A flexible gallium nitride-based LED and a method for preparing the same

Abstract

The present invention discloses a flexible gallium nitride-based LED and a preparation method thereof, belonging to the field of optoelectronics and luminous display; the flexible gallium nitride-based LED comprises, from top to bottom, a substrate; a wafer layer attached to the substrate; a p-type electrode arranged on the lower surface of the wafer layer; an LED device table arranged on the wafer layer; an n-type electrode arranged on the upper surface of the wafer layer; the substrate is made of a flexible material; the present invention can prepare a flexible, transparent, double-sided luminous, addressable vertical structure gallium nitride-based LED display device; compared with other multiple substrate transfers, complex pick-and-place technologies, wire bonding technologies, etc., the present invention can simplify the device manufacturing process, realize a flexible substrate, transparent, double-sided luminous vertical structure gallium nitride-based LED, and further realize the preparation of an addressable display device on this basis. In addition, the hollow n-type electrode prepared by the present invention increases the electrode ductility, reduces the probability of electrode breakage when the sample is bent, and makes the sample have better flexibility.

Description

Technical Field

[0001] The present invention relates to the fields of optoelectronics and luminous display, and in particular to a flexible gallium nitride-based LED and a preparation method thereof. Background Art

[0002] Flexible optoelectronic technology has been widely developed and may be applied to more advanced fields, such as wearable display devices, flexible semiconductor LEDs, etc. More specific features such as flexibility, bending, and light transmission are inevitable requirements for flexible optoelectronic applications. In recent years, although organic flexible display devices and quantum dot flexible LED display devices have developed rapidly, the reliability and stability of these materials are relatively poor. Gallium nitride-based inorganic material display devices have the characteristics of high brightness, high contrast, high resolution and high reliability, and can even be used under more severe conditions.

[0003] The most critical step in preparing these flexible devices is to integrate inorganic materials with flexible polymer substrates, which requires transferring the prepared tiny and extremely thin chips from the rigid substrate to the flexible polymer substrate. The proposed transfer technologies generally include motion-controlled transfer, shear-assisted transfer printing, gecko-like surface-assisted specific transfer, aphid-like transfer technology, etc. However, the shortcomings of the prior art are that the preparation process methods used often require multiple transfers of the substrate, and the key to the success of the transfer depends on the adhesion strength of the seal / ink interface, which places high requirements on the operator. In addition, in these schemes, they all rely on external equipment to assist in transferring the chip, which increases the complexity of the preparation process. In addition to the transfer process, the preparation of the electrode is also a factor that needs to be considered. The main method currently used is wire bonding technology, which is mainly used for chips of ordinary structure. The above process processes all show relatively complex characteristics and low yields. These are factors that inhibit the further development of flexible, transparent, and double-sided light-emitting chips.

[0004] Therefore, in view of the above difficulties, it is urgent to develop a new flexible GaN-based LED device structure and preparation process. If a flexible gallium nitride-based LED and its preparation method are used, not only can the process be simplified, but also the light emission of a single chip can be controlled by preparing interconnected electrodes, and then the light emission of multiple independent chips can be controlled to realize the display and application of patterns. Therefore, the applicant proposes a flexible gallium nitride-based LED and its preparation method. Summary of the invention

[0005] (I) Technical solution

[0006] The present invention is implemented by the following technical solution: a flexible gallium nitride-based LED, the flexible gallium nitride-based LED comprising, from top to bottom:

[0007] Flexible substrate;

[0008] Wafer layers attached to the substrate and,

[0009] A P-type electrode disposed on the lower surface of the wafer layer;

[0010] An LED device table disposed on a wafer layer;

[0011] A hollow n-type electrode disposed on the upper surface of the wafer layer;

[0012] The flexible substrate is made of flexible material.

[0013] As a further illustration of the above solution, the wafer layer includes: an n-type GaN layer, a quantum well active region, a p-type GaN layer, and,

[0014] An ITO current spreading layer deposited on the p-type GaN layer;

[0015] A single row of connected, interdigitated p-type electrodes is provided on the ITO current spreading layer.

