Semiconductor technology for environmental monitoring By manipulating metal oxides at the atomic level, the SENSOR Laboratory in Italy has created a new generation of miniature gas sensors. Climate Change and Environment © DigitalVision Semiconductors have electrical properties somewhere in between those of a conductor and those of an insulator. They are most commonly used to produce computer chips such as CPUs and memory chips. But other applications are possible. The SENSOR Laboratory of the University of Brescia is using semiconductor thin films to create some extraordinary gas sensors. This well-equipped laboratory has been active in the field for nearly two decades. They boast expertise in Physical Vapor Deposition (PVD) techniques. Here the PVD technique of magnetron sputtering was applied. Sputtering involves the removal of material from a solid cathode by bombarding it with positive ions emitted from a rare gas discharge. This material is then deposited onto the target. RF magnetron sputtering was used to deposit thin layers of aluminum-vanadium mixed oxides onto a machined silicon substrate. The technique was also applied for deposition of other metal oxides, namely titanium-indium oxides and titanium-tungsten oxides. Layer by layer deposition allowed for the creation of heterojunctions, junctions between semiconductors with different conductivities. The advantage of heterojunctions is that impact of material impurities is greatly reduced. Sensors constructed from these new materials can be used for environmental monitoring applications. Specifically, microscopic sensors were created to measuring ambient levels of harmful pollutant gases. The SENSOR Lab is pursuing further development and exploitation of this technology. These sensors could soon replace the tin-based sensors currently on the market if long-term stability issues are resolved.
