Freestanding low pressure chemical vapor deposition (LPCVD) silicon nitride (SiN) membrane resonators are widely investigated as Nano-Electromechanical System (NEMS) for their outstandingly low mechanical dissipation and high mechanical quality (Q) factor. The high Q-factor brings better sensitivities to force, displacement, and temperature excitations. However, integrated actuation methods are not trivial to implement on this platform and are required to harness their high Q-factor in practical applications.
The first goal of this research is to develop a recipe for fabricating large area low stress LPCVD SiN membrane since commercial membranes are relatively expensive and have limited flexibility in terms of geometries. Starting from 4 inches, 500 μm thick, (100) single crystal silicon wafers double-side coated with 100 nm LPCVD SiN, we successfully fabricate five different sizes (i.e., 1 mm, 1.5 mm, 3 mm, 6 mm and 12 mm) of square shape membrane chips. The developed recipe is universally applicable for any size (i.e., under 12 mm) of square shape SiN membrane from the same type of wafer. All recipe parameters are presented in this work, along with experienced challenges and their associated solutions.
The second part of this work is to develop an on-chip actuation method for these resonators. We develop a new method for creating acoustic waves in the silicon substrate using metal – silicon nitride – silicon capacitors. Acoustic waves due to the voltage-dependent mechanical stress arising from charge attractions was already observed previously in silicon substrate p-n junction resonators but is observed here for the first time in a capacitively coupled metal-dielectric-semiconductor (MDS) assembly. In the MDS system, we model three main possible actuation regimes, i.e., depletion, accumulation, and thermal expansion. Both depletion and accumulation rely on electrostatic attraction forces in MDS capacitors when an AC electrical current flows through. The same current can also generate thermal expansion forces resulting from resistive dissipation in the silicon. This contribution, however, is found to be negligible.
In experimental measurements on 1.5 mm membranes in high vacuum, the accumulation MDS is found to perform better than the depletion one in terms of membrane actuation amplitude. With 2 V drive voltage, the membrane achieves up to 10 nm displacement for fundamental mode (1, 1). The contribution of thermal expansion forces is found to be negligible, with resonator temperature changes smaller than 4 mK. A comparison of energy dissipation between a conventional external piezo actuation method and our approach is also presented, through which we find that both methods have comparable power consumption.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/43389 |
| Date | 16 March 2022 |
| Creators | Mu, Gengyang |
| Contributors | St-Gelais, Raphael |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Attribution-NonCommercial-NoDerivatives 4.0 International, http://creativecommons.org/licenses/by-nc-nd/4.0/ |
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