Plasma deposited thermocouple for non-invasive temperature measurement

This paper describes the realization of a temperature sensor based on plasma sputtered thermocouples. The thermocouples are realized in the vacuum with quite pure materials, negligible oxydation and with low contamination thus enabling accurate measurements and are made inert by means of a thin coating of tetraethoxysilane (TEOS) that seals them. The thermocouples have an overall thickness of few hundreds of nanometers and are designed to allow non invasive, though accurate temperature measurement to be obtained in adverse conditions, such as the ones found during lyophilization processes. Lyophilization is widely employed to obtain pharmacological active powders in an economical and massive way. The lyophilization process effectiveness depends on the thermal distribution inside the lyophilizing vials: if the temperature is too low the process become extremely slow thus greatly increasing the powder cost, but if the temperature is too high a melting of the frozen substance can occur that can make the powder useless. Tuning the drying process is therefore extremely important, but such an operation is quite difficult since the temperature greatly changes inside each lyophilizing vial due to the process itself and among vials due to their position within the apparatus. A local temperature measurement would therefore be necessary, but normal temperature sensors would alter the drying local condition making the measurement incorrect and indirect measurements proved to be not reliable. The proposed solution instead is almost inert, capable of performing accurate local measurements and can be used in a variety of conditions where size and possible contamination are of importance. A sensor prototype is described and its performance compared with conventional sensors highlighting the advantages of the proposed solution.