Display device and manufacturing method thereof

Abstract

A method for manufacturing a display device according to one embodiment of the present invention comprises the steps of: growing at least one light-emitting diode (LED) on a first substrate; coating the first substrate with discretionary material; etching the area surrounding the at least one LED; arranging a buffer material at a position spaced apart from the at least one LED; and transferring the at least one LED positioned on the first substrate to a second substrate.

Description

Display device and manufacturing method thereof

[0001] The present invention is applicable to all fields of technology related to display devices, and more specifically, relates to a display device using a micro LED (Light Emitting Diode) and a manufacturing method thereof. In particular, by simplifying the transfer process of an RGB LED light source, it can be applied to high-definition displays.

[0002] Recently, display devices with superior characteristics, such as thinness and flexibility, are being developed in the display technology field. In contrast, the major displays currently commercialized are represented by LCD (Liquid Crystal Display) and OLED (Organic Light Emitting Diode).

[0003] Meanwhile, a light emitting diode (LED) is a semiconductor light emitting device well known for converting electric current into light. Starting with the commercialization of a red LED using a GaAsP compound semiconductor in 1962, it has been used as a light source for display images in electronic devices including information and communication devices, along with a green LED of the GaP:N series. Therefore, a method for solving the above-described problem by implementing a display using the semiconductor light emitting device can be presented. The semiconductor light emitting device has various advantages such as a long lifespan, low power consumption, excellent initial driving characteristics, and high vibration resistance compared to a filament-based light emitting device.

[0004] The size of these semiconductor light-emitting devices has recently been reduced to tens of micrometers.

[0005] The technical problem to be solved by the present invention is to propose a method by which an LED chip separated from a sapphire substrate can be stably separated and stably transferred to a donor substrate or wiring substrate without impact, for example.

[0006] A method for manufacturing a display device to achieve the above object includes a step of growing at least one LED (Light Emitting Diode) on a first substrate, a step of applying an arbitrary material to the first substrate, a step of etching a periphery of the at least one LED, a step of arranging a buffer material at a position spaced apart from the at least one LED, and a step of transferring the at least one LED located on the first substrate to a second substrate.

[0007] For example, the above-mentioned buffer corresponds to nanofibers.

[0008] For example, the above-mentioned spaced location is less than 10um.

[0009] For example, the above arbitrary material corresponds to a polymer series material (ex: Su-8, etc.).

[0010] For example, the transferring step further includes a step of firstly transferring the at least one LED to the buffer material, and a step of secondly transferring the at least one LED arranged on the buffer material to the second substrate.

[0011] For example, the laser used in the first transcription step is applied to all LEDs simultaneously.

[0012] For example, the laser used in the secondary transcription step is applied sequentially to individual LEDs.

[0013] For example, the intensity of the laser used in the secondary transfer step is lower than the intensity of the laser used in the primary transfer step (e.g., a high-power laser for separating GaN from a sapphire substrate).

[0014] For example, the first substrate corresponds to at least one of a sapphire substrate or a silicon substrate.

[0015] For example, the second substrate corresponds to at least one of a donor substrate or a wiring substrate.

[0016] A display device manufactured by any of the above-described methods also falls within the scope of the present invention.

[0017] According to one embodiment of the present invention, there is a technical effect in which an LED chip separated from a sapphire substrate or the like can be stably separated.

[0018] Furthermore, there is a technical effect that allows an LED chip separated from a sapphire substrate, etc., to be stably placed on a donor substrate or wiring substrate.

[0019] Additionally, according to another embodiment of the present invention, there are additional technical effects not mentioned herein. Those skilled in the art will understand these effects upon reading the specification and drawings.

[0020] Figure 1 illustrates a method of transferring using a donor substrate according to a conventional technique.

[0021] Figure 2 illustrates a remote transcription method according to the prior art.

[0022] Figure 3 is a drawing for explaining the problems of the remote transfer method according to the prior art from the perspective of chip separation by laser.

[0023] FIG. 4 is a drawing for explaining a problem of a remote transfer method according to the prior art from the perspective of receiving a chip from a donor substrate.

[0024] FIG. 5 is a drawing for explaining conditions for stably separating an LED chip from a first substrate according to one embodiment of the present invention.

[0025] FIG. 6 is a drawing for explaining conditions for stably holding an LED chip on a second substrate according to one embodiment of the present invention.

[0026] Figure 7 is a drawing for explaining a buffer material required according to one embodiment of the present invention.

