Patent Description:
In recent years, miniaturized electro-optics devices are proposed and developed, including micro light emitting diode (micro LED). The micro LED-based display panels have the advantages of high brightness, high contrast ratio, fast response, and low power consumption. The micro LED-based display technology has found a wide range of applications in the display field, including smartphones and smart watches.

<CIT> discloses a method of selectively transferring micro devices from a donor substrate to contact pads on a receiver substrate. Micro devices being attached to a donor substrate with a donor force. The donor substrate and receiver substrate are aligned and brought together so that selected micro devices meet corresponding contact pads. A receiver force is generated to hold selected micro devices to the contact pads on the receiver substrate. The donor force is weakened and the substrates are moved apart leaving selected micro devices on the receiver substrate. Several methods of generating the receiver force are disclosed, including adhesive, mechanical and electrostatic techniques.

<CIT> provides a repairing method, manufacturing method, device and electronic apparatus of micro-LED are disclosed. The method for repairing micro-LED defects comprises: obtaining a micro-LED defect pattern on a receiving substrate; forming micro-LEDs (703b) corresponding to the defect pattern on a laser-transparent repair carrier substrate (<NUM>); aligning the micro-LEDs (703b) on the repair carrier substrate (<NUM>) with defect positions on the receiving substrate, and bringing the micro-LEDs (703b) into contact with pads at the defect positions; and irradiating the repair carrier substrate with a laser from the repair carrier substrate side, to lift-off the micro-LEDs from the repair carrier substrate (<NUM>).

<CIT> discloses an assembling method, a manufacturing method, an device and an electronic apparatus of flip-die. The method for assembling a flip-die, comprises: temporarily bonding the flip-die onto a laser-transparent first substrate, wherein bumps of the flip-die are located on the side of the flip-die opposite to the first substrate; aligning the bumps with pads on a receiving substrate; irradiating the original substrate with laser from the first substrate side to lift-off the flip-die from the first substrate; and attaching the flip-die on the receiving substrate. A faster assembly rate can be achieved by using the present invention. A smaller chip size can be achieved by using the present invention. A lower profile can be achieved by using the present invention.

<CIT> provides a manufacturing method of making a semiconductor device via multiple stages of alignment bonding and substrate removal. One example is an integrated full-color LED display panel, in which multiple wafers with different arrays of LEDs are integrated onto a host wafer with driver circuitry. The driver circuitry typically is an array of pixel drivers that drive individual LEDs on the display panel.

<CIT> provides a process and system for connecting a semiconductor chip to a substrate is provided. The process includes providing the substrate that is configured to receive the semiconductor chip that has a bonding pad. The substrate has a first side that is suited to be connected to the semiconductor chip and a second side that is opposite the first side. The process then includes designing a metallization bonding structure on the first side of the substrate.

<CIT> relates to a display device and, in particular, to a display device using a semiconductor light emitting diode.

The disclosure will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of some embodiments are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.

In fabricating a micro light emitting diode (micro LED) display panel, each of the micro LED has to be transferred from a growth substrate to a target substrate. Considering the display panel includes thousands to millions of micro LEDs, a pick-and-place transfer process is extremely time-consuming, and thus not suitable for large-scale fabrication of micro LED display panels. An improvement to the pick-and-place transfer is to use a printing head for transferring a plurality of micro LEDs at one time. Still, a process of transferring a large number of micro LEDs using a printing head is too complicated and time-consuming. Moreover, misalignment between the micro LEDs and the bonding contacts in the target substrate occurs frequently in the pick-and-place transfer or the transfer process using a printing head, resulting in defects in the display panel.

Accordingly, the present disclosure provides a method for transferring a plurality of micro light emitting diodes to a target substrate as recited in claim <NUM> that substantially obviate one or more of the problems due to limitations and disadvantages of the related art. In one aspect, the present disclosure provides a method for transferring a plurality of micro light emitting diodes to a target substrate. In some embodiments, the method includes providing a first substrate having an array of the plurality of micro LEDs; providing a target substrate having a bonding layer comprising a plurality of bonding contacts; applying the plurality of bonding contacts with an electrical potential; aligning the plurality of micro LEDs with the plurality of bonding contacts having the electrical potential; and transferring the plurality of micro LEDs in the first substrate onto the target substrate.

