Subthreshold Analog/RF Performance Enhancement of Underlap DG FETs With High- $k$ Spacer for Low Power Applications

摘要

This paper presents a systematic study of the subthreshold analog/RF performance for underlap double gate (UDG) NMOSFETs using high dielectric constant $(k)$ spacers. The conventional UDG-NMOSFETs offer reduced short-channel effects along with improved subthreshold analog/RF performance at a cost of higher distributed channel resistance and low on current. In this paper, we show that these drawbacks can be alleviated effectively by using high-$k$ spacers without any severe degradation in the subthreshold analog/RF performance. In order to show the improvement in the device performance, we have studied the effect of high-$k$ spacers on different subthreshold analog figures of merit such as the transconductance, transconductance generation factor, output resistance, and the intrinsic gain for different values of $k$ . Moreover, we have analyzed the RF performance as a function of intrinsic capacitance and resistance, transport delay, inductance, cutoff frequency, and the maximum oscillation frequency. In order to assess the gain bandwidth $(GBW)$ product, the circuit implementation of the UDG-NMOSFETs with different high-$k$ spacers was performed on a common source amplifier. Our results show an improvement in the GBW of about 38% for the devices with high- $k$ spacers compared to its low- $k$ counterpart.