AVS 47th International Symposium
    MEMS Wednesday Sessions
       Session MM-WeM

Paper MM-WeM1
Microfabricated Platform for Semiconducting Metal Oxide Thin Film Gas Sensors

Wednesday, October 4, 2000, 8:20 am, Room 309

Session: Microfabricated Sensors
Presenter: D.J. Frankel, University of Maine
Authors: D.J. Frankel, University of Maine
C. Silvestre, University of Maine
G. Bernhardt, University of Maine
S.C. Moulzolf, University of Maine
N. LeCursi, University of Maine
R.J. Lad, University of Maine
Correspondent: Click to Email
A sensor platform for chemiresistive and impedance based thin film gas sensors has been developed which can be fabricated using conventional microfabrication techniques. The platform utilizes a highly polished sapphire substrate with platinum electrodes, heater element, and resistance temperature detector (RTD). The use of highly polished and well characterized sapphire substrates allows controlled growth of thin metal oxide sensing films, yielding reproducible and well-defined microstructures. Techniques have been optimized that allow for more than 400 sensing devices to be fabricated on 3" diameter sapphire substrates using liftoff technology. Delamination of metallization on the sensor platform can be problematic, particularly following high temperature annealing. Strong adhesion between the platinum electrodes and sapphire substrate is achieved with a thin Zr adhesion layer. Adhesion is such that parallel gap welding of 4 mil Pt wire can be successfully obtained with bond strengths exceeding 100 grams force. Strong bonding is achieved after fabrication and following extended anneals up to 500C. These anneals are required to stabilize the resistance of the RTD and heater elements. The platform materials exhibit stable operation after accelerated temperature cycling between room temperature and the typical sensor operation temperature of 200-400C. We have also used microfabrication techniques to fabricate sensor platforms with a variety of electrode configurations, including under and on top of the metal oxide sensing film, that explore the effect of sensor resistance measurement configuration on sensor operation while keeping substrate effects constant.