<FIG> illustrate a process of transferring a plurality of micro light emitting diodes to a target substrate in some embodiments according to the present disclosure. Referring to <FIG>, the method in some embodiments includes providing a first substrate <NUM> having an array of the plurality of micro LEDs <NUM> on a first base substrate <NUM>. Referring to <FIG>, the method in some embodiments further includes providing a target substrate <NUM> having a bonding layer <NUM> including a plurality of bonding contacts <NUM> on a second base substrate <NUM>. Referring to <FIG>, the method in some embodiments further includes placing the first substrate <NUM> and the target substrate <NUM> so that the first substrate <NUM> and the target substrate <NUM> face each other; and moving the first substrate <NUM> and the target substrate <NUM> toward each other. Referring to <FIG>, the method in some embodiments further includes applying the plurality of bonding contacts <NUM> with an electrical potential (e.g., a positive electrical potential, indicated as positive charges in <FIG>), and aligning the plurality of micro LEDs <NUM> with the plurality of bonding contacts <NUM> having the electrical potential. Referring to <FIG>, the method in some embodiments further includes transferring the plurality of micro LEDs <NUM> in the first substrate <NUM> onto the target substrate <NUM>. Referring to <FIG>, the method in some embodiments further includes moving the first substrate <NUM> away from the target substrate <NUM>, thereby forming an array substrate <NUM>. The array substrate <NUM> includes the plurality of micro LEDs <NUM> transferred to the plurality of bonding contacts <NUM>.

Optionally, the electrical potential applied to the plurality of bonding contacts <NUM> is a positive electrical potential (e.g., greater than <NUM> V, greater than 5V, and greater than 10V). Optionally, the electrical potential applied to the plurality of bonding contacts <NUM> is a negative electrical potential (e.g., lower than - <NUM> V, lower than - 5V, and lower than - 10V).

In the present method, the alignment of the plurality of micro LEDs <NUM> with the plurality of bonding contacts <NUM> is assisted by the electrical potential applied to the bonding layer <NUM>. The electrical potential on the plurality of bonding contacts <NUM> polarizes the plurality of micro LEDs <NUM> during the alignment process, thereby generating an attractive force between the plurality of bonding contacts <NUM> and the plurality of micro LEDs <NUM> (now being polarized). The attractive force greatly enhances the accuracy and reliability of the alignment process, achieving highly efficient and precise transfer of the plurality of micro LEDs <NUM> from the first substrate <NUM> to the target substrate <NUM>.

In some embodiments, each of the plurality of micro LEDs <NUM> includes a micro p-n diode <NUM> and a metallization block <NUM> on the micro p-n diode <NUM>. The step of aligning the plurality of micro LEDs <NUM> with the plurality of bonding contacts <NUM> includes aligning the metallization block <NUM> with one of the plurality of bonding contacts <NUM> applied with the electrical potential, the metallization block <NUM> is placed between the micro p-n diode <NUM> and one of the plurality of bonding contacts <NUM> during the alignment process. Optionally, the bonding layer <NUM> is applied with the electrical potential during the entire alignment process. Optionally, the step of applying the plurality of bonding contacts <NUM> with the electrical potential is performed during moving the first substrate <NUM> and the target substrate <NUM> toward each other. Optionally, the step of applying the plurality of bonding contacts <NUM> with the electrical potential is performed prior to the step of moving the first substrate <NUM> and the target substrate <NUM> toward each other. Optionally, the step of applying the plurality of bonding contacts <NUM> with the electrical potential is performed prior to the step of moving the first substrate <NUM> and the target substrate <NUM> toward each other, and the electrical potential at the plurality of bonding contacts <NUM> is maintained throughout the step of moving the first substrate <NUM> and the target substrate <NUM> toward each other until the alignment process is finished.

