Hiroki Tsuda

Aerosol Deposition on Transparent Electro-Optic Films for Optical Modulators

Complex thin oxide films with electro-optic (EO) properties are promising for use in advanced optical devices because of their large EO effect. We developed a method of aerosol deposition (AD) for fabricating EO films. The mechanism for AD is based on the solidification by impact of submicron particles onto a substrate. Since particles in AD films preserve their crystalline structure during the formation of film, epitaxial growth is not necessary for exhibiting the EO effect. Highly transparent Pb(Zr, Ti)O3films, which have acceptable transmittance loss for use as optical devices, were directly deposited on glass substrates by AD. We found the Pb(Zr, Ti)O3 film by AD produced a fairly high EO coefficient (> 150 pm/V), approximately 10 times larger than that of LiNbO3. A FabryPerot (FP) optical modulator was developed with EO films fabricated by AD. We demonstrated the modulation of optical intensity with an electrical field applied to an EO film made of ferroelectric Pb (Zr, Ti)O3. key words: film deposition method, aerosol deposition, electro-optic, optical modulator

Ultra small electro-optic field probe fabricated by aerosol deposition

We developed a microscopic electro-optic field probe by directly depositing a lead zirconate-titanate [PbZr0.3Ti0.7O3] film onto the optical fiber edge using aerosol deposition. Its fabrication process is low-cost and relatively easy because there are no complicated procedures such as fine lithography and etching. The lateral size of the film is 125µm, which is the same as the diameter of a typical single mode fiber, and the thickness is approximately 5µm. An RF electro-optic signal was successfully measured over a microstrip line. The capability for detecting GHz range fields is also shown. Because it is very tiny and thin, the developed electro-optic probe has great potential for detailed electrical characterization in the microscopic regions of high performance electronic products such as the interconnecting parts between LSI packages and printed circuit boards and spaces among different LSI chips in a package.

Thickness dependence of electrical properties of PZT films deposited on metal substrates by laser-assisted aerosol deposition

Dependence of electrical properties-dielectric, ferroelectric, and piezoelectric properties-on film thickness was studied for lead-zirconate-titanate (PZT) thick films directly deposited onto stainless-steel (SUS) substrates in actuator devices by using a carbon dioxide (CO2), laser-assisted aerosol deposition technique. Optical spectroscopic analysis data and laser irradiation experiments revealed that absorption at a given wavelength by the film increased with increasing film thickness. Dielectric constant epsiv, remanent polarization value Pr, and coercive field strength Ec of PZT films directly deposited onto a SUS-based piezoelectric actuator substrate annealed by CO2 laser irradiation at 850degC improved with increasing film thickness, and for films thicker than 25 mum, e > 800, Pr > 40 muC/cm2, and Ec < 45 kV/cm. In contrast, the displacement of the SUS-based actuator with the laser-annealed PZT thick film decreased with increasing film thickness.

Fabry-Perot optical modulator fabricated by aerosol deposition

We developed a Fabry-Perot (FP) optical modulator with electro-optic (EO) films fabricated by aerosol deposition (AD). We found the ferroelectric Pb(Zr,Ti)O3 film by AD produced a fairly high EO coefficient (>150 pm/V), approximately 10 times larger than that of LiNbO3. Since thick EO films greater than 5 μm can be deposited on a transparent electrode layer or a metallic mirror layer of the FP optical modulator by AD, the FP optical modulator can achieve low capacitance, resulting in high modulation speed. Transmittance spectra of the FP optical modulator coincided with the optical simulation spectra, which indicated that optical scattering in AD films and at the surface/boundary were very small. We demonstrated an optical intensity modulation with applied electric field to EO film of ferroelectric Pb (Zr, Ti)O3. We obtained a 4-dB modulation with 50 V for the 10-μm-thick modulator with dielectric multilayer mirror on a glass substrate.

