<p> Lithium niobate has interesting characteristics such as the electro-optic effect, the acousto-optic effect, piezoelectricity and large nonlinear optical coefficients. Potential applications in MEMS field could be explored if microstructures are fabricated in lithium niobate substrates,. This thesis presents the fabrication and characterization of a lithium niobate MEMS device. As lithium niobate crystal is difficult to process using standard semiconductor techniques including both wet etching and dry etching, new methods are
required to process lithium niobate. In our project, picosecond laser pulses were chosen to
produce bridges on lithium niobate. Fabrication of grooves with high aspect ratio were attempted and grooves with clean morphology were obtained when laser pulses with low cutting speed, medium pulse energy, and large number of passes were employed. This shows picosecond laser machining is a viable method to process lithium niobate.</p> <p> Waveguides in Z cut lithium niobate crystal were fabricated using Ti-indiffusion techniques. After the fabrication of waveguides in lithium niobate, a SiO2 film with a thickness of 0.3μm was deposited as a buffer layer. Ti-Pt-Au electrodes for actuation function were then deposited through lift-off technique. Finally a bridge structure (80um in width and 600um in length) with a waveguide embedded in it was fabricated with picosecond laser. The insertion loss before and after laser machining was 6.99dB and 5.01dB respectively.</p> <p> Optical and electrical tests were performed in an effort to determine the resonance frequency of bridge. In the optical test, many bulk piezoelectric resonance peaks were presented in the frequency spectrum. After damping the vibration of substrate, these spikes disappeared and only a background noise with small spikes were obtained. As those small spikes are not reproducible, the optical test is not a viable method to determine resonance frequency of the bridge structure in our device. The electrical test was then carried out in a vacuum environment in order to find the resonance frequency. The spectrum presents a spike with large amplitude. However, the phase and amplitude of the spike remained the same when the vacuum condition was removed, which indicates the spike is not related to the resonance of the bridge. In summary, the resonance frequency of bridge structure could not be determined by these two approaches.</p> <p> Future work could involve directly investigating the material properties surrounding the machining region to see whether the piezoelectricity of the material has been damaged from laser ablation process. New laser machining process of lithium niobate may also need to be studied to avoid this damage to the substrate structure. Even though our device could not be driven to vibrate at its resonance frequency, it is worth making microstructures in lithium niobate substrates. The combination of optical, mechanical and electrical elements will make lithium niobate a great potential material for optical MEMS
applications.</p> / Thesis / Master of Applied Science (MASc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/21766 |
| Date | 10 1900 |
| Creators | He, Yuan |
| Contributors | Kleiman, Rafael N., Preston, John S., Engineering Physics |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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