[0016] As a further illustration of the above solution, the p-type electrode is made of a binary alloy, and the electrode shape is a metal electrode in the form of an interdigitated finger, connected in a single row and each row is parallel to each other.

[0017] As a further illustration of the above solution, the substrate is made of epoxy resin, or polyethylene terephthalate, or polyethylene naphthalate.

[0018] As a further illustration of the above solution, the side walls and part of the surface of the LED table are covered with insulating material.

[0019] As a further illustration of the above solution, the n-type electrode is made of a binary alloy, and the electrode shape is interdigitated and connected in a single row.

[0020] The present invention provides a method for preparing a flexible gallium nitride-based LED, wherein the method is used to prepare a flexible gallium nitride-based LED;

[0021] S1. epitaxially growing a gallium nitride-based epitaxial layer on a sapphire substrate;

[0022] S2, depositing an ITO current spreading layer and a p-type electrode layer on the epitaxial layer;

[0023] S3, spin coating a transparent flexible material on the p-type electrode layer to form a flexible substrate, and removing the sapphire substrate by laser stripping;

[0024] S4, reducing the thickness of the epitaxial layer and separating the mesas, so that a channel is formed between the mesas; and filling the channel with an insulating layer;

[0025] S5. Prepare an n-type electrode layer and peel off the insulating layer filled in the trench to complete the production.

[0026] As a further illustration of the above scheme, the epitaxially grown gallium nitride-based epitaxial layer on the sapphire substrate is a sequential epitaxial unintentionally doped gallium nitride (u-GaN) layer, an n-type GaN layer, a quantum well active region, and a p-type GaN layer;

[0027] The p-type electrode is made of a two-element alloy, and the electrode shape is a forked-finger-shaped metal electrode connected in a single row and each row is parallel to each other.

[0028] As a further illustration of the above scheme, S3 specifically spin-coats a certain thickness of epoxy resin on the p-type electrode layer, which can be used as a support in the subsequent laser stripping process after being cured by baking or UV irradiation, and a flexible substrate is spontaneously formed after the sapphire is removed.

[0029] As a further illustration of the above scheme, the method of S4 thinning the sample thickness adopts ICP method or polishing method;

[0030] The method for separating the S4 tabletop is to use ICP separation;

[0031] The n-type electrode is made of a binary alloy, and has an interdigitated shape and is connected in a single row;

[0032] The insulating layer filled in the stripping trench is chemically etched.

[0033] (III) Beneficial effects

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention proposes a new method for preparing a flexible LED, which can realize a transparent, double-sided luminous, vertical structure and addressable display device. Compared with the bonding process and multiple substrate transfer technology of ordinary chips, the present invention spontaneously forms a flexible substrate by directly spin-coating epoxy resin, and only requires one substrate peeling and transfer, avoiding complex and error-prone process, and maximizing the success rate of the chip; the transparent and double-sided light-emitting characteristics of the present invention can maximize the use of device luminescence, improve light extraction efficiency, and meet more diverse display design requirements; the vertical structure LED chip can also avoid the current congestion effect of ordinary structure LED chips; the hollow n-type electrode increases the effective length and extensibility of the electrode, and reduces the probability of electrode breakage due to sample bending; and through the combination of a single row of p-type electrodes and a single column of n-type electrodes, the present invention can realize the production of addressable display devices.

[0036] The present invention uses a simple process method and a one-time substrate transfer technology to realize a vertical structure gallium nitride-based LED display device with flexibility, transparency, double-sided light emission, and addressability. Compared with other multiple substrate transfers, complex pick-and-place technology, wire bonding technology, etc., the present invention can simplify the device manufacturing process, realize a vertical structure gallium nitride-based LED with a flexible substrate, transparency, and double-sided light emission, and further realize the preparation of an addressable display device on this basis. In addition, the hollow n-type electrode prepared by the present invention increases the ductility of the electrode, reduces the probability of electrode breakage when the sample is bent, and makes the sample more flexible. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0038] Figure 1 Schematic diagram of the structure of a gallium nitride epitaxial layer with a sapphire substrate in an embodiment of the present invention;

