Piezoresistive Ring-Shaped AFM Sensors with Pico-Newton Force Resolution

A new concept of Atomic Force Microscope (AFM) oscillating probes using electrostatic excitation and piezoresistive detection is presented. The probe is characterized by electrical methods in a vacuum chamber and by mechanical methods in air. The frequency-mixing measurement technique is developed to reduce the parasitic signal level. These probes resonant in the 1MHz range and the quality factor is measured about 53000 in vacuum and 3000 in air. The ring probe is mounted onto a commercial AFM set-up and the surface topography of PMMA sample (2 µm square) is obtained. The force resolution deduced from the measurements is about 10 pN/Hz0.5.