Gas Sensors Based on Ceramic MEMS Structures Made of Anodic Alumina and Yttria Stabilized Zirconia Films

Abstract

The application of thin ceramic films for the fabrication of MEMS devices enables the extension of their working temperature range up to 600°C, a decrease in heating power consumption, and a very considerable decrease in production cost of sensors and actuators based on this technology. These advantages are very important for the application of gas sensors under harsh environmental conditions, in autonomous and wireless sensor networks. The methods of the fabrication of MEMS platforms for metal oxide semiconductor and thermocatalytic gas sensors, fast thermometers, and flowmeters based on yttria stabilized zirconia (YSZ) and alumina membranes for gas sensors are described. Alumina membranes stable up to 800°C have thickness of about 12 microns and are produced by anodic oxidation of aluminum foil in diluted oxalic acid followed by high-temperature annealing. YSZ membrane with the same thickness is made by slip casting with consequent annealing under mechanic load. Platinum heaters are deposited onto the surface of the membrane by magnetron sputtering through metallic shadow mask. Perfect adhesion of platinum to ceramic material permits us to avoid the application of adhesive sub-layers, and, therefore, improves long-term stability of the heater at high temperature. The sensor chip has a shape of triangle cut by laser beam; the heater meander is located in the vertex of triangle. This approach simplifies the technology of the fabrication of the platform and decreases power necessary for the heating of the sensing layer up to working temperature of 400 – 600°C. It is shown that the application of such triangle shaped membranes permits a decrease in power consumption of the MEMS working at 450°C down to ~ 40 mW at continuous and down to < 1 mW at pulse heating of gas sensor with duty cycle of 1 %. Thermal response time of the microheater is of about 80 ms.