MMIC Amplifiers and Wafer Probes for 350 to 500 GHz

NASA’s Jet Propulsion Laboratory, Pasadena, California

Several different experimental monolithic microwave integrated circuit (MMIC) amplifiers have been designed to operate in frequency bands ranging from 350 to 500 GHz and were undergoing fabrication at the time of reporting the information for this article. Probes for on-wafer measurement of electrical parameters [principally, the standard scattering parameters (“S” parameters)] of these amplifiers have been built and tested as essential components of systems to be used in quantifying the performances of the amplifiers. These accomplishments are intermediate products of a continuing effort to develop solid-state electronic amplifiers capable of producing gain at ever-higher frequencies, now envisioned to range up to 800 GHz. Such amplifiers are needed for further development of compact, portable imaging systems and scientific instruments for a variety of potential applications that include detection of hidden weapons, measuring winds, and measuring atmospheric concentrations of certain molecular species.

Figure 1. **Gains of Seven Single-Stage MMIC Amplifiers** built around advanced InP HEMTs were predicted in computational simulations.

Seven of the experimental MMIC amplifiers are single-stage amplifiers; two are three-stage amplifiers. Conceptually, each amplifier is built around an InP-based high-electron-mobility transistor (HEMT) having a gate length of 35 nm, which has been developed at Northrop Grumman Corporation. It was previously demonstrated that the particular HEMT can be fabricated with a high degree of reproducibility, that its electrical characteristics are accurately represented by a device model needed to design an MMIC that incorporates it, and that an experimental single-stage MMIC built around it exhibits 5 dB of gain at 345 GHz.

The seven present single-stage amplifier designs were derived from that of the 345-GHz MMIC amplifier. They were designed by use of the aforementioned device model, with modified layouts chosen to satisfy requirements for both (1) compatibility with the HEMT manufacturer’s fabrication rules and (2) matching impedances at the affected frequency bands in the 350-to-500 GHz range. The designs utilize several different matching-circuit topologies, some of which resemble topologies heretofore required for multi-stage amplifiers. Figure 1 shows the gains of the single-stage amplifiers as predicted by computational simulations. The two three-stage amplifiers were designed to operate at frequencies from 400 to 500 GHz, with peak gains in the approximate range of 11 to 13 dB.

Figure 2. **Wafer Probes** are mounted on the terminals of a network analyzer, with the probe tips in contact with a calibration substrate.

The wafer probes were designed and built for use with a two-port swept-vector network analyzer that operates in the frequency range of 325 to 500 GHz. This network analyzer has been fully characterized for reproducibility and dynamic range. The probes include WR2.2 waveguides and waveguide-to-coaxial transitions developed at Cascade Microtech and Portland State University (see Figure 2). The insertion loss of the waveguide-to-coaxial transitions has been measured to be about 7 dB at 325 to 500 GHz.

This work was done by Lorene A. Samoska and King Man Fung of Caltech; Michael Andrews of Cascade Microtech, Inc.; Richard Campbell of Portland State University; and Linda Ferreira and Richard Lai of Northrop Grumman Corp. for NASA’s Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Electronics/Computers category. NPO-45588