Hermetically packaged GaN microwave power transistors developed and manufactured by United Monolithic Semiconductors (UMS) and Tesat-Spacecom (TESAT) have been qualified to fly on the European Space Agency’s (ESA) Biomass satellite, scheduled for launch in 2021. The devices successfully passed all product qualification tests, the first time European GaN RF components have been qualified following a rigorous European Space Components Coordination (ESCC). This is an important milestone for the use of GaN technology in space.
Biomass, the seventh Earth exploration mission of ESA, has the objective of observing the above-ground forest biomass and associated geophysical parameters, helping tackle one of the most important environmental challenges this century: understanding how the global carbon cycle is affecting the Earth’s climate.
Detection and observation of the biomass will use a P-Band (250 to 500 MHz) synthetic aperture radar transmitting with both vertical and horizontal polarization. Solid-state power amplifiers (SSPA) operating at 435 MHz, with a peak output of 120 W, will illuminate the biomass. The SSPAs use 15 W driver and 80 W output stages fabricated in GaN. GaN provides high power density and efficiency, with inherent radiation hardness. However, GaN microwave technology is new to space, never fully qualified to ESCC standards.
All qualification tests were passed without any failure or abnormal behavior of the devices. This represents a major step forward for European GaN development and will serve as a reference model for qualifying GaN for future ESA missions and formalizing new and updated ESCC standards for GaN. The achievement adds to the confidence in GaN’s maturity for scientific space missions, helping expand the use and acceptance of this relatively new microwave technology.
The Biomass mission was chosen in 2013. In 2014, UMS and TESAT were selected by ESA to develop, manufacture and qualify the required 15 and 80 W GaN devices. Special metal-ceramic packages were developed by TESAT to ensure hermetic chip protection, optimized electrical performance and the required thermal conductivity and temperature control. The two GaN transistors were developed and manufactured by UMS, based on UMS’ 0.5 µm gate length, AlGaN/GaN GH50 process. Assembly of the devices and subsequent product qualification tests were performed by TESAT.
Prior to this development, ESCC standards for qualifying GaN component technology had not been defined. The shared knowledge of ESA — gained from the GREAT2 program — and UMS was the starting point. Wafer acceptance, lot acceptance and hermetically packaged transistor qualification were based on ECSS Q-ST-60-12C and ESCC 5010 standards, modified to account for the higher test temperatures and operating voltages of GaN. They included a 3000 hour, CW accelerated life test for worst case thermal stress.
The program’s success reflects the combined efforts of UMS, TESAT, ESA and Airbus Defence and Space Ltd., the prime contractor for the Biomass satellite program.