Patent Publication Number: US-2021175400-A1

Title: Device with light-emitting diode

Description:
BACKGROUND 
     Field of Invention 
     The present disclosure relates to a device with a light-emitting diode. 
     Description of Related Art 
     The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art. 
     Traditional display manufacturing is a standardized process set. In recent years, there are more and more new types of displays such as a micro light-emitting diode display, a mini light-emitting diode display, and a quantum dot light-emitting diode display . . . etc., which are promising to dominate the future display market, and thus new display manufacturing processes are waiting to be set up. There are many steps contained in a manufacturing process set in order to produce one display, and reducing one of the steps thereof can reduce the cost and enhance the efficiency. 
     SUMMARY 
     According to some embodiments of the present disclosure, a device with a light-emitting diode includes a substrate, a first conductive pad and a second conductive pad, a light-emitting diode, a metal protrusion, a polymer layer, and a top electrode. The substrate has a top surface. The first conductive pad and the second conductive pad are on the substrate. The light-emitting diode is on the first conductive pad. The metal protrusion is on the second conductive pad. The polymer layer covers the top surface of the substrate, the first conductive pad, the second conductive pad, the metal protrusion, and the light-emitting diode, in which a distance from a top of the metal protrusion to the top surface of the substrate is greater than a thickness of the polymer layer. The top electrode covers the light-emitting diode, the polymer layer, and the metal protrusion such that the light-emitting diode is electrically connected with the second conductive pad. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows: 
         FIG. 1A  is a schematic cross-sectional view of a device with a light-emitting diode according to some embodiments of the present disclosure; 
         FIG. 1B  is a schematic cross-sectional view of an intermediate stage of the forming of the device  100  with the light-emitting diode  130  in  FIG. 1A ; 
         FIG. 2A  is a schematic cross-sectional view of a device with a light-emitting diode according to some embodiments of the present disclosure; and 
         FIG. 2B  is a schematic cross-sectional view of an intermediate stage of the forming of the device with the light-emitting diode in  FIG. 2A . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     In various embodiments, the description is made with reference to figures. However, certain embodiments may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, numerous specific details are set forth, such as specific configurations, dimensions, and processes, etc., in order to provide a thorough understanding of the present disclosure. In other instances, well-known semiconductor processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the present disclosure. Reference throughout this specification to “one embodiment,” “an embodiment” or the like means that a particular feature, structure, configuration, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Thus, the appearances of the phrase “in one embodiment,” “in an embodiment” or the like in various places throughout this specification are not necessarily referring to the same embodiment of the disclosure. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The terms “over,” “to,” “between” and “on” as used herein may refer to a relative position of one layer with respect to other layers. One layer “over” or “on” another layer or bonded “to” another layer may be directly in contact with the other layer or may have one or more intervening layers. One layer “between” layers may be directly in contact with the layers or may have one or more intervening layers. 
       FIG. 1A  is a schematic cross-sectional view of a device  100  with a light-emitting diode  130  according to some embodiments of the present disclosure. The device  100  includes a substrate  110 , a first conductive pad  120 A, a second conductive pad  120 B, a light-emitting diode  130 , a metal protrusion  140 , a polymer layer  150 , and a top electrode  160 . The substrate  110  has a top surface  1102 . The first conductive pad  120 A and the second conductive pad  120 B are on the top surface  1102  of the substrate  110 . The light-emitting diode  130  is bonded on the first conductive pad  120 A. The metal protrusion  140  is on the second conductive pad  120 B. 
     The light-emitting diode  130  includes a bottom electrode  132 , a first type semiconductor layer  134 , an active layer  136 , and a second type semiconductor layer  138 . The first type semiconductor layer  134  is on the bottom electrode  132 . The active layer  136  is on the first type semiconductor layer  134 . The second type semiconductor layer  138  is on the active layer  136 . The bottom electrode  132  is in contact with the first conductive pad  120 A when the light-emitting diode  130  is bonded to the first conductive pad  120 A. In the present embodiment, the light-emitting diode  130  is a vertical type light-emitting diode. 
     The polymer layer  150  covers the top surface  1102  of the substrate  110 , the first conductive pad  120 A, the second conductive pad  120 B, the metal protrusion  140 , and the light-emitting diode  130 . The polymer layer  150  has a thickness T1 which is equal to a distance from a top surface  1502  of the polymer layer  150  to the top surface  1102  of the substrate  110 . 
