Micro-Mechanical Temperature Sensors

Temperature is the most frequently measured physical quantity in the world. The field of thermometry is therefore constantly evolving towards better temperature sensors and better temperature measurements. The aim of this Ph.D. project was to improve an existing type of micro-mechanical temperature sensor or to develop a new one. Two types of micro-mechanical temperature sensors have been studied: Bilayer cantilevers and string-like beam resonators. Both sensor types utilize thermally generated stress.
Bilayer cantilevers are frequently used as temperature sensors at the micro-scale, and the goal was therefore to improve their sensitivity. Bilayer cantilevers are usually made by coating a ceramic cantilever with a metal. They were in this case coated with the polymer SU-8 to increase the sensitivity. The measured sensitivity of the fabricated cantilevers turned out to be one half of the expected value. The reduced sensitivity was due to initial bending of the cantilevers and poor adhesion between the two cantilever materials. No further attempts were made to improve the sensitivity of bilayer cantilevers.
The concept of using string-like resonators as temperature sensors has, for the first time, been studied in details both theoretically and experimentally. The measured sensitivity of silicon nitride, nickel and aluminum strings scales in accordance with the theory. A relative change of -15+/-1%/°C was demonstrated using low stressed aluminum strings. This value is more than 100 times higher than values reported by other groups for similar devices. A temperature resolution of 2.5x10^-4 °C was achieved using high Q silicon nitride strings. This temperature resolution is better than for other types of micro-scale resonating temperature sensors.
The anelastic behavior observed for the strings was least pronounced for the silicon nitride strings. This combined with their better temperature resolution makes them the best temperature sensor candidate.
The concept of using a string-based photothermal spectrometer for microand nano-particle detection has been investigated. Detection and identifi-cation of single micro-particles have been demonstrated successfully using a single color irradiation source. The current setup has the potential of detecting single sub-micrometer particles. The detection of wavelength dependent light absorption by micro-particles has also been demonstrated with success.