Ultra-Thin Piezoelectric Strain Sensor Array Integrated on a Flexible Printed Circuit Involving Transfer Printing Methods

Abstract

In this paper, we present a novel sensor array manufacturing process that involves transfer printing methods using a chip mounter with a vacuum collet. Using these methods, one can mount not only ultra-thin microsensors but also microcontroller and amplifier chips required for sensor device fabrication. We successfully transfer-printed a very fragile microelectromechanical systems-based 5-mm-long, 1-mm-wide, 5- $\mu \text{m}$ -thick high-aspect-ratio ultra-thin Pb(Zr, Ti)O3 (PZT) (1.9 $\mu \text{m}$ )/Si (3 $\mu \text{m}$ ) strain sensor onto a flexible printed-circuit (FPC) substrate with etched Cu wiring. Then, we connected the sensor to the wiring by printing a conductive paste using a screen printer. Large ferroelectric polarization–voltage hysteresis curves were obtained even after the transfer printing process. Since an output voltage corresponding to the magnitude of the strain from the developed sensor was generated, it was confirmed that ultra-thin sensors could be integrated to the FPC substrate by these transfer and screen printing techniques without damage. The PZT thin films have shown 0.18 mV/ $\mu \varepsilon $ of dynamic strain sensitivity according to the resonant vibration of the stainless plate.