Ultra thin films for sensing and heating of microprobes
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Abstract
This dissertation aims to advance the current state of cantilevers with integrated metal thermal and deflection sensing elements. Metallic sensing elements enable the use of alternative substrate materials (such as polymers), that tend to exhibit higher compliance properties and are more robust (less brittle) compared to Si or Si3N4 cantilevers. To this end, the research consists of exploring the properties of thin films with thicknesses of 100 nm or less and studying a number of applications in thermal sensing, micro-heating, and deflection sensing. In order to achieve these goals three fabrication processes for microcantilevers were developed. The minimum detectable temperature change of a cantilever with the 10 nm gold thermal sensing element was measured at 0.4 K, corresponding to 17 ppm changes in probe resistance. Finite element analysis simulations indicate a strong correlation between thermal probe sensitivity and probe tip curvature, suggesting that the sensitivity of the thermal probe can be improved by increasing the probe tip curvature, though at the expense of the spatial resolution provided by sharper tips. Simulations also indicated that new designs such as a bow-tie metallization design could yield an additional 5- to 7-fold increase in sensitivity. The gauge factor of the thin film is enhanced to 3.24 for a 10 nm gold sensor and 4.1 for the 5 nm gold sensor doubling that of bulk gold. The sensors on silicon cantilevers exhibited large dynamic range of tens of microns and were used to measure: the mechanical properties of materials, the melting points of materials, topographical imaging, and high throughput measurements. Moving nano-heater were used to direct chemical vapor deposition reactions (nano-CVD) demonstrating a tip-based nanofabrication (TBN) method. The silicon cantilevers with embedded thin film heaters were used for localized nano-CVD to grow copper (Cu) and copper oxide (CuO) from gases. Polyimide cantilevers with thin metallic sensing elements were coated with colorimetric sensing material and used for explosive detection enhancing the sensitivity by 30x compared to what was previously found when the colorimetric sensing material was used alone. Metal thin films on cantilevers with thicknesses