Principal Investigator Sang-Gook Kim
Project Website http://www-mtl.mit.edu/researchgroups/mems/docs/2007/MPDpage4.pdf
The ferromagnetic and piezoelectric properties of ceramic lead zirconate titanate (PZT) thin films have made PZT an appealing choice for micro-sensors and actuators. Significant work has been done integrating PZT with standard MEMS processes, including the development of PZT sol-gels for spin coating. Cracking is often a problem with PZT spin coating due to the brittle nature of the films coupled with the thermal strain experienced during annealing. This propensity for cracking limits the overall thickness deposited and the size out of plane features over which PZT can be reliably coated. Furthermore, spin coating requires a large volume of the expensive PZT precursor solution. We pro¬pose thermal ink-jet printing of a modified PZT sol-gel as a new method of depositing PZT films for MEMS applications. Preliminary work has shown ink jetting to be a reliable method for depositing PZT films of the correct thickness for MEMS applications and that annealed films can crystallize into the piezoelectric perovskite phase using the same thermal process developed for spin-coated PZT. The goal of this research is to develop a deposition process that will enable reliable manufacturing of high-quality PZT films with greater deposition flexibility and lower material costs than spin coating.
Thermal ink jetting technology supports a wide range of ink viscosities and solid particle contents. The ink composition can therefore be adjusted to control both the contact angle of solution with the substrate (1000Å Pt/ 200Å Ti) and the as-deposited film thickness. This flexibility allows for the deposition of films with thickness and uniformity that are acceptable for the fabrication of piezoelectric devices. Multiple layers can be deposited to attain the thickness as needed. Currently, annealed films have been prepared as thick as 0.5 µm, corresponding to an as deposited thickness of approximately 1µm. This is comparable to the current limit of standard spin-coated PZT sol-gel processed; printing of thicker films is under investigation.