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New Thermal Management of GaN RF PA’s: A Progress Report
Keywords: High Electron Mobility Transistor (HEMT), Gallium Nitride (GaN)-on-diamond, RF Power Amplifiers
Abstract: Synthetic diamond heat spreaders, GaN-on-Diamond wafers, and the transistors that embed them have emerged as a leading RF PA technology for use in next generation radar and other microwave defense applications, satellite communications, and cellular base stations. This is due to diamond's excellent thermal management properties. The authors report development progress on the state-of-the-art of diamond heat spreaders and GaN-on-Diamond wafers. Introduction: GaN-based transistors and their related RF Power Amplifiers (PAs) have emerged as the leading solid-state technology to replace traveling wave tubes in radar, EW systems, and satellite communications, and to replace Si LDMOS PAs in cellular base stations. However, significant thermal limitations prevent GaN PAs from reaching their intrinsic performance capability. Metallized synthetic diamond heat spreaders have recently been used to address this thermal management challenge, particularly in cellular base station applications. And GaN-on-Diamond wafer technology has previously been introduced by the authors as a viable approach for enabling GaN such that the thermal limitation is significantly diminished. In GaN-on-Diamond, the GaN epitaxy is transferred to diamond by first removing the host Si and transition layers beneath the AlGaN/GaN epitaxy, depositing a 30 nm proprietary dielectric onto the exposed AlGaN/GaN, and finally growing a 100 m thick CVD diamond onto the dielectric adhered to the epitaxial AlGaN/GaN films. Summary: In this paper, thermal modeling of a novel diamond-integrated package is compared to singulated diamond heat spreaders. Transistor performance recently reported by leading GaN groups – using the authors’ GaN-on-Diamond wafers – are reviewed, compared, and analyzed. In the reports, High Electron Mobility Transistors (HEMTs) are fabricated and tested for their DC, RF, and thermal characteristics. Special attention is given to the comparison of GaN-on-Diamond HEMTs with equivalently designed GaN-on-SiC – the prevailing GaN technology today. And finally, reliability data is assessed after GaN-on-Diamond devices have been aged at high-temperatures (200-350◦C) over 2-years. The authors also present the state-of-the-art data on their development efforts to mature 4” GaN-on-Diamond wafers into a production line.
Thomas Obeloer, Applications Engineering Manager
Element Six Technologies
Santa Clara, CA

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