Effects of Multigate-Feeding Structure on the Gate Resistance and RF Characteristics of 0.1- \mu} Metamorphic High Electron-Mobility Transistors

• Published in: IEEE transactions on microwave theory and techniques Vol. 57; no. 6; pp. 1487 - 1493
• Main Authors: Oh, J.-H., Han, M, Lee, S.-J., Jun, B.-C., Moon, S.-W., Lee, J.-S., Rhee, J.-K., Kim, S.-D.
• Format: Journal Article
• Language: English
• Published: IEEE 01.06.2009
• Subjects: Cutoff frequency; Gallium nitride; Gate resistance; HEMTs; maximum frequency of oscillation; mHEMTs; Millimeter wave communication; Millimeter wave technology; Millimeter wave transistors; MODFETs; Moon; multigate-feeding structure; power high electron-mobility transistor (HEMT); Radio frequency; small-signal parameter
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2009.2020671

We investigate the effects of a multigate-feeding structure on the gate resistance (R g ) and RF characteristics of the high electron-mobility transistors (HEMTs). In this structure, the increase of R g with the gatewidth (W) is minimized; therefore, high maximum frequency of oscillation (f max ) is achieved. Various numbers of gate feedings (N gf ) using the air-bridge interconnections are adopted for fabricating the 0.1-mum depletion-mode metamorphic HEMTs. From these structures, we observe great reduction in R g with the increase of N gf , and their relationship is given by R g prop 1/[2middot(N gf -1)] 2 , where N gf =2,3,4,...; on the other hand, the effects of N gf on other small-signal parameters are negligible. Calculated cutoff frequency (f T ) and f max from the extracted small-signal parameters all show good agreement with the measurement results. f T is slightly decreased with the increase of N gf due to the increase of gate-to-source capacitance. f max is, however, greatly increased with N gf , and this effect becomes greater at longer total gatewidth (W times number of gate fingers) . This is due to the smaller R g at greater N gf in the multigate-feeding structure. We propose that this gate-feeding structure provides a very effective way to suppress R g and maximize f max for the applications of the HEMTs with long W.