Fabrication of multipurpose piezoresistive Wheatstone bridge cantilevers with conductive microtips for electrostatic and scanning capacitance microscopy

Abstract

The fabrication and performance of a microprobe with multipurpose capabilities for scanning probe microscopy is presented in this article. Atomic force microscopy (AFM), scanning capacitance microscopy, and electrostatic force microscopy measurements can be simultaneously performed with the probe in which a silicon tip is integrated with a piezoresistive cantilever. Fabrication of the microprobe is based on double side bulk/surface micromachining of silicon on insulator (SOI) substrates. The novelty of this device is a highly doped silicon tip with a curvature radius of about 20 nm which is electrically isolated from the silicon cantilever by the buried oxide layer of the SOI substrate. At the beam supporting point a piezoresistive Wheatstone bridge is fabricated to allow the deflection of the microtip to be monitored. This cantilever displacement detection system enables measurements in vacuum and simplifies the design of the AFM head. Experimental measurements agree well with theoretical estimates of the sensitivity of the microprobe.