WO2021148895A1

WO2021148895A1 - Light processing device array and method for manufacturing thereof

Info

Publication number: WO2021148895A1
Application number: PCT/IB2021/050076
Authority: WO
Inventors: Boon S. Ooi; Jung-Hong Min; Tien Khee Ng
Original assignee: King Abdullah University of Science and Technology KAUST
Current assignee: King Abdullah University of Science and Technology KAUST
Priority date: 2020-01-22
Filing date: 2021-01-06
Publication date: 2021-07-29
Anticipated expiration: 2022-07-22

Abstract

A method for manufacturing a flexible and multifunctional red, green, and blue tandem micro light emitting device, LED, array, includes providing (1200) a red LED (100), a green LED (200), and a blue LED (200'); removing (1202) a substrate of each of the red, green and blue LEDs to obtain a red LED membrane (100S), a green LED membrane (200S), and a blue LED membrane (200'S); and bonding (1204) the red LED membrane (100S), the green LED membrane (200S), and the blue LED membrane (200'S) on top of each other and to a common substrate (810) with corresponding bonding layers (802). Each of the red LED membrane (100S), the green LED membrane (200S), and the blue LED membrane (200'S) is fully transparent to light while each of the red LED (100), the green LED (200), and the blue LED (200') is not fully transparent to light.

Description

LIGHT PROCESSING DEVICE ARRAY AND METHOD FOR MANUFACTURING THEREOF

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 62/964,341, filed on January 22, 2020, entitled “VERTICALLY-STACKED R/G/B TANDEM LEDS FOR HIGH-DENSITY MICRO LED ARRAYS,” the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

TECHNICAL FIELD

[0002] Embodiments of the subject matter disclosed herein generally relate to a system and method for making a stacked light emitting diode (LED) array, and more particularly, to a method for making red-, green-, and blue-color vertically- stacked micro LEDs based on inorganic materials, by transferring LED membranes.

DISCUSSION OF THE BACKGROUND

[0003] The AIGalnP-based materials are known for their capability to emit red light and also light in the near-infrared regime. Furthermore, the AIGalnN-based materials are most efficient for the ultraviolet, blue, and green regimes. Therefore, these materials are used in optoelectronic devices such as LEDs, laser diodes (LDs), and photodetectors (PDs) either to generate desired wavelengths or to detect them. The AIGalnP and AIGalnN materials are commonly grown on GaAs and c-plane sapphire, respectively, due to the ease of the production method. Inorganic micro LED arrays using AIGalnP and AIGalnN materials have attracted much attention recently because of their high-efficiency and the freedom to change the color from blue to red. In particular, the liquid crystal display (LCD) widely used in the existing displays has a disadvantage in that the efficiency of using light coming from a back light unit (BLU) by the liquid crystal is less than 5%. In addition, although organic LEDs (OLEDs), one of the next-generation displays, have a high-color gamut due to the self-emitting characteristics without the BLU, the OLEDs have several conundrums such as low modulation response speed due to the low-mobility and burn-in effect.

[0004] In order to overcome the shortcomings of the displays based on LCDs and OLEDs, development of micro LED arrays based on inorganic materials as AIGalnP and AIGalnN is receiving much attention. Micro LED arrays can reduce the pixel size to less than 10 pm, so it can be used for the small size display of Augmented Reality (AR) and Virtual Reality (VR) that requires more than 2000 pixel per inch (ppi) specification. Moreover, the micro LED arrays are durable for the external environment and have a fast modulation response speed due to the fast charge-carrier lifetime of inorganic materials. Thus, the micro LED arrays have a number of advantages over the existing displays that use LCDs and OLEDs technology. [0005] Micro LED arrays generally use three different inorganic LEDs or combine a color converter layer with a blue LED to achieve red, green and blue full color. To make the micro LED arrays, most developers have adopted a transfer method to realize the red/green/blue colors, for example using three types of inorganic LEDs consisting of AIGalnP and AIGalnN materials. First, mesa structures are formed on the LED structure grown on the substrate, and micro-size LEDs are manufactured through passivation and metallization. In order to transfer the fabricated LED to the driving circuit, mesa structures identical to the LED size are formed on a rigid substrate, and then a metal layer is formed to separately manufacture target substrates. After the target substrates and the LEDs are aligned, an electrostatic force is applied to the pixel to be transferred to the target substrates, and only the desired pixel is picked up and transferred to the driving circuit. This transfer process is repeated to complete the fabrication of red/green/blue color active matrix micro LED arrays [1 , 2]

[0006] Another micro LED array manufacturing method is a stamping method using polydimethylsiloxane (PDMS). First, LEDs are completed by LED mesa structures, passivation and metallization. The difference from the previous method is that the fabricated LED is not transferred directly to the driving circuit, but is pre transferred to the desired position and arrangement on a second substrate.

