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 solutio

Low-cost H2S gas sensor based on plastic optical fiber

A new simple and low-cost fiber optic sensor for cumulative detection of H2S and other sulphide compounds is described. The transducer is based on a plastic optical fiber and exploits a non-reversible chemical reaction, whose products interact with the evanescent field tails thus increasing the propagation losses with the exposure time. The sensor has a sensitivity of the order of few ppb

An Optic Solution for the Measurement of Gas Diffusion in Thin Films

Thin films are increasingly used both for the development of innovative gas sensors and for surface protection purposes due to availability of new surface treatments, such as those based on low pressure and atmospheric plasma processes. In many cases sequential treatments are required, where, after the initial deposition, the film is exposed to different chemical compounds that both react and diffuse inside the film, usually to enhance its properties. These reaction/diffusion processes depend on many parameters connected to the layer morphology and are, therefore, complex and difficult to preview. Several authors have studied the problem and have developed powerful mathematical models, whose validation, however, is difficult since making measurements during the transient process, especially for films with nanometric thickness, is not easy. In this paper, the authors investigate two optical solutions that can be applied to many practical cases to follow the diffusion process of gases in real time and thus tune and validate the models. The first solution is based on the well-known Surface Plasmon Resonance (SPR) phenomenon and allows precise evaluations to be obtained, but requires a lab-type setup. The other solution employs a Plastic Optical Fiber (POF) and exploits the evanescent field interaction to arrange a simple and cheap setup, that can be used also for in situ tests. Both approaches are applied to the study of the diffusion of sulfide vapors in silver with subsequent surface tarnishing, a topic that represents a practical case of relevant importance in the field of cultural heritage preservatio

Back plate electroplating for high aspect ratio processes

Purpose In this process the electrical contact is brought to the backside of a standard silicon wafer. The details of the entire process are disclosed, from the photolithography processes to the electrodepositing step, and a model for electrical contact was designed. Design/methodology/approach The localized Cu growth of high aspect ratio (AR) microstructures was obtained through an SU-8 photolithography by exploiting the optimal adhesion on the silicon surface and the possibility of generating thick layers with a single spun process Findings The experimental results showed an unexpected behaviour that is theoretically explained in detail considering the energy band theory. The obtained geometries showed a remarkable 6:1 AR without any adhesion problem. The non-invasive front-side manipulation represents a noteworthy improvement and simplification for the design of a multi-step production process. Originality/value An alternative technological approach, called back plate electroplating, has been carried out to obtain Cu growth on the front side of a standard n-type Si wafer through a back side electrical contact. This technique was then applied to fabricate a master for hot-embossing in a LIGA (Lithographie, Galvanoformung, Abformung)-like process flow. For this purpose, an SU-8 thick mask on a standard n-doped wafer was used. Finally, by using this process, it was possible to obtain high AR Cu geometries, avoiding any complex designing and patterning of the contacts on the front side and thus ensuring good adhesion of the SU-8. </jats:sec