31b is located between two adjacent pixels. A transparent material with a lower refractive index is filled between them. This results in a refractive index variation similar to the structure described above in the lateral direction. The periodic variation of the refractive index results in an optical bandgap. Its size and design depend particularly on the periodicity; for this purpose, this figure is only an example, and other periodicities can also be considered. This combination of various techniques achieves strong localization on the one hand and good directional radiation on the other. Crosstalk is prevented. The IC structure and relatively large contacts also improve the alignment and fixation of the two layer structures.

[0198] 1. A display device, comprising

[0199] An IC substrate component having a monolithic integrated circuit and IC substrate contacts arranged in a matrix; and

[0200] A monolithic pixelated optical chip includes a sequence of semiconductor layers having a first semiconductor layer and a second semiconductor layer, the first semiconductor layer having a first doping and the second semiconductor layer having a second doping, wherein the polarity of the charge carrier in the first semiconductor layer is different from that in the second semiconductor layer, and the sequence of semiconductor layers defines a stacking orientation; and

[0201] Among them, μ-LEDs are arranged in a matrix in a single pixelated optoelectronic chip; and

[0202] Each μ-LED has a μ-LED back side facing the IC substrate component and a first light source contact, which is adjacent to the first semiconductor layer in a contact manner and is electrically connected to one of the IC substrate contacts respectively; Its features are, The projected area of ​​the first light source contact on the back of the μ-LED is at most equivalent to half the area of ​​the back of the μ-LED; and The first light source contact is surrounded by a back absorber in a lateral direction perpendicular to the stacking direction.

[0203] 2. The display device according to item 931, characterized in that the first semiconductor layer and the second semiconductor layer have a p or n type conductivity of less than 104 Sm-1, preferably less than 3×103 Sm-1, and more preferably less than 103 Sm-1.

[0204] 3. The display device according to any one of the preceding items, characterized in that the thickness of the first semiconductor layer in the stacking direction is at most ten times, preferably at most five times, the maximum diagonal of the first light source contact in the lateral direction.

[0205] 4. The display device according to any one of the preceding items, characterized in that the pixel size of the μ-LED is less than 10 μm, preferably less than 5 μm, and particularly preferably less than 2 μm.

[0206] 5. The display device according to any one of the preceding items, characterized in that the projected area of ​​the first light source contact on the back surface of the μ-LED corresponds to a maximum of 25% of the area of ​​the back surface of the μ-LED, preferably a maximum of 10%.

[0207] 6. The display device according to any one of the preceding items, characterized in that the back-side absorber extends into the semiconductor layer sequence in the stacking direction.

[0208] 7. The display device according to any one of the preceding items, characterized in that, for each μ-LED, a second light source contact made of transparent material is arranged above the second semiconductor layer along the stacking direction, the light source contact being electrically connected to the transparent contact layer on the front side of the monolithic pixelated optoelectronic chip.

[0209] 8. The display device according to item 937, characterized in that the second light source contact is formed by the transparent contact layer itself.

[0210] 9. The display device according to any one of the preceding items, characterized in that the second light source contact is adjacent to the transparent contact layer, and the second light source contacts of the adjacently arranged μ-LEDs are separated from each other in a lateral direction perpendicular to the stacking direction by a front absorber.

[0211] 10. The display device according to any one of the preceding items, wherein the front absorber extends in the opposite direction to the stacking direction until and preferably into the second semiconductor layer.

[0212] 11. The display device according to any one of the preceding items, characterized in that, with respect to the stacking direction, the optical chip contact element is adjacent below the first light source contact, and its cross-sectional area is larger than the cross-sectional area of ​​the first light source contact.

[0213] 12. The display device according to any one of the preceding items further includes: Photoforming structures, particularly microlenses or photonic crystals, are arranged on a monolithic pixelated optoelectronic chip and guide the light emitted by the chip.

[0214] 13. The display device according to any one of the preceding items further includes a light conversion element on the surface of a monolithic pixelated optoelectronic chip.

[0215] 14. The display device according to any one of the preceding items, wherein, in the case of two adjacent μ-LEDs, one μ-LED is designed as a redundant element relative to the other μ-LED, the other μ-LED being provided with a fuse element in the IC substrate assembly, the fuse element being configured to replace the other μ-LED with the redundant element in the event of a failure of the other μ-LED, or to disconnect the redundant element from the power supply when the other μ-LED is functioning normally.

[0216] 15. A method for manufacturing a display device, In this process, an IC substrate component with a monolithic integrated circuit and IC substrate contacts arranged in a matrix, and a single pixelated optoelectronic chip are electrically connected; and In a monolithic pixelated optoelectronic chip, a sequence of semiconductor layers is grown, comprising a first semiconductor layer and a second semiconductor layer. The first semiconductor layer is doped with a first dopant, and the second semiconductor layer is doped with a second dopant. The polarity of the charge carriers in the first semiconductor layer differs from the polarity of the charge carriers in the second semiconductor layer, and the semiconductor layer sequence defines a stacking orientation. In this process, μ-LEDs arranged in a matrix are used in a single pixelated optoelectronic chip. Each μ-LED has a μ-LED back facing the IC substrate assembly and a first light source contact, which is adjacent to the first semiconductor layer in a contact manner and conductively connected to a corresponding one of the IC substrate contacts. Its features are, The size of the first light source contact should be such that its projected area perpendicular to the stacking direction occupies at most half the area of ​​the back side of the μ-LED; and The first light source contact is surrounded by a back absorber in a lateral direction perpendicular to the stacking direction.

