Miniature light emitting diode structure capable of improving light extraction efficiency

Abstract

The invention provides a miniature light-emitting diode structure. The miniature light-emitting diode structure comprises a lower electrode layer; the ODR total reflection structure is located on the lower electrode layer; the semiconductor light-emitting table top is positioned on the ODR total reflection structure and is used for emitting light; and the upper electrode layer is in contact with the top of the semiconductor light-emitting tabletop. According to the miniature light-emitting diode, the probability that light leaves the light-emitting tabletop is improved by increasing the light-emitting area of the side wall of the miniature light-emitting diode structure, and then the light-emitting efficiency of an LED chip is improved.

Description

Technical Field

[0001] The present invention generally relates to the field of lighting, and more particularly to a micro light emitting diode structure with improved light extraction efficiency. Background Art

[0002] Micro Light Emitting Diode (MLED) technology is a high-pixel density LED flat display technology that uses micron-sized LEDs as pixel elements and is assembled on a control backplane at a micron-sized period. The core structure of a MLED is a PN junction diode, which is composed of direct bandgap semiconductor materials. When the upper and lower electrodes apply a forward bias to the MLED to allow current to flow, electrons and holes recombine in the active region and emit single-color photons at the same time.

[0003] The light emitted by the LED is generated by spontaneous emission and is therefore non-directional, which results in a large divergence angle. The large divergence angle can cause various problems for micro-LED displays. On the one hand, due to the large divergence angle, only a small portion of the light emitted by the micro-LED can be utilized. This significantly reduces the efficiency and brightness of the micro-LED display system. On the other hand, due to the large divergence angle, the light emitted by one micro-LED pixel will illuminate its adjacent pixels, causing optical crosstalk between pixels, loss of clarity, and loss of contrast. Traditional solutions to reduce large divergence angles may not be able to effectively process all the light emitted by the micro-LED, and can only effectively utilize the central portion of the light emitted by the micro-LED, while the light emitted at more oblique angles is not effectively utilized.

[0004] In summary, it is necessary to provide a micro light emitting diode structure that can improve light extraction efficiency or improve light output effect. Summary of the invention

[0005] Based on the prior art, the task of the present invention is to provide a micro light-emitting diode structure, including: a lower electrode layer; an ODR total reflection structure, located on the lower electrode layer; a semiconductor light-emitting table, located on the ODR total reflection structure, emitting light; and an upper electrode layer, in contact with the top of the semiconductor light-emitting table.

[0006] In an embodiment of the present invention, the thickness of the ODR total reflection structure is N times of λ / 4n, where N is a positive integer and λ is the wavelength of light emitted by the semiconductor light-emitting mesa.

[0007] In an embodiment of the present invention, there is an inclination angle between the side wall of the semiconductor light emitting mesa and the bottom of the semiconductor light emitting mesa, and the inclination angle is less than or equal to 90°.

[0008] In an embodiment of the present invention, the thickness of the ODR total reflection structure satisfies: H / Tanθ<(W2-W1) / 2; wherein H is the height from the bottom of the lower electrode layer to the top of the upper electrode layer, θ is the inclination angle and is less than 90°, W1 is the width of the lower electrode layer, and W2 is the pixel pitch at which the micro-light-emitting diode structure is located.

[0009] In an embodiment of the present invention, the ODR total reflection structure comprises, from top to bottom, a combination of a conductive layer and a dielectric layer.

[0010] In an embodiment of the present invention, in the ODR total reflection structure, the conductive layer extends downward to contact the lower electrode layer.

[0011] In an embodiment of the present invention, the downwardly extending portion of the conductive layer is attached to the side wall surface of the dielectric layer.

[0012] In an embodiment of the present invention, the portion of the conductive layer extending downwardly covers the side wall surface of the dielectric layer.

[0013] In an embodiment of the present invention, the material of the dielectric layer is SiO2 or SiN; the thickness of the conductive layer is in the range of 50 to 250 nm.

[0014] In an embodiment of the present invention, the thickness of the ODR total reflection structure is greater than 500 nm.

[0015] In an embodiment of the present invention, the thickness of the ODR total reflection structure is in the range of 500 nm to 1000 nm.

[0016] In an embodiment of the present invention, the ODR total reflection structure is composed of a conductive layer.

[0017] In an embodiment of the present invention, the material of the conductive layer is a transparent conductive layer.