[0027] FIG. 8 illustrates preparatory steps for a remote transcription process according to one embodiment of the present invention.

[0028] Figure 9 illustrates a remote transcription process according to one embodiment of the present invention.

[0029] FIG. 10 is an image taken with a scanning electron microscope (SEM) of an LED chip temporarily arranged on a nanofiber according to one embodiment of the present invention.

[0030] FIG. 11 is an image of various LED chips stably and finally placed on a donor substrate or wiring substrate according to one embodiment of the present invention.

[0031] Hereinafter, embodiments disclosed in this specification will be described in detail with reference to the attached drawings. Regardless of the drawing numbers, identical or similar components will be given the same reference numbers, and redundant descriptions thereof will be omitted. The suffixes "module" and "part" used for components in the following description are assigned or used interchangeably only for the convenience of writing the specification, and do not in themselves have distinct meanings or roles. In addition, when describing the embodiments disclosed in this specification, if it is determined that a specific description of a related known technology may obscure the gist of the embodiments disclosed in this specification, a detailed description thereof will be omitted. In addition, it should be noted that the attached drawings are only intended to facilitate easy understanding of the embodiments disclosed in this specification, and should not be construed as limiting the technical matters disclosed in this specification by the attached drawings.

[0032] Furthermore, although each drawing is described for convenience of explanation, it is also within the scope of the present invention for a person skilled in the art to implement another embodiment by combining at least two drawings.

[0033] Additionally, when an element such as a layer, region or substrate is referred to as existing "on" another element, it will be understood that this may be directly on the other element, or that there may be intermediate elements in between.

[0034] The display device described in this specification is a concept that includes all display devices that display information as a unit pixel or a set of unit pixels. Therefore, it can be applied not only to finished products but also to components. For example, a panel corresponding to a part of a digital TV also independently corresponds to a display device in this specification. Finished products may include mobile phones, smart phones, laptop computers, digital broadcasting terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation systems, slate PCs, tablet PCs, Ultrabooks, digital TVs, desktop computers, etc.

[0035] However, it will be readily apparent to those skilled in the art that the configuration according to the embodiments described herein may be applied to a display-capable device, even if it is a new product type developed in the future.

[0036] In addition, the semiconductor light-emitting device mentioned in the specification is a concept that includes LED, micro LED, etc., and may be used interchangeably.

[0037] Figure 1 illustrates a method of transferring using a donor substrate according to a prior art. Transfer is performed in the order of (a), (b), and (c) in Figure 1.

[0038] First, as shown in (a) of Fig. 1, at least one LED (120) is arranged on a COW (chip on wafer) (110).

[0039] Furthermore, as shown in (b) of Fig. 1, after attaching an LED on a donor substrate (130) using a stamp (140), the LED is finally moved on a wiring substrate (150) as shown in (c) of Fig. 1.

[0040] However, when transfer is performed using a donor substrate as shown in Fig. 1 according to the conventional technology, manufacturing costs increase, tact time increases, and yield issues increase due to an increase in the number of processes.

[0041] Additionally, there are limitations to the fixed-price response, which means there are significant problems in actual commercialization.

[0042] Meanwhile, the remote transfer methods unveiled by some companies all require a donor substrate, making contact-based transfer inevitable. However, this presents limitations for large-area display devices and increases costs.

[0043] Accordingly, discussions on non-contact remote transcription are intensifying. In this regard, reference will be made to Figure 2 below for further discussion.

[0044] Figure 2 illustrates a remote transcription method according to the prior art.

[0045] As shown in Fig. 2, a method of selectively transferring a chip (230) from a sapphire substrate (220) to a wiring substrate (240) in one transfer using a laser (210) is used. Since it is not a contact method, it is not affected by the substrate and has the advantage of being able to apply the same technology to both small and large display devices.

[0046] Furthermore, because it employs a non-contact transfer method, it offers the advantage of easy repair. For example, if a pre-inspection is performed on the COW, transferring a chip at a failure location is not attempted, and a good chip can be remotely transferred to that location later. Furthermore, if a chip breaks during transfer, it is not yet bonded, making it simple to remove and remotely transfer to that exact spot.

[0047] However, the reason why the non-contact remote transfer method illustrated in Fig. 2 is difficult in practice (this is related to the transfer principle of GaN) will be explained in detail with reference to Fig. 3 below.

[0048] Figure 3 is a drawing for explaining the problems of the remote transfer method according to the prior art from the perspective of chip separation by laser.

