The leading companies in the development of LED and semiconductor all-solid-state lighting sources are: Lumi leds, HP/Agilent and Cree in the US, Nichia, ToyodaGosei, Sony, Toshiba and other large companies in Japan (such as NEC, Matsushita, Mitsubishi and Sumitomo, etc., Osram, Germany, etc. Most of these multinational companies have original patents that lead the trend of technology development and occupy the vast majority of market share. Some photovoltaic companies in Taiwan Province of China (such as Guolian Optoelectronics, Guangbao Electronics, Guanglei Technology, Yiguang Electronics, Dingyuan Optoelectronics, etc.) and some R&D units in Korea also have their own downstream processes and packaging as well as upstream material extension. A number of independent intellectual property rights have a certain market share.
According to the survey, Nichia, Cree, Lumileds, OSRAM, ToyodaGosei, Toshiba, and Rohm, which account for the majority of the market, own 80% to 90% of original invention patents in the field (focusing on material growth, device fabrication, Most of the rest of the companies have utility model patents (mainly for device reliability and product application development).
Material basis: technical route convergence
The study of GaN-based wide-bandgap semiconductor materials began in the 1960s and 1970s, but compared to other traditional III/V compound semiconductors (such as GaAs-based and InP-based materials), commercialization was applied in the early 1990s. It was realized in the medium term, so there are still many problems related to the research of its basic physical/chemical properties. In these respects, some famous universities and research institutions in the United States, Japan, South Korea and Europe enjoy research reputation. These academic units are also conducting various industrial technology research (based on MOCVD metal organic chemical vapor phase epitaxy) with cooperative enterprises. The basic physical/chemical properties of GaN-based materials are studied by techniques such as RS-MBE (Radio Frequency Source Molecular Beam Epitaxy). We have published statistics on academic papers published in the Journal of Crystal Growth and Applied Physics Letters, which were published in the past 10 years from 1993 to 2002. In the 877 research papers on GaN light-emitting devices surveyed, about 60% of the experimental samples (531 related papers) were obtained by epitaxial growth of MOCVD technology, and the remaining 40% of the experimental samples were RS-MBE. Obtained by other technical means such as HVPE.
It can be seen that, for the entire global industry, the technical route based on MOCVD epitaxial growth is the main technical trend of developing GaN-based optoelectronic materials and devices, and the technical routes such as RS-MBE are more suitable for basic academic research work. Therefore, this patent investigation report is mainly aimed at MOCVD epitaxially grown GaN materials.
Compared with blue-green light-emitting devices made of SiC, ZnS and other II/VI compound semiconductor wide-bandgap materials, GaN-based devices have long life, high luminous efficiency and relatively low price, and are recognized as all-solid-state lighting sources. The material of choice for die devices.
Epitaxial Technology: Competitive Focus In general, epitaxial growth of GaN-based materials is the core technology for developing GaN-based high-brightness LEDs and all-solid-state semiconductor white light illumination sources. It is the top priority of all key problems, so there is a problem on this issue. A large number of patents have been applied, such as high-quality GaN epitaxial growth equipment (US5433169, EP0887436), substrate pretreatment technology (JP7142763) buffer layer technology (JP2000124499 with AlN, JP7312350 with GaN, EP1111663 with SiNx), multi-buffer layer technology (US6495867), using superlattice blocking dislocations (US2001035531), lateral epitaxial overgrowth technology (EP0942459), and hanging epitaxial technology (US6285696) and the like.
We will outline the development of the technology in general. First, Nichia Corporation pioneered the patent for a dual-beam MOCVD system (US5433169). Due to the emergence of this new MOCVD system, the quality of MOCVD-grown GaN material crystals has been greatly improved.
Secondly, the emergence of buffer layer technology solves the problem of large lattice mismatch and thermal mismatch in the growth of GaN materials on heterogeneous substrates. Since the GaN material grown under the buffer layer technology still has a high defect density, which affects important technical indexes such as luminous intensity, working life and reverse characteristics of the light-emitting device, people have developed multi-buffering on this basis. Layer technology to obtain higher quality GaN single crystal materials.
