| Summary: | 博士 === 國立臺灣大學 === 物理研究所 === 100 === In this thesis, we first reported the investigation of polarization properties of piezoelectric material due to electric field and laser heating followed by the fabrication of optoelectronic devices based on those properties. It is believed that our studies shown here may open up a new route for the application of ferroelectric materials.
1.Direct observation of two-step polarization reversal by an opposite field in a substrate-free piezoelectric thin sheet
The domain switching behavior of a substrate-free lead magnesium niobate-lead titanate thin sheet by an opposite electric field (E) was examined by piezoresponse force microscopy. It is shown that the polarization reversal process involved two steps. First the polarization switched from the initial normal direction to an in-plane direction at -E < 5 kV/cm. Second, at -E > 5 kV/cm, the polarization was further switched from the in-plane direction to the opposite field direction. The preference of the in-plane polarization at -5 kV/cm was attributed to the thin-sheet geometry, which also manifested itself as a maximum in dielectric constant at the same field.
2.Voltage generation from piezoelectric-titanium unimorph cantilever by laser heating
Converting ambient thermal energy into electricity is of great interest in harvesting energy from the environment. Piezoelectric unimorph cantilevers (PUC) have previously been shown to be an effective biosensor and a tool for elasticity mapping. Here we show that PUC can be efficiently used to convert heat to electricity. By combining pyroelectric and piezoelectric feature, PZT-Ti bi-layer cantilever showed an enhanced induced voltage under laser heating, comparing to that of PZT layer alone. This type of device provides an efficient way for converting heat energy into electricity.
3.Highly sensitive graphene-PZT optothermal field effect transistors
We have developed a new type of pyroelectric field effect transistor (FET) based on a graphene-lead zirconate titanate (PZT) system. Under the incidence of a laser beam, the transconductance of FET can be varied by optothermal gating. The drain current can be increased or decreased by the laser light depending on the direction of the polarization of the PZT substrate. The drain current sensitivity of the optothermal FET can reach up to 360 nA/mW at a drain field of 6.7 kV/m which is 3 orders of magnitude larger than the pyroelectric current sensitivity and more than 5 orders of magnitude higher than that of the photogating transistors based on carbon nanotube on SiO2/Si substrate. Due to its high optical transparency and conductance graphene is an excellent component for the pyroelectric FET.
4.Single ZnO nanowire-PZT optothermal field effect transistors
A new type of pyroelectric field effect transistor (FET) based on a composite consisting of single zinc oxide nanowire and lead zirconate titanate (ZnO NW-PZT) has been developed. Under infrared (IR) laser illumination, the transconductance can be modulated by optothermal gating. The drain current can be increased or decreased as operated by IR illumination depending on the polarization orientation of the PZT substrate. Furthermore, by combining the photocurrent feature in the UV range and the optothermal gating effect in IR range, the wide range spectrum response of the tunable current modulated by light based on single ZnO NW-PZT transistors opens up a new route for the development of nanoscale optoelectronic devices.
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