Advances in the growth of sapphire has decreased the price of sapphire while enabling the growth of larger boules. These two advances have enabled sapphire to be used in a growing list of applications where the beneficial performance can be realized.
Substrates in the Microelectronics Field
Si and GaAs were used, respectively, for the first and second generation of traditional semiconductor applications. They pushed the development of the microelectronics and optoelectronic technology, and this information technology brought great changes to people's lives. But due to the limitation of the performance of the material itself, the first and second generation semiconductor materials only worked in an environment below 200 ℃. Their radiation resistance and high voltage breakdown properties could not meet the requirements of high temperature, high power, high frequency, high pressure, radiation resistance, and blue light emittance of the modern electronics technology.
New electronic devices require the third generation semiconductor, which is wide band-gap GaN and Sic. GaN has many advantages. Such as a wide forbidden band, high speed electronic saturation, good thermal conductivity, high disruptive intensity, low permittivity and strong heat stability. Therefore, the properties of third generation semiconductor materials would eventually lead to a broad application prospect in aerospace, detection, nuclear energy development, satellite communications, automobile engine, display, new lightinfg technology, laser printing, memories and other fields.
In the early 1970s, people started to explore GaN growth process, but could not grow high quality GaN crystals because of the material technical limitations. The new methods-Molecular beam extension (MBE) and chemical vapor deposition (CVD) appeared one after another, this greatly promoted the study of GaN. Although there is a big lattice mismatch between GaN and sapphire crystals, where sapphire is used as a substrate, it has advantages, such as the same structure with GaN crystals, and the high temperature stability, heat dissipation and good chemical properties. Sapphire also enabled larger wafers at relatively low cost At present, high quality GaN crystals can epitaxial on sapphire wafer with the improvement of growth technology. The (0001) sapphire surface has become the most ideal practical application of the substrate.
SOS Microelectronic Circuits
SOS (Silicon on Sapphire) microelectronic circuit, iis the way of growing a monocrystal Si film on sapphire wafers (1-102) crystal face which called heterogeneous extension method. Then produce semiconductor devices on the monocrystal Si film. Because the SOS microelectronics circuit has the advantages of high speed, low power consumption and radiation resistance, it has great importance in applications of mobile phones, desktop or laptop computers, high speed & high frequency radio communications, small satellite, and Aerospace applications. Sapphire has a similar thermal expansion coefficient with monocrystalline Si. First grow a monocrystalline Si layer (100 surface) using the heterogeneous extension method on (1-102) surface, then produce semiconductor devices on monocrystalline Si. Complete sapphire substrates with full structure are the main necessary conditions to get complete monocrystalline Si.
ZnO, InN and other wafers
IR transmitting window materials
Frequently-used IR transmitting window materials are including ZnS, ZnSe, GeAs, Sapphire, Spinel, ALON, Yttria, MgO, Diamond, and MgF2,etc.ZnS, ZnSe, GeAs have good transmitting performance at 8-12μm optical band, but broken down and loss of performance on high temperatures conditions. Diamond has excellent mechanical strength, optical parameters and thermal conductivity, but cause oxidation and graphitization in 650 ℃ so it is no longer in application. Many oxides also cannot use, because for severe thermal shock and pressure will cause dioxide atoms absorption in materials. High speed missile transparent nose materials ready to use only included Yttria, Spinel, ALON, and sapphire, etc. Sapphire crystal as fine transmitting wave materials has a good transmitting wave rate in the ultraviolet, visible and infrared light can satisfy many composite pattern control and guidance, such as TV, infrared imaging, radar, etc. At the same time sapphire crystal has excellent mechanical performance, chemical stability, good resistant performance at high temperature, high strength and hardness, so it can meet the transmitting wave materials strict requirements of ultra-high speed missiles. In the preparation of material process, sapphire crystal can grow into monocrystal, and then processing molding. Finished product have the same performance of monocrystal, but the other materials mainly use powder hot die casting sintering forming technology, with the lower performance than the original. Therefore, sapphire crystal has become the best choice of the national high-speed fighter and medium-wave transmitting window materials of missile.
Laser matrix, optical components and other purposes
Sapphire crystal is an excellent laser matrix material, mixed Ti sapphire crystal is today's best band tunable laser crystal in the world. It is wide band tunable and high gain. The tunable band range is 660 ~ 1200 nm. In 1982, Moulton first reported the achievement of laser oscillation with Sapphire. Sapphire is in very wide transmitting optical band, from almost ultraviolet band 0.9 nm to infrared light band in 5.5 um, and still has 80% penetration rate in 0.25 ~ 4.5 um. Because of the large sizes that can be obtained sapphire crystal has been used as spectral components of host material and used in large interference device of LIGO (Laser interferometer gravitational observatory), USA, which can detect gravitational waves. In the civil field, sapphire crystal has extensive applications such as uses in medical equipment, environmental protection equipment, laser equipment, chemical equipment, high vacuum measurement equipment, fiber guide plate in textile industry, bar code scanner window, and indestructible watch covers of RADO.
