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Technical Insight

Caldus raises temperature of silicon carbide contacts

A small Oregon company has developed the technology to form contacts to SiC that are chemically and electrically stable up to temperatures exceeding 1000 °C, writes Donald Hagge.
It has been recognized for several years that SiC possesses several fundamental advantages over silicon as a semiconductor material for devices in high-temperature and high-power solid-state electronics. In addition, SiC devices offer potential advantages for high frequency and logic circuit applications, power conversion (mixer diodes, MESFETs), single chip computers (n-MOS, CMOS, bipolar transistors), and non-volatile random access memory. The potential maximum average power, maximum operating temperature and thermal stability of SiC solid-state devices and circuits far exceeds Si- or GaAs-based devices. Technology barriers for commercial products have existed both in the availability of quality SiC material and for the formation of stable metallized contacts. Caldus Semiconductor Inc, a small company based in Beaverton, Oregon, has developed the technology to form metallized rectifying Schottky junctions and ohmic contacts to SiC that are chemically and electrically stable up to temperatures in the 1000 °C range. Innovative high-temperature packaging is also being developed. Specific to sensor technology, SiC substrate and refractory metal contact structures enable entirely new regimes of thermal processing that were not previously accessible. There are whole sets of materials and compounds that could never be used in conventional semiconductor processing because of the high temperatures involved. Semiconductor substrate and contact materials would migrate or melt. Piezoelectric and magnetic materials with Curie points between 300 and 900 K can now be processed on SiC sensor platforms. Ceramic gas sensing materials can be applied directly to the substrate as the active gate for an entirely new technology with corresponding improved sensitivity and the possibility of detector regeneration. A wide range of inert and consumable catalysis materials can be applied to the sensor platform for tunable catalyst technology, which offers new possibilities for smart thermal sensors in safety-critical devices. MEMS fuel cells are also now possible using wide bandgap SiC material and contact technology that can function at 1000 °C.

Commercial devices The first commercial products under development by Caldus are devices for temperature, pressure and gas sensing in the 200-1000 °C range. Since the company s metal-SiC technology has been demonstrated to be stable at temperatures as high as 1100 °C it will be possible to develop SiC sensors that are stable, durable, chemically inert, small and relatively inexpensive. Several issues are driving demand for the SiC products. Among them are energy conservation, national security, automotive and engine emission requirements, and wireless and space communications. However, Caldus plans to focus solely on sensing devices in the early stages of its growth, and will consider other products and markets once this initial strategy is successful. Currently, a large suite of electronic systems used in commercial, industrial, and military applications (including, but not limited to aerospace, automotive, electric power, nuclear power and space) would benefit significantly from components and packaging designed and optimized for higher temperatures under generally harsh environmental conditions. These types of electronic systems are positioned away from the source of heat or they require the use of cooling systems. This design philosophy forces the use of costly cabling, connectors, tubing and/or cooling systems and creates excess weight, excess volume and decreased reliability. Furthermore, these factors increase maintenance requirements and consequently have higher costs. About Caldus Caldus Semiconductor Inc was founded as 3C Semiconductor Corporation at the Oregon Graduate Institute of Science and Technology (OGI) to develop and market unique SiC devices. Caldus has created proprietary technology in response to a growing demand for semiconductor devices that operate reliably at much higher frequencies, power levels and temperatures than existing silicon devices. Three patents have been issued to the company and three more applications have been filed. Caldus believes that its technology will create products with significant performance and cost advantages relative to competitive products for some high-temperature applications. This market is the focus of the International High Temperature Electronics Conferences held in Albuquerque, NM every two years. The Oregon Research and Technology Development Fund (ORTDF) and OGI supported the SiC technology program within OGI. Additional venture-capital financing has been committed to Caldus, which has also won SBIR Phase I and II contracts from the Ballistic Missile Defense Organization.

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