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

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8 Author(s)
Jung-Hun Oh ; Millimeter-Wave Innovation Technol. Res. Center (MINT), Dongguk Univ., Seoul ; Min Han ; Sang-Jin Lee ; Byoung-Chul Jun
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We investigate the effects of a multigate-feeding structure on the gate resistance (Rg) and RF characteristics of the high electron-mobility transistors (HEMTs). In this structure, the increase of Rg with the gatewidth (W) is minimized; therefore, high maximum frequency of oscillation (fmax) is achieved. Various numbers of gate feedings (Ngf) 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 Rg with the increase of Ngf, and their relationship is given by Rgprop 1/[2middot(Ngf-1)]2, where Ngf=2,3,4,...; on the other hand, the effects of Ngf on other small-signal parameters are negligible. Calculated cutoff frequency (fT) and fmax from the extracted small-signal parameters all show good agreement with the measurement results. fT is slightly decreased with the increase of Ngf due to the increase of gate-to-source capacitance. fmax is, however, greatly increased with Ngf, and this effect becomes greater at longer total gatewidth (W times number of gate fingers) . This is due to the smaller Rg at greater Ngf in the multigate-feeding structure. We propose that this gate-feeding structure provides a very effective way to suppress Rg and maximize fmax for the applications of the HEMTs with long W.

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Microwave Theory and Techniques, IEEE Transactions on  (Volume:57 ,  Issue: 6 )