Wanted: diamond semiconductors for RF, microwave, and power electronics to operate in harsh environments

March 30, 2023
LADDIS focuses on diamond semiconductors substrates with diameters larger than 50 millimeters with good electrical, thermal, and mechanical properties.

ARLINGTON, Va. – U.S. military researchers are asking industry find new ways of fabricating device-grade, large diameter, single crystal diamond substrates for radio-frequency (RF) and power electronics that must operate in harsh environmental conditions.

Officials of the U.S. Defense Advanced Research Projects Agency (DARPA) in Arlington, Va., issued a solicitation Tuesday (DARPA-PA-21-05-03) for the Large Area Device-Quality DIamond Substrates (LADDIS) project.

LADDIS seeks to develop techniques for substrates for diamond semiconductors with diameters larger than 50 millimeters, dislocation density below 103 square millimeters, surface roughness below 0.2 nanometers, and good electrical, thermal, and mechanical properties.

Diamond is an ultra-wide bandgap semiconductor that offers a path for developing harsh-environment power electronics and RF and microwave components that are able to operate at high power levels and at high temperatures.

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At the same time, conventional electronics built on silicon, gallium arsenide, or wide band-gap materials are limited in breakdown voltage, power handling, and operating temperature. Diamond’s large bandgap and thermal conductivity can overcome these limitations.

Semiconductor fabrication technologies, however, remain a challenge. Reproducible large-diameter device-quality diamond substrates have hindered the demonstration of electronics with higher breakdown voltage or current compared to existing technology.

Diamond substrates today are no larger than 5 to 10 square millimeters and have dislocation density as high as 105 square millimeters, which degrades device performance and manufacturability.

Commercially available substrates also have large variability in material quality such that previous attempts at wafer size scaling exhibited dislocation density as high as 109 square millimeters, and can crack due to stress.

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Some chip fab technologies have been promising. Seed tiling, for example, has been used to incrementally scale the diameter of diamond substrates. Seed tiling is a variation of homoepitaxy in which individual diamond seeds are arrayed together, followed by lateral overgrowth using CVD to connect the individual seeds into one larger, single crystal seed.

This technique requires optimizing growth conditions to minimize defects at the tile boundary. In addition, new heteroepitaxial growth approaches have been developed, in which diamond grows from nucleation layers deposited on a different substrate.

Innovations in reactor design, substrate holders, and growth processes also have been shown to minimize thermal gradients and ensure a uniform growth rate, which lowers the built-in stress of the diamond material.

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Exploration of these techniques will provide insights into creating viable approaches for the manufacturing of large-diameter single-crystal diamond substrates.

The LADDIS program will provide the basis for developing a domestic, commercial source for diamond substrates to enable manufacturing of high power and high temperature microelectronics. These devices would support several U.S. Department of Defense (DOD) platforms and arrays by enabling kilowatt-class low-loss front end receiver protect circuitry, as well as 10-kilovolt-class low-loss switches necessary for future electric ship power systems.

The total award value for the 18-month LADDIS program is limited to $1 million. The program has one technical area developing diamond growth and polishing techniques. Proposals are limited to a single growth and polishing method, yet proposers may submit several standalone proposals for different growth approaches.

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Proposers will develop growth approaches such as homoepitaxial or heteroepitaxial to fabricate diamond substrates and demonstrate more than 30 millimeters diameter, single crystal substrates with low dislocation density.

Companies interested should upload proposals no later than 14 April 2023 to the DARPA BAA website at https://baa.darpa.mil.

Email questions or concerns to Thomas Kazior, the LADDIS program manager, at [email protected]. More information is online at https://sam.gov/opp/45fd25a01b9949c4bddff3f35a6e3291/view.

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