A Bulk Crystal Growing Process for Wide-Bandgap Substrate Materials
Summary:
Cermet, Inc. (Atlanta, GA), has developed a patented process and equipment for producing zinc-oxide and other crystals at a much lower cost than previously possible. The company’s efforts may increase the commercial viability of blue lasers—an emerging technology expected to increase data storage capabilities of electronic equipment such as digital video disc (DVD) systems. BMDO funded the technology through a Phase I and II STTR at Cermet and Georgia Tech Research Corporation and a Phase I SBIR at Cermet to produce materials useful in power electronics for ballistic missile defense. Cermet’s commercialization goal is to be a supplier to technology integrators. The company will be delivering substrates to a major electronics producer in mid 1999 to be tested for blue laser applications.
Technology Description:
Cermet, Inc. (Atlanta, GA), has developed a patented process and equipment for producing zinc-oxide crystals, which may be fabricated into 1- to 2-inch substrates. The company’s efforts could increase the commercial viability of blue lasers, an emerging technology for defense and commercial data storage applications. The cost of Cermet’s substrates will be competitive with the sapphire ones, which are roughly $150, now used for blue lasers, however, the zinc oxide substrates will eliminate the need for additional processing and associated costs, which can be high. When tested by an independent laboratory, the material was found to be of equal quality to competing zinc-oxide crystals available on the market. Cermet is also developing aluminum nitride and gallium nitride with this process.
In the competing approach for making blue lasers, technicians grow gallium nitride (GaN) on sapphire substrates. This approach can be problematic because sapphire substrates have a lattice mismatch with the GaN layers of about 16 percent, which stresses and damages the immediate surface layers of GaN. Technicians are therefore forced to place two or three sacrificial layers of GaN on the substrate, resulting in additional costs of $700 to $1,000 per layer. An alternative is zinc oxide, which only has a 2-percent lattice mismatch with GaN—not enough to seriously affect the operational integrity of the wafer. Zinc oxide crystals, however, until now, have been extremely costly to produce because they degrade when heated at atmospheric pressure. Cermet’s approach can produce high-quality zinc oxide crystals at a much lower cost than current vapor growth processes and, thus, may be the enabling technology for the blue laser’s entry into the commercial marketplace on a large scale.
The basis of Cermet’s technology pressurized melting process, which uses a high pressure chamber of more than 100 atmospheres, induction heating, and proprietary materials for its crucible. The system’s cooled crucible contains the precrystalline material. Radio frequency energy is used as the heat source, producing joule heating in the material until a molten phase is achieved. This entire melting and containment process is carried out in a controlled gas atmosphere ranging from 1 atmosphere to over 100 atmospheres, so that volatile materials are not produced and compounds do not decompose into atomic species. The system produces crystal cylinders that are then cut into wafers.
The system has been proven at temperatures higher than 3,600°C and melt environments in excess of 100 atmospheres. The process is especially useful for crystallizing materials that have one or more of the following characteristics:
•melting points above 1,450°C
•volatile component in the structure
•thermodynamic instabilities at or near the materials melting point at atmospheric pressure.
MDA Origins:
BMDO funded this work, totaling $660,000 through a Phase I and Phase II STTR contract with Cermet and Georgia Tech Research Corporation on the project “Aluminum Nitride Single Crystals Growth Using Pressurized Skull Melting.” Georgia Tech received about one-third of the funding to characterize the materials. In addition, the BMDO SBIR contract funded a Phase I contract called “Powder Synthesis and Bulk Crystal Growth of Gallium Nitride.” Both projects were aimed at developing better materials for high power electronics, such as wide-bandgap semiconductors, used in ballistic missile defense.
Spinoff Applications:
The commercial application with the most potential at this time is for blue lasers used in digital video disc (DVD) systems, which have just recently become available to consumers. Current systems use red lasers for write and readout; however, blue lasers, with their shorter wavelength, could dramatically improve these systems. More specifically, red lasers can store about 4.7 Gbs per side while blue ones can store about 12 GBs per side, which is enough for six hours of video and sound. Unfortunately, blue lasers currently are not economically feasible, largely due to the cost of the materials, i.e., crystals, required to produce them. Crystals produced using Cermet’s process will cost much less, increasing the feasibility of blue lasers for DVD systems and other data storage applications. This, in the future, could lower the cost and increase the length of movies on DVDs for home entertainment centers. According to the online January 14, 1999, edition of DVD Market News, more than 1 million DVD-video players were shipped to retailers in the United States alone since the product’s launch in March 1997.
Another application is alternative power generation, called thermophotovoltaics, in which a photovoltaic cell converts thermal radiation to electricity. Its solid state configuration could offer many advantages over existing generators. Unfortunately, there have been challenges in achieving the necessary efficiencies required for commercial or defense use. Recent success has been obtained by using doped rare earth oxides, which currently are very expensive to produce. Cermet’s process could reduce the cost of these crystals and, thus, the overall cost of the system.
Crystals produced with Cermet’s process could also be used for solar blind detectors, which can detect, for example, rocket plumes during daylight. They also can be used commercially for such novel applications as flame detection on hot water heaters.
Commercialization:
Cermet’s goal is to serve as a materials supplier to technology integrators. The company has patented the process and related equipment and is providing substrate samples for blue lasers to a major electronics corporation for testing. Centimeter-sized substrates will be available in the next few months for blue laser applications and crystals for thermophotovoltaic applications should be available by June 1999.
Company Profile:
Founded in 1991, Cermet is a materials research and development company with 7 employees It has about 4,500 ft2 of laboratory and office space. This facility is adequate to carry Cermet through a pilot production stage. The company has three crystal growth systems, one of which is a pilot production system. Two-inch to ten-inch diameter crucibles are available for crystal growth.
Contact Information:
Jeff Nause
Cermet, Inc.
1019 Collier road Suite C1
Atlanta GA 30318
Tel:404-351-0005
Fax:404-605-0208
email: jnause@cermetinc.com
email: cermetinc@juno.com
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