     The top electrode  160  covers the light-emitting diode  130 , the polymer layer  150 , and the metal protrusion  140  such that the light-emitting diode  130  is electrically connected with the second conductive pad  1206 . Specifically, the top electrode  160  is in contact with a top surface  1382  of the second type semiconductor layer  138  and the metal protrusion  140 . In some embodiments, the top electrode  160  is transparent so that light emitted from the light-emitting diode  130  can transmit through the top electrode  160  to enhance light extraction efficiency. In some embodiments, the top electrode  160  may be Indium Tin Oxide (ITO) or contains metal nanowires. 
     A distance D2 from a top of the metal protrusion  140  to the top surface  1102  of the substrate  110  (i.e., the largest longitudinal height of the metal protrusion  140 ) is greater than the thickness T1 of the polymer layer  150 . Furthermore, a distance D3 from the top surface  1382  of the second type semiconductor layer  138  to the top surface  1102  of the substrate  110  is greater than the thickness T1. In other words, the top surface  1382  of the second type semiconductor layer  138  and the top of the metal protrusion  140  are not completely covered by the polymer layer  150  and are both in contact with the top electrode  160 . Therefore, there is no need to further form openings in the polymer layer  150  to expose the second type semiconductor layer  138  and the second conductive pad  1206  since the distance D2 and the distance D3 are greater than the thickness T1. In addition, the top electrode  160  can directly formed on the top surface  1382  of the second type semiconductor layer  138 , the top of the metal protrusion  140 , and the top surface  1502  of the polymer layer. Therefore, there is no need to from the top electrode  160  in openings of which the aspect ratio may affect the efficiency of the electrical connection. Accordingly, the manufacturing cost can be reduced and the manufacturing efficiency can be improved. 
     The thickness T1 of the polymer layer  150  is greater than a distance D1 from the interface  1302  between the second type semiconductor layer  138  and the active layer  136  to the top surface  1102  of the substrate  110 . Therefore, the active layer  136  and the first type semiconductor layer  134  are covered by the polymer layer  150  such that the electrical insulation between the first type semiconductor layer  134  and the second type semiconductor layer  138  can be maintained. 
       FIG. 1B  is a schematic cross-sectional view of an intermediate stage of the forming of the device  100  with the light-emitting diode  130  in  FIG. 1A . The device  100  in  FIG. 1B  is at a stage before the top electrode  160  is formed and before the polymer layer  150 ′ is etched. Reference is made to  FIG. 1A  and  FIG. 1B . In the present embodiment, the distance D2 of the metal protrusion  140  is smaller than about 0.8 times the distance D3 and is greater than the distance D1 from the interface  1302  between the second type semiconductor layer  138  and the active layer  136  to the top surface  1102  of the substrate  110 . Before the polymer layer  150 ′ is etched, the top surface  1382  of the second type semiconductor layer  138  and the top of the metal protrusion  140  are both covered by the polymer layer  150 ′. The polymer layer  150 ′ includes a first portion  152  overlying the light-emitting diode  130 , a second portion  154  being free from overlapping with the light-emitting diode  130  and the second conductive pad  120 B, and a third portion  156  overlying the metal protrusion  140 . The first portion  152  has a thickness T3, and the second portion  154  has a thickness T4 that is a minimum longitudinal distance from the top of the metal protrusion  140  to the top surface of the polymer layer  150 ′. In this embodiment, the thickness T4 may be greater than the thickness T3. 
     In some embodiments, the etching can be performed by ashing and plasma etching, but the present disclosure is not limited in this regard. The etching rate from the uppermost surface of the polymer layer  150 ′ is substantially the same. In other words, the first portion  152 , the second portion  154 , and the third portion  156  are equally etched from the uppermost surface of the polymer layer  150 ′. In some other embodiments, the polymer layer  150 ′ may be a positive photoresist layer, and the etching can be performed by a partial exposure process followed by a development process. For example, the polymer layer  150 ′ is exposed under weak exposure dose by UV light, but the present disclosure is not limited in this regard. Specifically, the photo-sensitive materials of the first portion  152  is all degraded, and parts of the second portion  154  and the third portion  156  away from the substrate  110  are degraded. 
