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Novel materials for the design of cantilever transducers Open Access


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Type of item
Degree grantor
University of Alberta
Author or creator
Nelson-Fitzpatrick, Nathaniel
Supervisor and department
Evoy, Stephane (Electrical and Computer Engineering)
Examining committee member and department
Moussa, Walied (Mechanical Engineering)
Van, Vien (Electrical and Computer Engineering)
Evoy, Stephane (Electrical and Computer Engineering)
Brett, Michael (Electrical and Computer Engineering)
Bohringer, Karl (University of Washington)
Department of Electrical and Computer Engineering

Date accepted
Graduation date
Doctor of Philosophy
Degree level
Micro and nanocantilever structures have been used as transducers for a plethora of sensor applications. These transducer technologies have similar shapes, but the material properties and geometrical optimizations needed to improve sensitivity are rather different. This is a record of two different material and design strategies undertaken for static and resonant cantilever sensors. For resonant cantilever sensors we desire a material that is stiff and light. We fabricated silicon nanocantilevers using electron beam lithography and a cryogenic etching technique and assayed their resonance frequencies. The brittle nature of surface machined Si necessitated the move towards nanocantilevers made from glassy materials like Si3N4 and SiCN, which are difficult to deposit reliably in thicknesses below 50 nm. Alternatively, we fabricated and characterized atomic layer deposited (ALD) TiN films for nanocantilevers. We assayed chemical and physical characteristics of TiN films deposited between 120˚C and 300˚C with XPS, XRD, ellipsometry, and wafer bowing. We then fabricated nanoresonator beams out of TiN deposited at 200˚C. For static cantilever sensors we designed an Au-Ta nanocomposite alloy. Combining Au and Ta using magnetron co-sputtering we synthesized a material with low intrinsic stress while retaining the chemical affinity of Au to thiolized molecules. XRD, SEM, AFM, nanoindentation, stress measurements and nanocantilever resonance tests were performed to determine the bulk and surface characteristics of these Au-Ta alloys. The FCC <111> structure of Au was retained in films below 50 at.% Ta. Young's modulus was increased slightly by the addition of Ta while hardness was increased fivefold. The film's deposited stress was relieved upon inclusion of 5 at.% Ta. Chemical characteristics of Au-Ta films over the range of Pure Au to Au 40 at.% Ta was assessed using contact angle measurements, XPS, FTIR and cantilever measurements. As Ta concentration was increased the binding of 1-dodecanethiol was hindered. Low Ta films (5 and 10 at.% Ta) exhibited reduced but significant thiol binding, while higher concentrations displayed insignificant binding. We fabricated geometrically optimized cantilevers with a theoretical spring constant as low as 10.5 mN/m. The detection of dodecanethiol was demonstrated with these cantilevers, confirming intrinsic sensitivity to thiolized molecules.
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File title: A Highly Compliant Gold Nanocomposite Cantilever Sensor, Ph. D. Thesis
File author: Nathaniel Nelson-Fitzpatrick
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