Two types of MEMS-based oscillating AFM probes
Résumé
Most of the commercial Atomic Force Microscope ( AFM) oscillating probes are based on micro-scale cantilevers enabling measurement with pico-Newton force resolution in vacuum. However, the cantilever probes suffer from a degradation of both resonance frequency and quality factor when operating in liquids. Moreover, the laser-based vibration sensing unit also limits the integration and miniaturization as the cantilever width has to stay above 2 μm to control the diffraction effect. In such a context, two new concepts of MEMS-based atomic force microscope ( AFM) oscillating probes using ring-shaped resonator and I2 shaped resonator are presented. These probes are designed to feature MHz resonance frequencies and high quality factor of several thousands. Thanks to the integrated transduction methods including electrostatic driving/sensing, thermal driving and piezoresistive sensing, the optical detection unit is no longer needed. The probes are fabricated using standard silicon micromachining and the measured resonance frequency can reach up to 11 MHz with a quality factor of 1 500. Both probes are then mounted onto a commercial AFM set-up through a dedicated probe-holder and circuit board. Topographic images of patterned resist sample are obtained. The minimum force resolution deduced from the measurement is about 5pN/√Hz. The upcoming works consist of improving de detection scheme of the MEMS-based probes and realize high speed/quality AFM images in liquid.