Fabrication of Ferroelectric Nanocapacitors by Electron-beam Projection Patterning

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A projection lithography technique of electron beam was applied to the fabrication of ferroelectric nanocapacitors to increase throughput. First of all, we tried to fabricate stencil masks. The stencil mask with square holes of 300x300 nm^2 was successfully prepared by using Ti foils with a thickness of 2 μm and etching them by FIB. Well-collimated electron beam was necessary to prevent the broadening pattern size. The distance of 10 μm between the mask and the sample was optimum for preventing undesirable exposure by secondary electrons from the mask. Finally, fine 400x400 nm^2-sized PZT nanocapacitors with self-aligned top Pt electrodes were successfully fabricated by the electron-beam-projection-lithography.Parasitic capacitances attended in the measurement of hysteresis properties of ferroelectric microcapacitors were estimated. A scanning probe microscope with a conductive cantilever was used for contacting to various sized PZT capacitors. A parasitic capacitance on condition the … More cantilever was lifted up by 40 μm from the contact point was estimated to be 0.88 pF. From the capacitor area dependence of the hysteresis slopes, the increase in parasitic capacitance by bringing the cantilever near to substrates for contact was estimated to be 0.061 pF.In the second year, we tried to fabricated ferroelectric photonic crystals. Ferroelectric photonic crystals consisted of a PLZT matrix and 800 nm-pitch air-holes with a diameter of 560 nm were successfully fabricated by the electron-beam-induced patterning process. Hexagonal holes inscribed to the circles with a diameter of 400 nm in a precursor matrix changed to circular holes with a diameter of 560 nm after heat-treatment due to shrinkage of the matrix. The optical properties of CSD-derived PLZT films were also evaluated. The PLZT films showed the refractive index of 2.3 and the Kerr constant of 0.4x10^<-16> m^2/V^2. Therefore, it is expected that an applied voltage of 9.7 V to 1 μm-thick PLZT photonic crystals induces 1%-decrease in refractive index and 40^o-swinging of light with a wavelength of 1.55 μm. Less