Reliable AlGaN/GaN-HEMTs for Alphasat space mission
Fig. 1: Mean-time to failure (MTTF) as a function of channel temperature during lifetime tests at a drain voltage of 30 V and channel temperatures of 250°C (2 transistors 8x250 µm) and 280°C (2 transistors each: 8x250 µm and 8x125 µm).
Fig. 2: Viewgraphs of 2x50 µm AlGaN/GaN-HEMTs delivered by FBH for radiation environment experiment on board of Alphasat.
AlGaN/GaN-HEMTs are being commercialized today by various companies. Therefore, device performance, stability and reliability at operating conditions is a crucial topic. In the frame of the "GaN benchmarking project" funded by the European Space Agency (ESA), FBH systematically compared devices fabricated on epitaxial wafers from different vendors by applying its stable and reproducible process towards AlGaN/GaN-HEMT transistors for microwave applications [1]. The processed devices have been subjected to systematic reliability tests in order to point out the best performing epitaxial vendor. Device failure condition is defined as a degradation of drain current by 10%. For mean-time-to-failure (MTTF) estimation, thermally accelerated reliability tests at different channel temperatures have been undertaken. Assuming an exponential relationship between degradation time and channel temperature during operation, devices from best performing epi-vendors demonstrated an extrapolated lifetime of more than 107 hours (> 1000 years) for standard operation at a channel temperature of 125°C (Fig. 1) [2].
After demonstrating its stable and reproducible GaN-HEMT process, FBH was offered the opportunity to provide devices for a payload experiment on board of the Alphasat communication satellite [3]. Goal of this experiment is to test GaN devices from a selected European vendor at real-space conditions, in particular, to test their sensitivity to cosmic radiation. In this connection, FBH fabricated GaN devices especially optimized for the payload experiment designed by the University of Aveiro and EFACEC, both based in Portugal. The devices are incorporated in a 2 GHz oscillator experiment which enables remote sensing of its own parameters (e.g. output power, DC-currents etc.) once being space-borne in the geostationary orbit [4]. Fig. 2 shows a viewgraph of the delivered transistors.
In May 2011, all tests necessary to get the permission for installation on board of the Alphasat spacecraft have been passed successfully. The Alphasat launch is scheduled for mid 2012 with Ariane 5. The payload experiment monitoring space environmental effects is designed for a mission duration of three year. During this time, data concerning the radiation environment in geostationary orbit and its effects on GaN electronic components are continuously monitored and relayed to earth. These data are of particular importance for further optimization of GaN electronics for highly reliable space applications.
Publications:
[1] P. Kurpas, I. Selvanathan, M. Schulz, H. Sahin, P. Ivo, M. Matalla, J. Splettstoesser, A. Barnes, J. Würfl, "<link /fileadmin/fbh-berlin/english/ver10/pub76.htm _blank internal-url-new-window>Stable and reproducible AlGaN/GaN HFET processing highly tolerant for epitaxial quality variations", Compound Semiconductor Manufacturing Conference Digest (CS MANTECH), pp. 141-144, 2010.
[2] P. Kurpas, M. Schulz, I. Selvanathan, R. Lossy, H. Sahin, J. Splettstoesser, K. Hirche, R. Jost, A. Barnes, J. Würfl, G. Tränkle, "Reliability Benchmarking of AlGaN/GaN-HFETs On Epitaxial Wafers From Different Vendors", Proc. Reliability Of Compound Semiconductors (JEDEC ROCS) Workshop, May 16, 2011, Indian Wells, USA, pp. 137-140, 2011.
[3] Framework for the ESA Alphasat Programme: http://telecom.esa.int/telecom/media/document/Alphasat_fact_sheet_20100604_WEB.pdf
[4] H. Mostardinha, P. M. Cabral, N. B. Carvalho, P. Kurpas, M. Rudolph, J. Würfl, J. C. Pinto, A. Barnes, F. Garat, "<link /fileadmin/fbh-berlin/english/ver10/pub75.htm _blank internal-url-new-window>GaN RF Oscillator Used in Space Applications",
Proc. Workshop on Integrated Nonlinear Microwave and Millimetre-wave Circuits (INMMiC) 2010, 26.-27. April 2010, Göteborg, Sweden.
FBH research: 28.11.2011