Fabrication of (Ba0.6,Sr0.4)TiO3 Thick Films by Aerosol Deposition Method for Application to Embedded Multilayered Capacitor Structures

(Ba0.6,Sr0.4)TiO3 thick films were fabricated on Pt/Ti/SiO2/Si, stainless steel (SUS) and Cu substrates by aerosol deposition (AD) technique. The effect of substrate on physical and electrical properties of the fabricated films has been studied. The AD-formed films have an average grain size of 15.9 to 18.3 nm, substrate having a small effect on its value. Strain is affected by the substrate selection and it is smallest when Cu has been selected as the metal substrate for AD of (Ba0.6,Sr0.4)TiO3 powder, having a value of 0.00552. The leakage current of (Ba0.6,Sr0.4)TiO3 thick films deposited on Cu substrates is smaller that for films deposited on Pt/Ti/SiO2/Si and SUS substrates being less than 10-7 A/cm2 at 200 kV/cm applied electric field. The above results indicate that Cu is a good candidate for metallization in multilayered capacitor structure fabrication when AD technique is used for dielectric film formation.

Postdeposition annealing effect on (Ba0.6,Sr0.4)TiO3 thick films deposited by aerosol deposition method

The effect of thermal treatment on physical properties of (Ba0.6,Sr0.4)TiO3 (BST60) ferroelectric thick films deposited by aerosol deposition (AD) technique has been investigated by x-ray photoelectron spectroscopy (XPS) and complex impedance spectroscopy (CIS) to explain the leakage current behavior of the films. The leakage current increases when the thermal treatment temperature was increased. By XPS analysis it was found that the films are not formed entirely of BST60 phase. Carbonates of Ba or/and Sr and TiO2 coexist with the BST phase, and it is believed to play an important role in the properties of the AD-deposited BST60 thick films. CIS analysis revealed that the grain boundary region becomes less resistive with the increase in thermal treatment temperature. Also, it has been observed after comparing the electric modulus of green and thermally treated samples that the activation energy for electron-hole formation becomes smaller with the increase in thermal treatment temperature above 600 °C. Dec...

Lanthanum-Modified Lead Zirconate Titanate Electro-Optic Modulators Fabricated Using Aerosol Deposition for LSI Interconnects

We developed lanthanum-modified lead zirconate titanate (PLZT), electro-optic modulators using aerosol deposition (AD). AD of complex oxide films on Si substrates is achievable, leading to the possible integration of these modulators into semiconductor integrated circuits. Polarization was measured in PLZT optical waveguides that were 1.8 µm in width, and ferroelectric hysteresis loops were observed. Mach–Zehnder interferometer (MZI) PLZT modulators were demonstrated with 500-µm-length electrodes, and the insertion loss of the MZI modulators changed with applied electric field. Their change in insertion loss exhibited hysteresis loops, which were comparable to their ferroelectric ones. We obtained a 2-GHz optical output signal with a relevant bias voltage.

PLZT Electro-Optic Modulators on Si Substrates Using Aerosol Deposition for On-Chip Optical Interconnections

We developed lanthanum modified lead zirconate titanate, (Pb,La)(Zr,Ti)O3 (PLZT), electro-optic modulators on a Si substrate using aerosol deposition (AD) for on-chip optical interconnections. The modulator was designed as a 250 times 300 mum ring resonator with a 7 dB extinction ratio at 3 Vp-p. We observed the optical transmission of a PZT waveguide and the transmission loss was as small as 4 dB/mm.

Gigahertz-rate optical modulation on mach-zehnder plzt electro-optic modulators formed on silicon substrates by aerosol deposition

Mach-Zehnder (MZ) lanthanum-modified lead-zirconate-titanate (PLZT) electro-optic modulators were fabricated on a silicon substrate by aerosol deposition. The fabricated modulator has a reversed-ridge-waveguide structure (with a 1.8-µm-wide ridge) and electrodes for applying a voltage perpendicular to the PLZT core layer. The modulator also has an MZ interferometer structure in which the device length and the electrode length of phase shifter are 1.5mm and 500µm, respectively. Optical-characteristics measurements showed that the 2-GHz optical output signal was produced by the modulator. The optical performance proves the validity of using the modulators on silicon substrates for on-chip optical interconnects.

Optical properties of Pb(Zr,Ti)O 3 films prepared by aerosol deposition

Optical properties of Ferroelectric lead zirconate titanate [PZT, Pb(Zr,Ti)O3] films prepared on glass substrates at room temperature by aerosol deposition (AD) were investigated. The reflectance and transmittance of PZT films were measured in the wavelength range from ultraviolet to near infrared. Optical absorption of as-deposited films was found to be larger than that of the annealed films in the near infrared wavelength range. The results analyzed using optical models with the measured spectra indicate that the band gap energy of the PZT film increases with annealing.