AVS 46th International Symposium
    The Science of Micro-Electro-Mechanical Systems Topical Conference Thursday Sessions
       Session MM+MI-ThM

Paper MM+MI-ThM10
Process and Fabrication of a Thin Film PZT Pressure Sensor

Thursday, October 28, 1999, 11:20 am, Room 620

Session: Processing and Integration Technology
Presenter: E. Zakar, Army Research Lab
Authors: E. Zakar, Army Research Lab
M. Dubey, Army Research Lab
B. Piekarski, Army Research Lab
J. Conrad, Army Research Lab
R. Piekarz, Army Research Lab
R. Widuta, Army Research Lab
Correspondent: Click to Email
Piezoelectric crystals or ceramics are very attractive for static and dynamic pressure sensors. One of the very promising piezoelectric materials is PZT (Lead Zirconate Titinate - 52/48). MEMS technology was applied to fabricate several static PZT pressure sensors and capacitance method was used to characterize it. Sol-gel derived PZT thin films (250 - 500 nm) were deposited on platinized (SiO@sub 2@- 1000/ Ti - 20/ Pt - 170 nm) Si substrates. Top Pt electrode was sputtered deposited on PZT films and was patterned using ion milling. The PZT films were etched using Reactive Ion Etching (RIE) and ion milling. Comparative studies (etched surface, sidewalls and electrical properties) of ion milling and RIE of PZT and oxide were also completed. The RI etch rate of PZT was studied using different electrode shield (graphite, alumina, ardel) materials with power (100 to 500 W) and pressure of HC@sub 2@ClF@sub 4@ gas plasma. The measured RI etch rate of PZT varied from 10-100 nm/min. The ion-milling rate of Pt was 33nm/min, PZT-23nm/min and Oxide-31nm/min. A unique technique of soft and hard bake of photo resists along with change in incidence angles of ion beam were used to eliminate fencing problem during ion milling. Desired slope of the etched walls was also produced using above technique. The etched surface and side walls were smooth and clean up to 2µm feature size. Four level photo-mask process was used to fabricate the pressure sensors. A low stress PECVD oxide film was deposited (at 200°C) to isolate the top and bottom electrodes. The Pt electrodes further bonded with Ti/Au leads which were patterned using wet etching (KOH + I@sub 2@). Several pressure sensors with different dimensions (300x300 and 200x200 µm@super 2@) were fabricated. The average values of measured capacitance, 1023 and 453 pF, are in excellent agreement with calculated values.