Product Feature

RF and microwave switches based on PIN diodes or GaAs FETs have been key microwave design components

for decades, with each type establishing itself in specific applications based on its inherent characteristics. In short, GaAs FETs offer fast switching speed and can operate down to DC, but can handle typically only a few watts of RF power, while PIN diodes can handle much greater power levels, but consume more DC power. Truly high power levels remain the do-main of electromechanical switches, which can handle hundreds of watts but are also orders of magnitude greater in size and weight than solid-state switches.

Gallium nitride changes the equation. Hav-ing firmly established itself in RF power ampli-fiers for its ability to deliver higher RF output power than GaAs or silicon (above 3 GHz) over broader bandwidths, gallium nitride now offers another switching option that provides per-formance not achievable with other semicon-ductor technologies. The TGS2351-SM GaN MMIC SPDT switch from TriQuint Semi-conductor exemplifies what can be achieved with FET-based GaN MMICs. The reflective switch operates from DC to 6 GHz, can handle up to 40 W CW, switches in less than 35 ns, has insertion loss of less than 1 dB and isolation greater than 40 dB. The product offers a new realm of possibilities for designers addressing

defense, aerospace or high performance com-mercial RF design needs.

The high breakdown voltage that is a fun-damental characteristic of GaN lends itself well for use in high power RF switches. The high power-handling ability and wide 0/-40 V DC control voltage range of the TGS2351-SM are directly attributable to GaN’s high power density, which is also the key to its appeal in RF power amplifiers. The TGS2351-SM is fab-ricated using the company’s 0.25 µm HEMT GaN-on-SiC process. When compared to a FET switch fabricated in a typical 0.25 µm GaAs process, the TGS2351-SM can handle two and a half times the on-state power, eight times the off-state power and is highly stable with little or no performance degradation over temperature. RF power handling ability is shown in Figure 1.

For switch applications, TriQuint’s GaN process yields a breakdown voltage of 70 V DC compared to 13 V DC for GaAs and can handle current of more than 1 A/mm of device area versus 650 mA/mm for GaAs. In addition, the high thermal conductivity of the insulating SiC substrate reduces leakage caused by high RF voltage swing while also improving heat trans-

TriQuint SemiconductorHillsboro, OR

132 MICROWAVE JOURNAL n NOVEMBER 2011

GaN MMIC SwItCh haNdleS 40 w froM dC to 6 Ghz