At this point, GaN materials are sufficient to meet the needs of general high-brightness LED device fabrication, but to make GaN-based blue/green laser diodes on this basis, the defect density of GaN-based materials must be further reduced. Lateral lateral epitaxial overgrowth technique (EL OG, Epitxy)
The theory of hanging and overhanging is proposed to solve this problem. Of course, the epitaxial optimization technology represented by this ELOG is relatively expensive, and the GaN epitaxial material used for making high-power illumination die devices does not need to adopt this technical route, but its design idea is worth learning from, that is, the largest Limitly try to reduce the defect density in the epitaxial material and improve the overall performance of the device.
In GaN-based optoelectronic devices, a large number of patents focus on the structural design of the illuminating region, including: ordinary double heterojunction 0592224); general square quantum wells (including single quantum wells and multiple quantum wells, EP1189289 and JP11054847); Trapezoidal quantum well (US6309459); triangular quantum well and asymmetric quantum well (GB2361354); using undoped carrier confinement layer (US2002093020); adding buffer layer between active layer and p-type layer (US2001011731); The quantum barrier (MQB) acts as a carrier confinement layer (US2001030317) and so on. The purpose of these patent designs is to increase the luminous efficiency of the active region.
Device Fabrication: Based on the discussion of physical mechanisms and process technologies based on eight typical technologies, we have analyzed the patents for the complete device fabrication of GaN-based luminescence products. Several typical representative technologies are listed:
One is the US patent US5631190 (Methodforproducinghighefficiencylight-emittingdiodesandresuringingdiodestructures
), that is, a method of fabricating a high-efficiency light-emitting diode and implementing a diode structure. Its patent owner is CreeResearch.
The second is the US patent US5912477 (Highefficiency lightemittin gdiodes), which is a high-efficiency light-emitting diode. Its patent owner is CreeResearch.
The third is the patent WO0141223 (Scalable LED with improved current spread-ing), that is, a light-emitting diode with an improved current distribution layer. Its patent owner is CreeRe-search.
The fourth is the US patent US6526082 (P-con-tactfor GaN-based semiconductorsutilizing areverse-biased tunnel junction), that is, a P-type contact layer of a GaN-based semiconductor is fabricated by a reverse biased tunnel diode. Its patent owner is Lumileds.
The fifth is the US patent US2002017652 (Semiconductor chip for optoelectronics), that is, the method of manufacturing the die. Its patent owner is Osram.
The sixth is US6538302 (Semiconductor chip and method for the production of theore), that is, the semiconductor chip and its manufacturing method. Its patent owner is Osram.
Seven is the patent DE10064448. Its patent owner is Osram.
Eight is the US Patent US6078064 (Indiumgalliumnitridelightemittingdiode), which is an InGaN light emitting diode. Its patent owner is EPISTAR.
Other important patents related to GaN-based high-brightness LEDs and all-solid-state lighting source die devices are O03026029, US2003015708, US2003062525, and US2002017696.
In short, the fabrication of GaN-based devices based on the needs of industrial technology requires consideration of process operability and simplicity, as well as reliability and stability of the device with certain complexity and redundancy. One of the technological innovations we can explore.
Packaging Technology: Soldering and material filling patents focus on post-packaging processes such as grinding, dicing, splitting, soldering, resin and fluorescent material filling after the fabrication of high-brightness GaN die devices. Among them, intellectual property mainly focuses on welding and resin/fluorescent material filling.
In the welding problem, Nichia's early electrode design and packaging patents have been covered, such as JP7221103, JP8279643 and JP9045965. In the design of the device heat sink, Lumileds has a heat sink design technology, which is based on the industry-leading packaging technology of Si-based material flip chip bonding ("Flip-Chip"), including US2003089917, US6498355 and US6573537; "Flip- The chip" flip chip optimization design includes EP1204150 and EP1256987; the Power package includes US6492725.