[0039] Figure 2 This is a schematic diagram of the structure of an epitaxial wafer after ITO deposition in an embodiment of the present invention;

[0040] Figure 3 It is a schematic diagram of a three-dimensional cross-section of a wafer structure after ITO is deposited on an epitaxial wafer in an embodiment of the present invention;

[0041] Figure 4 This is a schematic diagram of the sample structure after the p-type electrode is deposited in an embodiment of the present invention;

[0042] Figure 5 This is a schematic diagram of the sample structure after spin coating a certain thickness of epoxy resin in an embodiment of the present invention;

[0043] Figure 6 This is a schematic diagram of the sample structure after laser stripping and removal of sapphire in an embodiment of the present invention;

[0044] Figure 7 This is a schematic diagram of the sample structure after the LED device table is separated in an embodiment of the present invention;

[0045] Figure 8 Schematic diagram of the structure of the insulating layer filled in the trench in an embodiment of the present invention;

[0046] Fig. 9 This is a schematic diagram of the structure after depositing an n-type electrode in an embodiment of the present invention;

[0047] Fig.10 is a schematic structural diagram of a complete device after the filler is removed according to an embodiment of the present invention;

[0048] Fig.11 is a cross-sectional view of a complete device in an embodiment of the present invention;

[0049] Fig.12 FIG. 4 is a top view of a complete device in an embodiment of the present invention. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0051] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0052] Example

[0053] S1. Epitaxial growth of GaN-based epitaxial layers on sapphire substrates; see Figure 1 The following epitaxial layers are sequentially grown on a sapphire substrate 1 by using an MOCVD method: an epitaxial layer 2 of unintentionally doped gallium nitride (u-GaN), an n-type GaN epitaxial layer 3, a multi-quantum well active layer 4, and a p-type GaN epitaxial layer 5.

[0054] S2, depositing an ITO current spreading layer and a p-type electrode layer on the epitaxial layer, wherein the p-type electrode is made of a two-element alloy and has an interdigitated shape, and is a metal electrode connected in a single row and parallel to each other. Figures 2 to 3 , an ITO layer 6 is deposited on the surface of p-type GaN, and after annealing, it is used as an ohmic contact layer and a current spreading layer. The epitaxial layers 2-5 plus the ITO layer 6 are collectively referred to as a wafer layer 21. Please refer to Figure 4 A single row of connected, interdigitated p-type metal electrodes is deposited on the wafer layer 21 using a photolithography or deposition process to form a p-type electrode layer 22, the material of which may be a metal combination such as Ni / Au, Ti / Au, or Cr / Au.

[0055] S3, spin coating a transparent flexible material on the p-type electrode layer 22 to form a flexible substrate, and then laser stripping to remove the sapphire substrate; see Figure 5Specifically, a certain thickness of transparent epoxy resin is spin-coated on the p-type electrode layer, which can be used as a support in the subsequent laser stripping process after curing by baking or UV irradiation. After removing the sapphire, a flexible substrate 31 is spontaneously formed. The thickness of the flexible substrate 31 can be 10-1000μm. In addition, in this step, the sample can also be inverted and bonded to a currently commercially available flexible substrate material such as PET, PEN, etc. as a flexible substrate, and then laser stripping and other process steps are performed. Please refer to Figure 6 The sapphire substrate 1 is removed by laser lift-off, the epitaxial layer is transferred to the flexible substrate 31, and the epitaxial layer 2 which is not intentionally doped with gallium nitride (u-GaN) is removed by ICP or polishing.

[0056] S4, reducing the thickness of the epitaxial layer and separating the mesas, so that a channel is formed between the mesas; filling the channel with an insulating layer; see Figure 7 , the wafer layer 21 processed in S3 is separated by ICP etching, and the LED table is etched out; see Figure 8 The trenches between the LED device mesas are filled with organic or inorganic insulating materials such as photoresist and silicon dioxide 32. The thickness of the filler is greater than the LED device mesas and covers the side walls and part of the surface of the LED mesas to prevent short circuits of the electrodes.

