Characterisation of PZT in Thin Film Bulk Acoustic Wave Resonators
- PDF / 162,016 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 115 Downloads / 234 Views
1075-J03-03
Characterisation of PZT in Thin Film Bulk Acoustic Wave Resonators Janine Conde, and Paul Muralt EPFL, Lausanne, 1015, Switzerland ABSTRACT Pb(Zr0.53, Ti0.47)O3 (PZT) thin films are potentially interesting as piezoelectric layer in bulk acoustic wave (BAW) resonators. We investigated properties and performance of {111} and {100} textured, dense films deposited by sol-gel techniques in the frequency range of 1 to 2 GHz. The resonators were fabricated on Si wafers using deep silicon etching to create a membrane structure and using platinum as top and bottom electrodes. The best response of the resonators was observed for {111} textured films at a bias voltage of -15kV/cm with values of around 10% for the coupling constant and around 50 for the quality factor. This voltage corresponds to the maximal value of the piezoelectric constant d33 and minimal value of the dielectric permittivity measured as a function of the electric field. Resonance and antiresonance frequencies were strongly influenced by a bias voltage, showing a hysteretic behaviour as expected for ferroelectrics. Both of these frequencies shifted in the same direction. As a consequence, the dc voltage can be potentially used to shift the whole band of a filter. In unipolar operation, the coupling constant could be varied from 6 to 10 %. Materials parameters were extracted from the admittance as a function of frequency. Dielectric, piezoelectric and elastic properties of textured PZT films are reported and compared to direct (low frequency) measurements and to literature values. It was found that PZT thin films have lower stiffness than the one of PZT bulk ceramics and it was observed that {111}-textured films are stiffer than {100}-textured films. INTRODUCTION The high performance of bulk acoustic wave (BAW) filters in mobile communication applications ensures great interest in these devices and their active piezoelectric material. When comparing with surface acoustic wave (SAW) filters, BAW filters offer superior power handling, smaller size, higher application frequencies [1] and easier system-on-chip integration [2], or even above IC integration [3]. Standard materials used as the piezoelectric active layer in thin film bulk acoustic resonators (TFBAR) are AlN and ZnO. Both exhibit high quality factors but relatively low electromechanical coupling coefficients, resulting in small filter bandwidths. The Pb(Zr, Ti)O3 (PZT) solid solution system has high coupling coefficients and is thus being studied as a candidate for high frequency broadband filter applications [4]–[8]. The drawback of PZT, in contrast to AlN and ZnO, is the observed high acoustical attenuation of the material; to date PZT in BAW resonators have too low quality factors. This acoustical attenuation or damping and its dependence on frequency have been discussed for PZT ceramics [9]. In this paper, the fabrication of thin film bulk acoustic resonators based on PZT shall be described and the relevant properties of the piezoelectric films shall be characterised. The influence of
Data Loading...
