High Performance RF Control Devices Using Capacitively Coupled Contacts (C3) Over III-N Heterostructures.

摘要

RF switches, power limiters and other control devices are essential components of modern RF systems. RF switches are important parts of wireless modules of various devices such as laptops, tablets, cell phones etc. and key components of satellites communication systems, radars, multi-band wireless and aerospace communications, phased array antennas. RF Power limiters (PL) are also important components of RF systems protecting linear amplifiers, detectors etc. from high-power stress. Traditionally, RF switches are fabricated using pin diodes or MEMS, Si MOSFETs or GaAs HEMTs. RF PLs are typically implemented using Schottky or pin-diodes. Traditional devices used in RF switch and PLs have a number of disadvantages and limitations. Si or GaAs based devices suffer from a low breakdown voltage and cannot handle high RF power. Pin-diodes require large forward currents and do not allow for fast turn-on. III-Nitride heterostructures open tremendous opportunities for RF control devices due to the record high sheet electron density in the 2D channel, extremely low channel resistance, high breakdown field and excellent temperature stability. In this dissertation a novel type of RF component using two-terminal III-Nitride heterostructure varactor with capacitively-coupled contacts (C3) is introduced which can be used as a RF switch as well as a power limiter or other control device type.This C3 varactor consists of two electrodes deposited on top of an AlGaN/GaN heterostructure forming capacitors between the electrode and the 2DEG channel. C3 electrodes allow for efficient RF signal injection into the 2DEG channel with low equivalent impedance at high frequencies. The C3 varactor has simple planar structure fully compatible with MMICs. The III-N C3 varactors have significant advantages over III-N 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 C3 switch exhibits 0.8 dB loss and 27 dB isolation at 18 GHz. The maximum switching power extrapolated from 2 GHz data is around +38 dBm. The fabricated PLs show 0.2-0.7 dB loss and limiting powers range from 17 to 40 dBm. The switching response is also very fast as it is in the ns range. The C3 PL shows superior performance compared to other known types, e.g. Schottky diode PLs. The fabricated C3 PLs and switches showed the output power variations within 0.5 dB during 100 hours of CW stress. They also demonstrated as low as 0.5 dB loss increase degradation at 200o C as compared to the room temperature performance. The achieved results show that novel C3 RF components have superior performance characteristics, can operate in a broad frequency range, and have a great potential for high-performance MMICs.