Supplementary information
Fabrication details
The multi-step process flow is sketched in Figure S1. The starting material is a Silicon-on-Insulator
(SOI) substrate with a 1 µm-thick buried oxide layer, and 100 nm thick top silicon layer. The top
silicon is boron doped to provide the desired hole concentration. After cleaning in a piranha mixture, a
20 nm-thick thermal oxide layer is grown on the top-silicon. This thermal oxide is patterned using
photolithography and hydrofluoric acid (HF) etching. After removing the photoresist with acetone and
iso-propanol, chlorine etching is used to etch top-silicon, with the silicon-oxide playing the role of an
etching mask. This process of etching silicon is extremely selective to oxide. After removing the
thermal oxide in HF and cleaning the wafer with standard procedures, LPCVD (low pressure chemical
vapor deposition) silicon-nitride is deposited at 800°C. Photolithography on silicon-nitride is done
followed by etching using SF6 chemistry. The photoresist is removed using acetone followed by isopropanol rinse. In order to ensure electrical contact with the silicon nano beams, an aluminum layer is
deposited on the silicon anchor pads by a lift-off process. The sample is subjected to HF-73% in order
to etch away the buried-oxide and thus release the beams, leading to the stress relaxation in the
actuator and to the deformation of the specimen. After releasing the wires, the sample is transferred to
a commercial probe-station (LakeShore CPX) equipped with standard MOSFET characterization tools
for electrical characterizations. All transport characterizations reported in this work were performed
under sufficiently high vacuum condition (~ 5x10-5 mbar) using an Agilent 4156C precision
semiconductor parameter analyzer.
Figure S1 Schematic illustration of the fabrication of elementary tensile test structures with
on-chip application of the loading through the release of the internal stress present in a silicon
nitride “actuator” beam.
Figure S2 Optical microscopy image of two mutually opposite array designed to minimize
dispersions from process variations to be mis-interpreted as piezo-resistance.
Figure S3 The output characteristics for (a) FW array and (b) REV array for Na ~ 1 × 1019
cm-3.