Fabrication, Characterization, and Signal Processing Optimization of Flexible and Wearable Piezoelectric Tactile Sensors

Piezoelectric microelectromechanical systems (MEMSs) meet the growing demand for sensors with small sizes and low power consumption. For tactile applications and pressure measurements, they are applied in various fields from robotics to healthcare. In this context, flexible devices are very important for their high responsivity and ability to conform to the analyzed surface. This work reports on miniaturized flexible and compliant piezoelectric devices to increase the number of integrable sensors for detecting and discriminating localized pressures and contacts per unit area with minimal crosstalk. For this purpose, a series of aluminum nitride (AlN)-based piezoelectric sensors with different diameters (from 5 to $500 \mu \text{m}$ ) was realized, and the generated electrical signal by sensor deformation was amplified by a differential voltage amplifier circuit. By the analysis of the shape of the piezoelectric signal as a function of the applied pressure, oscillations due to piezoelectric deformations, superimposed on the initial peak signal corresponding to the touch event, have been observed. The integral of the electrical signal was calculated for the most accurate representation to describe the sensor’s response. The best responsivity was obtained in samples with diameters of 200 and $500 \mu \text{m}$ . Furthermore, it was also found that the minimum distance between the edges of closed sensors, observing crosstalk below −20 dB, was around $500 \mu \text{m}$ .