Speaker
Description
Understanding the dynamical behavior of micro- and nano-mechanical systems (MEMS and NEMS) is essential in a wide variety of applications ranging from nonlinear dynamics to quantum technologies. Hence, it is important to be able to precisely monitor the mechanical properties of MEMS and NEMS devices. In this contribution, we show how to track and spatially map various properties of a mechanical resonator, specifically frequency shift, linewidth, and nonlinearity, by aptly choosing three closely-spaced drive frequencies and using phase-locked loops (PLLs). This technique tracks changes in the system faster and more efficiently, without the need for repeated frequency sweeps of the oscillator response, simply by employing three phase-locked tones.
The resonator we use to demonstrate our technique is a hexagonal micromechanical membrane made from high-stress silicon nitride (SiN) whose motion is read out using an interferometric setup. The fundamental out of plane mode around 1.7 MHz has a linewidth of only 22 Hz. Still, by selecting different setpoints, three PLLs can be locked to this single narrow resonance. In the event of a frequency shift, all three locked frequencies will move in unison. On the other hand, a change in linewidth will only change the separation between the two outer ones. Also, a change in the Duffing nonlinearity has a distinct signature. We demonstrate that the frequency and linewidth can be tracked during a large temperature ramp, where a regular network analyzer measurement would be way too slow. By scanning the membrane underneath the laser spot, spatial maps of feedback-induced effects are measured. The results are further improved by constructing an estimator. Finally, when adjusting the driving power also the Duffing nonlinearity is determined.
Our very robust method allows to investigate a plethora of unintentional features of our resonator like sign changes, thickness variations, or particles on the membrane. Thus, it enables a fast characterization, spatial mapping and monitoring of properties of changing micro- and nano-mechanical systems in real time.