PZT-Driven Micromagnetic Optical Devices
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PZT-Driven Micromagnetic Optical Devices H. Takagi1, J. H. Park1, M. Mizoguchi1, K. Nishimura1, H. Uchida1, M. Lebedev2, J. Akedo2 and M. Inoue1,3 1 Toyohashi University of Technology, 1-1 Hibari-Ga-Oka, Tempaku, Toyohashi, Japan. 2 National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan 3 JST-CREST, Saitama, 332-0012, Japan
ABSTRACT A magneto-optic spatial light modulator (MOSLM) driven by electric field is presented. Using finite element method simulation, the parameters of the MOSLM are decided including the 1 µm piezoelectric lead zirconate titanate (PZT)-based layer, the 200 nm bottom electrode, and the 8V electrical applied voltage. A flat surface magneto-optical bismuth-substituted iron garnet (Bi:YIG) based film having an array-pixels structure was created by a site-selected epitaxial method on a SGGG-based substrate. In order to avoid high temperature annealing process which may damage the Bi:YIG film, the PZT film was deposited by the aerosol deposition method (ADM) on the Bi:YIG film. By stress field induced by the PZT film to the Bi:YIG film with an external magnetic field, the pixels of the device were successfully switched.
INTRODUCTION A spatial light modulator (SLM) is real-time programmable device capable of modifying amplitude, phase and polarization of optical wave front by electrical controlled signal. Various types of SLMs with pixel arrays have been intensively developed. A MOSLM has the advantages of a high switching speed, a robustness and a nonvolatility. However, because this MOSLM requires a large driving current, power consumption is also large. To overcome the disadvantage, we had developed a MOSLM with a PZT driven by electric field and external magnetic field. In the PZT-driven MOSLM, the PZT film with piezoelectric effect gives a stress to a magneto-optical Bi:YIG layer. Then, by the magnetostriction effect, the coercivity of the layer was reduced. As the result of our previous PZT-driven MOSLM, a driving current was reduced less than 10 % as compared with that of the conventional MOSLM [1]. However, the Bi:YIG layer was damaged by high temperature annealing process at 650 °C for a crystallization of the PZT film fabricated by a sol-gel method. ADM [2] enables to deposit PZT films of the polycrystalline at the room temperature. By post-annealing them at 500 °C, they become better piezoelectric properties. In this study, we deposited the PZT films by ADM. The effective structure of the PZT-driven MOSLM was also investigated using finite element simulation. Based on this simulation, we fabricated the PZT-driven MOSLM.
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Mechanism of PZT-driven MOSLM When a magnetic material is applied the stress, the magnetic field is induced. According to the reference [3], the effective magnetic filed is given by equation (1). H eff = −3
λσ Ms
(1)
where, λ, σ, and Ms are magnetostriction, stress and a saturation magnetization, respectively. The structure of the PZT-driven MOSLM consists of SGGG substrate, Bi:YIG film, Pt/Ti bottom electrode, piezo
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