High aspect ratio asymmetric gate structures employed in novel self-aligned high electron mobility transistor technology

We report on the development and fabrication of high aspect ratio asymmetric gate structures defined by electron beam lithography. The asymmetric gate or ‘‘gamma’’ gate, as it is referred to, has substantially lower resistance compared to gates fabricated by more conventional techniques. The improved gate resistance is achieved by having an increased cross section (∼3×) over conventional T-shaped gates, which is provided by the asymmetric fabrication scheme. Concurrently, the gamma gate has been incorporated into a self-aligned high electron mobility transistor process, in which its asymmetric shape can be used to define the gate to source and gate to drain spacings independently. The unique tailoring capabilities of this fabrication technique, enables specific gate to source (Lgs), gate to drain (Lgd), and source to drain (Lsd) dimensions independent of the gate length (Lg). Devices fabricated using this technique, had an Lg of 0.10 μm, an Lgs of 0.20 μm, and an Lgd of 0.90 μm. The total Lsd self-aligned dimension was 1.20 μm, with a resultant aspect ratio of 12:1 for a given Lg of 0.10 μm.