ECCS-EPSRC: Advanced III-N Devices and Circuit Architectures for mm-Wave Future Generation Wireless Communication

Ubiquitous, high-performance communication is the backbone of our society, and promises to play an increasing role not only in individual's daily lives, but just as importantly in the background with communication among devices (e.g., vehicle-to- infrastructure for mobility, process control and monitoring in industrial and manufacturing, virtualization of full environments for the metaverse, among others). The resulting explosion in data that must be processed and communicated requires extraordinary bandwidth and network ubiquity, which in turn demands supporting electronics that is high performance, power efficient, and low cost.

This proposal targets advancements in the most critical link, the wireless power amplifier, that is essential to realizing a vision of ubiquitous, high-speed, transparent mobile communication. Power amplifiers are among the most critical elements in any communication system as they dictate the overall efficiency of the system. GaN-based HEMTs are especially promising for high-performance power amplifiers, but current GaN-based systems suffer from limited frequency coverage, efficiency and linearity due to a combination of factors, including device design and materials issues.

In this program, we leverage transformative advances in both GaN-based transistor design and novel circuit topologies to dramatically improve the efficiency, bandwidth, linearity, and cost of the key wireless elements of a communication system, through co-design. The technology is based on polarization-engineered graded channel GaN HEMTs that show a substantial improvement in linearity in comparison to conventional HEMTs.

By combining with thorough investigation of their underlying device physics including trap states and thermal management, we address major effects that degrade the performance of GaN at increasing frequencies (i.e. Ka band up to 40 GHz) by optimizing device design and fabrication. We will design harmonically terminated amplifiers based on our new class of contiguous modes, that allow designers wider choice of impedances for desired characteristics of efficiency, linearity and output power.

This will greatly enhance the promise and potential of future communication systems, such as 6G wireless communications.

The proposed technology development will be based on recent advances in polarization engineering in III-N materials and devices. We will demonstrate high-linearity, high-efficiency polarization-engineered GaN transistors, with performance sufficient to eliminate the need for external linearization in wireless power amplifiers. This program targets third-order intermodulation products below -30 dBc under large-signal conditions, sufficient to support a PAE > 50% under operational (rather than saturated) conditions.

At this performance level, the adjacent channel power ratio (ACPR) is anticipated to be sufficient to meet regulatory performance mandates without complex and costly linearizers. We will also demonstrate high-linearity broadband amplifiers with PAE > 50% and high tolerance to impedance mismatch, through the use of our new class of contiguous mode amplifiers to provide designers a flexible design space for optimizing linearity, output power and efficiency.

To advance physical understanding, an in-depth study of the underlying device physics of polarization engineered GaN HEMTs, with nanometer scale resolution. This will provide thorough understanding of process, device and memory effects at both the device and circuit level, which is critical to meeting the device and circuit performance targets.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.