Stamping patterns are made on the PDMS, and then the micro LEDs are transferred to the second substrate. This transfer process is repeated to complete the device, by arranging the micro LEDs in the desired position on the second substrate. That is, the micro LED arrays are first completed on the second substrate and then they are transferred to the driving circuit to complete the active matrix micro LED arrays at once [3] While this PDMS transfer method is economical and easy to use, the patterns for stamping must be manufactured separately, and there is a disadvantage in that a variation in the transfer yield occurs depending on the patterns.

[0007] A transfer method overcoming these disadvantages is a roll-to-roll transfer method, which uses a polymer film that can control the viscosity by a low temperature heat treatment. In this transfer method, micro-size LEDs are first manufactured by mesa structure, passivation, and metallization. A viscous polymer film is attached to the fabricated LEDs and then peeled off to produce a polymer film with micro-size LED attached. After that, the driving circuit onto which the micro-size LED need to be transferred is prepared under the micro LED film, the positions of the driving circuit and the micro LED film are aligned, and then the viscosity of the film is removed to perform the roll-to-roll transfer [4]

[0008] Most of the development with regard to the micro LED arrays is mainly focused on the direct transfer methods. However, in addition to the direct transfer methods, there are methods of transferring micro LEDs by applying a magnetic field to a desired position of the driving circuits by inking a block-shaped micro LEDs with a magnetic force in a solution. Specifically, the micro LED basic structure is formed by mesa formation, passivation, and metallization, and then the LED structure is additionally formed using a magnetic material in a block shape. The pre-formed micro LEDs are prepared in the solution and they are dispersed in the solution. After that, a groove is made in the driving circuit to match the block-shaped micro LED in the driving circuit. The micro LED solution is sprayed on the driving circuit and a magnetic force is applied to the driving circuit so that the block-shaped micro LEDs can be attached to the driving circuit’s groove to finally complete the active matrix micro LED arrays [5]

[0009] All of the above methods implement a full color using R/G/B LEDs. In contrast, it is possible to achieve the R/G/B full color by generating a blue monochromatic color into a micro-size LEDs and then forming red and green colors by using conversion layers into micro pixels. This method has a problem in that its efficiency is reduced due to the use of the color converter, when compared to the method of using R/G/B discrete devices. However, this method has the advantage of being a simple process with no transfer necessary as only one blue color micro LED driving device is required.

[0010] The existing transfer methods are not suitable for the ultra-small displays characterized by 2000 ppi because the size of the transferable LEDs is limited. It is possible to use the technology disclosed in [6] to obtain an ultra-small micro LED array.

[0011] As described above, the micro LED arrays are being developed based on the transfer methods, and in addition, various attempts are being made for using a color converter. However, the pick and place transfer methods require a transfer time of at least three days or more in order to realize a large 100-inch display. There is even the difficulty of implementing a complete display. In addition, even when transferring the LED at 100% yield, when the micro LEDs are bonded to the driving circuits, the display array may be distorted, causing screen distortion. Of course, it is possible to create and manage a space to maintain defective pixels separately in the micro LED arrays, but if this happens, there is a trade-off that makes it difficult to realize the small size pixel, which is the advantage of the micro LEDs. In addition to the problems discussed above with regard to the transfer method, the use of the color converter in the micro LED array also causes a problem that the high-efficiency characteristics of the micro LED are also degraded [7 - 10]

[0012] More seriously, as the high-efficiency inorganic LEDs are reduced to micro size, there is a fundamental problem in that the efficiency is greatly reduced by side wall damage and the full width at half maximum of each color of red/green/blue is substantially increased. In particular, if the size of the micro LED is reduced below ~ 10 pm, the external quantum efficiency (EQE) drops from 80% to below 30% and a leakage current increases significantly. In addition, the characteristics of the AIGalnP material for the red color and of the AIGalnN material for the green and blue colors are different. In the case of the AIGalnP-based LEDs, if the LED size decreases below ~ 10 pm, the EQE drops below 10%. In other words, as the size of the inorganic LEDs is reduced, there is an essential problem in that the high-efficiency characteristics of the inorganic LEDs disappear in comparison to the LCDs and OLEDs technologies. In this regard, a micro LED is considered herein a device that has a diameter or width less than 200 pm.