In terms of light extraction efficiency, Lumileds' flip-chip bonding technology uses high reflectivity ohmic electrodes and side tilting technology to increase daylighting (patent number US2001000209), but Osram prior to the extraction of SiC-based GaN-LEDs The concept of the end face "Faceting" has been pioneered and covers most of the related patents. In addition, HP (EP1081771), Cree (US5631190) also have their own characteristics in the collection of die light.
In terms of resin and fluorescent material filling, it is worth noting the development of new high-efficiency long-life visible light fluorescent materials, such as JP 9391191 of Nichia and EP1267424 of Lumileds. In short, there are a lot of "know-how" in the packaging technology of GaN-based high-power devices, which is worthy of further study.
Process technology: patent coverage is tight in dry etching. Due to the high hardness and chemical stability of GaN-based materials, common semiconductor wet etching techniques cannot meet the needs of industrial operation, so new types of dryness must be adopted. Etching technique, which does not use chemical acid-base solution corrosion, but achieves high etching rate, vertical sidewall, low damage, anisotropy and high selectivity by physical/chemical reactions such as gas phase plasma bombardment. It lays a foundation for the fabrication of GaN-based high-performance devices. In terms of ohmic electrodes, the ohmic contact problem of GaN materials, especially p-GaN materials, is one of the main obstacles hindering its commercial application in the early stage. Nichia applied for the following major patents: EP0622858 (1994), JP7221103 (1995) and JP8279643 (1997); ToyodaGosei started earlier in this area, mainly using different alloy materials and optimizing their annealing temperatures accordingly. For example, Ni/Au (JP10135515), Co/Au (JP10163529), Mn/Au (JP10270758), Ni/u (US6008539), and Ti/Ni (JP2002026390). There is also Lumileds
Patent US6526082 and so on.
In short, in the above two technical fields of dry etching and ohmic electrodes, the patent coverage is relatively strict, but the research groups are based on their own process conditions and technical advantages, and also have some room for innovation.
Substrate patent: scattered across multiple companies
Due to the extremely high melting temperature of the GaN-based material and the extremely high nitrogen saturated vapor pressure, it is very difficult to obtain a homoepitaxial large-area GaN single crystal, and a heterogeneous substrate is generally used for epitaxial growth.
At present, the heteroepitaxial growth method for large mismatched substrates has been matured. The patented substrate materials include: AlN, GaN, Sapphire, 6H-SiC, ZnO, Li AlO2, LiGaO2, MgAl2O4, Si, GaAs, 3C- SiC and MgO.
A company represented by Nichia/HP/Lumileds/Toyoda-Gosei uses a sapphire (sapphire) substrate for MOCVD heteroepitaxial growth of GaN materials. Among them, the four patents that Nichia applied for in 1994 and 1995 (the patent numbers are US5433169, JP7312350, EP0599224 and EP0622858 respectively) and the related patent of Lumileds (US6537513) are groundbreaking.
The company represented by Cree/Osram uses SiC substrate for MOCVD heteroepitaxial growth, and correspondingly develops and perfects the post-step process such as SiC substrate-based packaging technology. The patents of the representative patents are US5631190 and US2002093020. , US2003015708
And US2003062525 and so on.
Of course, in order to improve the crystal quality of the grown GaN material, many substrate pretreatment methods have been developed, and the patents in this area are mainly concentrated in the hands of leading companies such as Nichia, Cree, Toyoda-Gosei and Sony. Several large Japanese companies represented by Sony/Toshiba/Sanya are committed to the development of a new generation of ultra-large-capacity information storage DVD ("Blu-ray Disc") optical drive blue-violet laser diodes, all using Free-standing
A GaN-based material serves as a substrate for homoepitaxial growth.
