Micro-display array structure

Abstract

The utility model provides a micro-display array structure, comprising a driving circuit board, the surface of which is provided with a driving circuit; the plurality of micro display units are bonded on the surface of the driving circuit board; the passivation layer is formed on the surfaces of the micro-display units and the surface of the driving circuit board between the micro-display units, and the passivation layer is provided with openings on the upper surfaces of the micro-display units; the metal electrode layers are formed in openings in the upper surfaces of the micro display units; the transparent current expansion layer is deposited on the surface of the micro-display unit and the surface of the driving circuit board between the micro-display units; and the connecting metal layers are deposited among the micro display units. A metal electrode is formed on the surface of each micro-display unit for good ohmic contact, so that the working voltage can be effectively reduced; and meanwhile, the high-reflectivity metal in the metal electrode can effectively reflect light rays to enable the light rays to be emitted from other positions, so that the light emitting brightness of the product is ensured.

Description

Technical Field

[0001] The utility model relates to the technical field of semiconductors, in particular to a micro display array structure. Background Art

[0002] MicroLEDs are the core chips for AR (augmented reality) and VR (virtual reality) devices. Compared to technologies like LCOS (liquid crystal on silicon) and OLED (organic light-emitting diodes), MicroLEDs are considered the optimal solution due to their high resolution, low power consumption, high brightness, and long lifespan. To meet the miniaturization, high resolution, and high brightness requirements of AR / VR, a Si-based GaN (gallium nitride) epitaxial structure combined with CMOS wafer-level bonding has become a preferred solution.

[0003] Currently, there are two main driving methods for wafer-level bonded Micro LEDs:

[0004] The first method is to drive the P electrode of each light-emitting unit in the Micro LED individually, while driving the N electrodes of all light-emitting units together. For example, as described in Chinese Patent 202311703490.7, a transparent conductive material (such as ITO) is typically used to simultaneously connect the N-GaN layers of all light-emitting units. However, due to process limitations, this method cannot perform high-temperature annealing, and good ohmic contact cannot be formed between the transparent conductive material and the N-GaN. This results in an increase in the product's operating voltage and power consumption.

[0005] The second method is to jointly drive the P electrodes of all light-emitting units in the Micro LED, while driving the N electrodes of each light-emitting unit individually. For example, as described in Chinese patent 202110322711.0, a metal electrode is typically used to connect the N-GaN electrode of each light-emitting unit and then extend downward to the CMOS drive electrode at the bottom. In this case, the metal electrode covers the side of the light-emitting unit, blocking some of the light and affecting the product's brightness. Utility Model Content

[0006] In order to overcome the above shortcomings, the present invention provides a micro-display array structure, in which a metal electrode is formed on the surface of the semiconductor layer of each micro-display unit for ohmic contact, effectively solving technical problems such as increased operating voltage caused by the inability of transparent conductive materials to form ohmic contact with the semiconductor layer.

[0007] The technical solution provided by this utility model is:

[0008] The utility model provides a micro display array structure, comprising:

[0009] A driving circuit board, wherein a driving circuit is configured on a surface of the driving circuit board;

[0010] a plurality of micro-display units bonded to the surface of the driving circuit board;

[0011] A passivation layer is formed on the surface of the micro-display unit and the surface of the driving circuit board between the micro-display units, and the passivation layer has an opening formed on the upper surface of each micro-display unit;

[0012] a metal electrode layer formed in the opening on the upper surface of each micro display unit; and

[0013] a transparent current spreading layer deposited on the surface of the micro display unit and the surface of the driving circuit board between the micro display units; and

[0014] A connecting metal layer is deposited between each microdisplay unit.

[0015] The micro-display array structure provided by the present invention forms a metal electrode on the surface of each micro-display unit for ohmic contact, thereby conducting and driving the micro-display unit. This not only avoids the increase in operating voltage caused by the inability of the transparent conductive material to form ohmic contact with the micro-display unit; the metal electrode is only formed in the opening of the passivation layer, and there is no need to extend the metal electrode downward to the drive substrate, thereby reducing the obstruction of the side of the micro-display unit; at the same time, the high-reflectivity metal in the metal electrode can effectively reflect light so that it can be emitted from other positions, thereby ensuring the brightness of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the micro display array structure in one embodiment of the present invention;

[0017] Figure 2 This is a schematic diagram of forming a semiconductor light-emitting structure and a P-electrode layer on the surface of a growth substrate in the present invention;

[0018] Figure 3 This is a schematic diagram of bonding to a driver circuit board and removing the growth substrate in the present invention;

[0019] Figure 4 This is a schematic diagram of etching the semiconductor light-emitting structure and the bonding layer to form a micro-display unit in the present invention;

[0020] Figure 5 A schematic diagram of depositing a passivation layer and forming a metal electrode layer on the entire surface of a driver circuit board in the present invention;

[0021] Figure 6 This is a schematic diagram of depositing a transparent current spreading layer and a connecting metal layer on the entire surface of the driver circuit board in the present invention.