[0049] First, there is a problem that the chip (320) is separated from the sapphire substrate (310) due to too high energy.

[0050] The instantaneous gas pressure increases the stress on the chip (320), and this stress varies depending on the chip structure and process conditions. Furthermore, the force applied to the chip does not easily have an equal pressure distribution. That is, as shown in the following mathematical expression 1, the pressure applied to the left, center, and right sides of the chip is not equal.

[0051]

[0052] Due to the above formula, when the LED chip (320) is separated from the sapphire substrate (310), the initial emission angle (θi) increases as shown in the following mathematical formula 2.

[0053]

[0054] Meanwhile, since micro LED is a thin film with a thickness of several μm and has no relative weight like paper, it experiences air resistance, so the final emission angle (θf) is random and has the following condition as shown in mathematical expression 3.

[0055]

[0056] That is, in the process of separating GaN into Ga and N2 gas by a laser, the chip is separated from the sapphire substrate by the N2 gas pressure. However, the problem is that when separated, the chip is stressed by the gas pressure, so that the attachment area of ​​the chip is not separated equally, but as shown in FIG. 3, there is a problem that there is a high possibility that the chip (320) will fly in a random direction.

[0057] FIG. 4 is a drawing for explaining a problem of a remote transfer method according to the prior art from the perspective of receiving a chip from a donor substrate.

[0058] From the perspective of the donor substrate, it is not easy to simultaneously improve the breakage (1) and bounce-off (2) characteristics even if the conditions of the donor substrate are optimized due to the excessively strong energy of the LED chip emitted from the sapphire substrate when it reaches the donor substrate.

[0059] First, because the incident light has such high energy, the chip cannot avoid damage or bounce depending on the angle of incidence. Depending on the range of the angle of incidence, the following results occur.

[0060] θ~90 degrees: The possibility of breakage increases, but the possibility of bounce decreases.

[0061] θ~0 degrees: The possibility of breakage decreases, but the possibility of bounce increases.

[0062] On the other hand, increasing the elastic modulus of the donor substrate to maximize the buffering effect increases the possibility of breakage, but decreases the possibility of bounce-off.

[0063] And, in order to reduce the breakage problem, if the elastic modulus of the donor substrate is lowered, the possibility of breakage is lowered, but there is a problem that the possibility of bouncing off is increased.

[0064] That is, there is a fundamental problem that the chip is broken or has difficulty in positioning because the chip released from the sapphire substrate on the donor substrate or wiring substrate flies at a random angle (θ) with such strong energy.

[0065] Therefore, it has been previously argued that the implementation of non-contact remote transfer is difficult because the chip breakage problem and the position control problem are in a trade-off relationship.

[0066] According to one embodiment of the present invention, it is important to ensure that the LED chip can be stably separated from the sapphire substrate. This will be described below with reference to FIG. 5.

[0067] FIG. 5 is a drawing for explaining conditions for stably separating an LED chip from a first substrate according to one embodiment of the present invention.

[0068] As shown in FIG. 5, when the LED (520) is separated from the first substrate (510) by a laser (530), the following mathematical expression 4 is established.

[0069]

[0070] Here, assuming that θ is difficult to control randomly, D is a factor that is very sensitive to d. Therefore, in order to control the LED (520) to a desired position, the smaller d becomes, the smaller D becomes.

[0071] For example, since θ<=Φ / 2, the maximum value (Max) of tanθ is 1, and the minimum value (Min) is 0. If the spacing between LED chips is 50um and the positional error is assumed to be ±5um, the distance d of the chip flying to the donor substrate or wiring substrate must have a gap of 10um.

[0072] Meanwhile, the conditions under which a chip separated from a sapphire substrate (e.g., No. 510 shown in FIG. 5) can be stably positioned on a donor substrate or wiring substrate will be described later with reference to FIG. 6.

[0073] FIG. 6 is a drawing for explaining conditions for stably holding an LED chip on a second substrate according to one embodiment of the present invention.

[0074] As illustrated in the left drawing of Figure 6, the chip may be damaged or bounce off the donor substrate or wiring board depending on the angle of incidence at which it is struck. This situation can be explained by the relationship between the impact and the momentum of the chip.

[0075] As shown in the right-hand drawing of Figure 6, shock absorption is very important. However, when focusing on shock absorption, the rebound force must also be taken into account.

[0076] To address these various issues, one embodiment of the present invention proposes the introduction of a buffering material (e.g., nanofibers) during the transcription process. This will be described below with reference to FIG. 7.

