Monolithic full-color LED micro-display on an active matrix panel manufactured using flip-chip technology

• US 8,642,363 B2
• Filed: 05/08/2012
• Issued: 02/04/2014
• Est. Priority Date: 12/09/2009
• Status: Active Grant

• Current Assignee: Nano and Advanced Materials Institute Limited
• Original Assignee: Nano and Advanced Materials Institute Limited
• Inventors: Lau, Kei May, Liu, Zhaojun
• Primary Examiner(s): CHAUDHARI, CHANDRA P
• Application Number:
  US13/466,660
• Publication Number:
  US 20120223875A1
• Time in Patent Office: 637 Days
• Field of Search: 438/35, 438/237, 438/604
• US Class Current: 438/28
• CPC Class Codes: G09G 2300/0452 Details of colour pixel setup, e.g. pixel composed of a red, a blue and two green components
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 3/32 semiconductive, e.g. using light-emitting diodes [LED]
• CPC Class Codes: H01L 27/156 two-dimensional arrays
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 33/504 Elements with two or more wavelength conversion materials
• CPC Class Codes: H01L 33/508 having a non-uniform spatial arrangement or non-uniform concentration, e.g. patterned wavelength conversion layer, wavelength conversion layer with a concentration gradient of the wavelength conversion material
• CPC Class Codes: H01L 33/62 Arrangements for conducting electric current to or from the semiconductor body, e.g. lead-frames, wire-bonds or solder balls
• CPC Class Codes: H05B 45/44 with an active control inside an LED matrix
• CPC Class Codes: H10K 59/1216 the pixel elements being capacitors

Abstract

A high-resolution, Active Matrix (AM) programmed monolithic Light Emitting Diode (LED) micro-array is fabricated using flip-chip technology. The fabrication process includes fabrications of an LED micro-array and an AM panel, and combining the resulting LED micro-array and AM panel using the flip-chip technology. The LED micro-array is grown and fabricated on a sapphire substrate and the AM panel can be fabricated using PMOS process, NMOS process, or CMOS process. LED pixels in a same row share a common N-bus line that is connected to the ground of AM panel while p-electrodes of the LED pixels are electrically separated such that each p-electrode is independently connected to an output of drive circuits mounted on the AM panel. The LED micro-array is flip-chip bonded to the AM panel so that the AM panel controls the LED pixels individually and the LED pixels exhibit excellent emission uniformity. According to this constitution, incompatibility between the LED process and the PMOS/NMOS/CMOS process can be eliminated.

Claims

1. A method for manufacturing a monolithic Light Emitting Diode (LED) micro-display panel on an Active Matrix (AM) panel, the LED microarray panel comprising a plurality of LED pixels each including an n-electrode and a p-electrode, with the LED pixels arranged in a matrix including a plurality of rows and a plurality of columns, n-electrodes of LED pixels in a row of the matrix, electrically connected to a bus line, the p-electrode of each LED pixel individually electrically connected to an output of a corresponding driving circuit on the AM panel, the method comprising:

providing a substrate of the LED micro-display panel;

overlaying a plurality of layers of material on a surface of the substrate, with the plurality of overlaying layers of material configured in combination to emit light when activated;

patterning the plurality of overlaying layers of material by removing a part of each overlaying layers all the way down to the surface of the substrate;

depositing a current spreading layer on the patterned plurality of overlaying layers of material and surface of the substrate;

providing a metal multilayer on the current spreading layer;

patterning the metal multilayer in such a configuration that a first portion of the metal multilayer, which lies on the patterned plurality of overlaying layers of material, and a second portion of the metal multilayer, which lies on the surface of the substrate, and conductively disconnected from the substrate, thereby forming the monolithic LED micro-display panel;

providing a plurality of active control circuits on a surface of the AM panel; and

combining the monolithic LED micro-display panel with the AM panel using conductive solder material, with each of the monolithic LEDs electrically insulated from one another and independently controllable by corresponding ones of the active control circuit chips bonded thereto, with the plurality of active control circuits combined with the monolithic LEDs in such a way that each of the plurality of active control circuits combine with one of the monolithic LEDs of the LED microarray panel via the solder material, wherein the AM panel, pixel size and shape correspond to LED pixels.

2. The method of claim 1, further comprising:

providing a plurality of active control circuits on a surface of the AM panel in such a way that each active control circuit has a two-transistor-one-capacitor (2T1C) structure, which comprises a first transistor (T1) as a switch transistor, a second transistor (T2) as a driving transistor, and a capacitor (C), a gate electrode of the second transistor (T2) electrically connected to a drain electrode of the first transistor (T1) and an end of the capacitor (C),

wherein T2 serves as driving transistor, with a select (SEL) switching T1 to an ON mode, and resulting in a signal stored on the capacitor (C) and switching T2 to an ON mode and supply driving current to the respective LED pixel, connected to a drain electrode of T2, so that, after switching T1 to an OFF mode, a voltage at capacitor (C) keeps T2 in ON mode until a next frame.

