Piezoresistive response of nano-architectured TixCuy thin films for sensor applications

The present work reports on the development of piezoresistive TixCuy thin films, deposited on polymeric substrates (PET). The general idea was to analyse the influence of the Cu concentration on the signal response of the Ti-based transducers, exploring the possibility to use this thin film system as force and deformation sensors in biomedical sensing devices. The Glancing Angle Deposition, GLAD, technique was used to change the typical normal columnar growth microstructure into inclined (zigzag-like) architectures, aiming to tune the mechanical and electrical responses of the thin films, which may offer unique opportunities for several sensing devices. Inclined (zigzag grown) thin films were prepared with increasing amounts of Cu and characterized in terms of the most relevant properties for sensing applications. The piezoresistive response was analysed trough the evaluation of the Gauge Factor, K. The incident angles of the particle flux α = 45° were used to prepare the nano-architectured zigzag TixCuy thin films. The Gauge factor ranges from 1.24 ± 0.03 to 16.34 ± 0.43 for intermetallic Ti0.92Cu0.08 and pure Cu thin films, respectively. For the deposited thin films small voids are formed and the voids density decreases considerably with increasing Cu content. Taking in account the: electrical resistance linearity, low noise and the highest K value found for TixCuy films (K = 3.6 ± 0.1), the most promising results were obtained when the polymer was coated with a stoichiometry of Ti0.37Cu0.63. The overall set of results also show the viability of these materials to be used as piezoresistive sensors, namely in biological environments, such as catheters, needles or endoscopes with sensing capabilities.