Sputtering of Ga-doped ZnO nanocoatings on silicon for piezoelectric transducers

Abstract

In this study, lead-free, piezoelectric devices were fabricated by vacuum radiofrequency (RF) sputtering of Ga-doped, ZnO (GZO) nanocoatings at different deposition modes on silicon substrates. Several deposition rates were varied (2 to 16 nm/min) by tuning the sputtering voltage and pressure, in order to control the microstructure and surface morphology of the films. The dependences of the piezoelectric properties of GZO thin films on the different deposition conditions were investigated. Significant dependency of the films' microstructure and surface roughness was observed to the deposition modes used for fabrication. The results showed that after optimization, the surface roughness of the films grown using sputtering voltage 1.1 kV and Ar=2.5.10-2 Torr, is 6 nm. Films with such microstructures are characterized with crystallites orientation (002) and exhibit the highest piezoelectric coefficient of 96.3 pC/m, which is superior compared to other known, lead-free, piezoelectric materials. A simple, membrane-based, vibration sensor was fabricated at the optimal set of conditions to demonstrate the functionality of the coating in a real microelectromechanical (MEMS) device. The working range of the device is between 2 and 800 g and the piezoelectric voltage generated after minimum deformation of 5.4 nm (2g), was 9.66 mV.