[0057] S5, prepare an n-type electrode layer, and peel off the insulating layer filled in the trench to complete the production; the n-type electrode is made of a two-element alloy, and the electrode shape is interdigitated and connected in a single row; please refer to Fig. 9 , a single-row connected, interdigitated n-type electrode 23 perpendicular to the direction of the p-type electrode is prepared on the wafer layer by photolithography, deposition, etc., and the material thereof can be a metal combination such as Ni / Au, Ti / Au, Cr / Au, etc.; please refer to Fig.10 , remove the filler 32 in the groove between the LED device mesas by chemical etching or other methods. An upwardly arched suspended electrode structure is formed in the groove between the LED device mesas, so that the n-type metal electrode 23 forms a hollow n-type metal electrode. The hollow state of the n-type electrode increases the effective length and the ductility of the electrode, reduces the probability of electrode breakage due to sample bending, and increases the ductility of the device. The entire device is completed, and the cross-sectional view and top view of the entire device are shown in FIG. Fig.11 , 12 shown.

[0058] The advantages of the present invention are:

[0059] The present invention proposes a new method for preparing a flexible LED, which can realize a transparent, double-sided luminous, vertical structure and addressable display device. Compared with the bonding process and multiple substrate transfer technology of ordinary chips, the present invention spontaneously forms a flexible substrate by directly spin-coating epoxy resin, and only requires one substrate peeling and transfer, avoiding complex and error-prone process, and maximizing the success rate of the chip; the transparent and double-sided light-emitting characteristics of the present invention can maximize the use of device luminescence, improve light extraction efficiency, and meet more diverse display design requirements; the vertical structure LED chip can also avoid the current congestion effect of ordinary structure LED chips; the hollow n-type electrode increases the effective length and extensibility of the electrode, and reduces the probability of electrode breakage due to sample bending; and through the combination of a single row of p-type electrodes and a single column of n-type electrodes, the present invention can realize the production of addressable display devices.

[0060] The present invention uses a simple process method and a one-time substrate transfer technology to realize a vertical structure gallium nitride-based LED display device with flexibility, transparency, double-sided light emission, and addressability. Compared with other multiple substrate transfers, complex pick-and-place technology, wire bonding technology, etc., the present invention can simplify the device manufacturing process, realize a vertical structure gallium nitride-based LED with a flexible substrate, transparency, and double-sided light emission, and further realize the preparation of an addressable display device on this basis. In addition, the hollow n-type electrode prepared by the present invention increases the ductility of the electrode, reduces the probability of electrode breakage when the sample is bent, and makes the sample more flexible.

[0061] A flexible gallium nitride-based LED is further proposed, and the flexible gallium nitride-based LED includes, from top to bottom, a flexible substrate 31; a wafer layer 21 attached to the substrate; an LED device table arranged on the wafer layer, and the sidewalls and part of the surface of the table are covered with insulating materials; an n-type electrode 23 arranged on the surface of the wafer layer; the flexible substrate 31 is made of epoxy resin. The wafer layer 21 includes: an n-type GaN layer 3, a quantum well active region 4, a p-type GaN layer 5, and an ITO current spreading layer 6 deposited on the p-type GaN layer 5; a single-row connected, interdigitated p-type electrode 22 arranged on the ITO current spreading layer 6. The p-type electrode is made of a two-element alloy, and the electrode shape is an interdigitated, single-row connected metal electrode with each row parallel to each other. The n-type electrode is made of a two-element alloy, and the electrode shape is an interdigitated, single-row connected metal electrode.

[0062] It should be further pointed out that the flexible GaN-based LED prepared in this embodiment is a flexible, double-sided, addressable LED, and the current injection method is vertical, and the substrate of the final device is flexible and bendable, and the array is 16*16 or 32*32, thereby realizing a flexible display function; while the prior art is often a series LED array, which does not have the characteristics of flexible bending and addressability, and the injection method is lateral injection. There are three main reasons for achieving this technical effect: (1) Preparation of epoxy resin substrate; (2) Single row of p-type electrodes and single column of hollow n-type electrodes to achieve addressability.