Finally, it is important to note that before Nakamura of Japan's Nichia Corporation took the lead in achieving breakthroughs in GaN blue LEDs in 1994 and 1995, Cree (based on SiC), Toshiba (based on Sapphire and MgAl2O4) and Toyoda (based on Sapphire) The company has applied for several US patents for GaN-based epitaxial growth and substrate selection from 1991 to 1993. Therefore, the core patents for GaN material substrates are scattered in the hands of many major industry companies, and there is no monopoly. .
According to the survey, Nichia, Cree, Lumileds, OSRAM, ToyodaGosei, Toshiba, and Rohm, which account for the majority of the market, own 80% to 90% of original invention patents in the field (focusing on material growth, device fabrication, Most of the rest of the companies have utility model patents (mainly for device reliability and product application development).
Material basis: technical route convergence
The study of GaN-based wide-bandgap semiconductor materials began in the 1960s and 1970s, but compared to other traditional III/V compound semiconductors (such as GaAs-based and InP-based materials), commercialization was applied in the early 1990s. It was realized in the medium term, so there are still many problems related to the research of its basic physical/chemical properties. In these respects, some famous universities and research institutions in the United States, Japan, South Korea and Europe enjoy research reputation. These academic units are also conducting various industrial technology research (based on MOCVD metal organic chemical vapor phase epitaxy) with cooperative enterprises. The basic physical/chemical properties of GaN-based materials are studied by techniques such as RS-MBE (Radio Frequency Source Molecular Beam Epitaxy). We have published statistics on academic papers published in the Journal of Crystal Growth and Applied Physics Letters, which were published in the past 10 years from 1993 to 2002. In the 877 research papers on GaN light-emitting devices surveyed, about 60% of the experimental samples (531 related papers) were obtained by epitaxial growth of MOCVD technology, and the remaining 40% of the experimental samples were RS-MBE. Obtained by other technical means such as HVPE.
It can be seen that, for the entire global industry, the technical route based on MOCVD epitaxial growth is the main technical trend of developing GaN-based optoelectronic materials and devices, and the technical routes such as RS-MBE are more suitable for basic academic research work. Therefore, this patent investigation report is mainly aimed at MOCVD epitaxially grown GaN materials.
Compared with blue-green light-emitting devices made of SiC, ZnS and other II/VI compound semiconductor wide-bandgap materials, GaN-based devices have long life, high luminous efficiency and relatively low price, and are recognized as all-solid-state lighting sources. The material of choice for die devices.
Epitaxial Technology: Competitive Focus In general, epitaxial growth of GaN-based materials is the core technology for developing GaN-based high-brightness LEDs and all-solid-state semiconductor white light illumination sources. It is the top priority of all key problems, so there is a problem on this issue. A large number of patents have been applied, such as high-quality GaN epitaxial growth equipment (US5433169, EP0887436), substrate pretreatment technology (JP7142763) buffer layer technology (JP2000124499 with AlN, JP7312350 with GaN, EP1111663 with SiNx), multi-buffer layer technology (US6495867), using superlattice blocking dislocations (US2001035531), lateral epitaxial overgrowth technology (EP0942459), and hanging epitaxial technology (US6285696) and the like.
We will outline the development of the technology in general. First, Nichia Corporation pioneered the patent for a dual-beam MOCVD system (US5433169). Due to the emergence of this new MOCVD system, the quality of MOCVD-grown GaN material crystals has been greatly improved.
Secondly, the emergence of buffer layer technology solves the problem of large lattice mismatch and thermal mismatch in the growth of GaN materials on heterogeneous substrates. Since the GaN material grown under the buffer layer technology still has a high defect density, which affects important technical indexes such as luminous intensity, working life and reverse characteristics of the light-emitting device, people have developed multi-buffering on this basis. Layer technology to obtain higher quality GaN single crystal materials.
