Manufacturing Bits: Feb. 6

GaN trusted foundry; diamond bonding; high-density SiC.


GaN trusted foundry
HRL Laboratories–an R&D venture between Boeing and General Motors–has launched a new foundry service for use in advanced millimeter-wave (mmWave) gallium-nitride (GaN) technology applications.

HRL’s process, called T3-GaN, is a high-electron-mobility transistor technology. It will enable the fabrication of GaN-based monolithic microwave integrated circuits (MMICs) for a range of applications, such as next-generation high-data-rate wireless communications and high-resolution radar imaging.

HRL has experience in designing MMICs from the UHF to the mmWave range. This includes low-noise amplifiers, power amplifiers, mixers, switches, attenuators and phase shifters. It also has expertise in packaging the fabricated MMICs.

HRL processes GaN wafers in a 10,000-square-foot ISO Class 4 cleanroom. The foundry service, which is a U.S. Department of Defense Trusted Foundry, will begin an open subscription period soon for customers with verified U.S. government end-use.

Epitaxial growth is integral to HRL Laboratories’ T3 GaN foundry services. (Source: HRL Laboratories)

For customers that do not want to perform custom MMIC designs themselves, HRL offers related T3-GaN MMIC design services to U.S. government customers. “Eligible customers will be able to design into our world-class, state-of-the-art mmW T3-GaN fabrication process and receive custom, tailored circuits for their specific applications at a price much lower than a dedicated foundry run,” said Shawn Burnham, the HRL scientist in charge of the GaN foundry service. “They will be given access to a process design kit, which has already been used to demonstrate world-record power amplifier and low-noise amplifier performance.”

Diamond bonding
Fujitsu has developed what the company claims is the world’s first technology for bonding single-crystal diamond to a silicon carbide (SiC) substrate at room temperature.

This technology is used for heat dissipation applications in devices based on high-power GaN high-electron-mobility transistor (HEMT) processes. This, in turn will enhance the performance of weather radar and wireless communications.

High-frequency GaN-HEMT power amps make use of a SiC substrate. GaN-HEMT devices are used for long-range radio applications, including radar and wireless communications. They are also expected to be used in 5G millimeter-band mobile communications protocols.

In GaN-HEMT power amps, the heat is dispersed into the SiC substrate. Then, the heat is carried away by a heat sink. The problem? SiC has relatively high thermal conductivity, but the industry requires a material with even better thermal conductivity for higher power output applications.

Structure of conventional GaN-HEMT power amp (Source: Fujitsu)

One solution is single-crystal diamond, which has almost five times the thermal conductivity of SiC. In diamond applications, many use argon beams used to remove impurities in the material. But this may cause damage on the surface, which weakens the bonding strength.

To prevent the argon beam from forming a damaged layer on the diamond surface, Fujitsu and Fujitsu Laboratories have developed a new technique. The technology protects the surface with a thin metallic film before it is exposed to the beam. The metallic film is held to a thickness of 10nm or less. This, in turn, improves the bonding strength. It also enables the single-crystal diamond to be bonded at room temperature to a SiC substrate for GaN-HEMT.

Structure of GaN-HEMT power amp with bonded diamond. (Source: Fujitsu)

Using this technology, GaN-HEMT power amps for transmitters could increase the observable range of radar by a factor of 1.5. Then, when tested, the SiC/diamond interface was found to have a low thermal resistance of 6.7 × 10-8 m2K/W (square-meter kelvins per watt). In simulations, the technology would reduce thermal resistance of 200W-class devices by 61%.

High-density SiC
Using chip integration and packaging techniques, Mitsubishi Electric has developed a 6.5-kV full SiC power semiconductor module. The company claims the technology is the world’s highest power density among power semiconductor modules rated from 1.7- to 6.5-kV.

The chip area has been reduced thanks to integrating a MOSFET and diode on a single chip. It also uses die-bonding technology for the package. Mitsubishi Electric expects the module to lead to smaller and more energy-efficient power equipment for high-voltage railcars and electric power systems.

Prototype of 6.5 kV full-SiC power semiconductor module. (Source: Mitsubishi Electric)

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