     Therefore, the thickness T2 of the polymer layer  150 ′ is reduced to the thickness T1 as shown in  FIG. 1A  after the polymer layer  150 ′ is etched, and the thickness T1 is at most equal to a difference between the thickness T2 and the thickness T4. That is, after the polymer layer  150 ′ is etched, the top surface  1382  of the second type semiconductor layer  138  and the top of the metal protrusion  140  are exposed from the polymer layer  150 . Accordingly, with the configurations of thickness and distance as mentioned above, the top surface  1382  of the second type semiconductor layer  138  and the top of the metal protrusion  140  can be exposed in one step, and the step of forming a mask to pattern the polymer layer  150  can be omitted. Therefore, the manufacturing cost can be reduced and the manufacturing efficiency can be improved. 
     In some embodiments, the polymer layer  150 ′ is formed by spin coating or slit coating so as to form the configuration of the polymer layer  150 ′ and satisfy the relation: T2−T4&gt;D1 in one coating step. In some embodiments, the polymer layer  150  includes titanium oxide (TiO2) nanoparticles to increase a refractive index of the polymer layer  150  to further enhance the light extraction efficiency. 
     In some other embodiment, the thickness T3 may be greater than the thickness T4. Under this condition, for example, the distance D2 may be greater than 0.8 times the distance D3 but smaller than 1.2 times the distance D3. Before the polymer layer  150 ′ is etched, the top surface  1382  of the second type semiconductor layer  138  and the top of the metal protrusion  140  are both covered by the polymer layer  150 ′. After the polymer layer  150 ′ is etched, the thickness T2 of the polymer layer  150 ′ is reduced to the thickness T1 as shown in  FIG. 1A , and the thickness T1 is at most equal to a difference between the thickness T2 and the thickness T3. 
     During the exposure process, the exposure light may be partially reflected by the metal protrusion  140 . As a result, the exposure efficiency for the material of the third portion  156  of the polymer layer  150 ′ may be reduced such that a depth of the material of the third portion  156  that is degraded may be smaller than the depths of the material of the first portion  152  and the second portion  154  that is degraded. Therefore, a greater distance D2 of the metal protrusion  140  may prevent the exposure efficiency from being affected by the reflection characteristics of the metal protrusion  140 . 
     In some embodiments, the first type semiconductor layer  134  is a p-type semiconductor layer, and the second type semiconductor layer  138  is an n-type semiconductor layer. Under this condition, the thicker layer is the n-type semiconductor layer which has lower resistivity compared to the p-type semiconductor layer, which leads to better light-emitting efficiency because the p-type semiconductor layer which has higher resistivity and contact resistance is already fully in contact with the bottom electrode  132  before the light-emitting diode  130  is bonded to the first conductive pad  120 A. In some embodiments, a thickness of the p-type semiconductor layer (i.e., a thickness t1 of the first type semiconductor layer  134 ) is about 250 nm and a thickness of the active layer  136  is about 150 nm. In some embodiments, the light-emitting diode  130  further includes an electron blocking layer (not shown) between the active layer  136  and the first type semiconductor layer  134  so as to prevent electrons (which flow from the n-type semiconductor layer towards the active layer  136 ) from flowing out of the active layer  136  (and into the p-type semiconductor layer) and thus the light-emitting efficiency is enhanced. 
     In some embodiments, a ratio between a thickness t2 of the second type semiconductor layer  138  and a thickness t1 of the first type semiconductor layer  134  is greater than or equal to about 1.5. When the second type semiconductor layer  138  is thicker than the first type semiconductor layer  134 , there is a higher possibility for a thickness T1 of the polymer layer  150  to be greater than the distance D1. Therefore, the thickness relation between the second type semiconductor layer  138  and the first type semiconductor layer  134  can increase the tolerance of the criterion: T1&gt;D1 as mentioned above. In some embodiments, since the largest possible distance D1 is equal to or smaller than about 2 μm, the thickness T1 of the polymer layer  150  is greater than or equal to about 2 μm such that the electrical insulation between the first type semiconductor layer  134  and the second type semiconductor layer  138  can be better maintained. 
     Furthermore, in some embodiments, in case the light-emitting diode  130  is absent on the first conductive pad  120 A due to defects when the light-emitting diodes  130  are massively transferred to the substrate  110 , a portion of the polymer layer  150  overlying the first conductive pad  120 A will be thicker by using the polymer layer  150  forming process as described. For example, the portion of the polymer layer  150  overlying the first conductive pad  120 A may be as thick as the third portion  156 , and the first conductive pad  120 A can still be covered by the remaining polymer layer  150  after the developing process. Therefore, the electrical insulation between the top electrode  160  and the first conductive pad  120 A can be maintained, thereby preventing the electrical short that may occur in conventional manufacturing process. 
