Prototype cantilevers for SI-traceable nanonewton force calibration

Abstract

A series of extremely uniform prototype reference cantilevers has been created that can be used to calibrate the spring constants of atomic force microscopy (AFM) cantilevers and other micromechanical structures. By utilizing optimal combinations of material, design and the latest microfabrication processing techniques, arrays of cantilevers were created from single crystal (1 0 0) silicon. Nominal spring constants were estimated to be in the range 0.02 N m−1 to 0.2 N m−1. Resonance frequency measurements were used to assess the uniformity of devices from different portions of a silicon-on-insulator wafer and in different processing batches. Variations of less than 1% (relative standard deviation) in resonance frequency attested to the high degree of uniformity achieved. Independent calibration of cantilevers in an array using an electrostatic force balance indicated that the actual spring constants ranged from 0.0260 N m−1 ± 0.0005 N m−1 (±1.9%) to 0.2099 N m−1 ± 0.0009 N m−1 (±0.43%). The results confirm the feasibility of creating uniform reference cantilevers and calibrating them using a Système International d'Unités (SI)-traceable technique, making these devices excellent candidates as force calibration standards for AFM.