We developed a T-gate technology based on selective wet etching yielding 200 nm wide T-gate structures used for fabrication of High Electron Mobility Transistors (HEMT). Major advantages of our process are the use of only standard photolithographic process and the ability to generate T-gate stacks. A HEMT fabricated on AlGaN/GaN/sapphire with gate length Lg = 200 nm and double-stacked T-gates exhibits 60 GHz cutoff frequency showing ten-fold improvement compared to 6 GHz for the same device with 2 μm gate length. HEMTs with a double-level-T-gate (DLTG) structure exhibit up to 35% improvement of fmax value compared to a single T-gate device. This indicates a significant reduction of skin effect losses in DLTG structure compared to its standard T-gate counterpart. These results agree with the theoretical predictions.
Reduction of skin effect losses in double-level-T-gate structure
M. Mikulics, H. Hardtdegen, Y. C. Arango, R. Adam, A. Fox, D. Grützmacher, D. Gregušová, S. Stanček, J. Novák, P. Kordoš, Z. Sofer, L. Juul, M. Marso; Reduction of skin effect losses in double-level-T-gate structure. Appl. Phys. Lett. 8 December 2014; 105 (23): 232102. https://doi.org/10.1063/1.4903468
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