{"64679":{"#nid":"64679","#data":{"type":"news","title":"Silver-Diamond Composite Offers Cooling Capabilities for Electronics","body":[{"value":"\u003Cp\u003EResearchers at the Georgia Tech Research Institute (GTRI) are developing a solid composite material to help cool small, powerful microelectronics used in defense systems. The material, composed of silver and diamond, promises an exceptional degree of thermal conductivity compared to materials currently used for this application.\u003C\/p\u003E\n\u003Cp\u003EThe research is focused on producing a silver-diamond thermal shim of unprecedented thinness \u2013 250 microns or less.  The ratio of silver to diamond in the material can be tailored to allow the shim to be bonded with low thermal-expansion stress to the high-power wide-bandgap semiconductors planned for next generation phased-array radars.\n\u003C\/p\u003E\n\u003Cp\u003EThermal shims are needed to pull heat from these high-power semiconductors and transfer it to heat-dissipating devices such as fins, fans or heat pipes. Since the semiconductors work in very confined operating spaces, it is necessary that the shims be made from a material that packs high thermal conductivity into a tiny structure.\n\u003C\/p\u003E\n\u003Cp\u003EDiamonds provide the bulk of thermal conductivity, while silver suspends the diamond particles within the composite and contributes to high thermal conductivity that is 25 percent better than copper.  To date, tests indicate that the silver-diamond composite performs extremely well in two key areas -- thermal conductivity and thermal expansion.  \n\u003C\/p\u003E\n\u003Cp\u003E\u0027We have already observed clear performance benefits -- an estimated temperature decrease from 285 degrees Celsius to 181 degrees Celsius -- using a material of 50 percent diamond in a 250-micron shim,\u0027 said Jason Nadler, a GTRI research engineer who is leading the project. \n\u003C\/p\u003E\n\u003Cp\u003EThe researchers are approaching diamond percentages that can be as high as 85 percent, in a shim less than 250 microns in thickness. These increased percentages of diamond are yielding even better performance results in prototype testing.\n\u003C\/p\u003E\n\u003Cp\u003ENadler added that this novel approach to silver-diamond composites holds definite technology-transfer promise.  No material currently available offers this combination of performance and thinness. \n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003ENatural Thermal Conductors\u003C\/strong\u003E\n\u003C\/p\u003E\n\u003Cp\u003EDiamond is the most thermally conductive natural material, with a rating of approximately 2,000 watts per meter Kelvin, which is a measure of thermal efficiency.  Silver, which is among the most thermally conductive metals, has a significantly lower rating -- 400 watts per meter K. \n\u003C\/p\u003E\n\u003Cp\u003ENadler explained that adding silver is necessary to:\u003Cbr \/\u003E\n-  bond the loose diamond particles into a stable matrix;\u003Cbr \/\u003E\n-  allow precise cutting of the material to form components of exact sizes;\u003Cbr \/\u003E\n-  match thermal expansion to that of the semiconductor device being cooled;\u003Cbr \/\u003E\n-  create a more thermally effective interface between the diamonds.\n\u003C\/p\u003E\n\u003Cp\u003ENadler and his team use diamond particles, resembling grains of sand, that can be molded into a planar form.  \n\u003C\/p\u003E\n\u003Cp\u003EThe problem is, a sand-like material doesn\u0027t hold together well.  A matrix of silver -- soft, ductile and sticky -- is needed to keep the diamond particles together and achieve a robust composite material.\n\u003C\/p\u003E\n\u003Cp\u003EIn addition, because the malleable silver matrix completely surrounds the diamond particles, it supports cutting the composite to the precise dimensions needed to form components like thermal shims. And silver allows those components to bond readily to other surfaces, such as semiconductors.  \n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003ETailoring Thermal Expansion\u003C\/strong\u003E\n\u003C\/p\u003E\n\u003Cp\u003EAs any material heats up, it expands at its own individual rate, a behavior known as its coefficient of thermal expansion (CTE).  \n\u003C\/p\u003E\n\u003Cp\u003EWhen structures made from different materials -- such as a wide-bandgap semiconductor and a thermal shim -- are joined, it is vital that their thermal-expansion coefficients be identical.  Bonded materials that expand at different rates separate readily.\n\u003C\/p\u003E\n\u003Cp\u003EDiamond has a very low coefficient of thermal expansion of about two parts per million\/Kelvin (ppm\/K).  But the materials used to make wide-bandgap semiconductors -- such as silicon carbide or gallium nitride \u2013 have higher CTEs, generally in the range of three to five ppm\/K.\n\u003C\/p\u003E\n\u003Cp\u003EBy adding in just the right percentage of silver, which has a CTE of about 20 ppm\/K, the GTRI team can tailor the silver-diamond composite to expand at the same rate as the semiconductor material. By matching thermal-expansion rates during heating and cooling, the researchers have enabled the two materials to maintain a strong bond. \n\u003C\/p\u003E\n\u003Cp\u003EUnlike metals, which conduct heat by moving electrons, diamond conducts heat by means of phonons, which are vibrational wave packets that travel through crystalline and other materials.  