Top emitting lateral micro-led array and manufacturing method thereof

Abstract

A LED display and method of fabricating a LED display are provided. The device includes light emitting diodes (LEDs), each LED includes a mesa and a body, a transparent conductive layer disposed on an upper surface of the mesa, a passivation layer disposed on at least the TCL and the body of the LEDs, an n- contact of a conductive material disposed in an n-contact opening of the passivation layer to contact a LED layer, and a p-contact of the conductive material disposed in a p-contact opening of the passivation layer to contact the TCL. The LEDs may be disposed over a backplane, the backplane includes a plurality of n-electrodes and a plurality of p-electrodes, each n-electrode is adjacent to each p-electrode.

Description

TOP EMITTING LATERAL MICRO-LED ARRAY AND MANUFACTURINGMETHOD THEREOFBACKGROUNDField

[0001] Embodiments of the present disclosure generally relate to LED displays and methods of fabricating LED displays.Description of the Related Art

[0002] A light emitting diode (LED) panel uses an array of LEDs, with individual LEDs providing the individually controllable pixel elements. Such an LED panel can be used for a computer, touch panel device, personal digital assistant (PDA), cell phone, television monitor, and the like. An LED panel that uses micron-scale LEDs based on lll-V semiconductor technology (also called micro-LEDs) would have a variety of advantages as compared to organic light emitting diodes (OLEDs), e.g., higher energy efficiency, brightness, and lifetime, as well as fewer material layers in the display stack which can simplify manufacturing. However, there are challenges to the fabrication of micro-LED panels.

[0003] The process of transferring micro-LEDs to a backplane generally is a cumbersome procedure. This process can result in poor light-up yield, thermal instability, non-uniformity, and high costs. Therefore, there is a need for an improved LED display and method of fabricating a LED display.SUMMARY

[0004] In one embodiment, a device is provided. The device includes light emitting diodes (LEDs), each LED includes a mesa and a body, a transparent conductive layer disposed on an upper surface of the mesa, a passivation layer disposed on at least the TCL and the body of the LEDs, an n-contact of a conductive material disposed in an n-contact opening of the passivation layer to contact a LED layer, and a p-contact of the conductive material disposed in a p-contact opening of the passivation layer to contact the TCL. The LEDs may be disposed over a backplane, the backplane includes a plurality of n-electrodes and a plurality of p- electrodes, each n~electrode is adjacent to each p~electrode.

[0005] In another embodiment, a device is provided. The device includes a backplane, the backplane includes a plurality of n-electrodes and a plurality of p- electrodes, each n-electrode is adjacent to each p-electrode. Light emitting diodes (LEDs) are disposed over the backplane. Each LED includes a mesa and a body, a transparent conductive layer (TCL) disposed on an upper surface of the mesa, a passivation layer disposed on at least the TCL and the body of the LEDs, an n- contact of a conductive material disposed in an n-contact opening of the passivation layer to contact a LED layer, and a p-contact of the conductive material disposed in a p-contact opening of the passivation layer to contact the TCL.

[0006] In yet another embodiment, a method is provided. The method includes disposing at least one LED layer of a light emitting diode (LED) on a substrate, forming a mesa in the at least one LED layer, disposing a transparent conductive layer (TCL) on the mesa, forming a body in the at least one LED layer, disposing a passivation layer and patterning the passivation layer to form an n-contact opening and a p-contact opening, and disposing a conductive material. The conductive material is disposed in the n-contact opening to contact a LED layer to form an n- contact and the conductive material is disposed in the p-contact opening to contact the TCL to form a p-contact.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.

[0008] The disclosure contains at least one drawing executed in color. Copies of this disclosure with color drawings will be provided to the Office upon request and payment of the necessary fee. As the color drawings are being filed electronically via EFS-Web, only one set of the drawings is submitted.

[0009] Figures 1A and 1 B are cross-sectional views of a subpixel circuit of a display according to embodiments.

[0010] Figures 2A, 2B and 5 are cross-sectional views of a respective LED of a subpixel circuit according to embodiments.

[0011] Figure 3 is a flow diagram of a method of forming a subpixel circuit according to embodiments.

