High-performance RF components using capacitively-coupled contacts over III-N heterostructures

Abstract

We report a novel type of RF component using two-terminal III-Nitride heterostructure varactor with capacitively-coupled contacts (C3) which can be used as a RF switch as well as a power limiter(PL) or other control device type. This C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> varactor consists of two electrodes deposited on top of an AIGaN/GaN heterostructure forming capacitors between the electrode and the 2DEG channel. C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> electrodes allow for efficient RF signal injection into the 2DEG channel with low equivalent impedance at high frequencies. The C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> varactor has simple planar structure fully compatible with MMICs. The GaN C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> varactors have significant advantages over GaN heterostructure field-effect transistors (HFETs) as they allow for shorter channel, do not have gates or ohmic contacts and hence the fabrication is alignment- and anneal - free, they do not consume DC current and provide the DC block. The fabricated SPST C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> switch exhibits 0.8 dB insertion loss and 27 dB isolation at 18 GHz. The maximum switching power extrapolated from 2 GHz data is around 38 dBm. The fabricated varactor PLs show 0.2-0.7 dB loss and limiting powers in the range from 17 to 40 dBm. The C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> PL shows superior performance compared to other known types, e.g. Schottky diode PLs. The fabricated C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> PLs and switches showed the output power variations within 0.5 dB during 100 hours 24 dBm CW stress. They also demonstrated as low as 0.5 dB loss degradation at 2000 C as compared to the room temperature performance.