In some embodiments, the micro p-n diode <NUM> includes a compound semiconductor having a bandgap corresponding to a specific region in the spectrum. Optionally, the micro p-n diode <NUM> includes one or more layers based on II-VI materials (e.g. ZnSe) or III-V nitride materials (e.g. GaN, AlN, InN, and their alloys). Optionally, the micro p-n diode <NUM> is formed on a first base substrate <NUM>. Optionally, the first base substrate <NUM> is a growth substrate. Optionally, the first base substrate <NUM> is a flexible carrier substrate. Optionally, the growth substrate is made of one or a combination of silicon, SiC, GaAs, GaN and sapphire (Al2O3). Optionally, the first base substrate <NUM> is a sapphire growth substrate, and the micro p-n diode <NUM> is formed of GaN.

In some embodiments, the first substrate <NUM> includes a metallization layer <NUM> having multiple ones of the metallization blocks <NUM> in the plurality of micro LEDs <NUM>. Optionally, the metallization layer <NUM> includes an electrode layer and optionally a barrier layer. In one example, the electrode layer makes ohmic contact to a p-doped GaN layer of the micro p-n diode <NUM>. Optionally, the electrode layer includes a high work-function metal such as Ni, Au, Ag, Pd and Pt. Optionally, the electrode layer is made of a reflective material. Optionally, the electrode layer is made of a transparent material. The barrier layer functions to prevent diffusion of impurities into the micro p-n diode <NUM>, for example, prevent diffusion of components from the bonding layer into the micro p-n diode <NUM>. Optionally, the barrier layer includes Pd, Pt, Ni, Ta, Ti and TiW.

Optionally, the metallization layer <NUM> has a thickness in a range of approximately <NUM> to approximately <NUM>, e.g., approximately <NUM> to approximately <NUM>, approximately <NUM> to approximately <NUM>, approximately <NUM> to approximately <NUM>, approximately <NUM> to approximately <NUM>, approximately <NUM> to approximately <NUM>, approximately <NUM> to approximately <NUM>, approximately <NUM> to approximately <NUM>, and approximately <NUM> to approximately <NUM>.

Various appropriate materials and various appropriate fabricating methods may be used for forming the bonding layer <NUM>. Examples of appropriate bonding layer materials include indium, tin, gold, silver, molybdenum, aluminum, and laminates or alloys thereof. Optionally, the bonding layer <NUM> has a thickness in a range of approximately <NUM> to approximately <NUM>, e.g., approximately <NUM> to approximately <NUM>, approximately <NUM> to approximately <NUM>, approximately <NUM> to approximately <NUM>, approximately <NUM> to approximately <NUM>, approximately <NUM> to approximately <NUM>, approximately <NUM> to approximately <NUM>, and approximately <NUM> to approximately <NUM>.

In some embodiments, the step of applying the bonding layer <NUM> with the electrical potential includes applying the electrical potential to a signal line commonly connected to the plurality of bonding contacts <NUM>. <FIG> illustrates a process of applying an electrical potential to the plurality of bonding contacts in a target substrate in some embodiments according to the present disclosure. Referring to <FIG>, an electrical potential V is applied to the plurality of bonding contacts <NUM> through a signal line SL commonly connected to the plurality of bonding contacts <NUM>. In one example, the plurality of micro LEDs <NUM> are transferred to a target substrate for making a passive matrix micro LED display panel. Optionally, the electrical potential is applied to the plurality of bonding contacts <NUM> through a common electrode signal line commonly connected to the plurality of bonding contacts <NUM>.

<FIG> is a schematic diagram illustrating the structure of a first substrate and a target substrate during a process of transferring a plurality of micro light emitting diodes to the target substrate in some embodiments according to the present disclosure. Referring to <FIG>, the target substrate <NUM> includes an array of a plurality of thin film transistors TFT. Each of the plurality of thin film transistors TFT includes a drain electrode D electrically connected to one of the plurality of bonding contacts <NUM>, a source electrode S electrically connected to a common electrode <NUM>, and a gate electrode G electrically connected to a gate line GL. In some embodiments, the step of applying the electrical potential to the signal line commonly connected to the plurality of bonding contacts <NUM> includes applying a plurality of gate scanning signals respectively to a plurality of gate electrodes of the plurality of thin film transistors TFT to turn on the plurality of thin film transistors TFT; and applying the electrical potential to the common electrode <NUM> electrically connected to a plurality of source electrode of the plurality of thin film transistors TFT thereby applying the electrical potential to the plurality of bonding contacts <NUM>. Optionally, the common electrode <NUM> is a cathode.

