Shiuan Huei Lin

Phenanthrenequinone-doped poly(methyl methacrylate) photopolymer bulk for volume holographic data storage

We present the design and fabrication of a phenanthrenequinone-doped poly(methyl methacrylate) photopolymer material. Large blocks of samples were made, and the material showed negligible shrinkage after optical exposures. We recorded and reconstructed 250 holograms at a single spot, using a 1-cm(3) block.

Experimental characterization of phenanthrenequinone-doped poly(methyl methacrylate) photopolymer for volume holographic storage

We present an experimental study on the photopolymer poly- (methyl methacrylate) doped with phenathrenequinone molecules. Mate- rial characteristics for holographic data storage, including optical charac- teristics, scattering effect, relation between diffraction efficiency and number of holograms, and exposure schedule for multiple storage, are investigated. An experimental demonstration of multiple storage of digital data pages in a polymer cube is presented.

Analyses on physical mechanism of holographic recording in phenanthrenequinone-doped poly(methyl methacrylate) hybrid materials

The photoproducts in phenanthrenequinone (PQ)-dissolved methyl methacrylate (MMA) liquid samples and PQ-doped poly(methyl methacrylate) (PQ/PMMA) solid photopolymer samples have been ana- lyzed by various chemical measurements. A mechanism for holographic recording in our PQ/PMMA photopolymer is proposed. By UV-VIS trans- mission and photoluminescence spectral measurements, we find that under light exposure the molecular structure of PQ is transformed to be less conjugated. The measured results of mass spectra, Fourier trans- form infrared spectra, NMR spectra, and gel permeation chromatograph analyses provide some evidence for recognizing the molecular structure of the photoproducts in our PQ/PMMA photopolymers. The results show that under light exposure the PQ and MMA form new molecules, mainly an adduct of one PQ molecule with one MMA molecule. In addition, PQ also reacts as a photoinitiator to form PMMA oligomers in our samples. The structure change of the PQ molecule induces a strong change of the refractive index in the material. It provides a mechanism to record a phase hologram in our PQ/PMMA photopolymer. Holographic recordings in the samples are demonstrated, and the dynamic range of the sample is investigated.

A Novel Approach of Fabricating Germanium Nanocrystals for Nonvolatile Memory Application

A nonvolatile memory device embedded with Ge nanocrystal dots is fabricated by the thermal oxidation of Si 0 . 8 Ge 0 . 2 combined with a rapid thermal annealing at 950°C in N 2 gas. The tunnel oxide in the nonvolatile memory is controlled to be 4.5 nm thick and embedded with 5.5 nm Ge nanocrystals. A low operating voltage, 5 V, is implemented and a significant threshold-voltage shift, 0.42 V, is observed. When the electrons are trapped in the Ge nanocrystals, the effect of Coulomb blockade prevents the injection and storage of more electrons and decreases the leakage current. Also, the retention characteristics are tested to be robust.

Light-induced properties of Ru-doped Bi12TiO20 crystals

Absorption, light-induced absorption, photoconductivity and dark conductivity measurements are performed on Bi12TiO20 (BTO) crystals doped with different concentrations of ruthenium. It is found that a higher ruthenium addition shifts the optical absorption to the near-IR spectral region in comparison with non-doped BTO crystals and the absorption changes increase with increasing Ru content. The dark conductivity follows the Arrhenius law with an activation energy of 0.89 eV. From the measured light-induced absorption and nonlinear photoconductivity the participation of a shallow level in the charge transport mechanism in Ru-doped BTO crystals is suggested. Highly Ru-doped BTO samples possess infrared sensitivity and holographic gratings are successfully recorded at 790 and 825 nm, respectively.

Experimental observation of the slowdown of optical beams by a volume-index grating in a photorefractive LiNbO3 crystal

We investigate the group velocity of light in a one-dimensional volume-index grating inside a photorefractive LiNbO(3) crystal. The slowdown of the group electromagnetic propagation is observed experimentally by tuning of the wave number of the optical beam close to the outside edge of the forbidden bandgap. We obtain a large group index of up to 7.5 in a 3.5-cm crystal sample. The group index is compared with the result of a theoretical derivation. The results are presented and discussed.

Effect of ruthenium doping on the optical and photorefractive properties of Bi12TiO20 single crystals

Bi12TiO20 (BTO) single crystals nominally pure and doped with ruthenium are grown by top-seeded solution growth method. The effect of ruthenium concentration on optical and photorefractive properties is studied. Strong influence of doping on these properties is observed. It is shown that optical transmission of crystal samples with higher ruthenium content is shifted to the near IR spectral region, while the absorption coefficient is considerably increased. The optical activity of Ru doped crystals is further reduced in comparison with undoped BTO. Photochromic effect is observed in strongly doped crystal. Photorefractive properties are experimentally investigated using two-beam coupling. Response time and diffraction efficiency are changed with ruthenium content. � 2002 Elsevier Science B.V. All rights reserved.

DOPED POLY(METHYL METHACRYLATE) PHOTOPOLYMERS FOR HOLOGRAPHIC DATA STORAGE

In this paper, we report our investigations on thick holographic recording material of the phenanthrenequinone doped poly(methyl methacrylate) (PQ:PMMA) photopolymer. The design strategy and fabrication technique for making thick polymer samples with negligible shrinkage and good optical quality are presented. The physical mechanism for holographic recording in PQ:PMMA material is described, and methods for improving are proposed. Based on these methods, photopolymer samples with different compositions are fabricated and experimentally characterized. The results show that by modifying compositions, the material sensitivity and dynamic range for volume holographic recording have been improved.

Comparison of the recording dynamics of phenanthrenequinone-doped poly(methyl methacrylate) materials

A comparative analysis of phenanthrenequinone-doped poly(methyl methacrylate) materials fabricated at California Institute of Technology and National Chiao Tung University is performed in order to understand the differences exhibited in their recording and baking dynamics.

Pattern-Dependent Copper Microcorrosion from CMP

After chemical mechanical planarization (CMP) processes, copper microcorrosion was found in a specific pattern, which consisted of two sides of small trench islands connected by a long underlayer metal line. The depth of the copper recess was strongly dependent on the length of the underlayer metal line as well as the size of the trench islands. This phenomenon was different from typical photocorrosion; it was suggested to be induced by the additional electrochemical potential from the connection of the trench islands. Auger analysis proves that higher copper oxidation rate occurred on the specific pattern compared to those without connection. In addition, the pattern-dependent microcorrosion was identified by blocking the connection of the trench islands. A proposed model was given to account for the enhanced copper corrosion from the specific patterns during CMP.