[0018] In an embodiment of the present invention, the material of the conductive layer is one or more of graphene, indium tin oxide ITO, aluminum-doped zinc oxide AZO or fluorine-doped tin oxide FTO.

[0019] In an embodiment of the present invention, the micro-LED structure further includes a passivation layer, and the passivation layer covers the lower electrode layer, the ODR total reflection structure, the light-emitting mesa and the side surface of the upper electrode layer.

[0020] In an embodiment of the present invention, the material of the passivation layer is a dielectric material or an insulating material.

[0021] In an embodiment of the present invention, the material of the passivation layer is one or more of silicon oxide, silicon oxynitride, aluminum oxide, and silicon nitride.

[0022] In an embodiment of the present invention, the micro-LED structure further includes a pixel driving backplane, and the lower electrode layer is located on the pixel driving backplane and is electrically connected to the pixel driving backplane.

[0023] In an embodiment of the present invention, the pixel driving backplane adopts an integrated circuit chip.

[0024] In an embodiment of the present invention, the pixel driving backplane includes a substrate, a driving circuit and a contact pad, each micro light emitting diode structure corresponds to a contact pad, and the contact pad is electrically connected to the lower electrode layer.

[0025] In an embodiment of the present invention, the lower electrode layer is a metal bonding composite layer.

[0026] In an embodiment of the present invention, the material of the lower electrode layer is an alloy of one or more of the following metals: Cr, Al, Ti, Ni, Pt, Au and Sn.

[0027] In an embodiment of the present invention, the inclination angle of the side wall of the semiconductor light-emitting mesa ranges from 45° to 90°.

[0028] In an embodiment of the present invention, the semiconductor light-emitting mesa includes a first type epitaxial layer, a light-emitting layer and a second type epitaxial layer, the first type epitaxial layer is a semiconductor material having a first conductivity type and includes multiple semiconductor layers, the second type epitaxial layer is a semiconductor material having a second conductivity type and includes multiple semiconductor layers.

[0029] In an embodiment of the present invention, the light-emitting layer is a quantum well light-emitting layer.

[0030] The present invention also provides a micro-LED display chip, comprising a micro-LED pixel array, each of which comprises the micro-LED structure.

[0031] In the embodiment of the present invention, by increasing the sidewall light emitting area of ​​the micro-LED, the probability of photons leaving the LED chip can be increased, thereby improving the light extraction efficiency and increasing the proportion of small-angle light emission. At the same time, the micro-LED structure provided by the present invention can also achieve beam shaping and increase the proportion of small-angle light emission. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be further described below in conjunction with specific embodiments with reference to the accompanying drawings.

[0033] Figure 1 A schematic cross-sectional view of a micro light emitting diode structure according to an embodiment of the present invention is shown.

[0034] Figure 2A schematic cross-sectional view of a micro light emitting diode structure according to an embodiment of the present invention is shown.

[0035] Figure 3 A schematic cross-sectional view of a micro-light emitting diode structure array according to an embodiment of the present invention is shown.

[0036] Figure 4 A schematic diagram showing the curve of LEE20 changing with the thickness of the conductive layer.

[0037] Figure 5 A graph showing the light intensity and light emission angle of light emitted by a micro-LED structure according to an embodiment of the present invention. DETAILED DESCRIPTION

[0038] It should be noted that the components in the various figures may be shown exaggeratedly for the sake of illustration and are not necessarily true to scale. In the various figures, identical or functionally identical components are provided with the same reference numerals.

[0039] In the present invention, unless otherwise specified, "arranged on...", "arranged above..." and "arranged above..." do not exclude the existence of an intermediate between the two. In addition, "arranged on or above..." merely indicates the relative positional relationship between two components, and in certain cases, such as after reversing the product direction, it can also be converted into "arranged below or below...", and vice versa.

[0040] In the present invention, each embodiment is only intended to illustrate the aspects of the present invention and should not be construed as limiting.

[0041] In the present invention, unless otherwise specified, the quantifiers "a", "an" and "an" do not exclude the presence of a plurality of elements.

[0042] In the present invention, the term "connected" may refer to both being directly connected to each other or being indirectly connected to each other via an intermediate element.

[0043] In the present invention, the term "configuration" refers to the setting of the shape, structure, material and / or function of the target object to achieve the desired technical effect, wherein "configuration" includes a variety of alternative technical means for achieving the technical effect, which become obvious under the teaching of the present invention.

