TWI447933B - Vertical led with eutectic layer - Google Patents

Description

Vertical light-emitting diode with eutectic layer

The present invention relates to the field of light-emitting diode (LED) technology, and more particularly to a vertical light-emitting diode (VLED) structure.

Light-emitting diodes (LEDs) have been around for decades, and research and development efforts are continually moving toward improving their luminous efficiency, thereby increasing the number of applications that can be applied. Heat dissipation is a major limiting factor in improving luminous efficiency, and thus heat transfer processing is an important consideration for designers of LEDs.

When LEDs are driven with high currents, high component temperatures are created due to insufficient heat transfer from the active layer of the semiconductor die to the surrounding environment. High temperatures not only cause component damage and accelerated aging, but the optical properties of the LEDs also change with temperature. For example, the light output of an LED generally decreases as the temperature of the component increases. Furthermore, due to changes in the energy of the semiconductor band gap, the emission wavelength will change with temperature.

Conventional LED structures are formed on substrates such as sapphire, tantalum carbide, tantalum, niobium, ZnO or gallium arsenide, which are thermal insulators or have poor thermal conductivity properties. By replacing the substrate of the conventional LEDs with a preferred heat-conducting material such as molybdenum, a vertical light-emitting diode (VLED) structure has been created to improve heat dissipation, which is transmitted through a silver paste ( The silver epoxy or silver paste is glued or bonded to the component layer, and then the original substrate is peeled off by laser or removed by etching. Since the thin epitaxial layer of this structure is sandwiched between the n and p electrodes, the name VLED is won. In order to further improve heat dissipation, a recent VLED structure called metal vertical photo-excited LEDs (MvpLEDs, metal vertical photon LEDs) has been replaced with a metal-based substrate such as SiO without using a glue layer or a bonding layer. ₂ or a substrate composed of a poorly thermally conductive material of sapphire; in contrast, MvpLEDs use deposition techniques such as electroless or electrochemical deposition to form a metal-based substrate directly adjacent to the element layer without a centering glue or bonding layer To hinder heat transfer.

Also, the main path of heat dissipation in the prior art is through heat conduction from the active layer of the LED stack through the metal-based substrate and a relatively thick silver paste layer to the metal of a printed circuit board (PCB). Lead frame or pad. The problem with this design is that the silver paste has a low thermal conductivity and a high coefficient of thermal expansion (CTE). With such a low thermal conductivity, the relatively thick silver rubber layer is a bit like a thermal resistor; with this relatively high CTE, due to the stress caused by the expansion and contraction of the silver rubber layer, at a high temperature for a period of time, the conventional technology VLEDs also have reduced reliability.

Therefore, what is needed is an improved technique for fabricating VLEDs, preferably to improve luminous efficiency, exhibit greater heat dissipation, and increase reliability.

One embodiment of the present invention provides a vertical light-emitting diode (VLED) structure. The structure generally includes a eutectic layer, a metal-based substrate disposed adjacent to the eutectic layer, a light emitting diode stack disposed on the substrate, and an electrode connected to the light emitting diode stack . Some embodiments may include a reflective layer to help direct light in a single direction, thereby increasing luminous efficiency; and/or a metal protective layer for better adhesion, and thus increasing reliability.

Another embodiment of the present invention provides a vertical light-emitting diode (VLED) structure. The structure generally includes a lead frame, a metal-based substrate, a eutectic layer disposed between the lead frame and the metal-based substrate, a light-emitting diode stack disposed on the substrate, and a connection To the electrode of the LED stack. Some embodiments may include a reflective layer to help direct light in a single direction, thereby increasing luminous efficiency; and/or a metal protective layer for better adhesion, and thus increasing reliability.

Another embodiment of the present invention provides a vertical light emitting diode (VLED, vertical) Light-emitting diode) structure. The structure generally includes a eutectic layer, a lead frame disposed on the eutectic layer, a bonding layer disposed between the lead frame and a metal-based substrate, and a light emitting diode disposed on the substrate A laminate, and an electrode connected to the LED stack. The bonding layer can be a second eutectic layer. Some embodiments may include a reflective layer to help direct light in a single direction, thereby increasing luminous efficiency; and/or a metal protective layer for better adhesion, and thus increasing reliability.

Embodiments of the present invention provide a vertical light-emitting diode (VLED) structure that can be incorporated into MvpLEDs, and provide an improved heat transfer path and increased reliability compared to conventional VLEDs.

