4.8 MHz AFM nanoprobes with capacitive transducers and batch-fabricated nanotips

When capacitive transduction meets the thermomechanical limit: Towards femto-newton force sensors at very high frequency

“…The fabrication process was very similar to the one described in ref. [10] and made use of silicon-oninsulator (SOI) wafers. The resonator body was first etched in the whole 5 µm thick device SOI layer, followed by several thermal oxidation and chemical de-oxidation cycles.…”

Piezo-resistive ring-shaped AFM sensors with piconewton force resolution

“…The SNR can be estimated by calculation the ratio of device signal and noise floor around resonance frequency. Considering that at the resonance, 1 V AC excitation correspond to 2 nm vibration amplitude at the tip point, the minimal detectable amplitude of the ring probe is (7) The minimal detectable force is derived based on the minimal detectable amplitude (8) 5 3,000 0.6 21…”

“…As the first part of a research program, a new concept of AFM probes using bulk-mode silicon resonators and the measurements of interaction between a surface and the vibrating tip of the resonator had been proposed [2][3][4][5].The higher working frequency (4.9 MHz) and quality factor (1,500) [5] lead to a high speed imaging and a more accurate force sensitivity, which pave the way for the operation in liquid.…”

MEMS piezoresistive ring resonator for AFM imaging with pico-Newton force resolution

“…These ring probes have been mounted onto a commercial AFM set-up and topographic images successfully obtained. Lately, downscaled ring resonators with integrated nano-tips have been fabricated [9]. With an outer/inner radius of 30/20 μm, these ring probes work in air at 11 MHz with a quality factor of 1500.…”

“…However, one main drawback of capacitive transduction is that the electromechanical coupling coefficient is proportional to the electrode-to-resonator overlap area S and is inversely proportional to the square of the air gap g. Hence, decreasing the resonator dimensions to obtain higher frequencies must be accompanied by a drastic decrease of air gap spacing and without excessive reduction in S to maintain a sufficient coupling factor. However, reducing the gap width is not a simple task because narrow gaps (<500 nm) are more likely to be realized by other methods such as etching a laterally pre-grown SiO 2 layer on the resonator sidewall [9,10], which results in a more complex and demanding fabrication process.…”