Glasgow University patents SiC bonding

Monday 10th November 2008
The circular heating element and 5 x 5mm square SiC chip are both glowing red-hot. The diode being tested electrolumenesces blue light when forward biased. SiC devices repeatedly demonstrate proper operation at temperatures at 650C where silicon cannot go. Source: http://www.grc.nasa.gov/WWW/SiC

A University of Glasgow patent provides a method for bonding at least two parts where one part comprises silicon carbide by forming a layer of silica on the silicon carbide surface to provide a bonding surface, applying a bonding solution including hydroxide ions to the bonding surface of at least one of the partsand positioning the parts or the bonding surfaces so that a bond can be formed between them. The patent claims extend to assemblies obtained or obtainable by this method, and covers a device or assembly comprising silicon carbide bonded to another part by an interface material that comprises silica treated with a solution, preferably an aqueous solution, which includes hydroxide ions. The claims also extend to a device or assembly comprising silicon carbide bonded to another part by an interface material that comprises a siloxane network.

Key benefits claimed:

  • For precision construction, hydroxide bonding offers many advantages over traditional techniques.
  • The bonding is achieved at room temperature avoiding any thermal stresses.
  • The bond is very stable and vanishingly thin, which is a major benefit for applications where the 'vertical alignment' can be achieved by manufacturing tolerances of the components in combination with the very thin, uniform bond layer.
  • Hydroxide bonds are compatible with high vacuum applications, offer reliable and reproducible bonds and allow for fine adjustment of components before joining.


Among the applications are:* High precision alignment and bonding of SiC components for ground- and space-based applications * High strength, low mechanical loss joining of SiC parts * semiconductors  * astronomical instruments

(Right: SiC crystal, Courtesy:www. theodoregray.com) University of Edinburgh can also offers an SiC patent as an excellent material for fabrication of microsensors and microactuators for use in extreme conditions. The invention allows fabrication of a SiC MEMs device with improved physical properties, using a novel fabrication method. It allows released SiC cantilevers and bridge MEMs structures of controlled properties to be produced in a one-step-process. Test devices have been fabricated and their properties analysed. Very straight, stress free SiC beams have been produced using the process.

SiC in the market
In the SiC field, there's plenty of activity currently. Pacific Aerospace & Electronic in the US notes that titanium composite technology can produce electronic packages that are stronger and more reliable than aluminum alternatives, however, titanium's thermal dissipation characteristics are inadequate for some applications. Accordingly PA&E offers engineers the option of using integrated molybdenum/copper heat sinks and now, for applications where weight is a primary consideration, the company is offering an aluminum silicon carbide heat sink option. (http://www.pacaero.com)

Over the last two years, Dow Corning, which at one point appeared to have forgotten the material, has been steadily been reducing SiC micropipes — a key defect that has been a major challenge for the industry — from an average of well over 100 per cm² to less than 10 per cm² and is on track to be well under 5 per cm² by year end, said Jim Helwick, Gobal Business director, Dow Corning Compound Semiconductor Solutions.  At the same time, X-ray measurements of crystal quality show a better than five-fold improvement and average epitaxy defects were reduced 900% in 18 months.

 "These improvements are critical to drive efforts to move SiC device technology closer to high volume manufacturing,” Helwick said. "The rapid technical advances in compound semiconductors combined with growing market interest in improved energy efficiency and performance put Dow Corning in a good position to support our customers with a valuable new semiconductor technology.” (http://www.dowcorning.com/content/compsemi/compsemi4hcond/)

And in Europe, "Rohm is co-operating with Honda in developing SiC power transistors for use in Honda's high-power modules for the automotive industry. Silicon carbide MOSFETs offer the advantage of reduced heat dissipation or higher efficiency. There is also a strong incentive from governments to develop new technologies due to the CO2 taxation system for vehicles in Europe. More electronics is needed to ensure better CO2 profiles.Analyst Semicast predicts that the average electronics content per vehicle will, rise from $297 today to $375 by 2015," says Christian Andr, president Rohm, Europe. (http://tinyurl.com/5u8use)

Source:http://www.university-technology.com/details/s518
http://www.university-technology.com/details/silicon-carbide-microsystems

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