An exemplary LED structure

1 is a schematic cross-sectional view of a VLED structure 100 having a eutectic layer 110, in accordance with an embodiment of the present invention. An LED stack 104 is an essential component of any VLED structure and may comprise any suitable material, such as AlGaInN or AlGaInP. A substrate 108 can be located below the LED stack 104. The substrate 108 may comprise a single layer or a plurality of layers, and typically has a thickness of 10 to 400 μm. In any case, the substrate 108 may be a suitable metal or metal such as Cu, Ni, Ag, Au, Al, Cu-Co, Ni-Co, Cu-W, Cu-Mo, Ni/Cu, and Ni/Cu-Mo. A single element or combination of alloys. The material of the substrate 108 is selected to form a eutectic bond with the eutectic layer 110. Therefore, metal alloys can generally be used with respect to sapphire or other non-metallic substrate materials, and metal alloys generally have better heat transfer characteristics. An electrode 102 can be disposed over and coupled to the LED stack 104.

On the side of the LED stack 104 relative to the electrode 102 (as follows), a reflective layer 106 (or mirror as indicated in the figure) can be formed to reflect the light generated by the side of the LED stack 104. With this reflection, the light is not wasted and contributes to the total light emission, thus increasing the luminous efficiency. The reflective layer 106 may be composed of any suitable material such as AgNi, Ni/Ag/Ni/Au, Ag/Ni/Au, AuZn, AuBe, ITO/Ag, ITO/Ag ₂ O/Ag, ITO/Al or Ag/Ti. /Ni/Au. The reflective layer 106 may also use an alloy comprising Ag, Au, Cr, Pt, Pd, Rh or Al. At the time of manufacture, the reflective layer 106 has been deposited on the side of the aforementioned LED stack 104 before the substrate 108 is applied to the structure.

A common fused layer 110 is formed under the substrate 108. When the VLED is fabricated, the use of the eutectic layer 110 allows for a eutectic bond with high bonding strength and good stability at a low processing temperature, formed between the substrate 108 and the eutectic layer 110. Furthermore, as can be observed in Table 1, the eutectic (e.g., AuSn, CuMo, and CuW) has a higher thermal conductivity and a lower coefficient of thermal expansion than the Ag paste used in prior art VLED structures.

The higher thermal conductivity between the eutectic layer 110 and one of the leadframes (not shown) or other substrate connection components of the VLED structure 100 results in a reduction in the total thermal resistance between the active layer of the LED stack 104 and the surrounding environment. Because of this reduced thermal resistance, embodiments of the present invention can increase light output and reliability at a given operating current when compared to conventional VLEDs, thereby resulting in devices having greater luminous efficiency.

Furthermore, the eutectic properties of the lower coefficient of thermal expansion and the eutectic bonding itself can result in increased reliability when compared to conventional devices. When a high temperature occurs in the device, the expansion and shape of the eutectic layer 110 changes less than the corresponding layer of silver paste generally containing conventional VLEDs. Also, the eutectic bonding can result in a better adhesion of the substrate 108. For this reason, the eutectic layer 110 can maintain a tighter, fixed connection with the substrate 108 over the long term life of the VLED.

The eutectic layer 110 itself may comprise a single layer or a plurality of layers of any suitable material, such as Sn, In, Pb, AuSn, CuSn, AgIn, CuIn, SnPb, SnInCu, SnAgIn, SnAg, SnZn, SnAgCu, SnZnBi, SnZnBiIn or SnAgInCu. When the VLED structure 100 is fabricated, the eutectic layer 110 can be formed by deposition, sputtering, evaporation, electroplating, electroless plating, coating, inkjet, or printing. For certain embodiments, although the eutectic layer 110 may have a thickness between 0.01 and 100 μm, it typically has a thickness of 0.5 to 2 μm. This general thickness range is much thinner than the thickness of the Ag glue layer in conventional VLEDs, typically 5 to 20 μm. The reduced thickness of the eutectic layer 110 also improves the thermal conductivity of the VLED structure 100 of certain embodiments.

