Piezoelectric films for MEMS applications

Piezoelectric thin films offer an attractive means of sensing and actuation in microelectromechanical systems (MEMS). Relative to other means of generating motion at the microscale, piezoelectricity scales well in terms of energy density as dimensions are reduced. As a result, there is considerable motivation for utilizing such materials in miniaturized motors, switches, valves, etc. Use of ferroelectric thin films in these applications offers the possibility of increasing the sensitivity or actuation capabilities of the devices relative to alternatives such as AlN or ZnO. However, this comes at the cost of the need to integrate more difficult materials, and the introduction of appreciable temperature dependence in the response. This paper describes some of the trade-offs associated with the use of ferroelectrics in MEMS systems. Available piezoelectric coefficients range from c_31.f∼ -1 to -20 C/m². Emphasis will be placed on the composition, orientation, and grain size dependence of the piezoelectric properties in lead zirconate titanate films.