Transphorm to develop N-polar GaN for RF/mmWave for DoD

Article By : Steve Taranovich

Transphorm will be a production source and supplier of GaN epiwafers for DoD and commercial RF/mmWave and power electronics applications.

Transphorm Inc. has announced that the U.S. Department of Defense (DoD) Office of Naval Research (ONR) established the company as a U.S.-based dedicated production source and supplier of GaN epiwafers for DoD and commercial radio frequency (RF)/millimeter wave (mmWave) and power electronics applications.

The award goals are to create a base program for key technology development/transfer and an option program to establish production scale capability.

The program’s core objective is to commercialize nitrogen-polar (N-polar) GaN, a breakthrough technology beyond the incumbent Ga-polar GaN. N-polar GaN has the capability for the continued advancement of GaN-based electronics for modern RF electronics and future power conversion systems.

The technology, exclusively licensed to Transphorm, was invented under ONR and DARPA sponsorship at the University of California, Santa Barbara (UCSB) by the team of Professor Umesh Mishra, Distinguished Professor at UCSB and Transphorm’s co-founder, CTO and chairman¹.

“The N-polar orientation of the material is reversed from the traditional Ga-polar GaN currently being widely used in base station and DoD applications. The flip produces radical benefits in output power along with groundbreaking efficiencies to frequencies as high as 94 GHz,” said Dr. Mishra. “Applications span the frequency range of interest for 5G, 6G, and beyond and also fill a critical technological void for DoD systems.”

At 94 GHz, Mishra’s UCSB team has demonstrated mmWave devices with record power densities and high efficiencies. These devices simplify RF electronic systems by reducing the need for power combining multiple components and devices while also simplifying cooling systems, ultimately resulting in higher performance at reduced cost.

Leveraging Transphorm’s MOCVD/GaN epi capability

Currently in production with several customers, Transphorm is a leading supplier of high quality, high reliability (Q+R) HV GaN FETs. The company’s successful developments are driven by a vertically-integrated business approach, expertise, IP, and, particularly, a solid metalorganic chemical vapour deposition (MOCVD) epi growth platform with production scale. With this ONR program, the company will address epi capability on multiple platforms including SiC, Si, and sapphire substrates ranging from 4-inch to 6-inch and ultimately 8-inch wafers. In the RF and mmWave area, Transphorm will be a pure play epiwafer supplier focused solely on GaN materials.

Figure 1 Shown here is the fully fabricated device, with three field plates (FP): FP1 was connected to the gate, whereas FP2 and FP3 were terminated at the source. Epi layers are also shown. The drawing is not to scale. (Image courtesy of Reference 1)

III nitride materials

III nitride materials (AlN, GaN, InN, and their solid solutions) have a unique combination of physical properties for power switching applications. Among these properties are wide bandgap, high saturated drift rate, high breakdown voltage, high thermal conductivity, remarkable chemical and thermal stability, and more.

The inherent polarization fields in the III-nitrides are capable of creating a two-dimensional electron gas (2DEG) with high charge density and high mobility. This 2DEG becomes a highly conductive channel, which enables high on-current and low on-resistance (Ron). The high critical electric field allows the realization of very high breakdown voltages.

Due to these characteristics, nitrides are now considered as the most promising materials for fabrication of powerful high-frequency transistor structures capable of functioning at high temperatures and in hostile environments. These types of devices enhance performance of wireless communication systems, switching systems in the power industry, detectors for early detection of chemical or biological infection, etc.

Another application using an AlN substrate is in the manufacture of powerful high-frequency transistors and photodetectors, including solar blind detectors capable of working at high temperatures and in harsh environments.

—Steve Taranovich is a senior technical editor at EDN with 45 years of experience in the electronics industry.

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