[0012] Figures 4A-4! are schematic views of a substrate during a method a forming a subpixel circuit according to embodimentsDETAILED DESCRIPTION

[0013] Embodiments of the present disclosure generally relate to a LED display and method of fabricating a LED display.

[0014] Figures 1A and 1 B are cross-sectional views of a subpixel circuit 100 of a display. The display is a LED, such as a micro-LED, display. The subpixel circuit 100 includes a backplane 101. The backplane 101 may be a passive, active, amorphous-silicon (a-Si), thin film transistor (TFT), CMOS (Complementary Metal- Oxide-Sem iconductor), low-temperature polycrystalline silicon (LTPS), or oxide backplane. The backplane 101 includes a plurality of n-electrodes 103 and a plurality of p-electrodes 105. Each n-electrode 103 is adjacent to each p-electrode 105. The n-electrodes 103 are connected to wiring 107. The wiring 107 is connected to at least one port 109. The port 109 may be a TFT active matrix array with a thin-film transistor and a storage capacitor (not illustrated), column address and row address lines, column and row drivers, to drive LEDs. Alternatively, the port 109 is a passive matrix in the backplane 101 circuitry. In some embodiments, the backplane is a CMOS backplane.

[0015] LEDs 102 are disposed over, and in some embodiments on, the backplane. In some embodiments, the LEDs 102 are micro-LEDs. In some embodiments, the LEDs 102 emit UV light. In other embodiments, the LEDs emit light of other wavelengths. The LEDs 102 include mesa 104 and a body 106. A transparent conductive layer (TCL) 108 is disposed on an upper surface of the mesa104. In some embodiments, the TCL 108 includes transparent conductive oxide (TCO). A passivation layer 110 is disposed on at least the TCL 108 and the body 106 of the LEDs 102. In some embodiments, passivation layer 110 is further disposed on the sidewalls of the mesa 104 and the body 106. An n~contact opening 112 is disposed in the passivation layer 110 on a first portion 114 of the upper surface of the body 106 adjacent to the mesa 104. A p-contact opening 116 is disposed in the passivation layer 110 on the TCL 108. A conductive material 111 is disposed in the n~contact opening 112 to contact the LED 102 form an n-contact 113. The conductive material 111 is disposed in the p-contact opening 116 to contact the TCL 108 form a p-contact 115. In some embodiments, the conductive material 111 is disposed in the p-contact opening 116, on the passivation layer 110 over the mesa 104, and on the passivation layer 110 on a second portion 118 of the upper surface of the body 106. In addition to the TCL 108, the passivation layer 110 and the conductive material 111 are transmissive or semi-transmissive. The transmissive or semi-transmissive TCL 108, passivation layer 110, and conductive material 111 allow light to emit from the LEDs 102 to subpixels of the subpixel circuit 100. The TCL 108 conducts current into the mesa 104 to allow the LEDs 102 to emit light. The mesa size is less than the overall LED size resulting in a smaller emission area, smaller injection area than conventional LEDs. The smaller emission area, smaller injection area increases the density of the LEDs 102. The LEDs 102 with the increased density have an increased efficiency such that the light that is emitted is brighter than conventional LEDs with the same amount of current. I.e. , more light is extracted with the injection area of the mesa 104.

[0016] A light blocking material 120 is disposed over, and in some embodiments on, the backplane 101. The light blocking material 120 defines an upper surface 122 between the LEDs 102 such that the emitting surface of each of mesas is exposed to a color conversion material 124. The color conversion material 124 includes quantum dots. The quantum dots may be sized to produce wavelengths corresponding to different colors. In other embodiments, the color conversion material 124 includes nanostructures, photoluminescent materials, or organic substances. The optical density of the light blocking material 120 provides for color isolation between each of the LEDs 102 because the light blocking material 120blocks UV light. The light blocking material 120 includes thermal curable glue, UV curable glue, black matrix epoxy, metal particles, UV absorbing materials, or combinations thereof.