[0013] Thus, there is a need for a new method for forming the micro LEDs, without degrading its efficiency and overcoming the above noted problems. BRIEF SUMMARY OF THE INVENTION

[0014] According to an embodiment, there is a method for manufacturing a flexible and multifunctional red, green, and blue tandem micro light emitting device, LED, array. The method includes providing a red LED, a green LED, and a blue LED, removing a substrate of each of the red, green and blue LEDs to obtain a red LED membrane, a green LED membrane, and a blue LED membrane, and bonding the red LED membrane, the green LED membrane, and the blue LED membrane on top of each other and to a common substrate with corresponding bonding layers. Each of the red LED membrane, the green LED membrane, and the blue LED membrane is fully transparent to light while each of the red LED, the green LED, and the blue LED is not fully transparent to light.

[0015] According to another embodiment, there is a red, green, and blue tandem light processing device array that includes a common substrate, a red light emitting device, LED, membrane located over the common substrate, wherein the red LED membrane is a red LED with no substrate, a green LED membrane located over the red LED membrane, wherein the green LED membrane is a green LED with no substrate, a blue LED membrane located over the green LED membrane, wherein the blue LED membrane is a blue LED with no substrate, and plural electrodes. Each of the red LED membrane, the green LED membrane, and the blue LED membrane is transparent to light while each of the red LED, the green LED, and the blue LED is not transparent to light. [0016] According to yet another embodiment, there is a red, green, and blue tandem light processing device array that includes a common substrate, a red light emitting device, LED, membrane located over the common substrate, a green LED membrane located over the red LED membrane, and a blue LED membrane located over the green LED membrane. Each of the red LED membrane, the green LED membrane, and the blue LED membrane includes only a p-type region, an active region, and an n-type region, but no substrate. Each of the red LED membrane, the green LED membrane, and the blue LED membrane is fully transparent to light because of lack of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0018] Figure 1 is an illustration of a red LED, Figure 2 is a schematic diagram of a green/blue LED, and Figure 3 is a generic diagram of a red, green, or blue LED, each having a solid substrate;

[0019] Figure 4 is an illustration of a red LED membrane, Figure 5 is a schematic diagram of a green/blue LED membrane, and Figure 6 is a schematic diagram of a red, green or blue LED membrane, each having no solid substrate; [0020] Figure 7 illustrates the red, green or blue LED membrane having a current spreading layer and a supporting layer, but no solid substrate;

[0021] Figure 8A illustrates the red LED membrane being bonded to a common substrate, Figure 8B illustrates the green LED membrane being bonded to the red LED membrane, Figure 8C illustrates the blue LED membrane being bonded to the green LED membrane, and Figure 8D illustrates the stack of red, green and blue LED membranes with all the supporting layers removed and having a single solid substrate;

[0022] Figure 9 is a flow chart of a method for forming the stack of red, green and blue LED membranes; [0023] Figures 9A to 9H illustrate the steps of successively etching various layers from the stack of red, green and blue LED membranes to form a micro LED array;

[0024] Figure 10 illustrates the micro LED array used as a light generating device;

[0025] Figure 11 illustrates the micro LED array used as a light sensor; and

[0026] Figure 12 is a flow chart of a method for forming a micro LED array.

DETAILED DESCRIPTION OF THE INVENTION

[0027] The following description of the embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to a stack of LED membranes, each membrane being configured to generate one of red, green or blue light. However, the embodiments to be discussed next are not limited to these three colors, but may be applied to LED membranes that emit other colors or a reduced/increased number of colors.

[0028] Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0029] According to an embodiment, there is a method for transferring and fabricating red-, green-, blue-color stacked LEDs that involves LED membranes. Red-color LEDs are composed of (Al, Ga, In) P compound semiconductor materials, and the green- and blue-color LEDs are composed of (Al, Ga, In) N compound semiconductor materials, respectively. The red-, green- and blue-color LEDs are fabricated as membranes by removing their hard substrates (GaAs for the red-color LED and Si for the green- and blue-color LEDs). The obtained red/green/blue LED membranes are then vertically stacked on a common substrate to form the micro LED. By using the red/green/blue stacked LED membranes, a method of making the R/G/B tandem micro LEDs can be simplified.