[0022] Reference numerals:

[0023] 10-driving circuit board, 11-first bonding structure, 12-second bonding structure, 13-P electrode layer, 20-micro display unit, 21-first semiconductor layer, 22-light-emitting layer, 23-second semiconductor layer, 30-passivation layer, 40-metal electrode layer, 50-transparent current spreading layer, 60-connecting metal layer. DETAILED DESCRIPTION

[0024] In order to more clearly illustrate the implementation cases of the present invention or the technical solutions in the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without inventive work.

[0025] A first embodiment of the present invention is a micro display array structure, comprising:

[0026] A driving circuit board, wherein a driving circuit is configured on the surface of the driving circuit board; a plurality of micro-display units bonded to the surface of the driving circuit board; a passivation layer formed on the surface of the micro-display units and between the micro-display units, and the passivation layer has openings formed on the upper surface of each micro-display unit; a metal electrode layer formed in the openings on the upper surface of each micro-display unit; a transparent current spreading layer deposited on the surface of the micro-display units and between the micro-display units on the surface of the driving circuit board; and a connecting metal layer deposited between the micro-display units.

[0027] In this embodiment, the driver circuit board is used to drive the micro-display unit bonded to its surface, which is usually a printed circuit board with a CMOS driver circuit configured on the surface. The circuit configured on the surface is designed according to specific application requirements. The micro-display unit is formed by etching the semiconductor light-emitting structure bonded to the surface of the driver circuit board. That is, after the entire surface of the semiconductor light-emitting structure is bonded to the driver circuit board, the semiconductor light-emitting structure is etched according to preset rules to form a plurality of independent micro-display units. The shape of the micro-display unit can be designed according to actual application requirements, such as square, circular, polygonal, etc. The semiconductor light-emitting structure can be prepared using binary, ternary, and quaternary materials of various bands, which are not specifically limited here. The types of the first semiconductor layer, the light-emitting layer, and the second semiconductor layer in the semiconductor light-emitting structure can also be determined according to application requirements. For example, in one example, the first semiconductor layer is a P-type GaN layer, and the second semiconductor layer is an N-type GaN layer.

[0028] The semiconductor light-emitting structure is bonded to the driver circuit board via a bonding layer. Prior to bonding, a first bonding structure is formed on one side of the first semiconductor layer of the semiconductor light-emitting structure, and a second bonding structure is formed on the surface of the driver circuit board. The semiconductor light-emitting structure is bonded to the surface of the driver circuit board via the first and second bonding structures. The first and second bonding structures are formed from alloys such as Ti, Pt, Au, and Sn, with the thickness of either layer ranging from 0.3 µm to 0.5 µm (micrometers). The bonding layer, formed between the driver circuit board and the microdisplay unit, not only provides bonding but also enables the driver circuit board to electrically drive the microdisplay unit. Furthermore, to establish ohmic contact with the first semiconductor layer in the microdisplay unit, a P-electrode layer is typically formed between the bonding layer and the first semiconductor layer. Furthermore, to enable independent driving of each microdisplay unit, the bonding layer and P-electrode layer between each microdisplay unit are further etched through.

[0029] The passivation layer covers the entire surface of the micro-display units (including the surface of the second semiconductor layer, the sides of the semiconductor light-emitting structure, the P-electrode layer, and the bonding layer) and extends to the surface of the driver circuit board between the micro-display units. It is used to protect and isolate the micro-display units. It is made of one or more transparent insulating dielectrics such as SiO2, SiN, and Al2O3, and is generally 200nm-300nm thick. To facilitate conductivity of the second semiconductor layer, the passivation layer is etched into an opening on its surface for subsequent conductive connection. This opening is located on the upper surface of the second semiconductor layer and has a suitable size and shape to facilitate good ohmic contact with the metal electrode layer.

