  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, $\omega$, and consists of both a piezoresistance (PZR) and
piezocapacitance whose maximum values are $\pi_R = -1100 \times 10^{-11}$
Pa$^{-1}$ and $\pi_C = -900 \times 10^{-11}$ Pa$^{-1}$ respectively. These
values should be compared with the usual bulk PZR in p-type silicon, $\pi_R= 70
\times 10^{-11}$ 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 ($\omega_c$) and emission
rates. Under steady-state conditions (i.e. when $\omega \ll \omega_c$) 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 $\omega
\approx \omega_c$, 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.
