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Group4 Labs has developed and made commercially available for the first time, a composite semiconductor wafer that comprises of heteroepitaxial Gallium Nitride (GaN) compound semiconductor films atomically attached to specially treated free-standing polycrystalline chemical vapor deposited (CVD) diamond substrates.
The company's team of scientists and engineers has invented two key materials science technologies that have led to the breakthrough represented in the GaN-on-Diamond wafers introduced here: Firstly, the team has invented physio-chemical surface-science technologies to render coarse poly-crystalline CVD diamond substrates easily receptive to single-crystal epitaxial semiconductor films. Secondly, the team has invented an approach to atomically attach single-crystal heteroepitaxial semiconductor compounds to the specially treated (normally hostile) CVD diamond substrates.
This GaN-on-Diamond wafer system enables extremely rapid, efficient, passive, and cost-effective heat extraction from the heat-generating heteroepitaxial device layers since the heating layers reside less than twenty nanometers from the synthetic diamond – a close approximation to nature's most perfect thermal conductor. The GaN-on-Diamond epitaxial wafer system has been designed for customers that manufacture very high-power, high-temperature, and high-frequency transistor-based circuits. Such circuits are typically found in Power Amplifiers, Microwave and Millimeter wafer circuits all of which may be deployed in cellular base stations, radar sensing/communications equipment, weather and communications satellite equipment, inverters and converters typically used in hybrid and electric vehicles, etc.
Group4 Labs engineers are hard at work developing a new version of GaN-on-Diamond wafers that could be deployed in active optical devices such as lasers and LEDs. The new optical GaN-on-Diamond wafer would exhibit a GaN defect density of about 10cm or less, compared to our standard RF GaN-on-Diamond (10cm).
Thermal profile of GaN transistors on SiC substrates (left),
and Diamond substrates (right)
Figure 1. At an ambient temperature of 80°C, 100 W/cm GaN-on-Diamond transistor arrays operate nominally whereas other types of GaN transistors (e.g. GaN-on-SiC, GaN-on-Sapphire) require substantial heat extraction mechanisms to function. This assumes a separation of 10 µm between adjacent transistors. (Details in Simulations & Modeling*).
The company has estimated, proven or conjectured the theoretical concepts that underlie GaN-on-Diamond materials. The reader may refer to the following documents for further technical information.
How we make wafers
Slideshow on how we make wafers**
Dependence of a transistor-array’s packing (power) density on device (junction) temperature
Figure 2. At under 150°C, 100 W/cm GaN-on-Diamond transistor arrays can be packed hundreds of times more densely on a single wafer than GaN-on-SiC transistor arrays. (Details in Simulations & Modeling*, and Power density & thermal simulations*).
Dependency of a transistor’s temperature
on transistor-transistor separation
Figure 3. At 80°C for example, 100 W/cm GaN-on-Diamond transistor arrays can be packed nearly 100 times more densely in a package than GaN-on-SiC transistor arrays. (Details in Simulations & Modeling*).
Measured dependence of a transistor’s gate temperature on output power density
Figure 4. In a side-by-side comparison test, gate temperature and output power of two transistors of similar architectures and dimensions – one made of GaN-on-Diamond, and the other of GaN-on-SiC – were measured. The GaN-on-Diamond transistor’s gate temperature exhibited an expected half the power of the GaN-on-SiC device (Courtesy: Professor Eastman Cornell University; See Cornell: GaN-on-Diamond vs. GaN–on-SiC*published by Pr. Eastman at WOCSDICE 2007, Venice, Italy, May 20-23, 2007.).
* PDF downloads
** PPT downloads