Claims

1. A display device, comprising An IC substrate component having a monolithic integrated circuit and IC substrate contacts arranged in a matrix; and A monolithic pixelated optical chip includes a sequence of semiconductor layers having a first semiconductor layer and a second semiconductor layer, wherein the first semiconductor layer has a first doping and the second semiconductor layer has a second doping. The polarity of the charge carrier in the first semiconductor layer is different from that in the second semiconductor layer, and the sequence of semiconductor layers defines the stacking orientation; and Among them, μ-LEDs are arranged in a matrix in a single pixelated optoelectronic chip; and Each μ-LED has a μ-LED back side facing the IC substrate component and a first light source contact, which is adjacent to the first semiconductor layer in a contact manner and is electrically connected to one of the IC substrate contacts respectively; Its features are, The projected area of ​​the first light source contact on the back of the μ-LED is at most equivalent to half the area of ​​the back of the μ-LED; and The first light source contact is surrounded by a back absorber in a lateral direction perpendicular to the stacking direction.

2. The display device according to claim 1, characterized in that, The first semiconductor layer and the second semiconductor layer have a p or n type conductivity of less than 104 Sm-1, preferably less than 3×103 Sm-1, and more preferably less than 103 Sm-1.

3. The display device according to claim 1, characterized in that, The thickness of the first semiconductor layer in the stacking direction is at most ten times, preferably at most five times, the maximum diagonal of the first light source contact in the lateral direction.

4. The display device according to claim 1, characterized in that, The pixel size of μ-LEDs is less than 10μm, preferably less than 5μm, and particularly preferably less than 2μm.

5. The display device according to claim 1, characterized in that, The projected area of ​​the first light source contact on the back of the μ-LED corresponds to a maximum of 25% of the area of ​​the back of the μ-LED, preferably a maximum of 10%.

6. The display device according to claim 1, characterized in that, The back-side absorber extends into the semiconductor layer sequence in the stacking direction.

7. The display device according to claim 1, characterized in that, For each μ-LED, a second light source contact made of transparent material is arranged above the second semiconductor layer along the stacking direction. This light source contact is electrically connected to the transparent contact layer on the front side of the monolithic pixelated optoelectronic chip.

8. The display device according to claim 7, characterized in that, The second light source contact point is formed by the transparent contact layer itself.

9. The display device according to claim 1, characterized in that, The second light source contact is adjacent to the transparent contact layer, and the second light source contacts of the adjacently arranged μ-LEDs are separated from each other in the lateral direction perpendicular to the stacking direction by the front absorber.

10. The display device according to claim 1, characterized in that, The front absorber extends in the opposite direction to the stacking direction until it enters, and preferably into, the second semiconductor layer.

11. The display device according to claim 1, characterized in that, Relative to the stacking direction, the optical chip contact element is adjacent to the first light source contact point below, and its cross-sectional area is larger than that of the first light source contact point.

12. The display device according to claim 1, further comprising: Photoforming structures, particularly microlenses or photonic crystals, are arranged on a monolithic pixelated optoelectronic chip and guide the light emitted by the chip.

13. The display device according to claim 1 further includes a light conversion element on the surface of a monolithic pixelated optoelectronic chip.

14. The display device according to claim 1, wherein, In the case of two adjacent μ-LEDs, one μ-LED is designed as a redundant element relative to the other μ-LED, which is provided with a fuse element in the IC substrate assembly. This fuse element is configured to replace the other μ-LED with the redundant element in the event of a failure, or to disconnect the redundant element from the power supply if the other μ-LED is functioning normally.

15. A method for manufacturing a display device, in, An IC substrate component with a monolithic integrated circuit and IC substrate contacts arranged in a matrix and a single pixelated optoelectronic chip are electrically connected; and In a monolithic pixelated optoelectronic chip, a sequence of semiconductor layers is grown, comprising a first semiconductor layer and a second semiconductor layer. The first semiconductor layer is doped with a first dopant, and the second semiconductor layer is doped with a second dopant. The polarity of the charge carriers in the first semiconductor layer differs from the polarity of the charge carriers in the second semiconductor layer, and the semiconductor layer sequence defines a stacking orientation. In this process, μ-LEDs arranged in a matrix are used in a single pixelated optoelectronic chip. Each μ-LED has a μ-LED back facing the IC substrate assembly and a first light source contact, which is adjacent to the first semiconductor layer in a contact manner and conductively connected to a corresponding one of the IC substrate contacts. Its features are, The size of the first light source contact should be such that its projected area perpendicular to the stacking direction occupies at most half the area of ​​the back side of the μ-LED; and The first light source contact is surrounded by a back absorber in a lateral direction perpendicular to the stacking direction.

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