[0030] The fabrication of the LED membranes is proposed to use AIGalnP and AIGalnN materials, and the membranes are then transferred to a desired substrate to obtain the micro LED arrays. This method of manufacturing is believed to solve the problems of the existing micro LED arrays. The novel method of fabrication of the micro LED arrays transfers plural LED membranes, which are in the form of a film, compared to the conventional method of transferring each solid pixel one by one. Thus, the issue of yield and disparity after transfer can be solved and the transfer process time can be greatly reduced. In addition, by adopting a vertical transfer that using the LED membranes versus the horizontal transfer that uses the traditional pick and place methods minimizes efficiency reduction caused by the reduced size of the LEDs.

[0031] For example, in the case of the conventional horizontal transfer method, when the total pixel size is 100 pm, in order to realize the R/G/B full color, the size of each pixel should be about 30 pm. However, when the transfer is changed to the vertical type, the size of each LED can be tuned depending on the efficiency rate related to the characteristics of each LED in order to improve the total efficiency. In addition, the novel membrane transfer process can align the p/n junction of the LED in one direction. It is possible to manufacture the R/G/B color LEDs in the form of triple tandem LEDs by aligning the p/n junctions in one direction. The triple tandem LED has an advantage because the total number of electrodes can be reduced from six to four or two for emitting the R/G/B full color and white color.

[0032] The novel method summarized above is now discussed in more detail with regard to the figures. Figure 1 shows the configuration of the AIGalnP-based red LED, which is grown on a GaAs substrate, and Figure 2 shows the AIGalnN-based green and blue LEDs, which are grown on a Si substrate. More specifically, Figure 1 shows the AIGalnP-based red LED 100 being made on the GaAs substrate 110. The various layers of the red LED 100, starting from the top toward the GaAs substrate 110, include a 2 pm-thick GaP layer 112. The layer 112 serves as a p-contact and window layer. Next, a tensile strain barrier reducing (TSBR) layer 114 is present, to alleviate the lattice mismatch between the layer 112 and an AllnP layer 116. These three layers form the p-type region 120 of the red LED 100.

[0033] Next, the active layer 130 is present, which includes the multiple quantum wells (MQWs) defined by one or more pairs of GalnP/AIGalnP layers. The active layer 130 is sandwiched between the p-type region 120 and an n-type region 140, which includes AIGalnP and GaAs layers, which serve as contacts. An etch stop layer 142 is formed of GalnP to later wet etch the solid GaAs substrate 110. [0034] The green/blue LEDs 200 and 200’, which are shown in Figure 2, have a Si substrate 210 on which the following structure is placed: a p-GaN contact layer 212 and an electron blocking layer 214, which form the p-type region 220. Below this region, there is an MQWs layer 230 that includes GaN / InGaN / AIGaN layers. An n- type layer 240 is provided under the MQW layer 230. AIGaN / AIN buffer layers 242 and 244 are also present to mitigate the lattice mismatch between the n-GaN and the Si substrates 210. The structures of the R/G/B color LEDs 100/200/200’ can be changed for the purpose of improving efficiency, but the red color LED 100 uses the GaAs substrate and the blue and green color LEDs 200/200’ use the Si substrate. Note that the thickness of the various layers shown in Figure 2 and also the chemical composition of the MQW layer 230 may be different for the green LED 200 and the blue LED 200’. The structures of the LEDs 100, 200 and 200’ are shown in Figures 1 and 2 for illustrative purposes, but these configurations are known in the art and variations of these configurations can also be used for implementing the transfer method to be discussed next.

