Figure 1 depicts a monolithic microwave integrated-circuit (MMIC) single-stage amplifier containing an InP-based high- electron-mobility transistor (HEMT) plus coplanar-waveguide (CPW) transmission lines for impedance matching and input and output coupling, all in a highly miniaturized layout as needed for high performance at operating frequencies of hundreds of gigahertz. This is one in a series of devices that are intermediate products of a continuing effort to develop advanced MMIC amplifiers for sub-millimeter-wavelength imaging systems, scientific instrumentation, heterodyne receivers, and other applications.
The amplifier is designed for operation at a nominal frequency of 340 GHz. The HEMT in this amplifier has a gate length of 35 nm and two fingers each 15 μm wide. The CPWs have a ground- to-ground spacing of only 14 μm. The inclusion of quarter-wavelength-long CPWs for impedance matching and of on-chip shunt capacitors makes it possible to obtain about 5 dB of gain with respectable values of input and output return losses at the design frequency of 340 GHz (see Figure 2). This is among the highest gains per stage at this frequency reported to at the time of this work. Moreover, the measurement data suggest potential for further increase in gain with frequency beyond the 345-GHz limit of the test equipment used to perform the measurements.
This work was done by David Pukala, Lorene Samoska, King Man Fung, and Todd Gaier of Caltech and W. R. Deal, Gerry Mei, Vesna Radisic, and Richard Lai of Northrop Grumman Corporation for NASA's Jet Propulsion Laboratory. The contributors would like to acknowledge the support of Dr. Mark Rosker and the Army Research Laboratory. This work was supported by the DARPA SWIFT Program and Army Research Laboratory under the DARPA MIPR no.06-U037 and ARL Contract no. W911QX-06-C-0050.