Study On Manganin Thin Film Ultra-high Pressure Sensors

Manganin gauge is a kind of special sensor which is mainly used to measure the ultra-high pressures generated by shock waves. It has the highest measurement range, which can reach to 50 GPa, among all existing pressure sensors. To meet the demand of special engineering, the measurement range of the gauge must be extended and the rise time must be decreased. In this dissertation, a new kind of thin film manganin gauge was fabricated by adopting new structure, new sensing and packaging materials, and new fabrication technique. The main conclusions and original results are summarized as fellows.1 .The manganin ultra-high pressure sensors for gas gun were made by two-step thin film techniques, namely, manganin thin films were first deposited by magnetron sputtering on A12O3 substrates, and then covered by a layer of A12O3 thin films by electron beam evaporation. Consequently, the manganin sensing elements were 'cleanly' encapsulated in inorganic solid matrix and the high-pressure shunt effect was eliminated radically. Although the highest pressure in copper target was 107 GPa and that in alumina packaging was in the vicinity of 70 GPa, the gauge records showed a good plateau of about 1 um in duration and absence of shunt.2. The transducers were backed by slabs of Al2O3 ceramics and worked as back-configuration gauge. The combination of alumina to back-configuration structure extends the applicable range from 20 GPa to 100 GPa and makes the sensors have quicker response at higher stresses. Rise time of 19 ns was obtained due to the absence of stress reverberations.3. The gauges were calibrated from 30 to 70 GPa. The initial calibration curve was almost a straight line with piezoresistance coefficient of 0.0201+0.0002 GPa-1. The sensors had high sensitivity. Their sensitivity was about twice of that of other thin film manganin gauges and was very close to that of foil gauges. Based on impedance match method, the measurement range of the gauges can be extended to 100 GPa and above. This range is about 1 time higher than that of exiting manganingauges. The gauges showed high accuracy, high reproducibility and good linearity. The errors were less than +2% at a higher stress.4. In the early stage of experiment, an in-material thin film manganin gauge was studied. This in situ gauge was manufactured by single-step thin film processing, namely, manganin piezoresistance element was prepared on inorganic substrates such as ceramic, microcrystalline glass, etc by sputtering. Then, a thin layer of PTFE film is glued on the surface of the manganin film to package the sensing element. The response time of this gauge was found to ralated to the mounting mode of the transducer. The rise time was, when the substrate was faced to the impactor, much shorter than that when the PTFE film was faced to the impactor.5. Manganin thin films with low temperature coefficient of resistance were prepared by magnetron sputtering. The changes of TCR under difference deposition and heat treatment conditions were studied. It was found that the thin films and target were of similar composition. The optimal deposition temperature was 150-200 and the TCR of thin films were strongly influenced by the target temperature. The TCR of the as-deposited films were about 20X10-6/. After 200-350 heat treatment, the TCR will increase. But the TCR will decrease to 10 X 10-6/ when heat treated under 400 for one hour. Low TCR ensured the gauge was sensitive to pressure changes and insensitive to temperature changes.Two Chinese Invention Patents, which titled " Manganin thin film ultra-high pressure sensors" and "Preparation method of manganin thin films with low temperature coefficient of resistance", have been applied based on the above original work of this thesis.