[0035] The structures shown in Figures 1 and 2 are usually solid, i.e., they cannot be bent, and also they are mostly opaque to the light, i.e., a light ray would not be able to pass through the entire LED structure, from the substrate to the top layer, especially because of the solid substrates 110/210. This characteristic is schematically illustrated in Figure 3, where an incoming light ray 300 is completely absorbed/dissipated by the LED, and no corresponding light is exiting the substrate 110/210. Note that the generic LED shown in Figure 3 not only illustrates the lack of the transparency feature, but also shows the basic layers of these structures. For simplicity, from now on, the structure shown in Figure 3 is used to indicate an LED having a solid substrate. Because of the solid substrate, the LED structures 100,

200, and 200’ appear to be opaque when looked upon with the naked eye. However, if the substrates 110, 210 of these structures are removed up to the buffer layers 142/242/244, as shown in Figures 4 and 5, then the slimmed down corresponding LED structures 100S, 200S, and 200’S become transparent to light, as illustrated in Figure 6, where the incoming light 300 enters the top region of the slimmed down LED and exits the bottom region. This slimmed down version of a R/G/B LED is called herein an LED membrane. Thus, an LED membrane is similar to a traditional LED except that its substrate has been removed. Because of this feature, the LED membranes 100S/200S/200’S are transparent to light. The buffer layers 142/242/244 have the purpose of facilitating the removal of the substrate 110/220 without damaging the n-type layer 140/240. The buffer layers can also be removed.

[0036] After the substrate has been removed for each LED structure, an indium tin oxide (ITO) electrode 700 is deposited on the p-type region 120/220 of each LED structure 100S, 200S, 200’S as illustrated in Figure 7. The ITO electrode 700 acts as a current spreading layer and as an etch stop layer during the transfer process. The current spreading layer can be selected to have a transparency to light of about 70%. In one application, this layer is made of ZnO instead of ITO. A support layer 710 is formed over the ITO layer 700, and this layer supports the entire membrane during the transfer process. The annealing conditions of the ITO layer 700 can be different for each LED structure due to the different characteristics of the AIGalnP material and the AIGalnN material. Various metals and organic materials can be used for the support layer 710.

[0037] After the current spreading layer 700 and the support layer 710 are formed on the p-type regions of the LED membranes 100, 200, 200’, the GaAs and Si substrates are removed by wet etching, and the R/G/B color membranes 100S, 200S, and 200’S are obtained.

[0038] The process of transferring the LED membranes 100S, 200S, and 200’S can now begin and is illustrated in Figures 8A to 8D and described with regard to a flow chart illustrated in Figure 9. In step 901, a first adhesive bonding layer 802 (e.g., adhesive polymer as PDMS or SU8) is spread over a target substrate 810 and in step 902 the red LED membrane 100S is attached to the target substrate 810 with the first adhesive bonding layer 802, as illustrated in Figure 8A. The target substrate 810 may include electronics 812 associated with driving the LED membranes, so that the target substrate may be the driving circuit. Then, in step 904, the supporting layer 710 of the red LED membrane 100S is removed (e.g., with wet etching and the current spreading layer 700 acts as a wet stop layer). In step 906 a second adhesive bonding layer 802 is added on top of the current spreading layer 700 of the red LED structure 100S, and the green LED membrane 200S is placed in step 908 directly over the second adhesive bonding layer 802, to bond the green LED membrane to the red LED membrane, as shown in Figure 8B. In step 910, the supporting layer 710 of the green LED membrane 200S is removed, in step 912 a third adhesive bonding layer 802 is added on the top of the green LED membrane, and in step 914, the blue LED membrane 200’S is placed over the third adhesive bonding layer 802, as illustrated in Figure 8C. Note that the specific layers of each LED membrane are omitted in these figures for simplicity. Then, in step 916, the supporting layer 710 of the blue LED membrane 200’S is removed to form the stacked R/G/B micro LED array 800, as illustrated in Figure 8D. Note that the stack 800 in Figure 8D has the red, green and blue LED membranes added in this order onto the driving circuit 810. Other orders may be implemented if desired, as dictated by the intended application. [0039] A method for manufacturing a vertical tandem R/G/B LED is now discussed with regard to Figures 9A to 9H. The stack 800 obtained in Figure 8D is processed by etching the current spreading layer 700 of the blue LED structure 200’S, as illustrated in Figure 9A, up to the n-GaN layer 240. Next, the current spreading layer 700 of the green LED structure 200S is exposed by etching as shown in Figure 9B. Then, the n-type layer 240 of the green LED structure 200S is exposed by etching as shown in Figure 9C. It is noted that each etching step removes less surface area than the previous etching step, so that a pyramid-type structure is obtained. Next, the current spreading layer 700 of the red LED structure 100S is exposed by etching, as shown in Figure 9D. Then, the n-type layer 140 of the red LED structure 100S is exposed by etching, as shown in Figure 9E. The etching take place all around the layers illustrated in Figures 9A to 9E, but for simplicity, the etching is shown only on two sides of the structure 800. The size (e.g., diameter) of each of the etched region is illustrated in Figure 9E by reference symbols L1 to L6. In one embodiment, L1 is about 5 to 20 pm, L2 is about 10 to 30 pm, L3 is about 20 to 50 pm, L4 is about 30 to 80 pm, and L5 is about 50 to 150 pm. A length L6 of the entire LED array 900 is less than 200 pm.