To further increase the reliability, as shown in the VLED schematic of FIG. 2, some embodiments may also include a metal protection layer 202 interposed between the eutectic layer 110 and the substrate 108. The metal cap layer 202 can help prevent oxidation and diffusion of components in the eutectic layer 110 into the substrate 108, thereby increasing the lifetime of the eutectic layer 110, and thus increasing the lifetime and reliability of the defined VLED structure 100. The metal protective layer 202 generally has a thickness of 0.01 to 100 μm, which may include Ni, W, Mo, Pt, Ta, Rh, Au, V, TiW, TaN or Ni-Co, and may be deposited, sputtered, evaporated, Electroplated, electroless plating, coating, inkjet, and printing are formed.

In order to have means for mounting the VLED structure 100 to a PCB pad or other suitable surface, as illustrated in FIG. 4, embodiments of the present invention may include a leadframe 402. The leadframe 402 can be disposed below the eutectic layer 110 and coupled thereto via eutectic bonding to seek to benefit from increased heat transfer and reliability with the eutectic. As described above and further illustrated in FIG. 5, some embodiments having a lead frame 402 and a eutectic layer 110 may also have a metal protective layer 202 interposed between the metal-based substrate 108 and the eutectic layer 110. between. For some embodiments, as shown in FIG. 6, a second eutectic layer 602 can be formed under the leadframe 402 to provide a connection that is strong and reliable with a low thermal resistance to the adhesive surface. Like the eutectic layer 110 described above, the second eutectic layer 602 can be formed in the same manner from the same material and have the same thickness. For embodiments having a second eutectic layer 602, the eutectic layer 110 can be replaced by a bonding layer 604, which can comprise any suitable material, such as silver paste, for bonding the substrate 108 to Lead frame.

Furthermore, an embodiment having a second eutectic layer 602 can have a second metal protective layer (not shown) interposed between the second eutectic layer 602 and the leadframe 402. The second metal protective layer can help prevent oxidation and diffusion of components in the second eutectic layer 602 into the leadframe 402, thereby increasing the lifetime of the second eutectic layer 602, and thus increasing the lifetime and reliability of the defined VLED structure 100. degree. The second metal protective layer generally has a thickness of 0.01 to 100 μm, which may include Ni, W, Mo, Pt, Ta, Rh, Au, V, TiW, TaN or Ni-Co, and may be deposited, sputtered, steamed Formed by plating, electroplating, electroless plating, coating, inkjet, and printing.

Certain embodiments of the invention may include accessory features for certain applications. For example, for some embodiments, as shown in the VLED sketch of Figure 3, a portion of surface 302 of the LED stack 104 can be patterned in any desired manner to seek to improve light extraction. This surface pattern can increase the brightness of the VLED, thus increasing its luminous efficiency. And in some embodiments, the VLED structure 100 shown in any of the figures can be incorporated into an LED device, for example, by packaging the structure in a housing having a wire that provides the TED stack 104 and The external connection of the substrate 108 is electrically connected.

Although the above is directed to embodiments of the invention, without departing from the invention Other and additional embodiments of the invention are conceivable in the basic scope, and the scope of the invention is determined by the scope of the subsequent claims.

100‧‧‧Vertical LED structure

102‧‧‧Electrode

104‧‧‧Light Emitting Body Lamination

106‧‧‧reflective layer

108‧‧‧Substrate

110‧‧‧Composite layer

202‧‧‧Metal protective layer

302‧‧‧ surface

402‧‧‧ lead frame

602‧‧‧Second eutectic layer

604‧‧‧ joint layer

The above-described features of the present invention will be described in detail with reference to the preferred embodiments of the invention. However, it is to be understood that the appended claims are not intended to be limited

1 is a schematic cross-sectional view of a VLED having a eutectic layer; FIG. 2 is a cross-sectional view of a VLED having a eutectic layer and a metal protective layer, according to an embodiment of the present invention; An embodiment of the present invention, FIG. 3 is a schematic cross-sectional view of a VLED having a eutectic layer depicting a patterned surface of the LED stack; FIG. 4 is a eutectic layer and a wire in accordance with an embodiment of the present invention. FIG. 5 is a schematic cross-sectional view of a VLED having a eutectic layer, a metal protective layer, and a lead frame; and FIG. 6 is an embodiment of the present invention, FIG. 6 is a schematic cross-sectional view of a VLED of a VLED; A cross-sectional view of a VLED having a bonding layer, a leadframe, and a eutectic layer.