3. The method of claim 2, further comprising:

forming the AM panel by a process comprising;

providing a semiconductor substrate having a surface;

forming active channel of the transistors of active control circuits;

forming gate oxide of the transistors of active control circuits;

forming gate electrodes of the transistors of active control circuits;

forming source and drain of the transistors by using gate electrodes as a self-aligned mask;

forming source and drain electrodes and inter-connection metal line;

forming passivation layer; and

forming via holes on the passivation layer; and

,

forming the conductive solder material as a conductive solder bump array that connects the p-electrode of each LED pixel on the LED microarray with the output of each active control circuit on the AM panel in the conductive solder bump array, with a plurality of conductive solder bumps arranged in rows and columns corresponding to the outputs of active control circuits on the AM panel.

4. The method according to claim 3, further comprising:

defining patterns of the plurality of solder bumps on a photoresist;

forming a first ohm contact layer;

forming a thick metal layer on the photoresist;

removing the thick metal layer; and

reflowing in furnace.

5. The method according to claim 1, further comprising:

patterning the plurality of overlaying layers of material by Inductively Coupled Plasma (ICP) etching using Plasma-Enhanced Chemical Vapor Deposition (PECVD) grown SiO2 masks.

6. The method according to claim 1, further comprising patterning of the plurality of overlaying layers of material by removing a part thereof all the way down to the surface of the substrate by an etching process selected from the group consisting of wet etching and dry etching.

7. The method according to claim 1, wherein the substrate of the LED micro-display panel comprises at least one material selected from the group consisting of:

GaAs, SiC, semi-insulating GaAs, sapphire, and quartz.

8. The method according to claim 1, comprising:

grouping the LED pixels in groups of four pixels, with the LEDs emitting a single color of light for all pixels;

providing a mold configured to accept phosphors for the individual pixels in each group;

applying phosphors to the mold to transmit at least 3 primary transmission colors for respective ones of the pixels in each group;

applying phosphors to a fourth pixel in the group to transmit light selected from the group consisting of one of the three primary colors, white light, a non-primary color and a fourth primary color.

9. The method according to claim 1, wherein the LED micro-display panel comprises a mold configured to locate red, green, and blue phosphors.

10. The method according to claim 9, wherein the mold comprises a material selected from the group consisting of sapphire, quartz, glass, single crystal silicon, and metal.

11. The method according to claim 9, further comprising:

providing the substrate of the LED micro-display panel on a single crystal silicon wafer;

forming a number of molds onto the surface of the substrate, the molds corresponding to the red, green and blue phosphors onto the surface of substrate to provide a full-color display, the molds formed by etching through the single crystal silicon wafer, and mixing the red, green and blue color phosphors with silicon and then depositing the mixed phosphors and silicon into etching holes on the mold.

12. The method according to claim 1, further comprising configuring the LED pixels to have a circular or rectangular shape.

13. The method according to claim 1, wherein the LED pixels have a pixel size equal to or less than 500×

500 μ

m² in area or 500 μ

m in diameter.

14. The method according to claim 1, wherein the LED microarray has a display resolution of 8×

8 and a display area with a diagonal length of 8 micrometers as a basic unit, a plurality of said basic units can mounted alone the AM panel to obtain a large-scale display panel while improving a utilization rate of LED wafers used to provide the large scale display panel.

15. The method according to claim 1, wherein the LED pixels have a pixel size equal to or more than 10×

10 square μ

m² in area or 10 μ

m in diameter as a basic unit.

16. The method according to claim 1, wherein the LED microarray has a display resolution of a predetermined size and a display area with a diagonal length of a predetermined size as a basic unit;

and

a display area and resolution increased by integrating a plurality of basic units onto a corresponding AM panel.

17. The method according to claim 1, further comprising assembling basic units of the module to provide a standard wherein the resolution of the LED micro-display panel, selected from at least one of 240×

160 (HQVGA), 320×

240 (QVGA), 640×

480 (VGA), 800×

480 (WVGA), 800×

600 (SVGA), 1024×

768 (XGA), 1440×

900 (WXGA+), 1680×

1050 (WSXGA+), and 1920×

1200 (WUXGA).

18. The method according to claim 1, further comprising:

using, as the plurality of overlaying layers, a material comprising a p-GaN layer, a Multiple Quantum Well (MQW) layer, and n-GaN layer;

using, as the metal multilayer, a material comprising a Ti/Al/Ti/Au layer; and

using, as the current spreading layer, a thin layer comprising at least one layer selected from the group consisting of a Ni/Au layer and an Ag/ITO layer.