[0017] Connections 117 are disposed through connections vias in the light blocking material 120. The adjacent connections 117 are connected to the conductive material 111 of the n-contact 113 and the p-contact 115 of each of the LEDs 102. The adjacent connections 117 are connected to the n-electrode 103 and the p-electrode 105 of the backplane 101 . The connections 117 provide current to the n-contacts 113 and p-contacts 115. The n-contacts 113, p-contacts 115, and connections 117 described herein allow the LEDs 102 to be bonded to the backplane 101 with adhesive. Double-compression bonding and / or eutectic bonding is not necessary which increase throughput during fabrication. Each n- electrode 103 is in electrical communication to each n-contact 113 and each p- electrode 105 is in electrical communication to each p-contact 115.

[0018] Subpixel isolation (SI) structures 126 are disposed over the backplane 101 and between the LEDs 102. As shown in Figure 1A, the SI structures 126 are disposed on the light blocking material 120. As shown in Figure 1 B, the SI structures 126 are disposed on a layer 130. The layer 130 may be a planarization layer. The SI structures 126 define at least three subpixels 128. The subpixels 128 include a red subpixel 128a with a red color conversion material 124a to emit a red when the respective LED 102 of the red subpixel 128a is turned on, a green subpixel 128b with a green color conversion material 124b when the respective LED 102 of the red subpixel 128b is turned on, and a blue subpixel 128c with a blue color conversion material 124c when the respective LED 102 of the blue subpixel 128c is turned on. In other embodiments, the at least three subpixels 128 include the same color conversion material 124 to emit the same color. A redundant subpixel 128d includes a sacrificial material or the color conversion material 124. The color conversion material 124 of the redundant subpixel 128d may be configured to emit a red, green, or blue color.

[0019] Figures 2A and 2B are cross-sectional views of a respective LED 102 of the subpixel circuit 100. The LEDs 102 include a gallium nitride (GaN) containing layer201. The GaN containing layer 201 may include dopants. The dopants include, but are not limited to, aluminium (Al) or indium (In). The GaN containing layer 201 may be un-doped GaN. An n-GaN containing layer 202 is disposed over the GaN containing layer 201 . The n-GaN containing layer 202 may include dopants. The dopants include, but are not limited to, Al or In. The n-GaN containing layer 202 may be un-doped GaN. In the mesa 104 one or more quantum well layers 203 are disposed. A p-GaN containing layer 204 is disposed over the quantum well layers 203 in the mesa 104. The p-GaN containing layer 204 may include dopants. The dopants include, but are not limited to, Al or In. The p-GaN containing layer 204 may be un-doped GaN. The p-GaN containing layer 204 is in contact with the TCL 108. The n-GaN containing layer 202 is in contact with the n-contact 113 including the conductive material 111. In some embodiments, the LEDs 102 include a mirror layer 206. The mirror layer 206 enhances light extraction. The mirror layer 206 may include aluminium gallium nitride (AIGaN). As shown in Figure 2A, the mirror layer 206 is disposed between sublayers of the GaN containing layer 201. The mirror layer 206 may be formed by epitaxial deposition. As shown in Figure 2B, the mirror layer 206 is below the GaN containing layer 201 . In some embodiments, the mirror layer 206 is disposed after separation from a substrate 400 at the bottom of the GaN containing layer 201. In other embodiments, the mirror layer is disposed on the backplane 101 or the adhesive.

[0020] Figure 3 is a flow diagram of a method 300 of forming a subpixel circuit 100. Figures 4A-4I are schematic views of a substrate 400 during the method 300 a forming a subpixel circuit 100. At operation 301 , as shown in Figure 4A, at least one LED layer 401 is disposed on the substrate 400. In some embodiments, the at least one LED layer 401 includes the GaN containing layer 201 , the n-GaN containing layer 202, the one or more quantum well layers 203, and the p-GaN containing layer 204. In some embodiments, the mirror layer 206 is disposed between sublayers of the GaN containing layer 201 at operation 301 . In other embodiments, the mirror layer 206 is disposed on the substrate 400 prior to disposing the at least one LED layer 401 . The at least one LED layer 401 may be disposed via epitaxial deposition.

