High-efficiency, Radiation-hardened GaN HEMT based L-band Space Power Amplifier

ABSTRACT: An important objective for the Air Force is to reduce the operational costs of GPS satellite systems via higher efficiency electronics, such as power amplifiers. In this project, CFDRC, in collaboration with Vanderbilt University/ISDE and a leading GaN device manufacturer, propose a complementary experimental and modeling-based approach to develop a Solid State Power Amplifier (SSPA) for L-band GPS applications based on an innovative GaN HEMT design offering higher efficiency, radiation tolerance, and bandwidth. Gallium-Nitride (GaN) high-electron-mobility transistors (HEMTs) offer excellent electrical characteristics for high-power RF applications. Coupled with their reported total dose hardness, this makes GaN HEMTs a promising successor technology to GaAs for space-based power electronics. However, important design and characterization challenges remain towards demonstrating reliability and long-term operation in GPS environments. In Phase I, we will utilize a commercial 0.25 and 0.5-µm GaN HEMT technology offering high efficiency and bandwidth, and perform X-ray and proton-irradiation testing of discrete HEMTs. We will then perform detailed TCAD simulations to identify and verify physical mechanisms behind observed radiation response (total-ionizing-dose and displacement damage), and validate against data. Subsequently, we will investigate geometry and material-based GaN HEMT design modifications for improved radiation hardness. In Phase II, we will primarily focus on the HEMT-based L-band SSPA design, analyses, and optimization to meet GPS specifications, via extensive RF simulations, prototype fabrication, and detailed electrical/radiation characterization. Active participation by the GaN device manufacturer will ensure superior, space-qualified, L-band RF SSPA for Air Force GPS applications. BENEFIT: GaN-based devices and circuits are very promising for power electronics applications from power conditioning to microwave amplifiers and transmitters. Front-end applications are also interesting due to the intrinsic robustness and survivability of GaN HEMTs coupled with reasonable noise figures. Satellite communications, high-performance radars, and ground base stations represent target system applications. Due to their wide bandwidth operation, high output power and power density, thermal tolerance, and high breakdown voltages, GaN HEMTs can target applications that are not readily realizable with other device technologies. Engineers using GaN devices in circuit applications would profit greatly from the ability to model device performance under varying operating conditions, especially in adverse space radiation environments. The advanced, L-band SSPA design and cost-effective predictive simulation tools developed through this effort will greatly benefit all Positioning, Navigation, and Timing (PNT) contractors and associated DoD programs involved with developing space-oriented electronics (GPS, Space Radar, Space Tracking and Surveillance Systems). The simulation tools will also benefit manufacturers of commercial satellite electronics, including wide-band communication, satellite TV, phone, GPS, and other GaN-based RF solutions for high performance applications in the communications, industrial and scientific markets.