[0040] Then, part of each exposed layers are passivated with a passivation layer 902, as shown in Figure 9F. The passivation may be performed with dielectrics such as S1O2, AI2O3, and SiN_x to secure p/n contact regions of the LED membranes. Parts 904 of each exposed n-type layer or current spreading layer are left free of the passivation material, as also shown in Figure 9F. Four electrodes 906A to 906D are formed by metallization in each of the free parts 904, to establish an electrical contact with each of the n-type layers of the LED structures and also with their current spreading layers, as illustrated in Figure 9G. A top view of the obtained micro LED array 900 is shown in Figure 9H.

[0041] The fabricated R/G/B tandem micro LED array 900 can be used either to emit light that has R/G/B color or white light by using two or four of the four electrodes 906A to 906D. Thus, the R/G/B tandem micro LED array 900 can be used as a micro LED display 1000, as shown in Figure 10, when plural of the R/G/B tandem micro LED arrays 900-I are formed on a same substrate 1010. Although Figure 10 shows only three R/G/B tandem micro LED arrays 900-I, the value of I can be from one to tens of thousands, depending on the application. In this regard, if only electrodes 906D and 906C are activated, as illustrated for the R/G/B tandem micro LED array 900-1, then only blue light 1010 is emitted by the blue LED membrane 200’S, and no other light is emitted by the other LED membranes. If only the electrodes 906C and 906B are activated, as illustrated for the R/G/B tandem micro LED array 900-2, then green light 1012 is emitted by the green LED membrane 200S, and no other light is emitted by the other LED membranes. If only the electrodes 906B and 906A are activated, as illustrated for the R/G/B tandem micro LED array 900-I, then red light 1014 is emitted by the red LED membrane 100S, and no other light is emitted by the other LED membranes. Note that the lights 1010, 1012, and 1014 are emitted through the entire surface of the array as the membranes 100S, 200S, and 200’S are transparent, as previously discussed with regard to Figure 6. If all the electrodes 906A to 906D are supplied with electrical power, then the blue light 1010, the green light 1012, and the red light 1014 is simultaneously emitted by a single R/G/B tandem micro LED array 900-I, which means that white light can be generated. By controlling the amount of electrical current that is supplied to the electrodes, the spectrum of the white light can be adjusted as desired. In one application, it is possible to have two and only two electrodes, i.e. , 906A and 906D, so that only white light is generated. A controller 1020 may located on the substrate 1010 or away from the substrate, but electrically connected to each electrode 406A to 406D, and may be configured to send corresponding signals to one or more of the electrodes, to generate one or more wavelengths.

[0042] The R/G/B tandem micro LED array 900 may also be used as a receiver or light detector 1100, as shown in Figure 11. In this case, blue light 1010, or green light 1012, or red light 1014 or any combination of them may be shined on the R/G/B tandem micro LED array 900, which is supported by a substrate 1102. The corresponding LED membrane transforms the corresponding light into an electrical current, and a controller 1110 located on substrate 1102 or away from the substrate, but electrically connected to each electrode 406A to 406D, receives corresponding signals indicative of the incoming light, and can be programmed to calculate the intensity of the detected light. The technologies discussed herein can be applied to the integration of vertical RGB vertical light emitting superluminescent diodes (SLDs) and semiconductor diode lasers. Both the light generator 1000 and the light detector 1100 can be configured to have one unit 900 that includes the red, green and blue light LEDs formed on top of each other and this unit has a diameter or length less than 200 pm, which makes the entire LED array to be a micro LED array.

