Fabrication Of Microcalorimeter And Investigation On The Specific Heat Of Micro/nanometer Thin Films

Investigation on microscale thermal properties is a necessary development of thermal science, as well as one of the key factors to improve micro/nano devices' performance. This dissertation investigated the specific heat of thin films in micro/nano devices, including the design and fabrication of microcalorimeter, the construction of pulse calorimetry system, the measurements and analysis of thin films' specific heat.The basic structure of a microcalorimeter is a suspending dielectric membrane with heater and thermometer on it. Thermal analyses of the bulk-silicon-etched-type microcolarimeters and surface-micromachined-type microcalorimeters were performed with 3D finite element analysis and experiments. Results show that, the surface micro-machined structure has good thermal isolation and temperature uniformity in vacuum, excellent mechanical strength and good IC process compatibility, which make it better match the requirements of microcalorimeters than the bulk silicon fabricated structure. With the process flow designed according to the wafer foundry conditions, the surface micro-machined microcalorimeter for heat capacity measurement of micro/nanometer thin films was successfully manufactured. The microcalorimeter's temperature rise rate reaches 2 × 10~5K·s~-1 with heating power of 5.5mW. The located deposition process of the sample film was also devoleped.A pulse calorimetry system was constructed for measuring the heat capacity of thin films, and it was composed of a vacuum chamber, an electrical pulse source, and signal acquirement parts. The pulse calorimetry was simplified according to the characteristics of the microcalorimeter. Measurements show that, the empty microcalorimeters have very small heat capacity, and the adjacent microcalorimeters are quite similar to each.otber, which satisfied the requirements of the heat capacity measurement of thin films.The heat capacity of aluminum films and copper films of different thicknesses were measured in the temperature range of 300-420K, and the microstructure and sizes of the sample films are characterized to calculate the specific heat of the samples. The obtained specific heat of the 1150nm Al film and the 340nm Cu film agrees well with the literature data of their corresponding bulk materials. However, as the films' thickness decreases, remarkable size effect of the specific heat is observed.Aluminum and copper single crystal thin films were analysised with molecular dynamic simulation; and both the specific heat at constant volume cv and the specific heat at constant pressure cp were calculated in the temperature range of 300~500K. Due to the phonon softening of the surface atoms; the film's cv slightly increases as its thickness decreases; however; the enhancement of the film's cp is much larger than the cv. Therefore; it was deduced that the enhanced cp is mainly caused by the nonlinear vibration of the lattice (the thermal expansion). The results of both the molecular dynamic simulations and the experiments show size effect of the specific heat of nanometer thin films.