At this point, GaN materials are sufficient to meet the needs of general high-brightness LED device fabrication, but to make GaN-based blue/green laser diodes on this basis, the defect density of GaN-based materials must be further reduced. Lateral lateral epitaxial overgrowth technique (EL OG, Epitxy)
The theory of hanging and overhanging is proposed to solve this problem. Of course, the epitaxial optimization technology represented by this ELOG is relatively expensive, and the GaN epitaxial material used for making high-power illumination die devices does not need to adopt this technical route, but its design idea is worth learning from, that is, the largest Limitly try to reduce the defect density in the epitaxial material and improve the overall performance of the device.
In GaN-based optoelectronic devices, a large number of patents focus on the structural design of the illuminating region, including: ordinary double heterojunction 0592224); general square quantum wells (including single quantum wells and multiple quantum wells, EP1189289 and JP11054847); Trapezoidal quantum well (US6309459); triangular quantum well and asymmetric quantum well (GB2361354); using undoped carrier confinement layer (US2002093020); adding buffer layer between active layer and p-type layer (US2001011731); The quantum barrier (MQB) acts as a carrier confinement layer (US2001030317) and so on. The purpose of these patent designs is to increase the luminous efficiency of the active region.
Device Fabrication: Based on the discussion of physical mechanisms and process technologies based on eight typical technologies, we have analyzed the patents for the complete device fabrication of GaN-based luminescence products. Several typical representative technologies are listed:
One is the US patent US5631190 (Methodforproducinghighefficiencylight-emittingdiodesandresuringingdiodestructures
), that is, a method of fabricating a high-efficiency light-emitting diode and implementing a diode structure. Its patent owner is CreeResearch.
The second is the US patent US5912477 (Highefficiency lightemittin gdiodes), which is a high-efficiency light-emitting diode. Its patent owner is CreeResearch.
The third is the patent WO0141223 (Scalable LED with improved current spread-ing), that is, a light-emitting diode with an improved current distribution layer. Its patent owner is CreeRe-search.
The fourth is the US patent US6526082 (P-con-tactfor GaN-based semiconductorsutilizing areverse-biased tunnel junction), that is, a P-type contact layer of a GaN-based semiconductor is fabricated by a reverse biased tunnel diode. Its patent owner is Lumileds.
The fifth is the US patent US2002017652 (Semiconductor chip for optoelectronics), that is, the method of manufacturing the die. Its patent owner is Osram.
The sixth is US6538302 (Semiconductor chip and method for the production of theore), that is, the semiconductor chip and its manufacturing method. Its patent owner is Osram.
Seven is the patent DE10064448. Its patent owner is Osram.
Eight is the US Patent US6078064 (Indiumgalliumnitridelightemittingdiode), which is an InGaN light emitting diode. Its patent owner is EPISTAR.
Other important patents related to GaN-based high-brightness LEDs and all-solid-state lighting source die devices are O03026029, US2003015708, US2003062525, and US2002017696.
In short, the fabrication of GaN-based devices based on the needs of industrial technology requires consideration of process operability and simplicity, as well as reliability and stability of the device with certain complexity and redundancy. One of the technological innovations we can explore.
Packaging Technology: Soldering and material filling patents focus on post-packaging processes such as grinding, dicing, splitting, soldering, resin and fluorescent material filling after the fabrication of high-brightness GaN die devices. Among them, intellectual property mainly focuses on welding and resin/fluorescent material filling.
In the welding problem, Nichia's early electrode design and packaging patents have been covered, such as JP7221103, JP8279643 and JP9045965. In the design of the device heat sink, Lumileds has a heat sink design technology, which is based on the industry-leading packaging technology of Si-based material flip chip bonding ("Flip-Chip"), including US2003089917, US6498355 and US6573537; "Flip- The chip" flip chip optimization design includes EP1204150 and EP1256987; the Power package includes US6492725.
In terms of light extraction efficiency, Lumileds' flip-chip bonding technology uses high reflectivity ohmic electrodes and side tilting technology to increase daylighting (patent number US2001000209), but Osram prior to the extraction of SiC-based GaN-LEDs The concept of the end face "Faceting" has been pioneered and covers most of the related patents. In addition, HP (EP1081771), Cree (US5631190) also have their own characteristics in the collection of die light.
In terms of resin and fluorescent material filling, it is worth noting the development of new high-efficiency long-life visible light fluorescent materials, such as JP 9391191 of Nichia and EP1267424 of Lumileds. In short, there are a lot of "know-how" in the packaging technology of GaN-based high-power devices, which is worthy of further study.
Process technology: patent coverage is tight in dry etching. Due to the high hardness and chemical stability of GaN-based materials, common semiconductor wet etching techniques cannot meet the needs of industrial operation, so new types of dryness must be adopted. Etching technique, which does not use chemical acid-base solution corrosion, but achieves high etching rate, vertical sidewall, low damage, anisotropy and high selectivity by physical/chemical reactions such as gas phase plasma bombardment. It lays a foundation for the fabrication of GaN-based high-performance devices. In terms of ohmic electrodes, the ohmic contact problem of GaN materials, especially p-GaN materials, is one of the main obstacles hindering its commercial application in the early stage. Nichia applied for the following major patents: EP0622858 (1994), JP7221103 (1995) and JP8279643 (1997); ToyodaGosei started earlier in this area, mainly using different alloy materials and optimizing their annealing temperatures accordingly. For example, Ni/Au (JP10135515), Co/Au (JP10163529), Mn/Au (JP10270758), Ni/u (US6008539), and Ti/Ni (JP2002026390). There is also Lumileds
Patent US6526082 and so on.
In short, in the above two technical fields of dry etching and ohmic electrodes, the patent coverage is relatively strict, but the research groups are based on their own process conditions and technical advantages, and also have some room for innovation.
Substrate patent: scattered across multiple companies
Due to the extremely high melting temperature of the GaN-based material and the extremely high nitrogen saturated vapor pressure, it is very difficult to obtain a homoepitaxial large-area GaN single crystal, and a heterogeneous substrate is generally used for epitaxial growth.
At present, the heteroepitaxial growth method for large mismatched substrates has been matured. The patented substrate materials include: AlN, GaN, Sapphire, 6H-SiC, ZnO, Li AlO2, LiGaO2, MgAl2O4, Si, GaAs, 3C- SiC and MgO.
A company represented by Nichia/HP/Lumileds/Toyoda-Gosei uses a sapphire (sapphire) substrate for MOCVD heteroepitaxial growth of GaN materials. Among them, the four patents that Nichia applied for in 1994 and 1995 (the patent numbers are US5433169, JP7312350, EP0599224 and EP0622858 respectively) and the related patent of Lumileds (US6537513) are groundbreaking.
The company represented by Cree/Osram uses SiC substrate for MOCVD heteroepitaxial growth, and correspondingly develops and perfects the post-step process such as SiC substrate-based packaging technology. The patents of the representative patents are US5631190 and US2002093020. , US2003015708
And US2003062525 and so on.
Of course, in order to improve the crystal quality of the grown GaN material, many substrate pretreatment methods have been developed, and the patents in this area are mainly concentrated in the hands of leading companies such as Nichia, Cree, Toyoda-Gosei and Sony. Several large Japanese companies represented by Sony/Toshiba/Sanya are committed to the development of a new generation of ultra-large-capacity information storage DVD ("Blu-ray Disc") optical drive blue-violet laser diodes, all using Free-standing
A GaN-based material serves as a substrate for homoepitaxial growth.
Finally, it is important to note that before Nakamura of Japan's Nichia Corporation took the lead in achieving breakthroughs in GaN blue LEDs in 1994 and 1995, Cree (based on SiC), Toshiba (based on Sapphire and MgAl2O4) and Toyoda (based on Sapphire) The company has applied for several US patents for GaN-based epitaxial growth and substrate selection from 1991 to 1993. Therefore, the core patents for GaN material substrates are scattered in the hands of many major industry companies, and there is no monopoly. .
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