Radio Frequency Characteristics of Multifinger 0.1 μm Metamorphic High-Electron-Mobility Transistors Depending on Number of Gate Fingers and Gate Width

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We investigate the effects of the number of gate fingers ($N$) and gate width ($W$) on the high-frequency characteristics of 0.1 μm depletion-mode metamorphic high-electron-mobility transistors (MHEMTs). The extracted gate-to-source capacitance ($C_{\text{gs}}$), gate-to-drain capacitance ($C_{\text{gd}}$), intrinsic transconductance ($g_{\text{m,int}}$), and drain conductance ($G_{\text{ds}}$) are proportional to total gate width ($w_{\text{t}}$), whereas intrinsic resistance ($R_{\text{i}}$) and source resistance ($R_{\text{s}}$) are inversely proportional to $w_{\text{t}}$. Gate resistance ($R_{\text{g}}$) linearly increases at various slopes with non-zero gate resistances at zero gate width depending on $N$. The cutoff frequency ($ f_{\text{T}}$) and maximum frequency of oscillation ($ f_{\text{max}}$) are calculated using a small-signal model and curve-fitting equations extracted from each small-signal parameter. $ f_{\text{T}}$ is almost constant; however, $ f_{\text{max}}$ is a strong function of $R_{\text{g}}^{1/2}$ and is affected by both $N$ and $w_{\text{t}}$. A large $w_{\text{t}}$ produces a low $ f_{\text{max}}$; however, at a given $w_{\text{t}}$, increasing the number of gate fingers is more efficient than increasing single gate width for maximizing the $ f_{\text{max}}$.
2007-10-15