[0077] Figure 7 is a drawing for explaining a buffer material required according to one embodiment of the present invention.

[0078] In general, the impulse is obtained by the following mathematical formula 5, and the time must be increased to reduce the impulse.

[0079]

[0080] Meanwhile, the repulsive force is obtained by the following mathematical formula 6, and in order to reduce the repulsive force, the time must be reduced.

[0081]

[0082] In other words, to solve the chip breakage problem, it is important to minimize the impact force. To achieve this, t (time) can be increased.

[0083] On the other hand, to solve the chip bounce problem, it is important to minimize the elastic coefficient. To achieve this, if k can be set close to 0, the repulsive force will also converge to 0.

[0084] However, since t (time) depends on the elastic modulus (k), it is impossible to increase t (time) while setting k (elastic modulus) close to 0.

[0085] That is, if the elastic coefficient (k) is reduced, the momentum time (t) is reduced, so shock absorption is weakened, and if the momentum time (t) of the chip flying to the donor substrate is prolonged through continuous motion, there is a problem in that the chip bounces back due to increased repulsive force caused by elasticity.

[0086] However, the above assumptions are logical developments that only apply to a single property, and when a single property or multiple properties act in combination, they can be defined differently from the above formula.

[0087] In order to design a buffer for a remote warrior, an improved formula is needed for the conventional relational formula (Equation 6) above.

[0088] And, the present invention derived the following as a formula that conforms to the law of conservation of momentum.

[0089] Mathematical expression 7 below is a conventional relational expression.

[0090]

[0091] Meanwhile, in the case of a conventional single property, the following mathematical expression 8 is satisfied.

[0092]

[0093] On the other hand, the new equations according to the present invention that introduce a buffer material are as follows: Equations 9, 10, and 11.

[0094]

[0095]

[0096]

[0097] Here, h is specified as a structural thickness factor.

[0098] Furthermore, as an embodiment of the present invention, mathematical expression 12 in the case where composite properties are introduced as a buffer material is as follows.

[0099]

[0100] Here, dt is the shock absorption factor and △h is the repulsion control factor.

[0101] In the above equations that separate the time and momentum velocity for shock absorption using multiple material properties, ∫ is the elastic modulus of the material, which continues the time of momentum, and ∑ is a good example of a randomly entangled structure like cotton.

[0102] Therefore, nanofibers are suitable as a cushioning material according to one embodiment of the present invention, and h can be a variable factor such as the thickness or thickness of the nanofibers to reduce the repulsive force.

[0103] Figure 8 illustrates preparatory steps for a remote transcription process according to one embodiment of the present invention.

[0104] As illustrated in (a) of Fig. 8, at least one LED (Light Emitting Diode) (820) is grown on a first substrate (810). Here, the first substrate (810) corresponds to, for example, at least one of a sapphire substrate or a silicon substrate.

[0105] Furthermore, as illustrated in (b) of Fig. 8, an arbitrary material (830) is applied to the first substrate. Here, the arbitrary material corresponds to, for example, a polymer series material (e.g., Su-8, etc.).

[0106] In addition, as illustrated in (c) of Fig. 8, an exposure device (840) is used to irradiate, for example, UV light onto the substrate. The aforementioned exposure device (840) is divided into a stepper and a scanner, depending on the method. A stepper is a method that shines light on a specific area like taking a picture with a camera, and a scanner is a method that forms a pattern by moving light constantly like a document scanner.

[0107] And, as shown in (d) of Fig. 8, the area around at least one LED is etched. At this time, as described above in Fig. 5, it is preferable to set d to about 10 um or less.

[0108] Additionally, as shown in (e) of Fig. 8, nanofibers (850), which are an example of a buffer material, are arranged at a location spaced apart from at least one LED.

[0109] And, it is designed to transfer at least one LED located on the first substrate to the second substrate. Here, the second substrate corresponds to, for example, at least one of a donor substrate or a wiring substrate, and a more specific process of transferring to the second substrate will be described with reference to FIG. 9 below.

[0110] Figure 9 illustrates a remote transcription process according to one embodiment of the present invention.

[0111] The first substrate illustrated in (a) of Fig. 9 is the substrate illustrated in (e) of Fig. 8 set up in the reverse direction.

[0112] As shown in (b) of Fig. 9, at least one LED is first transferred to a buffer material (e.g., nanofiber, No. 850 shown in Fig. 8).

[0113] Next, as shown in (c) of Fig. 9, at least one LED (940) arranged on the buffer material (930) is transferred to the second substrate (950).