[0030] The metal electrode layer is formed in the opening of the passivation layer and is made of one or more metals such as Cr, Al, Ti, Pt, and Au to form a single or multilayer structure with a thickness of 100nm-200nm. It achieves ohmic contact with the second semiconductor layer. Compared with the traditional solution of using ITO to directly contact and conduct electricity with the second semiconductor layer, it can better achieve ohmic contact, thereby reducing the operating voltage of the Micro LED. At the same time, to reduce the impact of the metal electrode layer blocking light and causing a decrease in brightness, the metal electrode layer includes a first metal layer and a second metal layer. The first metal layer is located on the surface of the second semiconductor layer and is made of a high-reflectivity metal such as Ag or Al. It has a thickness greater than 100nm. In addition to acting as an ohmic contact, it also reflects light, facilitating the reflection of blocked light and emitting it from other locations, thereby ensuring the product's brightness. The second metal layer is generally thicker than 10nm and is laminated and covered on the surface of the first metal layer. The second metal layer is further protected by the first metal layer. In one embodiment, the second metal layer is formed by stacking multiple layers of Ti and Ni metals. The total thickness of the first metal layer and the second metal layer is 100 nm-200 nm.

[0031] The device also includes a transparent current spreading layer deposited on the surface of each microdisplay unit. This layer covers the metal electrode layer and passivation layer of all microdisplay units on the driver circuit board. The metal electrode layer indirectly connects the microdisplay units, thereby connecting the metal electrode layers of all microdisplay units together. The metal electrode layer is located between the microdisplay units and the transparent current spreading layer, preventing direct contact between the two units and preventing ohmic contact problems. The transparent current spreading layer is made of a conductive material that is transparent to the emission wavelength of each microdisplay unit and does not affect light output, such as ITO (tin-doped indium oxide), ICO (cerium-doped indium oxide), or IZO (zinc-doped indium oxide). A connecting metal layer is further deposited on the surface of the transparent current spreading layer between the microdisplay units. It is typically made of a combination of metals such as Cr, Al, Ti, Pt, and Au, with a thickness of 500-2000 nm, to strengthen the interconnection between the microdisplay units.

[0032] The following is an example to illustrate the micro display array structure: Figure 1As shown, a driving circuit for driving array-arranged micro-display units 20 is configured on the surface of a whole driving circuit board 10. A plurality of micro-display units are bonded to the driving circuit board 10 through a bonding layer (including a first bonding structure 11 and a second bonding structure 12), and the bonding layer between different micro-display units is pierced. It should be understood that the figure only shows the structure of two of the micro-display units by way of example, and other micro-display units not shown are also arranged in an array on the surface of the driving circuit board; a P-electrode layer 13 is also included between the bonding layer and the first semiconductor layer to form a good ohmic contact with the first semiconductor layer; the first semiconductor layer 21, the light-emitting layer 22, and the second semiconductor layer 23 in the micro-display unit 20 are stacked in sequence to form a semiconductor structure for the entire surface. Etching is performed, and usually the sidewalls etched by each microdisplay unit have a certain slope; after etching the semiconductor structure, the step of etching and isolating the bonding layers between different microdisplay units is also included, that is, the first bonding structure 11, the second bonding structure 12 and the P-electrode layer 13 are further etched to make the bonding layers corresponding to each microdisplay unit independent of each other, so as to facilitate independent driving of the microdisplay unit; the passivation layer 30 is entirely covered on the surface of the microdisplay unit and the driving circuit board, and an opening is formed on the surface of the second semiconductor layer of each microdisplay unit for subsequent conductive connection to the second semiconductor layer; the metal electrode layer 40 is deposited in the opening of the passivation layer to achieve good ohmic contact with the second semiconductor layer, which is beneficial to reducing the operating voltage. In one example, the metal electrode layer includes a first metal layer and a second metal layer (not shown), wherein the first metal layer is located on the surface of the second semiconductor layer and is made of a high-reflectivity metal such as Ag and Al. In addition to acting as an ohmic contact, it also reflects light, which is beneficial for the blocked light to be emitted from other positions after reflection, thereby ensuring the brightness of the product; and a second metal layer is further formed on the surface of the first metal layer, and the first metal layer is covered and protected by the second metal layer.

[0033] In addition to the above structure, the circuit board also includes a transparent current spreading layer 30 deposited across the entire surface of the driver circuit board 10 and a connecting metal layer 60 deposited between each microdisplay unit 20. In this embodiment, after forming metal electrodes on the microdisplay unit surfaces, the transparent current spreading layer 30 (ITO) is further deposited across the entire surface, and the connecting metal layer 60 is deposited within the grooves between the microdisplay units 20 to interconnect the microdisplay units 20. The transparent conductive layer can be made of a transparent metal oxide material, such as ITO or FTO, with a thickness of 150nm-300nm. A metal electrode layer is formed between the transparent current spreading layer and the second semiconductor layer, eliminating direct contact with the second semiconductor layer and thus preventing ohmic contact. The connecting metal layer 60 can be made of any conductive metal, such as Cr, Al, Ti, Pt, Au, and combinations thereof. Its thickness can be adjusted based on actual needs, with a preferred range of 500nm-2000nm.

