3:30 PM - EL05.04.01
Diamond for High Power RF Electronic Devices
Kevin Crawford1,James Weil1,Pankaj Shah1,Mahesh Neupane1,Dmitry Ruzmetov1,A Birdwell1,Tony Ivanov1
U.S. Army Research Laboratory1
Show Abstract
Interest in the diamond material system for electronic applications has rapidly increased in recent years, becoming a global scale area of interest. With its ultrawide band-gap of 5.47 eV, extremely high thermal conductivity of > 20 Wcm-1K-1 and intrinsically high breakdown field of 10 MV/cm, diamond is a promising candidate in achieving next generation high-power electronic devices [1-4]. Progress in this area has been typically hindered by the lack of matured doping techniques and on-going development of novel fabrication strategies to overcome the challenges in working with diamond [5]. The U.S. Army Research Laboratory is investing in the development of surface transfer doped diamond field effect transistors for RF power applications [6-8]. Surface transfer doping offers an alternative to substitutional doping that alleviates the challenges of introducing impurity dopants into diamond’s tightly packed carbon lattice. Historically, spontaneous accumulation of volatile atmospheric adsorbents on the hydrogen terminated diamond surface when exposed to air has provided the necessary surface acceptor states for transfer doping [1, 9]. However, this method of transfer doping when exposed to ambient air is highly sensitive to environmental conditions such as temperature, humidity and molecular composition [9]. More recent results demonstrate enhanced surface transfer doping utilising high electron affinity transition metal oxides, such as MoO3. By further encapsulating these materials with thick dielectric, we observe excellent long-term and thermal stability. This approach of encapsulated metal oxide has been incorporated into our diamond MESFET designs, improving output current density and stability of devices in both atmosphere and with elevated temperatures. Through a novel approach to gate lithography, gate-source spacing has been reduced to < 100 nm for a 400 nm gate length. Comparing a range of gate-source and gate-drain spacings showed improved peak output current and transconductance, while also significantly improving device breakdown. These results show great scope for improvement of diamond power devices through adoption of tailored design features, such as asymmetric gates, and incorporation of robust, encapsulated, transition metal oxides for superior doping.
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