Platinum (Pt) thin film layers on Si/SiO2 wafer are nowadays receiving considerable attention for many MEMS devices which operate at high temperature conditions, as for example micromachined chemoresistive sensors for gas detection [1,2]. In this application, the temperature working condition of the sensing layer is between 400°C and 700°C. In the present work, because of the Pt poor adhesion on Si/SiO2, an adhesion layer was deposited between the Si/SiO2 substrate and the film of Pt. At room temperature a Chromium (Cr) adhesion layer can be used, but not in corrosive environment and at higher temperature, due to its high oxidation and inter-diffusion rate, respectively. A Titanium (Ti) adhesion layer is an alternative for corrosive environment, but not for higher temperatures up to 600 °C; in this condition is possible to take place an atomic inter-diffusion between the Pt film and the adhesion layer of Ti [3], changing the electric conductance properties of the Pt bulk, increasing the electric resistance and reducing the adhesion of Pt on Si/SiO2. The introduction of a ceramic adhesive thin film of Alumina (Al2O3) as a new adhesion layer, proved to be a good solution for MEMS devices with Pt, working at high temperatures and in biological environment. Al2O3 is a ceramic electrical insulator, has a relatively high thermal conductivity, appropriate for heating systems, and resists to strong acid and alkali attack at elevated temperatures. Thin films of Cr, Ti and Al2O3 were deposited on Silicon/Silicon dioxide (Si/SiO2) wafer by electron beam. The properties of these metals used as adhesion layers on Pt electrode in gas sensors device application were investigated. The electric behaviors were measured for different annealing temperatures. All these metallic layers showed a good adhesion onto Si/SiO2 and also good Au wire bondability at lower temperature than 400°C , but for higher temperature than 400°C the thin Cr/Pt and Ti/Pt films showed poor adhesion, due to the inter-diffusion between Pt and the metallic adhesion layers [3]. Al2O3 was tested as a new adhesion layer to improve the adherence on the Pt film at higher temperature. The proposed Al2O3 metallic layer confirmed a good behavior working at high temperatures, showing the better performance for Al2O3/Pt metallic film in the gas sensor application due to better electrical behavior like conductivity and increased TCR behavior (Temperature Coefficient of Resistance). The application of Al2O3 as a new adhesion layer material for gas and biological sensors produced by electron bombardment represents an excellent alternative to improve the adherence between the Pt film and the substrate of Si/SiO2.
Platinum Metallization For MEMS Application
Guarnieri, Vittorio;Lorenzelli, Leandro;
2012-01-01
Abstract
Platinum (Pt) thin film layers on Si/SiO2 wafer are nowadays receiving considerable attention for many MEMS devices which operate at high temperature conditions, as for example micromachined chemoresistive sensors for gas detection [1,2]. In this application, the temperature working condition of the sensing layer is between 400°C and 700°C. In the present work, because of the Pt poor adhesion on Si/SiO2, an adhesion layer was deposited between the Si/SiO2 substrate and the film of Pt. At room temperature a Chromium (Cr) adhesion layer can be used, but not in corrosive environment and at higher temperature, due to its high oxidation and inter-diffusion rate, respectively. A Titanium (Ti) adhesion layer is an alternative for corrosive environment, but not for higher temperatures up to 600 °C; in this condition is possible to take place an atomic inter-diffusion between the Pt film and the adhesion layer of Ti [3], changing the electric conductance properties of the Pt bulk, increasing the electric resistance and reducing the adhesion of Pt on Si/SiO2. The introduction of a ceramic adhesive thin film of Alumina (Al2O3) as a new adhesion layer, proved to be a good solution for MEMS devices with Pt, working at high temperatures and in biological environment. Al2O3 is a ceramic electrical insulator, has a relatively high thermal conductivity, appropriate for heating systems, and resists to strong acid and alkali attack at elevated temperatures. Thin films of Cr, Ti and Al2O3 were deposited on Silicon/Silicon dioxide (Si/SiO2) wafer by electron beam. The properties of these metals used as adhesion layers on Pt electrode in gas sensors device application were investigated. The electric behaviors were measured for different annealing temperatures. All these metallic layers showed a good adhesion onto Si/SiO2 and also good Au wire bondability at lower temperature than 400°C , but for higher temperature than 400°C the thin Cr/Pt and Ti/Pt films showed poor adhesion, due to the inter-diffusion between Pt and the metallic adhesion layers [3]. Al2O3 was tested as a new adhesion layer to improve the adherence on the Pt film at higher temperature. The proposed Al2O3 metallic layer confirmed a good behavior working at high temperatures, showing the better performance for Al2O3/Pt metallic film in the gas sensor application due to better electrical behavior like conductivity and increased TCR behavior (Temperature Coefficient of Resistance). The application of Al2O3 as a new adhesion layer material for gas and biological sensors produced by electron bombardment represents an excellent alternative to improve the adherence between the Pt film and the substrate of Si/SiO2.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