[0063] The prior art often only uses epoxy resin to prepare insulating layers or packaging layers. The present invention directly uses epoxy resin as a flexible substrate to improve the flexible bending performance. For existing epitaxial structures, the addressable function is often based on a transfer substrate (non-conductive substrates such as glass). The present invention uses a flexible substrate made of epoxy resin (flexible substrates such as PET). It should also be pointed out that after the epoxy resin is formed by photocuring or baking, in addition to the characteristics of flexibility, it also has a certain strength. Addressability is based on a vertically structured chip. Each device can be controlled to emit light through a single row of p-type electrodes and a single column of n-type electrodes. The basis for independent control is that the n and p-type electrodes are each connected in a single column and a single row. The part that contributes to addressability is the special design of the single column and single row of n and p-type electrodes (please refer to Fig. 9 ). Only in this way can certain display numbers or letters, patterns and flexible wearable or flexible displays be achieved.

[0064] The implementation schemes in the above embodiments can be further combined or replaced, and the embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various changes and improvements made to the technical solutions of the present invention by professional and technical personnel in this field all belong to the protection scope of the present invention.

Claims

1. A method for preparing a flexible gallium nitride-based LED, characterized in that: The method is used to prepare the following flexible gallium nitride-based LED; The flexible GaN-based LED includes, from top to bottom: Flexible substrate; the flexible substrate is made of epoxy resin; Wafer layer attached to a flexible substrate and, A single row of connected, interdigitated p-type electrodes disposed on the lower surface of the wafer layer; An LED device table disposed on a wafer layer; A single-row connected, interdigitated hollow n-type electrode disposed on the upper surface of the wafer layer and perpendicular to the direction of the p-type electrode; The wafer layer includes an n-type GaN layer, a quantum well active region, a p-type GaN layer, and an ITO current spreading layer deposited on the p-type GaN layer; a single-row connected, interdigitated p-type electrode arranged on the ITO current spreading layer; The p-type electrode is made of a two-element alloy, and the electrode shape is a forked-finger-shaped metal electrode connected in a single row and each row is parallel to each other; The sidewalls and part of the surface of the LED device table are covered with insulating material; The method comprises the following steps: S1. epitaxially growing a gallium nitride-based epitaxial layer on a sapphire substrate; S2, depositing an ITO current spreading layer and a p-type electrode layer on the epitaxial layer; S3, spin coating a transparent flexible material on the p-type electrode layer to form a flexible substrate, and removing the sapphire substrate by laser stripping; S4, reducing the thickness of the epitaxial layer and separating the mesas, so that a channel is formed between the mesas to form a single device; filling an insulating layer in the channel; S5, preparing an n-type electrode layer, and stripping off the insulating layer filled with the trench, to complete the manufacturing, specifically: A single-row, interconnected, interdigitated n-type electrode is prepared on the wafer layer perpendicular to the direction of the p-type electrode; the filler in the trench between the LED device countertops is removed to form an upwardly arched suspended electrode structure in the trench between the LED device countertops, so that the n-type metal electrode forms a hollowed-out n-type metal electrode.

2. The method for preparing a flexible GaN-based LED according to claim 1, characterized in that: The epitaxially grown gallium nitride-based epitaxial layer on the sapphire substrate sequentially epitaxies an unintentionally doped gallium nitride (u-GaN) layer, an n-type GaN layer, a quantum well active region and a p-type GaN layer.

3. The method for preparing a flexible GaN-based LED according to claim 1, characterized in that: In S3, a certain thickness of epoxy resin is specifically spin-coated on the p-type electrode layer, and after curing by baking or ultraviolet irradiation, it can be used as a support in the subsequent laser lift-off process, and a flexible substrate is spontaneously formed after the sapphire is removed.

4. The method for preparing a flexible GaN-based LED according to claim 1, characterized in that: In S4, the method for reducing the thickness of the sample is an ICP method or a polishing method; In S4, the method for separating the table surface is ICP separation; The n-type electrode is made of a binary alloy, and has an interdigitated shape and is connected in a single row; The insulating layer filled in the stripping trench is chemically etched.

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