[0043] A method for manufacturing a red, green, and blue tandem light emitting device, LED, array 1000 or 1100 is now discussed with regard to Figure 12. The method includes a step 1200 of providing a red LED 100, a green LED 200, and a blue LED 200’, a step 1202 of removing a substrate of each of the red, green and blue LEDs to obtain a red LED membrane 100S, a green LED membrane 200S, and a blue LED 200’S membrane 200’S, and a step 1204 of bonding the red LED membrane 100S, the green LED membrane 200S, and the blue LED 200’S membrane 200’S on top of each other and to a common substrate 810 with corresponding bonding layers 802. Each of the red LED membrane 100S, the green LED membrane 200S, and the blue LED 200’S membrane 200’S is transparent to light while each of the red LED 100, the green LED 200, and the blue LED 200’ is not transparent to light.

[0044] The method may further include, before the step of removing, forming a current spreading layer on top of each of the red LED, the green LED, and the blue LED, and adding a support layer to each of the current spreading layers. In one embodiment, each of the current spreading layers has a transparency of 70% or higher. In this or another embodiment, the current spreading layers are made of ITO and the support layer is a metal or polymer. The step of bonding may include bonding the red LED membrane directly to the common substrate, removing the support layer from the red LED membrane, bonding the green LED membrane directly to a top of the red LED membrane, removing the support layer from the green LED membrane, bonding the blue LED membrane directly to a top of the green LED membrane, and removing the support layer from the blue LED membrane.

[0045] In one application, the red, green and blue LED membranes are configured to collectively or individually act for light-emission, wavelength detection, photovoltaic and optical modulation functionalities. In one application, the bonded red, green and blue LED membranes conform to any shape of surface, concave or convex (because of the lack of the solid substrate), to vary the angle of view for outgoing or incoming light.

[0046] In one application, the red LED is based on AIGalnP formed on a GaAs substrate and the green and blue LEDs are based on AIGalnN formed on a Si substrate. The method may further include etching successively the red LED membrane 100S, the green LED membrane 200S, and the blue LED 200’S membrane 200’S to expose corresponding n-type regions for each LED membrane. The method may further include depositing metallic electrodes on each of the exposed corresponding n-type regions for each LED membrane, and also depositing a metallic electrode on top of one of the red LED membrane 100S, the green LED membrane 200S, and the blue LED 200’S membrane 200’S to form the tandem LED array 900.

[0047] The disclosed embodiments provide a method for making a micro LED array with LED membranes. It should be understood that this description is not intended to limit the invention. On the contrary, the embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.

[0048] Although the features and elements of the present embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein. [0049] This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.

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Claims

WHAT IS CLAIMED IS:

1. A method for manufacturing a flexible and multifunctional red, green, and blue tandem micro light emitting device, LED, array, the method comprising: providing (1200) a red LED (100), a green LED (200), and a blue LED (200’); removing (1202) a substrate of each of the red, green and blue LEDs to obtain a red LED membrane (100S), a green LED membrane (200S), and a blue LED membrane (200’S); and bonding (1204) the red LED membrane (100S), the green LED membrane (200S), and the blue LED membrane (200’S) on top of each other and to a common substrate (810) with corresponding bonding layers (802), wherein each of the red LED membrane (100S), the green LED membrane (200S), and the blue LED membrane (200’S) is fully transparent to light while each of the red LED (100), the green LED (200), and the blue LED (200’) is not fully transparent to light.

2. The method of Claim 1, wherein the red, green and blue LED membranes are configured to collectively or individually for light-emission, wavelength detection, photovoltaic and optical modulation functionalities.

3. The method of Claim 1, wherein the bonded red, green and blue LED membranes are configured to conform to any shape of surface, concave or convex, to vary the angle of view for outgoing or incoming light.

4. The method of Claim 1, further comprising, before the step of removing: forming a current spreading layer on top of each of the red LED (100), the green LED (200), and the blue LED (200’); and adding a support layer to each of the current spreading layers.

5. The method of Claim 2, wherein each of the current spreading layers has a transparency of 70% or higher.

6. The method of Claim 2, wherein the step of bonding comprises: bonding the red LED membrane directly to the common substrate; removing the support layer from the red LED membrane; bonding the green LED membrane directly to a top of the red LED membrane; removing the support layer from the green LED membrane; bonding the blue LED membrane directly to a top of the green LED membrane; and removing the support layer from the blue LED membrane.

