A Tall Gate Stem GaN HEMT With Improved Power Density and Efficiency at Ka-Band

Ping Hsun Lee, Yueh Chin Lin, Heng Tung Hsu, Yi Fan Tsao, Chang Fu Dee, Pin Su, Edward Yi Chang*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


In this letter, AlGaN/GaN HEMTs with tall-gate-stem structures were realized to improve the power performance of Ka-band devices, and a film thinning process is adopted in the fabrication process to reduce the parasitic capacitance caused by the thick silicon nitride film. According to the S-parameter measurement results, devices owning a tall-gate-stem structure and undergoing the film thinning process have higher cut-off frequency (fT) and maximum oscillation frequency (fmax) values with lower extracted parasitic capacitance. For the load-pull measurement result, the AlGaN/GaN HEMT with a tall gate stem has improved output power density (Pout) and power added efficiency (PAE) at Ka-band. The device with the elevated stem shows a steady-state current density of 883 mA/mm and a maximum transconductance of 323 mS/mm at 20 V bias, and it achieves fT of 39.5 GHz, fmax of 112.9 GHz with the maximum PAE of 24.6% and the maximum Pout of 6.6 W/mm at 38 GHz.

Original languageEnglish
Pages (from-to)36-42
Number of pages7
JournalIEEE Journal of the Electron Devices Society
StatePublished - 2023


  • AlGaN/GaN HEMT
  • output power density
  • power added efficiency
  • tall-gate-stem structure


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