       FIG. 2A  is a schematic cross-sectional view of a device  200  with a light-emitting diode according to some embodiments of the present disclosure.  FIG. 2B  is a schematic cross-sectional view of an intermediate stage of the forming of the device with the light-emitting diode in  FIG. 2A . The device  200  in  FIG. 2B  is at a stage before the top electrode  260  is formed and before the polymer layer  250 ′ is etched. Reference is made to  FIG. 2A  and  FIG. 2B . The device  200  in  FIG. 2A  is similar to the device  100  in  FIG. 1A , and the difference is that a distance D4 from a top of the metal protrusion  240  to the top surface  1102  of the substrate  110  is higher than the distance D3 from the top surface  1382  of the second type semiconductor layer  138  of the light-emitting diode  130  to the top surface  1102  of the substrate  110 . The structure shown in  FIG. 2B  is similar to the structure shown in  FIG. 1B , the difference is that before the polymer layer  250 ′ is etched, a top of the metal protrusion  240  is not completely covered by the polymer layer  250 ′. In other words, the metal protrusion  240  is already exposed from the polymer layer  250 ′ before the polymer layer  250 ′ is etched. Accordingly, with the configurations of thickness and distance as mentioned above, the top surface  1382  of the second type semiconductor layer  138  and the top of the metal protrusion  240  can be exposed after one etch step, and the step of forming a mask to pattern the polymer layer  250 ′ can be omitted. Therefore, the manufacturing cost can be reduced and the manufacturing efficiency can be improved. Furthermore, since the metal protrusion  240  is not completely covered by the polymer layer  250 ′ before the polymer layer  250 ′ is etched, the reflection of the exposure light by the metal protrusion  240  would not affect the exposure efficiency and the electrical connection quality. 
     In some embodiments, the light-emitting diode  130  is a micro light-emitting diode having a lateral length less than or equal to about 50 μm. It is further noted that a preferable condition for a sum of a thickness t3 of the bottom electrode  132  and a thickness t4 of the first conductive pad  120 A is smaller than or equal to about 2 μm. The 2 μm is a balance of size (i.e., the lateral length ≤about 50 μm) of the micro light-emitting diode and a capability to have an interstitial diffusion between the bottom electrode  132  and the first conductive pad  120 A when the micro light-emitting diode is bonded to the first conductive pad  120 A. As a result, no melting process is performed during the bonding, and the micro light-emitting diode is better protected from damaging during bonding and a position of the micro light-emitting diode relative to the first conductive pad  120  can be better controlled. 
     Due to the tiny size of the micro light-emitting diode, the alignment between the micro light-emitting diode and an opening for exposing the second type semiconductor layer of the micro light-emitting diode in a conventional manufacturing method may become more challenging. Therefore, by exposing the second type semiconductor layer of the micro light-emitting diode and the second conductive pad in one step can replace the step of forming the opening for exposing the top surface of the second type semiconductor layer, thereby preventing the electrical short due to the misalignment between the said opening and the micro light-emitting diode. Furthermore, in the conventional manufacturing method, it is more difficult to form the top electrode  160  in the opening (i.e., contact hole) with a smaller size. Therefore, the method of the present disclosure can omit the step of forming the top electrode  160  in openings that expose the second type semiconductor layer and the second conductive pad  120 B, thereby improving the electrical connection quality. Accordingly, the design rule for forming a display device with a micro light-emitting diode can be achieved easier, or the pitch can even be shrink, thereby preventing the misalignment problem and improving the electrical connection quality. 
     In summary, the device with a light-emitting diode of the present disclosure provides a metal protrusion of which a distance from the top to the top surface of the substrate is greater than a thickness of the etched polymer layer, and the device can be obtained by exposing the top surface of the second type semiconductor layer of the light-emitting diode and the top of the metal protrusion from a polymer layer covering thereon in one etching step. Therefore, the step in conventional manufacturing process that forming a mask for pattern an opening to exposing the second conductive pad can be omitted, and the manufacturing cost can be reduced and the manufacturing efficiency can be enhanced. 
     Although the present disclosure has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the method and the structure of the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims.