The LED chip 16 kinds of substrate, denotation and chip structure analysis
Sources: guangdong LED
OFweek semiconductor lighting webex LED technology developed rapidly in recent years, substrate, extension and chip core technology breakthrough progress.
1, graphical substrate
LED epitaxial present commonly used graphical substrate (PSS), PSS is divided into micron grade of PSS and nanoscale nPSS, micron grade PSS have various shapes graphics, graphical highly generally 1.1 to 1.6 mu m, 2.5 ~ 3 microns in diameter, cycle about 4 microns, using micro optical projection and plasma dry etching technique, can generally be helpful 30 ~ 40%. NPSS generally adopt nano-imprinting technology, graphic size is about 260 nm, cycle of about 460 nm, general can raise photosynthetic efficiency is about 70%.
(1) nPSS substrate
On the template and demanding substrate parallel degree, nPSS advantages: LED luminous efficiency higher, better uniformity and low cost. As in the sapphire substrate by nano-imprinting lithography was cycle is 450 nm hole of hexagonal arrays of the green LED output optical power is three times the original.
(2) nanometer column PSS
British Salem's new technology, adopt unique nanometer lithography on sapphire substrate, forming on the surface of the nanometer column, epitaxial growth on the substrate can relieve stress by 85%, thus greatly reduce the defects, can improve the luminous intensity of 80 ~ 120%, LED lighting, industrialization level of 200 lm/w, Droop, and improving the effect of attenuation slow down about 30%.
Summary: PSS can improve greatly the LED luminous efficiency, especially in nanoscale nPSS that could improve the LED luminous efficiency, larger PSS is LED the trend of the development of core technology at present stage. Have different views on PSS in lower cost.
2, homogeneous substrate
Homogeneous substrate is GaN substrate, there are different ways to grow GaN substrate, generally USES HVPE (hydride vapor phase epitaxy) or sodium flow method, the production of GaN substrate to well solve the problem of residual stress and surface rough, substrate thickness of about 400 ~ 400 microns, can now industrialization. GaN substrate of advantages: low dislocation density (105 ~ 106 / cm2), internal quantum efficiency can reach more than 80%, short growth time about 2 hours, save a lot of raw material, can greatly reduce the cost.
(1) to achieve high brightness leds
Toyota synthesis by GaN substrate c surface growth LED chip, was its area is 1, the flux can achieve 400 lm.
(2) HVPE growth GaN substrate industrialization
Mitsubishi chemical, sumitomo electric industries and Hitachi wire company HVPE method is used to grow GaN substrate, the thickness of about 450 microns, the dislocation density (106 ~ 107 / cm2), mitsubishi chemical recently announced that can provide 6 "GaN substrate, and plans in 2015 to cost down to one over ten of the current. Dongguan gallium in GaN substrate (pku) can batch production.
(3) the internal quantum efficiency
Japan's subsidiary sodium flow method is used to grow GaN substrate, low defect density, 90% internal quantum efficiency, under the 200 ma, the photosynthetic efficiency of 200 lm/w, can provide 4 "GaN substrate, the substrate is to accelerate the development of low defect 6".
(4) large size GaN substrate
Sumitomo electric industries and cooperative development with 4 "and 6" GaN substrate, using crystal manufacturing technology and intelligent stripping layer transfer technology to produce ultra-thin high quality GaN substrate, with low defect density, and announced that can provide GaN substrate.
(5) LiGaO2 substrate
South China university of technology research and development on LiGaO2 substrate by using laser molecular beam epitaxy growth non-polar GaN substrate, the thickness of 2 microns, as composite substrate growth GaN chip, requirements to dislocation density of 1 x 106 / cm2, internal quantum efficiency is 85%, the conversion efficiency is 65%.
(6) the winning product
Soraa companies in the United States the nakamura fix two GaN - on - GaN technology to make the LED replacement lamp, be judged to be SVIPLA semiconductor materials science "in the past 30 years one of the most important achievements". The LED crystal integrity of more than 1000 times, so that each lamp USES a LED device possible.
Summary: the GaN - on - GaN homogeneous substrate growth LED to the defect density (105 ~ 106 / cm2), can greatly improve the LED luminous efficiency, and Droop when the current density is not obvious, to realize using single chip LED general lighting light source, LED the core technology to a new level. In nakamura to fix two words to summary: we believe in the GaN - on - GaNLED, we've really write a new chapter, the LED technology namely LED2.0 version.
3 and a half, non-polar, polar substrate
(Al2O3) sapphire crystal surface polarity C, M, R surface polarity and nonpolar a-side. Substrate, nonpolar or half polarities growth difficult, can greatly reduce the defect density. The nonpolar substrates growth LED, can make screen, TV, mobile phones, such as back light, no orientation, not external diffusion, and can be used to record the light, laser, solar panels.
(1) nonpolar, half polarity sapphire substrate
The Salem photoelectric use nonpolar LED on sapphire growth, reduce the defect density, its denotation patches of light conversion efficiency can be improved 7 times, greatly improve the brightness and effectively improve the dollar/lumen value.
(2) "npolo" LED
Seoul semiconductor using non-polar GaN substrate growth LED called "npolo" LED, 1 was in chip to realize the flux 500 lm, Seoul semiconductor CEO Li Zhenxun said: the same as 5 times as the brightness of the surface significantly improved, the future can be increased by more than 10 times, is the ultimate goal of the LED light source.
(3) the non-polar GaN substrate
Mitsubishi chemical using non-polar GaN blue LED substrate growth, the least defect density is only 1 x 104 / cm2. Project goals, in 1 was chip luminescence brightness can reach 1000 lm luminous flux.
(4) the nonpolar, half polarity GaN substrate industrialization
Sumitomo corporation announced that it had developed a polar and non-polar GaN substrate materials, can provide the white LED half polar and non-polar substrates.
(5) uv LED by nonpolar substrates
Seoul semiconductor using non-polar GaN substrate development uv LED phosphors with R, G, B group can realize high color rendering index of white light lighting and color performance range of back light.
Summary: adopting half polar and nonpolar sapphire and GaN substrate grow LED core technology, has been a breakthrough, May 1 was chip to realize the flux 1000 lm, using single chip as an LED lamp light source possible.
4, new structure chip
LED core technology, new technology and the LED chip structure. Chip structure design is to consider how to improve the external quantum efficiency, namely the light extraction efficiency of the chip, chip heat dissipation performance and adopts new structure on the cost reduction process. There are many kinds of new structure chip.
(1) the hexahedron light emitting chip
All the six faces of hexahedron light emitting chip to chip out of the light, by adopting the technology of polyhedral surface coarsening, reduce the reflection interface of photons, enhance the light extraction rate.
(2) DA chip structure
Take advantage of SiC substrate, a Cree company has launched DA series product, USES the transparent substrate SiC as a shiny surface, the SiC substrate to create a 3 d structure, namely on the outer edge of the SiC substrate set V groove, light from one side of V groove, in order to enhance the light extraction effect of high refractive index SiC substrate, and is a large current flip chip, luminous layer on one side of the packages, and obtain the high quality of the heat dissipation, the eutectic bonding, without gold line, area is almost half of the original, significantly reduce the cost, and realize the double price. And in the third generation of silicon carbide technology SC3 platform, by matching the latest packaging technology, announced that lights up to 276 lm/w.
(3) single chip white light
Samsung using nanoscale hexagonal pyramid structure to make white LED technology, can realize half polar and non-polar GaN substrate growth, favorable light extraction of ascension, for nanostructures tiny can effectively reduce the strain, achieve a better quality of crystal, and the cooling performance is good. Send green light, yellow light, red light at the same time, the internal quantum efficiency of 61%, 45% and 29% respectively. White LED realize single chip hair color combinations, a breakthrough. Will improve the quality of light and avoid the energy loss caused by wavelength shift, and can reduce the encapsulation process, improve reliability and reduce packaging costs, to achieve the technical route of white LED.
Summary: the LED chip structure research and development has a new structure appear constantly, in improving photosynthetic efficiency, heat dissipation performance, reduce the cost on a breakthrough unceasingly. More attention to single chip hair color into white LED research and development progress, will be LED lighting technology developing a feasible technique route.
5, substrate and extension of new technology
The following introduce several kinds of the LED substrate, the denotation of core technology in the study of new technology is a pioneering.
(1) extension offset growth technology
At the university of California USES the mask and hierarchical migration technology growth low wrong GaN, as shown.
Schematic diagram of SiO2 thickness of 200 nm, SiNX 120 nm thick. First layer, low temperature 530 ℃ growth 25 nm nucleation under 1040 ℃ after extension GaN, to offset growth, resistance gear fault growth, attains the dislocation density of 7 x 105 / cm2, can greatly improve internal quantum efficiency, reduce Droop effect. On the epitaxial USES innovative technology, a breakthrough, will greatly improve the LED performance metrics.
(2) 3 d silicon GaN technology
Aledia company adopts 3 d silicon-based GaNmicrowire technology, making 3 d silicon LED chip cost is only one 5 of the traditional 2 d plane leds. Based on the technology to upgrade the microwire production technology, using large size crystal and solution of low cost material, the technology has been in the French LETI - CEA company started to use.
(3) the gallium oxide beta Ga2O3 substrate
Gallium oxide Ga2O3 has many kinds of structure forms: alpha, beta, gamma, delta, epsilon, etc., including beta structure is the most stable, forbidden band width is 4.8 ~ 4.9 ev, has now made of high quality, low defect density Ga2O3MOSFET, potential excellent device.
Japan's tamura production of light waves and the subsidiary company the beta - Ga2O3 substrate grow GaN blue phosphors, chip size 2 mm square, plus 6 a current, it can be 500 lm luminous flux, planning target of 2000 ~ 2000 lm.
(4) rare earth oxides REO composite substrate
According to a report in the July 2013 report semiconductor compounds: in Si REO composite substrate on growth, and growth of large garden, GaN and eliminating stress, reduce become warped degrees, massive growth, REO stable performance and reduce the cost, and has higher DBR reflection effect. Has been growing, the composite substrate such as gadolinium oxide, erbium oxide, good results are achieved.
(5) medium composite substrate
Shanghai blue recently released: through the combination of buffer layer and dielectric substrate technology, make the various parameters reach or exceed the level of the sapphire substrate for PSS, breakthrough results.
Summary: the above introduced several kinds of new technology research, is a pioneering innovation, industrialization, once will be subversive breakthrough technology, opened up a LED lighting technology development on another important technical route.