Nanostructured functional Ti–Ag electrodes for large deformation sensor applications

Abstract

This paper reports on the development of thin film-based stretchable electrodes, suitable for different types of sensors. Columnar Ti-Ag thin films with a Ag content of 8 at.% were prepared by D.C. magnetron sputtering on carbon nanotube/poly(vinylidene fluoride) CNT/PVDF piezoresistive composites. GLancing Angle Deposition, GLAD, technique was used to change the typical normal columnar growth microstructure obtained by conventional sputtering, into different growing architectures, such as inclined columns and zigzag profiles, in order to tune mechanical and electrical responses of the materials. Three different incident angles of the particle flux, α = 40º, 60º and 80º, were used to deposit Ti-Ag thin films with the different architectures. Upon uniaxial stretching of the prepared zigzag thin films, the resistance of the thin film starts increasing smoothly for strains up to 3%. Above 10% strain, a sharp increase of the electrical resistance is observed due to film mechanical failure and therefore interruption of the electrical conductivity pathways. Furthermore, the influence of the thin film architecture was also studied with respect to the performance of piezoresistive sensors based on carbon nanotube/poly(vinylidene fluoride), CNT/PVDF, composites in which Ti-Ag coated films served as electrodes for signal acquisition. Electromechanical tests were thus performed in composites with CNT contents close to the percolation threshold, where the electromechanical response, characterized by the Gauge Factor, is the largest. The stability of the piezoresistive response was analyzed for the various architectures of the GLAD sputtered Ti-Ag electrodes, including incident angle and number of zigzag periods. It is shown that thin film architecture has a pronounced influence in the overall sensor response, A c c e p t e d M a n u s c r i p t 2 where the best results are obtained for piezoresistive polymer composites coated with Ti-Ag films, produced with intermediate (α = 60º) incident angles.

Study of the electrical behavior of nanostructured Ti–Ag thin films, prepared by Glancing Angle Deposition

“…Additionally, this binary intermetallic-like compound offers excellent biocompatibility, good wear and corrosion resistance, which together with proper multifunctional properties, extends its potential use in biomedical applications [1,2]. The suitable electromechanical response is very important for the bioelectrodes lifetime and was previously discussed by the authors with promising results, showing that the electrical signal acquisition was not compromised during the mechanical deformations promoted on the device [3]. Therefore, the possibility to produce nanostructurally controlled sculptured TiAg x thin films, with particular engineering design, tuned by the experimental atomic process, will be a surplus value.…”

“…In previous studies developed by the authors [1][2][3], intermetallic-like thin films of titanium-silver (Ti-Ag) were produced and optimized in order to functionalize flexible polymer-based bioelectrodes for sensing devices. The growing interest of using this system is particularly evident in the biomedical field, and is an outcome of the symbiosis between the titanium biocompatibility and the silver antimicrobial properties [4][5][6][7].…”

Piezoresistive response of nano-architectured Ti x Cu y thin films for sensor applications

“…An emerging and attractive method to build up strain sensing materials is being developed, focusing on the development of systems where the electrode material itself acts as sensor [16]. This is particularly challenging given the relatively high and complex mechanical solicitations that are expected in several of these mechanical-based applications, i.e., bending, elongation and torsion.…”

“…In this work, the GLancing Angle Deposition (GLAD) technique [26] was selected in order to modify the microstructural features of the thin films, and indirectly their physical-chemical responses to strong mechanical solicitations, maintaining the functional properties [16,27]. Keeping the substrates in motion, Fig.…”

“…1); 3) repeat steps 1 and 2 to the desired number of zigzags. Furthermore, by combining oblique incidence of the impinging sputtered particles with the motion of the substrate holder, different types of microstructural growth can be tailored among normal columns, zigzags and spirals [16,[28][29][30][31].…”