Evaluation of the piezoresistive and electrical properties of polycrystalline silicon-germanium for MEMS sensor applications

Giant piezoresistance in silicon-germanium alloys

“…6 The state of the art material in the industry is poly-silicon, with G < 10, which can be improved to G 20 by using p-type poly-SiGe. 7 Recently, gauge factors of G 1000 were reported for silicon oxycarbonitride polymer-derived ceramic 5 and a G = 843 for a silicon-metal hybrid. 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.…”

Piezoresistivity and electrical properties of poly-SiGe deposited at CMOS-compatible temperatures

“…3 we can observe that the resistivity of poly-Si 38 Ge 62 reduces with increasing boron concentration, as expected. The layer exhibits slightly higher resistivity than our previous layer [6], which is probably caused by the smaller grain size and lower number of active carriers (due to the lower deposition and annealing temperatures).…”

“…5 the temperature coefficient of resistance (TCR) of poly-Si 38 Ge 62 vs. doping dose is plotted together with the TCR of poly-Si 36 Ge 64 (dashed line) from our previous work [6]. The TCR of this new layer exhibits similar behaviour as the film from [6], varying from strongly negative values for low doping to slightly positive values for high doping, with a cross-over point with TCR~0 for doping doses around 2·10 15 cm -2 . From the figure we can observe that the TCR of the new layer is slightly lower than that reported in [6], especially at higher doping levels, which might be due to smaller grain size [10].…”

“…The piezoresistivity is estimated by measuring the resistance variation when a uniform and uniaxial stress provided by a four point bending fixture is applied to the films. The obtained results are compared to those of our previous poly-Si 36 Ge 64 layer, deposited at 500ºC and annealed at 570ºC, reported in [6]. Finally, finite element simulations of a possible application to a pressure sensor are performed to illustrate the potential of using this new layer for MEMS piezoresistive sensor applications.…”

“…In earlier work [6] we already studied the piezoresistive and electrical properties of poly-Si 51 Ge 49 and poly-Si 36 Ge 64 for different doping concentrations (from 5·10 17 to 1·10 20 cm -3 ), obtaining very promising results. However, the processing temperatures used during the deposition and annealing of these layers were too high (above 500ºC) to allow for the monolithic integration of MEMS above CMOS.…”