Solid state radio frequency (RF) switches are important components of radar transmit/receive (T/R) modules, satellite communication systems, Joint Tactical Radio Systems (JTRS), and the like. A promising RF switch technology uses Heterostructure Field Effect Transistors (HFETs). Recently, high power switches made of AlGaN/GaN HFETs demonstrated superior performance over other RF switching devices in terms of maximum power density, bandwidth, operating temperature, and breakdown voltage.
Many applications, including JTRS and low-noise receivers, require RF switches with a very low insertion loss, e.g., typically below 0.1 dB. A low loss switch dissipates little RF power. As a result, it can be fabricated over a low cost substrate, such as sapphire. Low insertion loss in an HFET is due to a high channel conductance of the device, which is proportional to a total length of the device periphery. Exceptionally high 2D electron gas densities at the AlGaN/GaN interface make a group III-Nitride HFET with a total periphery of two to five mm an ideal candidate for RF switching applications.
The feasibility of high-power broad-band monolithically integrated group III-Nitride HFET RF switches has been demonstrated. Large signal analysis and experimental data for a large periphery group III-Nitride switch indicate that the switch can achieve switching powers exceeding +40 to +50 dBm. The design of a driving/control circuit is an important consideration for achieving high power switching. In general, the driving/control circuit should provide fast response to control pulses, while providing good isolation for the signal being switched. To this extent, the impedance of the driving/control circuit must be much lower than the gate-to-channel impedance of the HFET at high frequencies. Therefore, it is often important for each of the HFET's gates to be connected to the control signal supplies through a low-pass filter, which for robustness and cost efficiency can be monolithically integrated with each HFET.