Development of Thin-Film Based Microdevices and Process Enhancement for Making the Same
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Microdevices driven by Lead Zirconate Titanate (PbZrxTi1-xO3 or PZT) have received wide attention recently, because they could potentially outperform other MEMS devices in terms of bandwidth, energy density, and actuation strength. PZT integrated microdevice is undoubtedly promising, but its development and fabrication still remains challenging. To cope with such challenges and develop a well functional microdevice with adoption of thin-film PZT in sub-millimeter range requires thorough understand on its properties and fundamental behaviors both in theoretical and practical way. First of all, I developed and improved the microfabrication procedure of PZT thin film microsensor and microactuator. Such procedure includes modified sol-gel preparation, stable fabrication of bottom electrode with proper micro surface texture, microdevice wire bonding and packaging. Meanwhile, during the study I characterized the patterns of thin-film PZT defects. Through parametric study, the degree of bottom electrode porosity is revealed to be the most critical parameter surpassing others strongly affects the deposited thin-film PZT quality. A second parametric study is simultaneously carried out to ensure the fabrication repeatability of low porous bottom electrode. These contributions not only greatly improve the yield of thereafter lab-fabricated thin-film PZT but also provide an effective way for quick prediction of ongoing PZT fabrication yield based on the judgment of one parameter. Fabrication of satisfied thin-film PZT could be difficult, however, measuring material piezoelectric properties of just-prepared PZT could be even challenging. Although there are many currently available solutions, they are either complicated or expensive. Most important, they are not applicable for thin-film PZT application. I developed an easy, low cost, but effective method to deal with the thin film piezoelectric coefficient d33 through a mini impact hammer approach. Such method is proved to be suitable for both bulk and thin-film PZT. More practically, it can be adopted as a fast way for lab-prepared PZT quality evaluation. PZT deposition requires a Pt/Ti bi-layer bottom electrode to be annealed retaining condensed structure. The heat treatment will inevitably pull electrode to be porous. It is well known that electrode with pores can greatly affect thin-film PZT material properties. For such reason, I designed and fabricated a special nonporous bottom electrode which inherits the porous electrode surface micro texture but with pores sealed. Although due to the limited experimental results no strong evidence shows new electrode surpasses traditional one in all ways, it contains large effective electrode area by covering the pores earns it better chance to outperform porous electrode.
- Mechanical engineering