Taking piezoelectric microsystems from the laboratory to production

Abstract

Reliable integration of piezoelectric thin films into silicon-based microsystems on an industrial scale is a key enabling technology for a wide range of future products. However, current knowledge in the field is mostly limited to the conditions and scale of academic laboratories. Thus, knowledge on performance, reliability and reproducibility of the films and methods at industrial level is scarce. The present study intends to contribute to the development of reliable technology for integration of piezoelectric thin films into MEMS on an industrial scale. A test wafer design that contained more than 500 multimorph cantilevers, bridges and membranes in the size range between 50 and 1,500 μm was developed. The active piezoelectric material was a ∼2 μm thin film of lead zirconate titanate (PZT) deposited by a state-of-the-art chemical solution deposition (CSD) procedure. Automated measurements of C(V) and dielectric dissipation factor at 1 kHz were made on more than 200 devices at various locations across the wafer surface. The obtained standard deviations were 4.5 and 11% for the permittivity and dissipation factor, respectively. Values for the transverse piezoelectric charge coefficient, e _31,f, of up to −15.1 C/m² were observed. Fatigue tests with a 5 kHz signal applied to a typical cantilever at ± 25 V led to less than 10% reduction of the remanent polarisation after 2 × 10⁷ bipolar cycles. Cantilever out-of-plane deflection at zero field measured after poling was less than 1.1% for a typical 800 μm cantilever.