State-of-the-art GaAs Schottky diode technology, which is being used for local oscillators (LOs) in heterodyne receivers and transmitters for radar applications, has limitations in terms of power-handling capabilities. That makes it difficult to generate necessary LO power to drive multi-pixel heterodyne receivers beyond 500 GHz, and to extend the operation frequency of single-pixel receivers beyond 2 THz up to 4.7 THz (63 μm OI line).

Gallium nitride (GaN) has emerged as a very promising material for electronic devices due to its wide direct bandgap (3.4 eV), which results in a high breakdown voltage field, and its high peak and saturated electron drift velocity. High breakdown voltage materials allow superior power handling capabilities. This innovation consists of using GaN Schottky diode-based frequency multipliers instead of the traditional GaAs Schottky multipliers in order to improve the power handling capabilities of frequency multiplied LO sources by a factor of 5 to 10. GaN Schottky diode multipliers are less efficient than the GaAs versions due to the lower mobility of GaN. However, in the lower multiplication stages, up to 300 GHz, the penalty in efficiency is not very important, and the exceptional electrical properties can be fully exploited.

A method for producing the GaN Schottky devices has been developed. Appropriate GaN Schottky diode device models have been produced, verified, and used for the design of these frequency multipliers. A new GaN fabrication process has been applied to the design fabrication and tests of frequency doublers and triplers at 110 GHz (tripler), 180 GHz (doubler), 230 GHz (tripler), and 270 GHz (tripler). These frequencies of operation correspond with the first multiplication stages of LO sources required for heterodyne receivers at 1.9 THz and 4.7 THz, as well as high-power radar imagers at 230 GHz. All the designs have a nominal input power of 1 W, 5 times higher than state-of-the-art designs based on GaAs diodes, and have a frequency bandwidth of around 15 to 17%. Predicted conversion efficiencies are 25% for the 110-GHz tripler, 20% for the 180-GHz doubler, 14% for the 230-GHz tripler, and 7% for the 270-GHz tripler.

This work was done by Jose V. Siles, Choonsup Lee, Goutam Chattopadhyay, and Robert H. Lin of Caltech for NASA’s Jet Propulsion Laboratory. For more information, contact This email address is being protected from spambots. You need JavaScript enabled to view it..

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:

Innovative Technology Assets Management
Mail Stop 321-123
4800 Oak Grove Drive
Pasadena, CA 91109-8099
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Refer to NPO-49345.

NASA Tech Briefs Magazine

This article first appeared in the August, 2014 issue of NASA Tech Briefs Magazine.

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