A novel tapping-mode stylus with a polyvinylidene fluoride unimorph sensor

Abstract

In order to scan a surface with high-step micro-features non-destructively and accurately, anovel tapping-mode stylus fabricated with a strip of thin piezoelectric polyvinylidenefluoride (PVDF) film is proposed. Besides the flexible piezoelectric PVDF film, the stylusalso consists of a piezo-actuator, which actuates the PVDF strip to vibrate near itsresonant frequency, and a tungsten probe which adheres under the PVDF film. Thevibrating PVDF film acts as both the cantilever and the vibrating deflectiondetector as used in a tapping-mode atomic force microscope. Operated with anX–Y scanner, the tapping stylus can scan the surface like a tapping-mode scanning probemicroscope.In this paper, the structure and mechanism of the stylus is explained andan evaluation of the stylus is estimated: the maximum error and standarddeviation along the vertical direction are about 2.0 and 0.5 nm respectively;the spring constant of the PVDF is experimentally estimated to be about183 N m−1. Due to the flexibility of the PVDF film and the large aspect of the tungsten probe, thestylus can scan surfaces with high steps non-destructively. Compared with a tapping-modeAFM, the structure of the stylus is simpler because the PVDF strip acts as both thecantilever of the AFM and its vibration-detecting sensor, which is usually an optical leverand photodiodes. In addition, the tungsten tip is anti-wear and there is no optical error.