The University of California at Santa Barbara (UCSB) and collaborators introduce a multidisciplinary Center for Advanced Nitride Electronics, with the objective of developing a fundamental scientific understanding of mechanisms governing the noise behavior of wide bandgap GaN-based transistors and circuits, and methods to exploit this knowledge to achieve breakthrough performance in ultra-low-noise electronics for high frequency systems. The Center's effort encompasses revolutionary new concepts in materials integration, device physics, and noise modeling, in concert with established classical methods of attack, each executed by a superb team of scientists and engineers. At UCSB (U. Mishra (Director), R. York (Co-director), S. Denbaars, S. Nakamura, J. Speck, E.Hu), the California Institute of Technology (A. Hajimiri), the University of Michigan (J.Singh), Ohio State University (S. Ringel), Wright State University (D. Look), and VA Tech (R. Trew). We also anticipate collaborations with NRAO (M. Pospieszalski) and ARL (W. Caraway) in microwave noise and phase-noise characterization of devices/circuits.

The program is divided into three interlinked thrusts: I) Materials, Interfaces and Characterization; II) Device Structures, Processing and Modeling; and III) Noise Modeling and Circuit Demonstrations. We will advance HVPE, MOCVD and MBE growth technologies and employ post-growth high temperature/high pressure annealing to improve material quality and reduce point defect density. Surface contributions to noise are addressed by investigating low damage recess etching and passivation using conventional dielectrics. A central feature of our program is a revolutionary device technology integrating highly polar dielectric films, to both effectively passivate the Gallium Nitride surface and enhance the sheet charge in the channel. Non-polar higher order oxides are being used as gate dielectrics to produce very high g_m devices essential for low noise. We are examining the fundamental causes of both phase noise and microwave noise in the Gallium Nitride system, separating the impact of materials, device design, circuit topology and sub-system architecture, using classical and emerging formalisms. Ultra-low phase noise GaN-based oscillators and power amplifiers, and low-noise receiver amplifiers, will be demonstrated and characterized.

Gallium Nitride based transistors offer a unique opportunity to simultaneously achieve both high power and low microwave and phase noise from amplifiers. The reason for the high power is well understood to be the combination of high current and high voltage available (from AlGaN/GaN HEMTs as an example) because of the high carrier density and high breakdown fields in this material system. The recently demonstrated low microwave noise is a consequence of the low channel sheet resistance afforded by the structure. Although systematic studies of phase noise in GaN electronics has yet to be carried out (the purpose of this program), there is reason for optimism. The conventional argument for lower phase noise is the promise of higher linearity in wide bandgap materials afforded by the larger available I-V space; improved linearity minimizes the upconversion of 1/f noise into the band of interest, inherently a nonlinear process. High breakdown voltages also allow for high power at low quiescent current, minimizing shot noise contributions. These viewpoints are supported by extensive empirical data in more conventional materials systems (e.g. GaAs) where it is found that high breakdown devices-with larger output impedance and improved linearity-have excellent phase-noise properties. More recently, advances in quantitative modeling of phase noise now indicate exactly how the noise conversion processes relate to physical device and circuit parameters, and these considerations show unequivocally that devices with high transconductance and high speed/high mobility are critical for effective circuit suppression of phase noise. We offer a top-down and highly integrated research effort aimed at demonstrating breakthrough results in high-power, low phase-noise GaN electronics.