Piezoresistance of top-down suspended Si nanowires

Abstract

Measurements of the gauge factor of suspended, top-down silicon nanowires are presented. The nanowires are fabricated with a CMOS compatible process and with doping concentrations ranging from 2 × 10(20) down to 5 × 10(17) cm(-3). The extracted gauge factors are compared with results on identical non-suspended nanowires and with state-of-the-art results. An increase of the gauge factor after suspension is demonstrated. For the low doped nanowires a value of 235 is measured. Particular attention was paid throughout the experiments to distinguishing real resistance change due to strain modulation from resistance fluctuations due to charge trapping. Furthermore, a numerical model correlating surface charge density with the gauge factor is presented. Comparison of the simulations with experimental measurements shows the validity of this approach. These results contribute to a deeper understanding of the piezoresistive effect in Si nanowires.

High-sensitivity linear piezoresistive transduction for nanomechanical beam resonators

“…From equations (12) and (13) and the estimations made for the deflection at rest and first-mode vibration amplitude (a 1 E1 nm, d 0 ¼ 5-50 nm), we infer gauge factor values in the range from a few units to a few hundreds. This is the range expected from a conventional piezoresistive effect in SiNWs depending on the doping level 24 . Therefore, high-sensitivity piezoresistive transduction, enhanced by an asymmetric beam profile at rest, does not require extraordinarily large piezoresistive coefficients as those reported on high-resistivity bottom-up NWs, which reach up to 1,000 and above 21 .…”

“…Therefore, high-sensitivity piezoresistive transduction, enhanced by an asymmetric beam profile at rest, does not require extraordinarily large piezoresistive coefficients as those reported on high-resistivity bottom-up NWs, which reach up to 1,000 and above 21 . Nevertheless, larger gauge factors are still expected for bottom-up NWs as compared with their top-down counterparts according to the literature 23,24 . In fact, a larger gauge factor for bottom-up SiNWs explains why the quadratic component of the resistance variation with vibration is only detected for these devices (Fig.…”

“…The so-called giant piezoresistance effect has indeed been explored for electrical read-out of highfrequency SiNW resonators 2 . Several studies in top-down SiNWs have not been able to find giant values of piezoresistance coefficients 23,24 .…”

Giant piezoresistance in silicon-germanium alloys

“…8 A lot of excitement was produced by the report of giant piezoresistivity in silicon nanowires, 9,10 with the latest room temperature value reported being G = 280. 11 The earliest work hinting at a higher piezoresistive effect in n-type SiGe alloys of high Ge compositions was performed by R. W. Keyes in 1957. 12 He found a piezoresistive effect 15% larger than in pure Ge at a Ge composition of x = 0.96.…”

Medium doped non-suspended silicon nanowire piezoresistor using SIMOX substrate

“…A number of publications have shown the enhanced sensitivity of silicon piezoresistors [12]- [14]. Overall, the piezoresistance coefficient has been found to increase with decreasing nanowire doping and cross-sectional area.…”