[0114] According to another embodiment of the present invention, the laser (910) used in the primary transfer step in (b) of FIG. 9 is applied to all LEDs simultaneously, and the laser (920) used in the secondary transfer step in (c) of FIG. 9 is applied sequentially to individual LEDs.

[0115] According to another embodiment of the present invention, if the laser (910) used in the primary transfer step in (b) of FIG. 9 is a high-power laser that separates at least one LED chip from a sapphire substrate, the laser (920) used in the secondary transfer step in (c) of FIG. 9 is designed to melt and cut nanofibers.

[0116] FIG. 10 is an image taken with a scanning electron microscope (SEM) of LED chips temporarily arranged on nanofibers according to an embodiment of the present invention. FIG. 11 is an image of various LED chips stably and finally arranged on a donor substrate or a wiring substrate according to an embodiment of the present invention. FIG. 10 and FIG. 11 are drawings for demonstrating the effects of the present invention.

[0117] First, when the first transfer as shown in (b) of Fig. 9 is completed, it can be confirmed that the LED chip (1010) is separated from the sapphire substrate and is well arranged in the nanofiber (1000), as shown in Fig. 10. Fig. 10 corresponds to an image captured with a scanning electron microscope (SEM).

[0118] And, when the secondary transfer as shown in (c) of Fig. 9 is completed, it can be confirmed that the LED chip is stably transferred to the second substrate, i.e., the donor substrate or wiring substrate, regardless of the size and shape of the chip, as shown in Fig. 11.

[0119] The experiment for Fig. 11 was confirmed on a 4-inch wafer, and Fig. 11 (a) shows the application of the present invention when the LED chip is less than 40 um, and Fig. 11 (b) shows the application of the present invention when the LED chip is less than 20 um.

[0120] Figure 11 (c) shows the application of the present invention when the shape of the LED chip is circular, and Figure 11 (d) shows the application of the present invention when the shape of the LED chip is flip type.

[0121] In any case, when non-contact transfer was performed as in the present invention, the LED chip was transferred stably.

[0122] The above description is merely an example of the technical idea of ​​the present invention, and those skilled in the art will appreciate that various modifications and variations can be made without departing from the essential characteristics of the present invention.

[0123] Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical idea of ​​the present invention but to explain it, and the scope of the technical idea of ​​the present invention is not limited by these embodiments.

[0124] The scope of protection of the present invention should be interpreted by the claims below, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the rights of the present invention.

[0125] With respect to various embodiments for implementing the present invention, duplicate descriptions are omitted as they have been described above in the previous table of contents, Best Mode for Carrying Out the Invention.

[0126] Since the present invention can be applied to display devices in various fields, its industrial applicability is recognized.

Claims

1. In a method for manufacturing a display device, A step of growing at least one LED (Light Emitting Diode) on a first substrate; A step of applying any material to the first substrate; A step of etching the periphery of at least one LED; A step of attaching a buffer material at a location spaced apart from at least one of the LEDs; and A step of transferring at least one LED located on the first substrate to a second substrate A method for manufacturing a display device, characterized in that it includes:

2. In paragraph 1, The above cushioning material is, A method for manufacturing a display device characterized by corresponding to nanofibers.

3. In paragraph 1, A method for manufacturing a display device, characterized in that the above-mentioned spaced position is 10 um or less.

4. In paragraph 1, Any of the above substances, A method for manufacturing a display device characterized by corresponding to a polymer series material.

5. In paragraph 1, The above transcription steps are: First, a step of transferring at least one LED to the buffer material; and Secondary step of transferring at least one LED arranged on the buffer material to the second substrate A method for manufacturing a display device, characterized in that it further includes:

6. In paragraph 5, The laser used in the above primary transcription step is applied to all LEDs simultaneously, A method for manufacturing a display device, characterized in that the laser used in the second transfer step is sequentially applied to individual LEDs.

7. In paragraph 5, Rather than the high-power laser used in the first transfer step to separate GaN from the sapphire substrate, A method for manufacturing a display device, characterized in that the output of the laser used in the second transcription step is small.

8. In paragraph 1, A method for manufacturing a display device, characterized in that the first substrate corresponds to at least one of a sapphire substrate and a silicon substrate.

9. In paragraph 1, A method for manufacturing a display device, characterized in that the second substrate corresponds to at least one of a donor substrate or a wiring substrate.

10. A display device manufactured by the method according to any one of claims 1 to 9.

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