[0034] In actual application, the preparation process of the micro-display array structure includes:

[0035] S10, forming a semiconductor light emitting structure and a P electrode layer 13 on the surface of the growth substrate, such as Figure 2 As shown, the semiconductor light emitting structure includes, from bottom to top, a second semiconductor layer 23 , a light emitting layer 22 and a first semiconductor layer 21 .

[0036] S20, flipping and bonding the semiconductor light emitting structure to the driving circuit board through the bonding layer, and removing the growth substrate; specifically, Figure 3 As shown, a first bonding structure 11 is formed on the surface of a driver circuit board 10, and a second bonding structure 12 is formed on the surface of a semiconductor light-emitting structure. The semiconductor light-emitting structure is bonded to the surface of the driver circuit board via the first and second bonding structures. After bonding, the semiconductor structure is flipped upside down, and from bottom to top along the driver circuit board, a first semiconductor layer 21, a light-emitting layer 22, and a second semiconductor layer 23 are formed.

[0037] S30, etching the semiconductor light emitting structure until the P electrode layer, forming a mesa on the surface of the remaining portion of the P electrode layer, such as Figure 4 As shown, micro display units 20 are arranged in an array on the surface of the driving circuit board and are independent of each other.

[0038] S40, further etching along the side of the table to the driver circuit board; at this time, if Figure 4 As shown, the etched materials are mainly metal materials in the P-electrode layer 13 and the bonding layer (including the first bonding structure 11 and the second bonding structure 12), that is, the P-electrode layer and the bonding layer between each micro-display unit are etched through and separated, so as to realize the independent driving of the corresponding micro-display unit by the driving circuit board through the bonding layer and the P-electrode layer.

[0039] S50 , depositing a passivation layer on the entire surface of the driving circuit board, and etching openings in the passivation layer on the surface of the second semiconductor layer of each micro display unit.

[0040] S60, depositing metal material in the opening on the surface of the second semiconductor layer of each micro display unit to form a metal electrode layer. Figure 5 As shown, the metal electrode layer 40 is deposited in the opening of the passivation layer 30 on the surface of the second semiconductor layer.

[0041] S70, depositing a transparent current spreading layer 50 on the entire surface of the driving circuit board. Figure 6 As shown, the transparent current spreading layer 50 covers the surface of the passivation layer and the surface of the metal electrode layer 40 .

[0042] S80 , depositing a connection metal layer 60 between each micro display unit.

[0043] It should be noted that the above embodiments can be freely combined as needed. The above description is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention, and such improvements and modifications should also be considered as the scope of protection of the present invention.

Claims

1. A micro display array structure, characterized in that: include: A driving circuit board, wherein a driving circuit is configured on a surface of the driving circuit board; a plurality of micro-display units bonded to the surface of the driving circuit board; A passivation layer is formed on the surface of the micro-display unit and the surface of the driving circuit board between the micro-display units, and the passivation layer has an opening formed on the upper surface of each micro-display unit; a metal electrode layer formed in an opening on an upper surface of each micro display unit; and a transparent current spreading layer deposited on the surface of the micro-display unit and the surface of the driving circuit board between the micro-display units; and A connecting metal layer is deposited between each microdisplay unit.

2. The micro display array structure according to claim 1, wherein: The micro display unit includes, from bottom to top, a first semiconductor layer, a light emitting layer, and a second semiconductor layer; The passivation layer forms an opening on the surface of the second semiconductor layer of each micro display unit.

3. The micro display array structure according to claim 1, wherein: The passivation layer is made of a transparent insulating material and has a thickness of 200nm-300nm.

4. The micro display array structure according to claim 1, wherein: The thickness of the metal electrode layer is 100nm-200nm.

5. The micro display array structure according to claim 1, wherein: The metal electrode layer comprises: A first metal layer for achieving ohmic contact between the upper surface of each micro-display unit and the transparent current spreading layer and for reflecting light emitted from the micro-display unit is formed on the upper surface of the micro-display unit; The second metal layer is used to protect the first metal layer and is formed on the surface of the first metal layer.

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