Introducing silver between the diamond-particle interfaces helps phonons move from particle to particle and supports thermal efficiency. \n\u003C\/p\u003E\n\u003Cp\u003E\u0022It\u0027s a challenge to use diamond particles to fill space in a plane with high efficiency and stability,\u0022 Nadler said. \u0022In recent years we\u0027ve built image-analysis and other tools that let us perform structural morphological analyses on the material we\u0027ve created. That data helps us understand what\u0027s actually happening within the composite -- including how the diamond-particle sizes are distributed and how the silver actually surrounds the diamonds.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EA remaining hurdle involves the need to move beyond performance testing to an in-depth analysis of the silver-diamond material\u0027s functionality. Nadler\u0027s aim is to explain the thermal conductivity of the composite from a fundamental materials standpoint, rather than relying solely on performance results.  \n\u003C\/p\u003E\n\u003Cp\u003EThe extremely small size of the thermal shims makes such in-depth testing difficult, because existing testing methods require larger amounts of material. However, Nadler and his team are evaluating several testbed technologies that hold promise for detailed thermal-conductivity analysis.\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EResearch News \u0026amp; Publications Office\u003Cbr \/\u003E\nGeorgia Institute of Technology\u003Cbr \/\u003E\n75 Fifth Street, N.W., Suite 314\u003Cbr \/\u003E\nAtlanta, Georgia  30308  USA\u003C\/strong\u003E\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EMedia Relations Contacts\u003C\/strong\u003E: Kirk Englehardt (404-407-7280)(\u003Ca href=\u0022mailto:kirk.englehardt@gtri.gatech.edu\u0022\u003Ekirk.englehardt@gtri.gatech.edu\u003C\/a\u003E) or John Toon (404-894-6986)(\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E).\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: Rick Robinson\n\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EResearchers at the Georgia Tech Research Institute (GTRI) are developing a solid composite material to help cool small, powerful microelectronics used in defense systems. The new material is composed of silver and diamond.\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"A new composite material could help cool high-power electronics."}],"uid":"27303","created_gmt":"2011-02-28 01:00:00","changed_gmt":"2016-10-08 03:08:18","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2011-02-28T00:00:00-05:00","iso_date":"2011-02-28T00:00:00-05:00","tz":"America\/New_York"},"extras":[],"hg_media":{"64680":{"id":"64680","type":"image","title":"Silver-diamond composite materials","body":null,"created":"1449176765","gmt_created":"2015-12-03 21:06:05","changed":"1475894569","gmt_changed":"2016-10-08 02:42:49","alt":"Silver-diamond composite materials","file":{"fid":"192067","name":"tlk30065.jpg","image_path":"\/sites\/default\/files\/images\/tlk30065_0.jpg","image_full_path":"http:\/\/www.tlwarc.hg.gatech.edu\/\/sites\/default\/files\/images\/tlk30065_0.jpg","mime":"image\/jpeg","size":1566428,"path_740":"http:\/\/www.tlwarc.hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/tlk30065_0.jpg?itok=2GrGCacw"}},"64681":{"id":"64681","type":"image","title":"Diamond materials","body":null,"created":"1449176765","gmt_created":"2015-12-03 21:06:05","changed":"1475894569","gmt_changed":"2016-10-08 02:42:49","alt":"Diamond materials","file":{"fid":"192068","name":"tis30065.jpg","image_path":"\/sites\/default\/files\/images\/tis30065_0.jpg","image_full_path":"http:\/\/www.tlwarc.hg.gatech.edu\/\/sites\/default\/files\/images\/tis30065_0.jpg","mime":"image\/jpeg","size":1387493,"path_740":"http:\/\/www.tlwarc.hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/tis30065_0.jpg?itok=xW6H8EfD"}},"64682":{"id":"64682","type":"image","title":"Diamond material","body":null,"created":"1449176765","gmt_created":"2015-12-03 21:06:05","changed":"1475894569","gmt_changed":"2016-10-08 02:42:49","alt":"Diamond material","file":{"fid":"192069","name":"thg30065.jpg","image_path":"\/sites\/default\/files\/images\/thg30065_0.jpg","image_full_path":"http:\/\/www.tlwarc.hg.gatech.edu\/\/sites\/default\/files\/images\/thg30065_0.jpg","mime":"image\/jpeg","size":662179,"path_740":"http:\/\/www.tlwarc.hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/thg30065_0.jpg?itok=XTk8hD5C"}}},"media_ids":["64680","64681","64682"],"related_links":[{"url":"http:\/\/www.gtri.gatech.edu\/","title":"Georgia Tech Research Institute"}],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"136","name":"Aerospace"},{"id":"144","name":"Energy"},{"id":"154","name":"Environment"},{"id":"147","name":"Military Technology"},{"id":"149","name":"Nanotechnology and Nanoscience"},{"id":"135","name":"Research"}],"keywords":[{"id":"12178","name":"composite"},{"id":"437","name":"cooling"},{"id":"1366","name":"defense"},{"id":"416","name":"GTRI"},{"id":"12176","name":"Jason Nadler"},{"id":"2832","name":"microelectronics"},{"id":"171070","name":"silver-diamond"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cp\u003E\u003Cstrong\u003EJohn Toon\u003C\/strong\u003E\u003Cbr \/\u003EResearch News \u0026amp; Publications Office\u003Cbr \/\u003E\u003Ca href=\u0022http:\/\/www.gatech.edu\/contact\/index.html?id=jt7\u0022\u003EContact John Toon\u003C\/a\u003E\u003Cbr \/\u003E\u003Cstrong\u003E404-894-6986\u003C\/strong\u003E\u003C\/p\u003E","format":"limited_html"}],"email":["jtoon@gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}