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April 2nd, 2012

Alfred U. researchers participating in solid oxide fuel cell interconnects, GaN-on-diamond substrate projects

Published on April 2nd, 2012 | By: pwray@ceramics.org

Left, prototype of SOFC stack. Right, samples of interconnects being developed in a public–private partnership with Alfred University, Solid Cell, RocCera and the the New York State Energy Research and Development Authority. Credit: Solid Cell.

Alfred University recently announced two interesting projects where their ceramics and glass experts are working with private-sector partners that could have significant impact the energy and sensor fields.

The first project involves a AU collaborating with a company called Solid Cell in a New York state-funded project to improve solid oxide fuel cells. The university’s Olivia Graeve will be, in particular, working with Solid Cell to lead research to develop improved SOFC interconnects.

These interconnects serve to physically separate but electrically connect the electrodes in SOFCs. The challenge to make durable interconnects has been a major hurdle in developing and commercializing SOFCs, which operate at very high temperatures (typically 800°C or higher) in an environment filled with caustic chemicals that can attack and weaken all but the toughest materials.

Metals alloys, until recently, have been the go-to material for interconnects, but so far they frequently fail at the high temperature regimes. Efforts are being made to reduce SOFC operating temperatures to 600°C or lower, but in the meantime many SOFC developers, such as Solid Cell, are interested in alternatives to metal alloy interconnects.

Graeve also teaches materials science and engineering at the Inamori School, and her group’s work will be to find a ceramic alternative. “This project with Solid Cell is very synergistic and takes advantage of our expertise areas in a very meaningful way,” she says in an email.

The idea is that ceramic materials are highly durable at high temperatures and can be formulated to be both conductive and resistant to chemical attack. This is apparently part of a ongoing joint effort. According to a 2011 Solid Cell release, the goal at that time was to “demonstrate the feasibility of replacing traditional ceramic powder synthesis with a low-cost process. The proprietary technology will reduce the time, energy and handling requirements of synthesis, while producing a nanopowder with improved physical properties.” A Solid Cell representative, Arkady Malakhov, explains that this new project is an extention of prior work, moving from feasibility to actual production of the interconnets.

The work is being funded by the New York State Energy Research and Development Authority, and also includes the involvement RocCera, which is assisting with fabrication technology

For more information on the interconnects topic, Solid Cell has available online the presentation it made a few months ago at ACerS’s ICACC’12 conference in Daytona Beach.

Sacrificial substrate for diamond nanocoating

In the second example, S.K. Sundaram and Scott Misture, professors at the school, are working with Group4 Labs Inc. to create a system to provide a sacrificial substrate that will be just one part of a novel technology that adds a thin diamond coating to semiconductors to hasten heat extraction. Group4 Labs wants to be able to use this new system on solid-state lighting, sensing and communication applications.

The task undertaken by Sundaram and Misture, both Inamori Professors of materials science in AU’s Kazuo Inamori School of Engineering, is to devise a substrate that — once removed — will allow a micrometer-sized layer of diamond coating to attach to the semiconductor surface. The diamond coating, in turn, then will act as a substrate additional coatings.

The trick is to find a way to get the diamond to stick to the substrate, and, here, the key is to find an inexpensive substrate with a thermal expansion coefficient that matches the diamond. In other words, the diamond and the substrate must be able to undergo the same thermal expansion and contraction or else one of the materials will separate and crack. Once the diamond-substrate is sandwiched with the semiconductor material, the substrate is carefully removed, leaving the diamond coating behind.

According to an AU news release, Misture and Sundaram think that cordierite glass-ceramics will likely be the candidate for the substrate because it and the diamond have compatible thermal expansions. In addition, both have chemical and thermal stability during processing. The release notes, “Misture and Sundaram hope to accomplish that by manipulating the glass chemistry and controlling a specific crystal phase’s crystallizing out.”

Group4 Labs, based in Fremont, Calif., is something of startup company that is attempting to leverage gallium-nitride-on-diamond technology to (according to the company’s website) and says its GaN-on-diamond can reduce transistor temperatures by over 500°C and thereby improve power output and efficiency. The company has been working on a joint LED project in New York State, but also recently announced that it will be partnering in four DARPA contracts related to “Near Junction Thermal Transport” with the goal of “address thermal hurdles and energy efficiency in the 21st century where energy consumption is costly and unsustainable.”


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