[0044] It should also be noted that in the embodiments of the present invention, for the sake of clarity and simplicity, only a portion of the parts or components may be shown, but those of ordinary skill in the art will understand that under the teachings of the present invention, the required parts or components may be added according to the needs of the specific scenario. In addition, unless otherwise specified, the features in different embodiments of the present invention may be combined with each other. For example, a feature in the second embodiment may be used to replace a corresponding or functionally identical or similar feature in the first embodiment, and the resulting embodiment also falls within the disclosure scope or recorded scope of the present application.

[0045] It should also be noted that within the scope of the present invention, the terms "same", "equal", "equal to" and the like do not mean that the values ​​of the two are absolutely equal, but allow a certain reasonable error, that is, the terms also cover "substantially the same", "substantially equal", "substantially equal to". By analogy, in the present invention, the terms "perpendicular to", "parallel to" and the like indicating directions also cover the meanings of "substantially perpendicular to" and "substantially parallel to".

[0046] In the embodiment of the present invention, by increasing the side wall light emitting area of ​​the micro light emitting diode, the probability of photons leaving the LED chip can be increased, thereby improving the light extraction efficiency and increasing the proportion of small-angle light emitting.

[0047] Figure 1 FIG. 4 is a schematic cross-sectional view of a micro-light emitting diode structure according to an embodiment of the present invention. Figure 1 As shown, the micro light emitting diode structure includes a pixel driving backplane 110 , a lower electrode layer 120 , a conductive layer 130 , a light emitting mesa 140 , an upper electrode layer 150 , and a passivation layer 160 .

[0048] For convenience, "upper" is used to mean away from the pixel driving backplane 110, "lower" means towards the pixel driving backplane 110, and other directional terms such as top, bottom, above, below, directly below, below, etc. are also interpreted accordingly.

[0049] Micro-LEDs are basic elements that constitute micro-LED pixels. Each micro-LED pixel may include one or more micro-LED structures. Multiple micro-LED pixels are arranged in an array to form a micro-LED display screen or a micro-LED chip. For example, each pixel in a color micro-LED chip may include multiple micro-LED structures of different colors, while each pixel in a monochrome micro-LED chip may include only a micro-LED structure of one color.

[0050] In an embodiment of the present invention, the size of each micro-LED chip does not exceed 1 cm, preferably does not exceed 20 microns. The micro-LED structure is formed in the micro-LED chip in an array form, and the resolution is, for example, 720*480, 640*480, 1920*1080, 1280*720, 2K or 4K. The diameter of the micro-LED structure is in the nanometer range, for example, 20nm to 100nm. In some embodiments, the pitch of the micro-LED array, that is, the minimum center-to-center distance between the micro-LEDs, can be between about 2 microns and about 50 microns. In some embodiments, the number of pixels on the micro-LED chip can be between thousands and millions.

[0051] In some embodiments, the pixel driving backplane 110 can adopt an integrated circuit chip. The pixel driving backplane 110 includes a substrate, a driving circuit and a contact pad 111. Each micro-light emitting diode corresponds to a contact pad 111, and the contact pad 111 is electrically connected to the lower electrode layer 120. Each driving circuit is a pixel driver. In some cases, the driving circuit is a thin film transistor pixel driver or a silicon CMOS pixel driver. In one embodiment, the substrate of the pixel driving backplane 110 is a Si substrate. In another embodiment, the substrate of the pixel driving backplane 110 is a transparent substrate, such as a glass substrate. Examples of other substrates include GaAs, GaP, InP, SiC, ZnO and sapphire substrates. The pixel driving backplane 110 is used to control the lighting and extinguishing of the micro-light emitting diodes in each pixel. In one embodiment, the material of the contact pad 111 is an alloy of one or more of the following metals: Ni, Al, Ti, Cu, Pt and Au.

[0052] In some embodiments of the present invention, the pixel drive backplane can be electrically connected to each micro-LED in the micro-LED array via a separate metal interconnect. In some embodiments, each micro-LED can be electrically controlled individually by the pixel drive backplane. In some embodiments, the pixel drive backplane can be electrically connected to the electrodes of the micro-LED chip via metal interconnects. In some embodiments, a dielectric layer can be formed in the gaps between the micro-LEDs. In some embodiments, a dielectric layer can also be formed in the gaps between the interconnects.