<FIG> illustrate an electrical field-assisted alignment of a plurality of micro light emitting diodes with a plurality of bonding contacts in some embodiments according to the present disclosure. Referring to <FIG>, the electrical potential applied to one of the plurality of bonding contacts <NUM> forms an electrical field E, which polarizes one of the plurality of metallization blocks <NUM>. The electrical field E induces a polarized charge distribution in the one of the plurality of metallization blocks <NUM>. In one example, and as shown in <FIG>, the electrical potential is a positive electrical potential. The electrical field E induces a polarized charge distribution in the one of the plurality of metallization blocks <NUM> such that negative charges accumulate on a first side of the one of the plurality of metallization blocks <NUM> proximal to the one of the plurality of bonding contacts <NUM>, and positive charges accumulate on a second side of the one of the plurality of metallization blocks <NUM> distal to the one of the plurality of bonding contacts <NUM>. The first side of the one of the plurality of metallization blocks <NUM> having the negative charges accumulated is attracted to the one of the plurality of bonding contacts <NUM>. Due to this attractive force between the one of the plurality of metallization blocks <NUM> and the one of the plurality of bonding contacts <NUM>, they are aligned with respect to each other.

Referring to <FIG>, the one of the plurality of metallization blocks <NUM> and the one of the plurality of bonding contacts <NUM> are misaligned. Due to the distribution of the electrical field E, the one of the plurality of metallization blocks <NUM> is subject to two forces, a first force Fd pulling the one of the plurality of metallization blocks <NUM> toward the one of the plurality of bonding contacts <NUM>, and a second force Fc re-aligning the one of the plurality of metallization blocks <NUM> and the one of the plurality of bonding contacts <NUM> with respect to each other.

In some embodiments, the step of transferring the plurality of micro LEDs <NUM> onto the target substrate <NUM> includes debonding the plurality of micro LEDs <NUM> from the first substrate <NUM>. Various appropriate debonding methods may be used for debonding the plurality of micro LEDs <NUM> from the first substrate <NUM>. In some embodiments, a laser lift-off process can be performed to separate the plurality of micro LEDs <NUM> from the first substrate <NUM> (see <FIG>). The laser lift-off process uses a collimated high-energy UV laser beam (e.g., <NUM>). Optionally, the laser lift-off process is an excimer laser lift-off process. In some embodiments, a chemical lift-off process can be performed to separate the plurality of micro LEDs <NUM> from the first substrate <NUM>. In some embodiments, a mechanical lift-off process can be performed to separate the plurality of micro LEDs <NUM> from the first substrate <NUM>. In some embodiments, the step of debonding the plurality of micro LEDs <NUM> from the first substrate <NUM> includes one or a combination of a laser lift-off process, a chemical lift-off process, and a mechanical lift-off process. Optionally, the plurality of micro LEDs <NUM> are then immersed in a bath (e.g., an acetone bath) to further separate the plurality of micro LEDs <NUM> from the first substrate <NUM>.

In some embodiments, subsequent to transferring the plurality of micro LEDs <NUM> onto the target substrate <NUM>, the method further includes soldering the plurality of micro LEDs <NUM> respectively onto the plurality of bonding contacts <NUM>. Optionally, the step of soldering the plurality of micro LEDs <NUM> respectively onto the plurality of bonding contacts <NUM> is performed by reflow soldering. Optionally, the step of soldering the plurality of micro LEDs <NUM> respectively onto the plurality of bonding contacts <NUM> is performed by laser-assisted soldering in which laser radiation is absorbed by the plurality of bonding contacts <NUM> thereby soldering the plurality of micro LEDs <NUM> respectively onto the plurality of bonding contacts <NUM>. Optionally, the step of soldering the plurality of micro LEDs <NUM> respectively onto the plurality of bonding contacts <NUM> is performed by laser welding. Optionally, the step of soldering the plurality of micro LEDs <NUM> respectively onto the plurality of bonding contacts <NUM> is performed by infrared soldering.