7. The method of Claim 1, wherein the red LED is based on AIGalnP formed on a GaAs substrate and the green and blue LEDs are based on AIGalnN formed on a Si substrate.

8. The method of Claim 1, further comprising: etching successively the red LED membrane (100S), the green LED membrane (200S), and the blue LED membrane (200’S) to expose corresponding n- type regions for each LED membrane; and depositing passivation layers (902) on the side wall of each ITO layer and n- type region, wherein the passivation layers (902) is one of S1O2, SiN_x, AIN, and AI2O3, and the passivation layers (902) are formed with openings for regions of metallic electrodes; and depositing the metallic electrodes on each of the exposed corresponding n- type regions for each LED membrane, and also depositing a metallic electrode on top of one of the red LED membrane (100S), the green LED membrane (200S), and the blue LED membrane (200’S) to form the tandem LED array (900).

9. A red, green, and blue tandem light processing device array (1000, 1100) comprising: a common substrate (1010, 1102); a red light emitting device, LED, membrane (100S) located over the common substrate (1010), wherein the red LED membrane (100S) is a red LED (100) with no substrate; a green LED membrane (200S) located over the red LED membrane (100S), wherein the green LED membrane (200S) is a green LED (200) with no substrate; a blue LED membrane (200’S) located over the green LED membrane (200S), wherein the blue LED membrane (200’S) is a blue LED (200’) with no substrate; and plural electrodes (906A to 906D), wherein each of the red LED membrane (100S), the green LED membrane (200S), and the blue LED membrane (200’S) is transparent to light while each of the red LED (100), the green LED (200), and the blue LED (200’) is not transparent to light.

10. The array of Claim 9, wherein the red, green and blue LED membranes are configured to collectively or individually act for light-emission, wavelength detection, photovoltaic and optical modulation functionalities.

11. The array of Claim 9, wherein the bonded red, green and blue LED membranes are configured to conform to any shape of surface, concave or convex, to vary the angle of view for outgoing or incoming light.

12. The array of Claim 9, further comprising: a current spreading layer located on top of each of the red LED membrane (100S), the green LED membrane (200S), and the blue LED membrane (200’S).

13. The array of Claim 10, wherein each of the current spreading layers has a transparency of 70% or higher.

14. The array of Claim 9, wherein the red LED membrane is directly bonded to the common substrate with a first bonding layer, the green LED membrane is directly bonded to a top of the red LED membrane with a second bonding layer, and the blue LED membrane is directly bonded to a top of the green LED membrane with a third bonding layer, and wherein the red LED is based on AIGalnP formed on a GaAs substrate and the green and blue LEDs are based on AIGalnN formed on a Si substrate.

15. The array of Claim 9, wherein the plural electrodes are formed directly on exposed corresponding n-type regions for each LED membrane, and also on top of one of the red LED membrane (100S), the green LED membrane (200S), and the blue LED membrane (200’S).

16. The array of Claim 9, further comprising: a controller configured to send electrical signals to the plural electrodes to generate one or more wavelengths.

17. The array of Claim 9, further comprising: a controller configured to receive electrical signals from the plural electrodes to estimate an intensity of one or more incoming light rays.

18. The array of Claim 9, wherein the plural electrodes include only two electrodes.

19. The array of Claim 9, wherein the plural electrodes include only four electrodes.

20. A red, green, and blue tandem light processing device array (1000, 1100) comprising: a common substrate (1010, 1102); a red light emitting device, LED, membrane (100S) located over the common substrate (1010); a green LED membrane (200S) located over the red LED membrane (100S); and a blue LED membrane (200’S) located over the green LED membrane (200S), wherein each of the red LED membrane (100S), the green LED membrane (200S), and the blue LED (200’S) membrane (200’S) includes only a p-type region (120, 220), an active region (130, 230), and an n-type region (140, 240), but no substrate, and wherein each of the red LED membrane (100S), the green LED membrane (200S), and the blue LED membrane (200’S) is fully transparent to light because of lack of the substrate.

21. The array of Claim 20, wherein the red, green and blue LED membranes are configured to be collectively or individually to act for light-emission, wavelength detection, photovoltaic and optical modulation functionalities.

22. The array of Claim 20, wherein the bonded red, green and blue LED membranes are configured to conform to any shape of surface, concave or convex, to vary the angle for view of outgoing or incoming light.