Citation: Fakhri, E.; Plugaru, R.;
Sultan, M.T.; Hanning Kristinsson, T.;
Örn Árnason, H.; Plugaru, N.;
Manolescu, A.; Ingvarsson, S.;
Svavarsson, H.G. Piezoresistance
Characterization of Silicon
Nanowires in Uniaxial and Isostatic
Pressure Variation. Sensors 2022, 22,
6340. https://doi.org/10.3390/
s22176340
Academic Editor: Haim Abramovich
Received: 25 July 2022
Accepted: 18 August 2022
Published: 23 August 2022
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Communication
Piezoresistance Characterization of Silicon Nanowires in
Uniaxial and Isostatic Pressure Variation
Elham Fakhri
1,
*, Rodica Plugaru
2
, Muhammad Taha Sultan
1,3
, Thorsteinn Hanning Kristinsson
1
,
Hákon Örn Árnason
1
, Neculai Plugaru
2
, Andrei Manolescu
1
, Snorri Ingvarsson
3
and Halldor Gudfinnur Svavarsson
1,
*
1
Department of Engineering, Reykjavik University, Menntavegur 1, 102 Reykjavik, Iceland
2
National Institute for Research and Development in Microtechnologies-IMT Bucharest,
077190 Voluntari, Romania
3
Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavik, Iceland
* Correspondence: elhamf20@ru.is (E.F.); halldorsv@ru.is (H.G.S.)
Abstract:
Silicon nanowires (SiNWs) are known to exhibit a large piezoresistance (PZR) effect, making
them suitable for various sensing applications. Here, we report the results of a PZR investigation
on randomly distributed and interconnected vertical silicon nanowire arrays as a pressure sensor.
The samples were produced from p-type (100) Si wafers using a silver catalyzed top-down etching
process. The piezoresistance response of these SiNW arrays was analyzed by measuring their I-V
characteristics under applied uniaxial as well as isostatic pressure. The interconnected SiNWs exhibit
increased mechanical stability in comparison with separated or periodic nanowires. The repeatability
of the fabrication process and statistical distribution of measurements were also tested on several
samples from different batches. A sensing resolution down to roughly
1 mbar
pressure was observed
with uniaxial force application, and more than two orders of magnitude resistance variation were
determined for isostatic pressure below atmospheric pressure.
Keywords: silicon nanowires; MACE; piezoresistivity
1. Introduction
Low-dimensional structures may possess unique mechanical, electrical, optical, and
thermoelectric properties. Particularly, silicon nanowires (SiNWs) have demonstrated prop-
erties suitable for various advanced applications [
1
–
3
], including low-cost thermoelectric
devices and chemo-biological sensors with ultrahigh sensitivity [
4
,
5
]. The integration of
SiNWs in electronic devices is favoured by their compatibility with the well-established
Si-SiO
2
electronic industrial technology. Bulk silicon has been known for a while to exhibit
high piezo resistance (PZR) effect [
6
]. In bulk semiconductors, the PZR-effect takes place, in
principle, due to a change in the electronic structure and modification of the charge-carriers
effective masses. This phenomenon has found practical applications in many Si-based
devices, such as pressure transducers [
7
], cantilevers for atomic force microscopy [
8
],
accelerometers [9], biosensors [10], and multi-axis force sensing tools [11].
Recently, nanowires have been shown to possess the ability to significantly increase the
PZR response [
12
]. A giant PZR was observed in p-doped SiNWs with diameters of
50 nm
to
350 nm
and a length of microns initially under tensile uniaxial stress [
13
]. However,
the PZR effect in n-doped nanowires was found to be comparable to that in the bulk
counterpart, both for tensile and compressive uniaxial stress [14].
On the theoretical side, the origin of the PZR effect in SiNWs has long been under
debate, and most frequently, it is referred to as anomalous PZR [15]. It has been related to
quantum confinement effects [
16
], surface charge effects [
17
–
19
], strain-induced bandgap
shift [
20
], or changes in the charge carrier’s effective masses [
21
]. A complex model
Sensors 2022, 22, 6340. https://doi.org/10.3390/s22176340 https://www.mdpi.com/journal/sensors
