Giant, anomalous piezo-impedance of silicon-on-insulator
A giant, anomalous piezo-response of fully-depleted silicon-on-insulator (FD-SOI) devices under mechanical stress is demonstrated using impedance spectroscopy. This piezo-response strongly depends on the measurement frequency, $ω$, and consists of both a piezoresistance (PZR) and piezocapacitance whose maximum values are $π_R = -1100 \times 10^{-11}$ Pa$^{-1}$ and $π_C = -900 \times 10^{-11}$ Pa$^{-1}$ respectively. These values should be compared with the usual bulk PZR in p-type silicon, $π_R= 70 \times 10^{-11}$ Pa$^{-1}$. The observations are well described using models of space charge limited electron and hole currents in the presence of fast electronic traps having stress-dependent capture ($ω_c$) and emission rates. Under steady-state conditions (i.e. when $ω\ll ω_c$) where the impedance spectroscopy measurements yield results that are directly comparable with previously published reports of PZR in depleted, silicon nano-objects, the overall piezo-response is just the usual, bulk silicon PZR. Anomalous PZR is observed only under non-steady-state conditions when $ω\approx ω_c$, with a symmetry suggesting that the electro-mechanically active fast traps are native Pb$_0$ interface defects. The observations suggest new functionalities for FD-SOI, and shed light on the debate over the PZR of carrier depleted nano-silicon.