100‧‧‧Vertical LED structure

102‧‧‧Electrode

104‧‧‧Light Emitting Body Lamination

106‧‧‧reflective layer

108‧‧‧Substrate

110‧‧‧Composite layer

Claims (41)

A light emitting diode structure comprising: a substrate comprising at least one of a metal and a metal alloy material; a eutectic layer thermally coupled to the substrate, wherein the eutectic layer comprises Sn, In, Pb, AuSn, CuSn, AgIn, At least one of CuIn, SnPb, SnInCu, SnAgIn, SnAg, SnZn, SnAgCu, SnZnBi, SnZnBiIn, and SnAgInCu; a light emitting diode stack disposed on the substrate; and an electrode connected to the LED stack Floor. The luminescent diode structure of claim 1, wherein the eutectic layer comprises a plurality of layers. The light-emitting diode structure of claim 1, wherein the eutectic layer has a thickness of 0.01 to 100 μm. The light-emitting diode structure of claim 1, wherein the eutectic layer is formed by at least one of deposition, sputtering, evaporation, electroplating, electroless plating, coating, inkjet, and printing. The light-emitting diode structure of claim 1, wherein the substrate comprises a single layer or a plurality of layers. The light-emitting diode structure of claim 1, wherein the substrate comprises Cu, Ni, Ag, Au, Al, Cu-Co, Ni-Co, Cu-W, Cu-Mo, Ni/Cu, and Ni/ At least one of Cu-Mo. The light-emitting diode structure of claim 1, wherein the substrate has a thickness of 10 to 400 μm. The light emitting diode structure of claim 1 further includes a reflective layer disposed between the substrate and the light emitting diode stack. The light-emitting diode structure of claim 8, wherein the reflective layer comprises AgNi, Ni/Ag/Ni/Au, Ag/Ni/Au, Ag/Ti/Ni/Au, AuZn, AuBe, ITO/Ag. At least one of ITO/Ag ₂ O/Ag, ITO/Al, and an alloy containing Ag, Au, Cr, Pt, Pd, Rh, or Al. Such as the light-emitting diode structure of claim 1 of the patent scope, wherein the light-emitting diode The polar body layer is at least one of AlGaInN and AlGaInP. The light-emitting diode structure of claim 1, wherein a portion of the surface of the light-emitting diode stack is patterned to improve light extraction. The light-emitting diode structure of claim 1 further includes a lead frame for external connection, disposed under the eutectic layer. A light emitting diode structure comprising: a substrate comprising at least one of a metal and a metal alloy material; a eutectic layer thermally coupled to the substrate; a metal protective layer disposed between the substrate and the eutectic layer; A light emitting diode stack is disposed on the substrate, and an electrode is connected to the light emitting diode stack. The light-emitting diode structure of claim 13, wherein the metal protective layer comprises at least one of Ni, W, Mo, Pt, Ta, Rh, Au, V, TiW, TaN and Ni-Co. The light-emitting diode structure of claim 13, wherein the metal protective layer has a thickness of 0.01 to 100 μm. The light-emitting diode structure of claim 13, wherein the metal protective layer is formed by at least one of deposition, sputtering, evaporation, electroplating, electroless plating, coating, inkjet, and printing. A light emitting diode comprising: a casing; a substrate comprising at least one of a metal and a metal alloy; a eutectic layer thermally coupled to the substrate, wherein the eutectic layer comprises Sn, In, Pb, AuSn, CuSn At least one of AgIn, CuIn, SnPb, SnInCu, SnAgIn, SnAg, SnZn, SnAgCu, SnZnBi, SnZnBiIn, and SnAgInCu; a light emitting diode stack disposed on the substrate, and an electrode to provide the light emitting diode The external connection of the laminate and the substrate. The light-emitting diode of claim 17 further includes a metal protective layer disposed between the substrate and the eutectic layer. The light-emitting diode of claim 17 further comprising a reflective layer disposed between the substrate and the light-emitting diode stack. The light-emitting diode of claim 17, wherein a portion of the surface of the light-emitting diode stack is patterned to improve light extraction. A light emitting diode structure comprising: a eutectic layer, wherein the eutectic layer comprises Sn, In, Pb, AuSn, CuSn, AgIn, CuIn, SnPb, SnInCu, SnAgIn, SnAg, SnZn, SnAgCu, SnZnBi, SnZnBiIn, and SnAgInCu At least one of the two; a lead frame for external connection, disposed adjacent to the eutectic layer; a bonding layer disposed between the lead frame and a