A molybdenum MEMS microhotplate for high-temperature operation

This paper presents a fabrication process for high-temperature MEMS microhotplates that uses sputtered molybdenum as a conductive material. Molybdenum has a high melting point (2693 degrees C, bulk) and is simpler to deposit and pattern in larger series than platinum. Molybdenum is sensitive to oxidation above 300 degrees C, so during fabrication it is protected by PECVD silicon oxide. The electrical resistivity is linear with the temperature up to 700 degrees C at least. Molybdenum microhotplate has a higher maximum operating temperature than platinum which is demonstrated by the observation of the boiling of barium carbonate (BaCO3) microcrystals at 1360 degrees C. Annealing at 1100 degrees C is effective in extending the operating range. The molybdenum microhotplate performs far better than platinum also in terms of long-term resistance drift. The material properties of the sputtered molybdenum are studied and the overall performances of the microhotplate are tested, with regard to power consumption, temperature uniformity and dynamic behavior. (C) 2011 Elsevier B.V. All rights reserved.