Abstract
In order to design and optimize high-sensitivity silicon nanowire-field-effect transistor (SiNW FET) pressure sensors, this paper investigates the effects of channel orientations and the uniaxial stress on the ballistic hole transport properties of a strongly quantized SiNW FET placed near the high stress regions of the pressure sensors. A discrete stress-dependent six-band k.p method is used for subband structure calculation, coupled to a two-dimensional Poisson solver for electrostatics. A semi-classical ballistic FET model is then used to evaluate the ballistic current-voltage characteristics of SiNW FETs with and without strain. Our results presented here indicate that [110] is the optimum orientation for the p-type SiNW FETs and sensors. For the ultra-scaled 2.2 nm square SiNW, due to the limit of strong quantum confinement, the effect of the uniaxial stress on the magnitude of ballistic drive current is too small to be considered, except for the [100] orientation. However, for larger 5 nm square SiNW transistors with various transport orientations, the uniaxial tensile stress obviously alters the ballistic performance, while the uniaxial compressive stress slightly changes the ballistic hole current. Furthermore, the competition of injection velocity and carrier density related to the effective hole masses is found to play a critical role in determining the performance of the nanotransistors.
Highlights
Based on CMOS-MEMS technology [1], micro FET sensors such as the CMOS humidity sensor [2,3] and the CMOS pressure sensor [4,5], are an interesting topic of investigation in terms of the development of miniaturized and high performance sensors
[110] and [111] orientations, except for the [100] orientation, turns out negligible in the case considered, which can be attributed to an only slight variation of the non-parabolic valence structure under the strong quantum confinement
In order to design and optimize high-sensitivity SiNW FET sensors, we have provided a detailed examination of the impact of the orientations and the uniaxial stress on the hole subband structure and the relative ballistic transport characteristic of the p-type SiNW transistor by using the stressdependent k.p method which is discretized with the nine-point finite difference method, and the top-ofthe-barrier ballistic transport model
Summary
Based on CMOS-MEMS technology [1], micro FET sensors such as the CMOS humidity sensor [2,3] and the CMOS pressure sensor [4,5], are an interesting topic of investigation in terms of the development of miniaturized and high performance sensors. Understanding the effect of wire orientations and quantum confinement on the ballistic transport in SiNWs is becoming increasingly important [14,15]. We apply a top-of-the-barrier ballistic FET model [23] to explore the effects of the orientation and the stress on ballistic hole transport properties of the p-type SiNW FETs. We find that the SiNW FET performance displays a strong orientation dependence, the effect of strain on the ballistic drain current of the ultra-scaled cross section. SiNW FETs with the [110] and [111] orientations, except for the [100] orientation, turns out negligible, which can be attributed to an only slight variation of the hole effective mass due to the strong quantum confinement. The competition of injection velocity and carrier density related to the effective hole masses is found to play a critical role in determining the performance of the nanotransistors
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