19. The method according to claim 1, wherein the current spreading layer forms p-electrodes of the LEDs, and the metal multilayer forms n-electrodes of the LEDs and reflective layers on the p-electronics, and wherein the array of the multiple LEDs are arranged in rows, the method further comprising:

connecting the n-electrodes of LEDs in a same row to a common N-bus line that is connected to a ground of the AM panel; and

connecting the p-electrodes of the multiple LEDs individually to outputs of corresponding active control circuit chips by flip-chip bonding the multiple LEDs.

20. The method according to claim 1, further comprising configuring the bus line to limit a forward voltage variation of the LED pixels in the row of the matrix, the configuration to limit forward voltage variation consisting at least one of a varied bus width and a double-side ground structure.

21. The method according to claim 1, further comprising:

providing a passivation layer on the metal multilayer; and

defining openings in the passivation layer containing contact pads configured for the flip-chip bonding with the conductive solder material of the AM panel.

22. The method according to claim 21, further comprising:

using, as the contact pads contained in the openings, a material comprising Ni/Au; and

using, as the passivation layer on the metal multilayer, a material comprising at least one material selected from the group consisting of;

SiO₂, SiNx, polyimide and photoresist.

23. A method for manufacturing an assembly of a monolithic Light Emitting Diode (LED) micro-display panel including a plurality of LEDs thereon and an Active Matrix (AM) panel, comprising:

providing a substrate of the AM panel;

providing active control circuit chips on the substrate of the AM panel, by mounting a plurality of active control circuits on a surface of the AM panel wherein each of the plurality of active control circuits has a two-transistor-one-capacitor (2T1C) structure, which comprises a first transistor (T1) as a switch transistor, a second transistor (T2) as a driving transistor, and a capacitor (C), a gate electrode of the second transistor (T2) electrically connected to a drain electrode of the first transistor (T1) and an end of the capacitor (C);

providing conductive solder material on the active control circuit chips; and

using flip-chip bonding to mount the active control chips to the plurality of monolithic LEDs via the conductive solder material to combine the AM panel with the monolithic LED micro-display panel.

24. The method according to claim 23, further comprising:

depositing a passivation layer on the AM panel;

defining holes on the passivation layer;

depositing a seed layer by sputtering on the passivation layer;

coating a photoresist on the seed layer;

patterning the photoresist by photolithography; and

forming the conductive solder material as a conductive solder bump array that connects an electrode of each LED pixel on the LED microarray with the output of each active control circuit on the AM panel in the conductive solder bump array, with the solder bump array corresponding to the outputs of active control circuits on the AM panel.

25. The method according to claim 23, further comprising using a Complimentary Metal-Oxide Semiconductor (CMOS) fabrication process to fabricate the active control circuit chips on the substrate of the AM panel.

26. The method according to claim 23, further comprising:

thinning and dicing the LED micro-display panel; and

flip-chip mounting the diced LED micro-display panel onto the AM panel, with each of the plurality of LEDs on the diced LED micro-display panel faces positioned to correspond to one of the active control circuit chips on the AM panel.

27. A method for manufacturing a monolithic Light Emitting Diode (LED) micro-display panel on an Active Matrix (AM) panel, comprising:

providing a substrate of the LED micro-display panel;

overlaying a plurality of layers of material on a surface of the substrate, and configuring the plurality of overlaying layers of material in combination to emit light when activated;

patterning the plurality of overlaying layers of material by removing a part of each overlaying layers all the way down to the surface of the substrate;

depositing a current spreading layer on the patterned plurality of overlaying layers of material and surface of the substrate;

providing a metal multilayer on the current spreading layer;

patterning the metal multilayer so as to conductively disconnect a first portion of the metal multilayer, which lies on the patterned plurality of overlaying layers of material, from a second portion of the metal multilayer, which lies on the surface of the substrate, thereby forming the monolithic LED micro-display panel; and

combining the monolithic LED micro-display panel with the AM panel, said AM panel comprising a plurality of active control circuit chips with conductive solder material, said combining comprising flip-chip bonding the monolithic LEDs to the active control circuit chips via the conductive solder material, with each of the monolithic LEDs electrically insulated from one another and independently controllable by corresponding ones of the active control circuit chips bonded thereto;

grouping the LED display to form pixels in groups of four pixels, with the LEDs emitting a single color of light for all pixels;

providing a mold configured to accept phosphors for the individual pixels in each group;

applying phosphors to the mold to transmit at least 3 primary transmission colors for respective ones of the pixels in each group;

applying phosphors to a fourth pixel in the group to transmit light selected from the group consisting of one of the three primary colors, white light, a non-primary color and a fourth primary color.