High-sensitivity linear piezoresistive transduction for nanomechanical beam resonators

Abstract

Highly sensitive conversion of motion into readable electrical signals is a crucial and challenging issue for nanomechanical resonators. Efficient transduction is particularly difficult to realize in devices of low dimensionality, such as beam resonators based on carbon nanotubes or silicon nanowires, where mechanical vibrations combine very high frequencies with miniscule amplitudes. Here we describe an enhanced piezoresistive transduction mechanism based on the asymmetry of the beam shape at rest. We show that this mechanism enables highly sensitive linear detection of the vibration of low-resistivity silicon beams without the need of exceptionally large piezoresistive coefficients. The general application of this effect is demonstrated by detecting multiple-order modes of silicon nanowire resonators made by either top-down or bottom-up fabrication methods. These results reveal a promising approach for practical applications of the simplest mechanical resonators, facilitating its manufacturability by very large-scale integration technologies.

Tuning piezoresistive transduction in nanomechanical resonators by geometrical asymmetries

“…This pre-strain situation happens as a consequence of an asymmetric beam profile at rest. As it is demonstrated previously, 10 the larger the value of the pre-strain, the larger will be the piezoresistive transduced signal. This effect is more relevant in NEMS structure rather than in MEMS structure because the relative value of the pre-strain with respect to the strain induced during the oscillation is larger in small, ultra-thin beams.…”

“…10 The influence of the geometrical asymmetry of the devices on the electromechanical transduction is analyzed taking into account the model developed previously. 10 The onset of the linearized piezoresistive transduction occurs when the DCB is in a pre-strained situation in equilibrium, and then its longitudinal strain is modulated around this equilibrium position. This pre-strain situation happens as a consequence of an asymmetric beam profile at rest.…”

“…Recently, it has been shown that geometrical asymmetries present in DCBs cause an enhancement of the piezoresistive transduction, allowing to obtain large read-out electrical signals from silicon nanowire resonators obtained by top-down and bottom-up fabrication methods. 10 Here, we show that piezo-resistive read-out signals in DCB nanomechanical resonators can be tuned by engineering the asymmetry of the device, and in particular, by inducing deliberate asymmetries that enhance the transduction of specific resonant modes.…”

“…The first fabrication step consists in local gallium implantation of the SOI layer by FIB, to define the silicon nanowire, the side gate electrode (when required), and the contact pads and lines (ii). The ion dose used for the implantation is 10 16 atÁcm…”

Thermo-coupled Surface Cauchy–Born theory: An engineering finite element approach to modeling of nanowire thermomechanical response

“…Hence, NWs serve as ultra-small mechanical components, where size reduction proves to be extra advantageous in sensing applications. The main advantages are associated with i) their high frequencies of operation leading to high sensitivities and high resolution, ii) their ability of deterministic integration with higherorder structures such as electrodes, and iii) the ease of their use as transducers, especially through piezoresistivity in Si NWs (Erdem Alaca, 2009;He and Yang, 2006;Sansa et al, 2014;Walther et al, 2012), and stretchable conductors with metal NWs (Xu and Zhu, 2012;Yao and Zhu, 2015).…”