In some embodiments, the first substrate <NUM> is a growth substrate, and the plurality of micro LEDs <NUM> are directly transferred to a target substrate <NUM> to form an array substrate having the plurality of micro LEDs <NUM>.

In some embodiments, the first substrate <NUM> is a carrier substrate, e.g., a flexible carrier substrate. Accordingly, prior to transferring the plurality of micro LEDs <NUM> from the first substrate <NUM> to the target substrate <NUM>, the method in some embodiments further includes fabricating the plurality of micro LEDs <NUM> on a growth substrate; and transferring the plurality of micro LEDs <NUM> in the growth substrate onto the first substrate <NUM>.

In some embodiments, prior to transferring the plurality of micro LEDs <NUM> in the first substrate <NUM> onto the target substrate <NUM>, the method further includes adjusting a first pitch of the plurality of micro LEDs <NUM> in the first substrate <NUM> such that the first pitch matches with a second pitch of the plurality of bonding contacts <NUM> in the target substrate <NUM>. Optionally, the first pitch of the plurality of micro LEDs <NUM> in the first substrate <NUM> is adjusted by stretching the first substrate <NUM> (e.g., a flexible carrier substrate).

In another aspect not forming part of the claimed invention, the present disclosure provides an array substrate having a plurality of micro LEDs transferred by a method described herein. <FIG> is a schematic diagram illustrating the structure of an array substrate having a plurality of micro LEDs transferred by a transferring method in some embodiments according to the present disclosure. Referring to <FIG>, the array substrate <NUM> in some embodiments includes a second base substrate <NUM>, a bonding layer <NUM> having a plurality of bonding contacts <NUM> on the second base substrate <NUM>, a metallization layer <NUM> having a plurality of metallization blocks <NUM> and on a side of the bonding layer <NUM> distal to the second base substrate <NUM>, and a plurality of micro p-n diodes <NUM> on a side of the metallization layer <NUM> distal to the bonding layer <NUM>.

In another aspect not forming part of the claimed invention, the present disclosure provides a display apparatus having an array substrate described herein or fabricated by a method described herein. Examples of appropriate display apparatuses include, but are not limited to, an electronic paper, a mobile phone, a tablet computer, a television, a monitor, a notebook computer, a digital album, a GPS, etc..

Claim 1:
A method for manufacturing an array substrate, comprising:
providing a first substrate(<NUM>) having an array of a plurality of micro light emitting diodes, micro LEDs;
providing a target substrate(<NUM>) having a bonding layer comprising a plurality of bonding contacts(<NUM>);
applying the plurality of bonding contacts with an electrical potential;
aligning the plurality of micro LEDs with the plurality of bonding contacts having the electrical potential; and
transferring the plurality of micro LEDs in the first substrate onto the target substrate; and characterized in that the method further comprises:
moving the first substrate (<NUM>) away from the target substrate (<NUM>) to form the array substrate (<NUM>) having the plurality of micro LEDs transferred to the plurality of bonding contacts;
wherein applying the plurality of bonding contacts with the electrical potential comprises applying the electrical potential to a signal line commonly connected to the plurality of bonding contacts;
wherein the target substrate comprises an array of a plurality of thin film transistors, each of which comprising a drain electrode electrically connected to one of the plurality of bonding contacts, a source electrode electrically connected to a common electrode, and a gate electrode;
wherein applying the electrical potential to the signal line commonly connected to the plurality of bonding contacts comprises:
applying a plurality of gate scanning signals respectively to a plurality of gate electrodes of the plurality of thin film transistors to turn on the plurality of thin film transistors; and
applying the electrical potential to the common electrode electrically connected to a plurality of source electrode of the plurality of thin film transistors thereby applying the electrical potential to the plurality of bonding contacts.