[0053] In one embodiment, the lower electrode layer 120 is a metal bonding composite layer. The light-emitting table 140 of the micro-light-emitting diode can be bonded to the surface of the pixel driving backplane 110 through the metal bonding composite layer 120, and the bonding can be completed by eutectic bonding, hot pressing bonding and transient liquid phase (TLP) bonding. In one embodiment, the metal bonding composite layer 120 can be arranged on the pixel driving backplane 110. In another embodiment, the metal bonding composite layer 120 grows on the pixel driving backplane 110. In one embodiment, the thickness of the metal bonding composite layer 120 is 0.1 micron to 3 microns. In a preferred embodiment, the thickness of the metal bonding composite layer 120 is 0.3μm. In some embodiments, the material of the metal bonding composite layer 120 is an alloy of one or more of the following metals: Cr, Al, Ti, Ni, Pt, Au, Ag and Sn. The metal bonding composite layer 120 may include an ohmic contact layer and a metal bonding layer. In some cases, the metal bonding composite layer 120 includes two metal layers. One of the two metal layers is deposited on a layer above the metal bonding layer in the LED. The corresponding bonding metal layer is deposited on the pixel driving backplane 110. For example, the metal bonding composite layer 120 can be Au Au bonding, Au Sn bonding, Au In bonding, Ti Ti bonding, Cu Cu bonding, or a combination of the above. For example, if Au Au bonding is selected, the two layers of Au require a Cr layer as an adhesive layer and a Pt layer as an anti-diffusion layer respectively. The Pt layer is located between the Au layer and the Cr layer. The Cr and Pt layers are located at the top and bottom of the two bonded Au layers. In some embodiments, when the thickness of the two Au layers is approximately the same, under high pressure and high temperature, the Au on the two layers diffuse mutually to bond the two layers together.

[0054] In some embodiments, the metal bonding composite layer 120 may also function as a reflector to reflect light emitted from the light emitting mesa 140 above.

[0055] In some embodiments, the conductive layer 130 is formed on the bottom surface of the light-emitting mesa 140 to form an electrical connection between the light-emitting mesa 140 and the metal bonding composite layer 120. In some embodiments, the conductive layer 130 can be a conductive transparent layer that is transparent to the light emitted by the light-emitting mesa 140 to improve conductivity and transmittance. In some embodiments, the upper electrode layer 150 is formed on the top surface of the light-emitting mesa 140, and the upper electrode layer 150 is electrically connected to the current spreading structure or the top electrode (not shown).

[0056] In one embodiment, the conductive layer 130, the upper electrode layer 150 and their connecting parts can be a combination of one or more materials such as graphene or indium tin oxide (ITO) or aluminum doped zinc oxide (AZO) or fluorine doped tin oxide (FTO) or other transparent conductive oxides (TCO).

[0057] In some embodiments, the light-emitting mesa 140 may include a first type epitaxial layer 141, a light-emitting layer 142, and a second type epitaxial layer 143. That is, in the three-layer structure, the first type epitaxial layer 141 is closest to the pixel driving backplane 110; the light-emitting layer 142 is located above the first type epitaxial layer 141 and is further away from the pixel driving backplane 110; the second type epitaxial layer 143 is located above the light-emitting layer and is farthest away from the pixel driving backplane 110. In some embodiments, the light-emitting layer 142 is formed by a plurality of stacked quantum well layers, in particular, superlattice stacked quantum well layers. Preferably, the superlattice stacked quantum well layers include a plurality of pairs of quantum well layers stacked with quantum barrier layers. In some embodiments, the first type epitaxial layer 141 is a semiconductor material having a first conductivity type and includes a plurality of semiconductor layers. The main matrix material of the first type epitaxial layer 141 may be, but is not limited to, composed of at least two or more elements of Ga, N, As, P, In, and Al. The first type epitaxial layer 141 includes but is not limited to a waveguide layer, a confinement layer, a transition layer, and a window layer; in addition, an ohmic contact layer may be formed below the window layer. In some embodiments, the second type epitaxial layer 143 is a semiconductor material having a second conductivity type and includes a plurality of semiconductor layers. The main matrix material of the second type epitaxial layer 143 may be but is not limited to at least two or more elements of Ga, N, As, P, In, and Al. In addition, the second type epitaxial layer 143 may include from top to bottom but is not limited to a confinement layer and a waveguide layer; in addition, in some embodiments, an ohmic contact layer may be formed on the confinement layer. The first type epitaxial layer 141 is electrically connected to the conductive layer 130, and the second type epitaxial layer 143 is electrically connected to the upper electrode layer 150.

[0058] In some embodiments, the first conductivity type may be N-type and the second conductivity type may be P-type; or the first conductivity type may be P-type and the second conductivity type may be N-type. The N-type semiconductor epitaxial layer includes but is not limited to N-type Si-doped GaN, Si-doped AlGaN, Si-doped AlGaInP, Si-doped GaAs or Si-doped AlInP; the P-type semiconductor epitaxial layer includes but is not limited to Mg-doped GaN, Mg-doped AlGaN, Mg-doped InGaN, Mg-doped InAlGaN, Mg-doped AlInP, Mg-doped AlGaInP, Mg-doped GaP or C-doped GaP. The quantum well layer includes but is not limited to InGaN / GaN ring, InGaP / AlGaInP ring.

[0059] In some embodiments, the electrode polarity of the conductive layer 130 is determined by the first type epitaxial layer 141, and the electrode polarity of the upper electrode layer 150 is determined by the second type epitaxial layer 143. The electrode polarity of the conductive layer 130 is opposite to the electrode polarity of the upper electrode layer 150. The conductive layer 130 can be, for example, a P electrode or an anode electrode, and the upper electrode layer 150 is an electrode with an opposite polarity to that of the conductive layer 130, such as an N electrode or a cathode electrode, and vice versa.

[0060] In one embodiment, the light-emitting mesa 140 may be a platform with a trapezoidal cross-section, and the bottom lateral dimension of the light-emitting mesa is larger than the top lateral dimension. There is an inclination angle between the side wall of the semiconductor light-emitting mesa 140 and the bottom of the semiconductor light-emitting mesa, and the inclination angle is less than or equal to 90. In one embodiment, the inclination angle range of the side wall of the light-emitting mesa is: 45° to 90°. In one embodiment, the bottom lateral dimension of the light-emitting mesa exceeds 2 microns. In one embodiment, the top lateral dimension of the light-emitting mesa does not exceed 1.5 microns. In one embodiment, the lateral dimension of the metal bonding composite layer is larger than the bottom lateral dimension of the light-emitting mesa.

[0061] In some embodiments, the light emitting mesa 140 can emit red light, blue light, green light, or light of any other color.

[0062] In some embodiments, the passivation layer 160 covers the side surfaces of the metal bonding composite layer 120, the conductive layer 130, and the light emitting table 140. In some embodiments of the present invention, the passivation layer 160 may also cover the side surfaces and a portion of the top surface of the upper electrode layer 150, and a portion of the top surface of the upper electrode layer 150 is exposed so as to form an electrical connection with the top electrode. In other embodiments of the present invention, the passivation layer 160 does not cover the top surface and the side surfaces of the upper electrode layer 150, so that the upper electrode layers 150 of adjacent LED structures can be connected to each other as a whole to form a common cathode or anode. In some embodiments of the present invention, the passivation layer 160 covers the side surfaces of the metal bonding composite layer 120, the conductive layer 130, the first type epitaxial layer 141, the light emitting layer 142, and a portion of the side surfaces of the second type epitaxial layer 143.

[0063] In one embodiment, the material of the passivation layer is a transparent insulating material, for example, one or more of silicon oxide, silicon oxynitride, aluminum oxide, and silicon nitride.

[0064] In general, the thickness of the conductive layer 130 can be in the range of 50 to 250 nm so as to realize the electrical connection between the first type epitaxial layer 141 and the metal bonding composite layer 120. The light emitted by the light-emitting mesa 140 is generated by spontaneous emission and is therefore non-directional, wherein part of the light passes through the upper electrode layer 150 and leaves the light-emitting mesa 140 directly or after being reflected by the metal bonding composite layer or other structures; part of the light passes through the passivation layer 160 and leaves the light-emitting mesa 140 directly or after being reflected by the metal bonding composite layer or other structures. The light leaving the light-emitting mesa is converged by structures such as reflective structures and / or microlenses and then emitted from the front of the micro LED chip or display screen, so as to be effectively used for display or lighting, etc. If the light emitted by the light-emitting mesa 140 cannot leave the light-emitting mesa, this part of the light will not be effectively utilized.

[0065] In some embodiments of the present invention, it is proposed to increase the probability of light leaving the light-emitting surface by increasing the sidewall light-emitting area of ​​the micro-LED structure, thereby improving the light-emitting efficiency of the LED chip. Figure 1 As shown, the thickness of the conductive layer 130 may be greater than or equal to 500 nm. For example, the thickness of the conductive layer 130 is in the range of 500 nm to 1000 nm. When the thickness of the conductive layer 130 increases, the sidewall light exit area increases directly, thereby increasing the light extraction efficiency.

[0066] In some embodiments of the present invention, the thickness of the conductive layer 130 is an integer multiple of λ / 4n, where λ is the operating wavelength of the micro-LED and n is the refractive index of the conductive layer 130. The conductive layer 130 is combined with the lower electrode layer 120 to form an omnidirectional reflector (ODR) structure to improve the reflectivity to increase the light extraction efficiency, wherein the lower electrode layer 120 serves as an ODR reflective metal and the conductive layer 130 serves as an ODR dielectric layer.

[0067] Figure 2 FIG. 4 is a schematic cross-sectional view of a micro-light emitting diode structure according to an embodiment of the present invention. Figure 2 As shown, the micro light emitting diode structure includes a pixel driving backplane 210 , a lower electrode layer 220 , a conductive layer 230 , a light emitting mesa 240 , an upper electrode layer 250 , a passivation layer 260 and a transparent medium layer 270 . Figure 2 The micro-LED structure shown is similar to Figure 1 The difference between the two lies in the structure of the conductive layer 230 and the transparent medium layer 270 disposed between the conductive layer 230 and the lower electrode layer 220. Figure 1 and Figure 2 Detailed description of similar structures in , only the differences between the two are described in detail.

[0068] like Figure 2 As shown, the transparent dielectric layer 270 is disposed between the conductive layer 230 and the lower electrode layer 220, so that the light emitting area of ​​the side wall is increased to increase the light emitting rate. The material of the transparent dielectric layer 270 can be SiO2 or SiN. In order to achieve electrical connection between the conductive layer 230 and the lower electrode layer 210, the conductive layer 230 includes a lateral portion 231 extending from the bottom of the light emitting table 240 and a side wall portion 232 extending along the side wall to the lower electrode layer so as to be electrically connected to the lower electrode layer 240. The side wall portion 232 covers the lateral portion 231, the transparent dielectric layer 270 and the side wall of the lower electrode layer 240. The total thickness of the conductive layer 230 and the transparent dielectric layer 270 is greater than 500nm.

[0069] In some embodiments of the present invention, the lower electrode layer 220 acts as a reflective metal and is combined with the conductive layer 230 and the transparent dielectric layer 270 to form an ODR structure. The conductive layer 230 and the transparent dielectric layer 270 act as ODR dielectric layers. The material of the lower electrode layer 220 is an alloy of one or more of the following metals: Cr, Al, Ti, Ni, Pt, Au, Ag, and Sn. The thickness of the conductive layer 230 and the transparent dielectric layer 270 is an integer multiple of λ / 4n, where λ is the operating wavelength of the micro-light emitting diode and n is the refractive index of the ODR dielectric layer. When the thickness of the ODR dielectric layer increases, the side wall light emitting area of ​​the LED structure increases, thereby improving the light extraction efficiency. At the same time, due to the presence of the transparent dielectric layer 270, the thickness of the conductive layer 230 can be reduced to reduce the absorption of light by the conductive layer 230. For example, the thickness of the conductive layer 230 can be in the range of 50 to 250 nm.

[0070] Figure 3 FIG. 4 is a cross-sectional view of a micro-LED structure array according to an embodiment of the present invention. Figure 3 As shown, each micro-LED structure in the micro-LED structure array can be Figure 1 or Figure 2 That is, the ODR dielectric layer 330 may be similar to Figure 1 The conductive layer 130 shown, or the ODR dielectric layer 330 may be similar to Figure 2 The combined structure of the conductive layer 230 and the transparent dielectric layer 270 is shown. The thickness of the ODR dielectric layer 330 is an integer multiple of λ / 4n, where λ is the operating wavelength of the micro-LED and n is the refractive index of the ODR dielectric layer 330. When the thickness of the ODR dielectric layer 330 increases, the sidewall light emitting area of ​​the LED structure increases, thereby improving the light extraction efficiency.

[0071] In one embodiment of the present invention, the thickness T of the ODR dielectric layer 330 is ODR It is related to the tilt angle θ of the light-emitting mesa. When the tilt angle θ is 90°, the thickness T of the ODR dielectric layer 330 is ODR There is no limit to the maximum thickness of the ODR dielectric layer 330. When the tilt angle θ is less than 90°, the thickness T of the ODR dielectric layer 330 is ODR The thickness T of the ODR dielectric layer 330 is limited by the bottom width W1 of the micro-LED structure, the spacing W2 of the micro-LEDs (ie, the minimum center-to-center distance between the micro-LEDs), and the height H of the micro-LEDs. ODR The following formula should be satisfied:

[0072] H / Tanθ<(W2-W1) / 2

[0073] Where H is the height from the bottom of the lower electrode layer to the top of the upper electrode layer, that is, the height of the micro-LED H = T ODR +T 下电极层 +T 发光台面 +T 上电极层 , T 下电极层 is the thickness of the lower electrode layer, T 发光台面 is the thickness of the light-emitting table, T 上电极层 is the thickness of the top electrode layer.

[0074] In the embodiment of the present invention, by increasing the thickness of the conductive layer of the micro light emitting diode structure, beam shaping can be achieved and the proportion of small-angle light emission can be increased.

[0075] Table 1 shows the light output efficiency LEE90 within the normal angle of ±90°, the light output efficiency LEE20 within the normal angle of ±20°, and the proportion of light output within the normal angle of ±20° under different thicknesses of the conductive layer.

[0076] Table 1

[0077] Conductive layer thickness LEE90 LEE20 ±20° ratio 0.1μm 1.86％ 0.49％ 26.10％ 0.25μm 2.33％ 0.61％ 26.10％ 0.63μm 2.17％ 0.68％ 31.7％ 1.0μm 2.28％ 0.70％ 30.70％

[0078] It can be seen from Table 1 that when the thickness of the conductive layer increases from 0.1 μm to 1.0 μm, LEE20 increases continuously. Figure 4 The figure shows the curve diagram of LEE20 changing with the thickness of the conductive layer. Figure 4 In the figure, the horizontal axis represents the thickness of the conductive layer, and the vertical axis represents LEE20.

[0079] Figure 5 A curve diagram showing the light intensity and light output angle of the light emitted by the micro-LED structure according to an embodiment of the present invention is shown, wherein the horizontal axis represents the light output angle and the vertical axis represents the light intensity. Figure 5 The middle curve 501 represents the relationship between the intensity of the light emitted from the micro-LED structure with a conductive layer thickness of 0.1 μm and the light-emitting angle, the curve 502 represents the relationship between the intensity of the light emitted from the micro-LED structure with a conductive layer thickness of 0.25 μm and the light-emitting angle, the curve 503 represents the relationship between the intensity of the light emitted from the micro-LED structure with a conductive layer thickness of 0.63 μm and the light-emitting angle, and the curve 504 represents the relationship between the intensity of the light emitted from the micro-LED structure with a conductive layer thickness of 1.0 μm and the light-emitting angle. From Tables 1 and Figure 4 and Figure 5 It can be seen that as the thickness of the conductive layer increases, LEE20 gradually increases. When the thickness of the conductive layer is 1.0μm, the ±20° light output ratio increases by 15% relative to the thickness of the thinnest conductive layer.

[0080] In one embodiment of the present invention, a micro-LED display chip is further provided, comprising a micro-LED pixel array, each of which comprises the micro-LED structure described in the above embodiment.

[0081] Although some embodiments of the present invention have been described in this application document, it will be appreciated by those skilled in the art that these embodiments are merely shown as examples. Those skilled in the art may conceive of numerous variations, alternatives, and improvements under the teachings of the present invention without departing from the scope of the present invention. The appended claims are intended to define the scope of the present invention and thus cover methods and structures within the scope of these claims themselves and their equivalents.

Claims

1. A micro light emitting diode structure, comprising: Lower electrode layer; ODR total reflection structure, located on the lower electrode layer; A semiconductor light-emitting table, located on the ODR total reflection structure, emits light; The upper electrode layer is in contact with the top of the semiconductor light-emitting mesa.

2. The micro light emitting diode structure according to claim 1, characterized in that: The thickness of the ODR total reflection structure is N times of λ / 4n, where N is a positive integer and λ is the wavelength of light emitted by the semiconductor light-emitting mesa.

3. The micro light emitting diode structure according to claim 2, characterized in that: There is an inclination angle between the side wall of the semiconductor light emitting mesa and the bottom of the semiconductor light emitting mesa, and the inclination angle is less than or equal to 90°.

4. The micro light emitting diode structure according to claim 3, characterized in that: The thickness of the ODR total reflection structure satisfies: H / Tanθ<(W2-W1) / 2; wherein H is the height from the bottom of the lower electrode layer to the top of the upper electrode layer, θ is the inclination angle and is less than 90°, W1 is the width of the lower electrode layer, and W2 is the pixel pitch where the micro light-emitting diode structure is located.

5. The micro light emitting diode structure according to claim 1, characterized in that: The ODR total reflection structure comprises, from top to bottom, a combination of a conductive layer and a dielectric layer.

6. The micro light emitting diode structure according to claim 5, characterized in that: In the ODR total reflection structure, the conductive layer extends downward to contact the lower electrode layer.

7. The micro light emitting diode structure according to claim 6, characterized in that: The downwardly extending portion of the conductive layer is attached to the side wall surface of the dielectric layer.

8. The micro light emitting diode structure according to claim 7, characterized in that: The downwardly extending portion of the conductive layer covers the side wall surface of the dielectric layer.

9. The micro light emitting diode structure according to claim 5, characterized in that: The material of the dielectric layer is SiO2 or SiN; the thickness of the conductive layer is in the range of 50 to 250 nm.

10. The micro light emitting diode structure according to claim 1, characterized in that: The ODR total reflection structure is composed of a conductive layer.

11. The micro light emitting diode structure according to claim 5 or 10, characterized in that: The material of the conductive layer is a transparent conductive layer.

12. The micro light emitting diode structure according to claim 11, characterized in that: The material of the conductive layer is one or more of graphene, indium tin oxide ITO, aluminum-doped zinc oxide AZO or fluorine-doped tin oxide FTO.

13. The micro light emitting diode structure according to claim 1, characterized in that: The invention also comprises a passivation layer, wherein the passivation layer covers the lower electrode layer, the ODR total reflection structure, the light-emitting mesa and the side surface of the upper electrode layer.

14. The micro light emitting diode structure according to claim 13, characterized in that: The material of the passivation layer is a dielectric material or an insulating material.

15. The micro light emitting diode structure according to claim 14, characterized in that: The material of the passivation layer is one or more of silicon oxide, silicon oxynitride, aluminum oxide, and silicon nitride.

16. The micro light emitting diode structure according to claim 1, characterized in that: It also includes a pixel driving backplane, and the lower electrode layer is located on the pixel driving backplane and is electrically connected to the pixel driving backplane.

17. The micro light emitting diode structure according to claim 16, characterized in that: The pixel driving backplane adopts an integrated circuit chip.

18. The micro light emitting diode structure according to claim 17, characterized in that: The pixel driving backplane includes a substrate, a driving circuit and a contact pad. Each micro light emitting diode structure corresponds to a contact pad, and the contact pad is electrically connected to the lower electrode layer.

19. The micro light emitting diode structure according to claim 1, characterized in that: The lower electrode layer is a metal bonding composite layer.

20. The micro light emitting diode structure according to claim 1, characterized in that: The material of the lower electrode layer is an alloy of one or more of the following metals: Cr, Al, Ti, Ni, Pt, Au and Sn.

21. The micro light emitting diode structure according to claim 1, characterized in that: The inclination angle of the side wall of the semiconductor light-emitting mesa ranges from 45° to 90°.

22. The micro light emitting diode structure according to claim 1, characterized in that: The semiconductor light-emitting mesa includes a first type epitaxial layer, a light-emitting layer, and a second type epitaxial layer. The first type epitaxial layer is a semiconductor material with a first conductivity type and includes multiple semiconductor layers. The second type epitaxial layer is a semiconductor material with a second conductivity type and includes multiple semiconductor layers.

23. The micro light emitting diode structure according to claim 22, characterized in that: The light-emitting layer is a quantum well light-emitting layer.

24. A micro light emitting diode display chip, comprising a micro light emitting diode pixel array, each micro light emitting diode pixel comprising the micro light emitting diode structure according to claim 1.

Images