鋯鈦酸鉛(PZT)壓電厚膜在雷射激發產生的壓電及焦電現象

Abstract

Recently Prof. Shih’s group has developed a piezoelectric-nonpiezoelectric bilayer structure that can be used as a sensor for small molecules and cells as well as a finger to probe elastic properties of soft tissues. The same structure can also generate voltage when it is deformed by a mechanical force. In this thesis, I describe the generation of voltage by applying a laser beam to the bilayer structure. It is hypothesized that the laser can heat the sample and the differential shrinkage of piezoelectric and nonpiezoelectric layers can result in the stress of the piezoelectric layer causing charge generation. This type of device will have tremendous application potential in converting heat into electricity The induced voltage comes from two possible mechanisms. First, the laser heats up the PZT layer and the Ti layer and the difference in thermal expansion coefficient causes the cantilever to bend. Another possible mechanism is the pyroelectric effect. As the PZT is heated, the polarization changes resulting in the generation of induced voltage. In order to investigate whether the signal is due to the piezoelectricity effect, we examined the PZT layer only and removed the Ni electrodes on both sides of PZT layer. We then sputtered a thin Au layer as the electrodes on both sides and focused the laser beam on the new sample. We found only a few mV of induced voltage, much smaller than that obtained with the Ni electrodes. However, due to the similarity of thermal expansion coefficient of Ni and Au, and the lower reflectivity of Ni than Au, both pyroelectric effect and piezoelectric effect are possible mechanism for the observed behavior. More future study is needed to reach a clear conclusion about the mechanism. On the other hand, for the PZT layer with Ni electrodes bonded to a Ti layer, the mechanism is clearly piezoelectric.