substrate, wherein the substrate comprises at least one of a metal and a metal alloy material; A light emitting diode stack is disposed on the substrate, and an electrode is connected to the light emitting diode stack. The luminescent diode structure of claim 21, wherein the eutectic layer comprises a plurality of layers. The light-emitting diode structure of claim 21, wherein the eutectic layer has a thickness of 0.01 to 100 μm. The light-emitting diode structure of claim 21, wherein the eutectic layer is formed by at least one of deposition, sputtering, evaporation, electroplating, electroless plating, coating, inkjet, and printing. The luminescent diode structure of claim 21, wherein the substrate comprises a single layer or a plurality of layers. The light-emitting diode structure of claim 21, wherein the substrate comprises Cu, Ni, Ag, Au, Al, Cu-Co, Ni-Co, Cu-W, Cu-Mo, Ni/Cu, and Ni/ At least one of Cu-Mo. The light-emitting diode structure of claim 21, wherein the substrate has a thickness of 10 to 400 μm. The light emitting diode structure of claim 21, further comprising a reflective layer disposed between the substrate and the light emitting diode stack. The light-emitting diode structure of claim 28, wherein the reflective layer comprises AgNi, Ni/Ag/Ni/Au, Ag/Ni/Au, Ag/Ti/Ni/Au, AuZn, AuBe, ITO/Ag At least one of ITO/Ag ₂ O/Ag, ITO/Al, and an alloy containing Ag, Au, Cr, Pt, Pd, Rh, or Al. The light-emitting diode structure of claim 21, wherein the light-emitting diode stack is at least one of AlGaInN and AlGaInP. The light-emitting diode structure of claim 21, wherein a portion of the surface of the light-emitting diode stack is patterned to improve light extraction. The light-emitting diode structure of claim 21, wherein the bonding layer is a second eutectic layer comprising Sn, In, Pb, AuSn, CuSn, AgIn, CuIn, SnPb, SnInCu, SnAgIn, SnAg, SnZn At least one of SnAgCu, SnZnBi, SnZnBiIn, and SnAgInCu. A light emitting diode structure comprising: a eutectic layer; a lead frame for external connection disposed on the eutectic layer; a metal protective layer disposed between the lead frame and the eutectic layer; a layer disposed between the lead frame and a substrate, wherein the substrate comprises at least one of a metal and a metal alloy, the bonding layer being a second eutectic layer comprising Sn, In, Pb, AuSn, CuSn, AgIn, At least one of CuIn, SnPb, SnInCu, SnAgIn, SnAg, SnZn, SnAgCu, SnZnBi, SnZnBiIn, and SnAgInCu; a light emitting diode stack disposed on the substrate, and an electrode connected to the LED stack Floor. The light-emitting diode structure of claim 33, wherein the metal protective layer comprises at least one of Ni, W, Mo, Pt, Ta, Rh, Au, V, TiW, TaN, and Ni-Co. The light-emitting diode structure of claim 33, wherein the metal protective layer has a thickness of 0.01 to 100 μm. For example, the structure of the light-emitting diode of claim 33, wherein by sinking At least one of product, sputtering, evaporation, electroplating, electroless plating, coating, inkjet, and printing is used to form the metal protective layer. A light emitting diode structure comprising: a first eutectic layer thermally coupled to a lead frame for external connection; a first metal protective layer disposed between the lead frame and the first eutectic layer; a second eutectic layer disposed on the lead frame and thermally coupled to a substrate, wherein the substrate comprises at least one of a metal and a metal alloy material; a second metal protective layer disposed on the second eutectic layer Between the substrates; a light-emitting diode stack disposed on the substrate, and an electrode connected to the light-emitting diode stack. The light-emitting diode structure of claim 37, wherein the first and second eutectic layers comprise Sn, In, Pb, AuSn, CuSn, AgIn, CuIn, SnPb, SnInCu, SnAgIn, SnAg, SnZn, At least one of SnAgCu, SnZnBi, SnZnBiIn, and SnAgInCu. The light-emitting diode structure of claim 37, wherein the first and second metal protective layers comprise at least Ni, W, Mo, Pt, Ta, Rh, Au, V, TiW, TaN and Ni-Co one of them. The light emitting diode structure of claim 37, further comprising a reflective layer disposed between the substrate and the light emitting diode stack. The light-emitting diode structure of claim 37, wherein a portion of the surface of the light-emitting diode stack is patterned to improve light extraction.