[0021] At operation 302, as shown in Figures 4B and 4C, the at feast one LED layer 401 is etched. Etching the at least one LED layer 401 forms the mesas 104. In some embodiments, the mesas 104 includes the one or more quantum well layers 203 and the p-GaN containing layer 204. In some embodiments, as shown in Figure 4C, an n-contact aperture 402 is also formed by etching the at feast one LED layer 401 . The n-contact aperture 402 exposes the n~GaN containing layer 202 such that the conductive material 111 of the n-contact 113 contacts the n-GaN containing layer 202 in further operations. Figure 5 is a cross-sectional view of a respective LED 102 of the subpixel circuit 100. The n-contact aperture 402 is formed in the body 106.

[0022] At operation 303, the TCL 108 is disposed on the mesas 104. At operation 304, as shown in Figures 4D and 4E, the at least one LED layer 401 is singulated. The singulation of the at least one LED layer 401 forms the bodies 106 of the LEDs 102. At operation 305, as shown in Figures 4F and 4G, the passivation layer 110 is disposed and patterned. In some embodiments, passivation layer 110 is further disposed on the sidewalls of the mesa 104 and the body 106. The passivation layer 110 is disposed on at least the TCL 108 and the body 106 of the LEDs 102. Patterning the passivation layer 110 forms an n-contact opening 112. In some embodiments, the n-contact opening 112 is disposed in the passivation layer 110 on a first portion 114 on the upper surface of the body 106 adjacent to the mesa 104. In other embodiments, the n-contact opening 112 is disposed in passivation layer 110 in the n-contact aperture 402. A p-contact opening 116 is disposed in the passivation layer 110 on the TCL 108.

[0023] At operation 306, as shown in Figures 4H and 4I, a conductive material111 is disposed. A conductive material 111 is disposed in the n-contact opening112 to contact the LED 102 form an n-contact 113. The conductive material 111 is disposed in the p-contact opening 116 to contact the TCL 108 form a p-contact 115. In some embodiments, the conductive material 111 is disposed in the p-contact opening 116, on the passivation layer 110 over the mesa 104, and on the passivation layer 110 on a second portion 118 of the upper surface of the body 106. In addition to the TCL 108, the passivation layer 110 and the conductive material 111 are transmissive or semi-transmissive. The transmissive or semi-transmissiveTCL 108, passivation layer 110, and conductive material 111 allows light to emit from the LEDs 102 to subpixels of the subpixel circuit 100. The TCL 108 conducts current into the mesa 104 to allow the LEDs 102 to emit light. The mesa size is less than the overall LED size resulting in a smaller emission area, smaller injection area than conventional LEDs. The smaller emission area, smaller injection area increases the density of the LEDs 102. The LEDs 102 with the increased density have an increased efficiency such that the light that is emitted is brighter than conventional LEDs with the same amount of current. I.e., more light is extracted with the injection area of the mesa 104.

[0024] In further operations, the LEDs 102 are bonded to the backplane 101. The LEDs 102 are removed from the substrate 400 and are bonded to the backplane 101. The n~contacts 113, p-contacts 115, and connections 117 described herein allow the LEDs 102 to be bonded to the backplane 101 with adhesive. Double-compression bonding and / or eutectic bonding is not necessary which increase throughput during fabrication. In some embodiments, the mirror layer 206 is disposed after separation from the substrate 400 at the bottom of the GaN containing layer 401. In other embodiments, the mirror layer is disposed on the backplane 101 or the adhesive. The light blocking material 120 Is disposed over, and in some embodiments on, the backplane 101. Connections 117 are disposed through connections vias in the light blocking material 120. The connections 117 are formed by etching the light blocking material 120 to form openings. Connection material that is conductive is disposed in the openings and is connected to the conductive material 111 of the n-contact 113 and the p-contact 115 of each of the LEDs 102. The connections 117 provide current to the n-contacts 113 and p-contacts 115. The SI structures 126 are disposed over the backplane 101 and between the LEDs 102. The SI structures 126 are disposed on the light blocking material 120. As shown in Figure 1 B, the SI structures 126 are disposed on the layer 130. The color conversion material 124 is deposited and subsequently cured.

