Microwave performance enhancement in Double and Single Gate HEMT with channel thickness variation

In Single Gate HEMT (SGHEMT) shortening of gate length (Lg)(Lg) below 100 nm leads to reduction in Transconductance (gm)(gm), which reduces the unloaded voltage gain (gm/gd)(gm/gd) of the device, thereby reducing the maximum frequency of oscillation (fmax)(fmax). The main reason for this reduction in gmgm with LgLg in the Single Gate HEMT (SGHEMT) is its inability to maintain the desired channel aspect ratio (αα). At such a miniaturization level, αα not only depends on the channel depth (d)(d) but also on the channel thickness (dc)(dc) of the device [5]. Moreover, the variation of dcdc may switch the device characteristics from quantum regime to classical regime [27] and [28]. The Double Gate HEMT (DGHEMT) [22] and [23] has emerged as a solution for further reduction in LgLg and provides enhancements over SGHEMT by virtue of its double gate and also for same dcdc due to double heterojunctions, which virtually increases the value of αα. In the present work, extensive simulation work has been carried out using ATLAS device simulator [35] in order to study the effect of dcdc and LgLg on DGHEMT and SGHEMT. An analytical model has also been proposed for SGHEMT and DGHEMT to incorporate the effect of variation of dcdc and LgLg.