Nano-precision micromachined frequency output profilometer

This work presents a new class of MEMS based frequency output force and displacement probes with sub-nm displacement resolution. The sensor consists of a probe tip attached to a microcantilever coupled to a thermal-piezoresisitve resonator. Application of a displacement to this probe tip causes deflection of the cantilever due to the applied force. Consequently, the force acting on the cantilever is transferred to the piezoresisitve beam, modulating its stiffness and thus the resonance frequency. Such devices can be used as atomic force microscope (AFM) probes or high resolution surface profilometers with fully electrical operation eliminating the bulky and complex optical detectors typically used in such systems. As a proof-of-concept, such a microcantilever coupled to a 2.1MHz thermal-piezoresisitve resonator has been demonstrated with a displacement sensitivity of 1.5Hz/nm. The Allan deviation for such resonators operated as self-sustained oscillators is measured to be 0.1-0.2ppm. On analysis of the measured data, a frequency resolution in the order of 1Hz is expected to be achievable. This, in turn, translates to ∼0.4nm of displacement and ∼11nN of force resolution for such sensors.