A submillimeter-wave monolithic integrated- circuit (S-MMIC) amplifier has been designed and fabricated using an indium phosphide (InP) 35-nm gate-length high electron mobility transistor (HEMT) device, developed at Northrop Grumman Corporation. The HEMT device employs two fingers each 15 micrometers wide. The HEMT wafers are grown by molecular beam epitaxy (MBE) and make use of a pseudomorphic In0.75Ga0.25As channel, a silicon delta-doping layer as the electron supply, an In0.52Al0.48As buffer layer, and an InP substrate. The three-stage design uses coplanar waveguide topology with a very narrow ground-to-ground spacing of 14 micrometers. Quarter-wave matching transmission lines, on-chip metal-insulator-metal shunt capacitors, series thin-film resistors, and matching stubs were used in the design. Series resistors in the shunt branch arm provide the basic circuit stabilization. The S-MMIC amplifier was measured for S-parameters and found to be centered at 320 GHz with 13–15-dB gain from 300–345 GHz.
This chip was developed as part of the DARPA Submillimeter Wave Imaging Focal Plane Technology (SWIFT) program (see figure). Submillimeter-wave amplifiers could enable more sensitive receivers for earth science, planetary remote sensing, and astrophysics telescopes, particularly in radio astronomy, both from the ground and in space. A small atmospheric window at 340 GHz exists and could enable ground-based observations. However, the submillimeter-wave regime (above 300 GHz) is best used for space telescopes as Earth’s atmosphere attenuates most of the signal through water and oxygen absorption. Future radio telescopes could make use of S-MMIC amplifiers for wideband, low noise, instantaneous frequency coverage, particularly in the case of heterodyne array receivers.
This work is aimed at pushing the MMIC and transistor technologies toward higher frequencies and, at these higher frequencies (>300 GHz), a wealth of spectral lines of molecular species exist and could be studied with more sensitive receivers. There are potential applications for future millimeter-wave Earth observational instruments such as the Scanning Microwave Limb Sounder, GeoSTAR, and other planetary instrument concepts being proposed, such as the Microwave Sounding Unit for Mars. These future instruments and missions need high-gain, low-noise amplifiers at or above 180 GHz. Implementation of high-gain, low-noise amplifiers would greatly improve the signal-to-noise ratio of future heterodyne receivers.
This work was done by David Pukala, Lorene Samoska, King Man Fung, and Todd Gaier of Caltech and William Deal, Richard Lai, Gerry Mei, and Stella Makishi 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.