In the fabrication of broad band optical waveguide modulators, a certain technology must be used to prepare 15-20-µm-thick Au electrodes on the SiO 2 surface covering the waveguides. A thin transition metal film is commonly inserted between the Au and SiO 2 to improve adhesive strength. The transition metal film used in this study is Ti. Here, the SiO 2 surface is precoated with Si prior to the Ti film formation, demonstrating a significant improvement in adhesive strength. The Si layer works as a barrier against oxidation of the Ti film due to the SiO 2 , Ieading to a homogenous film growth of metallic Ti.

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The CHF3 electron cyclotron resonance (ECR) plasma etched LiNbO3 (LN) surface was analyzed chemically and crystallographically to investigate the dry-etch machining process for LN crystal, which was recently needed to obtain broader-band optical modulators. The etched surface was entirely covered with amorphous-like precipitates having ~70 nm diameter. These precipitates (or a part of them) were thought to be LiF from Auger electron and x-ray photoelectron spectroscopy. The results indicated that the LiF was formed and remained on the etched surface while the Nb was almost completely removed.

Two types of LiNbO 3 (0001) single-crystal substrates (LN), a ent LN(0001) substrates that contain low and high amounts conventional LN containing .10 19 cm ؊3 OH ions, and a of OH ions and are attributed to dry annealing have been sysdehydrated LN were annealed in a dry O 2 atmosphere, and tematically investigated using atomic force microscopy (AFM) their surface morphologies were investigated using atomic within the temperature range of 400Њ-1000ЊC. The results force microscopy. For the conventional LN with more OH reveal a surface roughening in the LN with greater OH contents ions, the surface was significantly roughened in the temperwithin the lower temperature range, where an outward diffusion ature range of 600؇-800؇C, accompanied by a large outward of OH from the substrate occurs, supporting the results by diffusion of OH, and then it evolved to a steplike morphol- Koide et al. 5 Furthermore, at higher annealing temperatures, the ogy at higher temperatures. However, the dehydrated LN growth of well-regulated steps is observed for both of the LN surface changed gradually at temperatures of .700؇C to substrates. The step height has been measured to be a factor of flat terraces without any roughening process. The step n/6 (where n is an integer) of the c-axial length of LN. heights of the annealed surfaces corresponded to n/6 (where n is an integer) of the c-axis length of the LN crystal. The II. Experimental Procedure dehydrated LN substrate, along with the dry-annealing process, achieved fairly flat surfaces.Two different LN substrates, 0.5 mm thick with mechanochemically polished (0001) faces, were cut into 10 mm ϫ 15 mm plates. Fourier transform infrared spectroscopy (FTIR) I. Introductionrevealed that the one substrate contained 4.2 ϫ 10 19 cm Ϫ3 OH F ERROELECTRIC LiNbO 3 (LN) single-crystal substrates have ions (hereafter called "HOH") whereas the other had 4.6 ϫ 10 18 been widely applied in the fabrication of various optical cm Ϫ3 OH ions (hereafter called "LOH"). The LOH substrate waveguide devices, such as optical modulators. 1 Because such was supplied by Nihon Kessho Koogaku Co. (Tatebayashi, waveguides are commonly prepared by a thermal diffusion Gunma, Japan) and had been thermally dehydrated before the process of metal ions or protons, thermally induced deteripolishing process. 5 The HOH and LOH samples were enclosed oration of the substrate has been investigated to improve the in a platinum box and annealed in a tube-type furnace at 150ЊC fabrication processes and the device characteristics. The introfor 5 h and further at temperatures in the range of 400Њ-1000ЊC duction of moisture into the annealing atmosphere, for instance, for 10 h, whereas dry O 2 with a dew point of less than Ϫ70ЊC has been effective in reducing the outward diffusion of lithium was introduced into the furnace at a flow rate of 500 cm 3 /min. and in decreasing the generation of microdomains. 2,3 NozawaThe time that was required to heat the furnace from 150ЊC to and Miyazawa 4 recently reported that the growth of microthe ...

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