[0025] While the foregoing Is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departingfrom the basic scope thereof, and the scope thereof is determined by the ciaims that foiiow.

Claims

Claims:1 . A device, comprising: light emitting diodes (LEDs), each LED includes: a mesa and a body; a transparent conductive layer (TCL) disposed on an upper surface of the mesa; a passivation layer disposed on at least the TCL and the body of the LEDs, an n-contact of a conductive material disposed in an n-contact opening of the passivation layer to contact a LED layer; and a p-contact of the conductive material disposed in a p-contact opening of the passivation layer to contact the TCL.

2. The device of claim 1 , wherein the LEDs are disposed over a backplane, the backplane including a plurality of n-electrodes and a plurality of p~electrodes, each n-electrode adjacent to each p-electrode.

3. The device of claim 2, wherein the backplane is a CMOS (Complementary Metal~Oxide~Sem iconductor) backplane.

4. The device of claim 2, wherein a light blocking material is disposed over the backplane, connections are disposed through connections vias in the light blocking material.

5. The device of claim 1 , wherein the LEDs comprises: a gallium nitride (GaN) containing layer; an n-GaN containing layer disposed over the GaN containing layer; one or more quantum well layers disposed in the mesa; and a p-GaN containing layer disposed over the quantum well layers in the mesa.

6. The device of claim 5, wherein the n-GaN containing layer is in contact with the n~contact including the conductive material. / . The device of claim 5, wherein a mirror layer is disposed between sublayers of the GaN containing layer or below the GaN containing layer.

8. The device of claim 2, wherein the n-electrodes are connected to wiring.

9. The device of claim 8, wherein the wiring is connected to at least one port.

10. The device of claim 9, wherein the at least one port is a thin film transistor (TFT) active matrix array or a passive matrix in circuitry of the backplane.

11. A device, comprising: a backplane, the backplane includes a plurality of n-electrodes and a plurality of p-electrodes, each n-electrode is adjacent to each p-electrode; light emitting diodes (LEDs) disposed over the backplane, each LED includes: a mesa and a body; a transparent conductive layer (TCL) disposed on an upper surface of the mesa: a passivation layer disposed on at least the TCL and the body of the LEDs, an n-contact of a conductive material disposed in an n-contact opening of the passivation layer to contact a LED layer; and a p-contact of the conductive material disposed in a p-contact opening of the passivation layer to contact the TCL.

12. The device of claim 11 , wherein the LEDs comprises: a gallium nitride (GaN) containing layer; an n-GaN containing layer disposed over the GaN containing layer; one or more quantum well layers disposed in the mesa; and a p-GaN containing layer disposed over the quantum well layers in the mesa.

13. The device of claim 12, wherein the n-GaN containing layer is in contact with the n~contact including the conductive material.

14. The device of claim 12, wherein a mirror layer is disposed between sublayers of the GaN containing layer or below the GaN containing layer.

15. A method, comprising: disposing at least one LED layer of a light emitting diode (LED) on a substrate; forming a mesa in the at least one LED layer; disposing a transparent conductive layer (TCL) on the mesa; forming a body in the at least one LED layer; disposing a passivation layer and patterning the passivation layer to form an n-contact opening and a p-contact opening; and disposing a conductive material, wherein: the conductive material is disposed in the n-contact opening to contact a LED layer to form an n-contact; and the conductive material is disposed in the p-contact opening to contact the TCL to form a p-contact.

16. The method of claim 15, wherein the LED is bonded to a backplane.

17. The method of claim 16, wherein a light blocking material is disposed over the backplane.

18. The method of claim 17, wherein connections are disposed through connections vias in the light blocking material.

19. The method of claim 18, wherein adjacent connections are connected to the conductive material of the n-contact and the p-contact of the LED, an n-electrode is in electrical communication to the n-contact and a p~electrode is in electrical communication to the p-contact.

20. The method of ciaim 15, wherein the at least one LED layer includes: a gallium nitride (GaN) layer; an n-GaN containing layer disposed over the GaN containing layer; one or more quantum well layers disposed in the mesa; and a p-GaN containing layer disposed over the quantum well layers in the mesa.

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