Osamu Nakao

Photorefractive effect of BaTiO 3 single crystals grown in inert atmospheres

BaTiO3 single crystals were grown by the top-seeded solution growth technique in inert atmospheres of nitrogen gas and of argon gas and in air. They were then annealed at 1200°C in air. These crystals, prepared from a mixture of 99.999% pure BaCO3 powder and 99.99% pure TiO2 powder, contained virtually equal amounts of transition-metal impurities (Fe, Co, Ni, etc.). The maximum beam-coupling gain of the two crystals grown in inert atmospheres was 6 cm−1, and that of the crystal grown in air was 3 cm−1; the sign of the beam-coupling gain of the crystals was positive. We found that the crystals grown in inert atmospheres exhibited high gains without having been doped with any transition-metal elements.

Influence of Poling Conditions on Properties of BaTiO3 Single Crystal

A BaTiO3 single crystal, whose dimensions were 3.9×3.9×3.6 mm3, was mechanically and electrically poled to remove its 90° and 180° ferroelectric domain walls, respectively. After mechanical poling, four-step electrical poling was applied to the crystal, which did not include 90° domain walls, with the aim of removing the 180° domains gradually. In each of these steps, the dielectric constant of the crystal was measured using an impedance analyzer. Prior to the electrical poling, the dielectric constant in the [001] direction was 137 at 100 kHz (unclamped) and 133 at 10 MHz (clamped). By applying four-step poling, these values varied gradually with the progress of poling, and became 130 and 58, respectively, after the final step, i.e., in a single-domain state.

Influence of 180° domains on ferroelectric properties of BaTiO3 single crystal

Mechanical poling was applied to a BaTiO3 single crystal grown by the top‐seeded solution growth (TSSG) method to remove its 90° domain walls, and then four‐step electrical poling was applied to rearrange the 180° domain configuration. In each of these steps, the dielectric constant (from 50 kHz to 10 MHz) was measured by using an impedance analyzer, and the 180° domains were observed by the etching method. The dielectric spectra were confirmed to vary with rearrangement in 180° domain configuration. Dielectric constant ec in the 〈001〉 direction was 130 at 100 kHz and 58 at 10 MHz. Dielectric constant ea in the 〈100〉 direction was 4700 at 100 kHz and 1900 at 10 MHz.

Enhanced two‐wave mixing in a photorefractive waveguide having a periodically reversed c‐axis by electrical poling technique

Propagation angle sensitivity of two‐wave mixing is observed in a photorefractive BaTiO3 waveguide having a periodically reversed c‐axis. The periodic reversal of the c‐axis is realized for the first time by adopting an electrical poling technique in which the polarization of the applied electric field is cyclically reversed along the waveguide axis.

Dielectric and photorefractive dependence on 180° domain structure of BaTiO3 single crystal

Abstract Dielectric and photorefractive dependence on 180° domain was investigated by employing the BaTiO3 single crystal. Dielectric constant depends on the volume ratio between antiparalell domains. When the antiparalell domains were equal in volume, ϵ c and ϵ a were 130 and 2600 respectively. In the single-domain state, ϵ cunclamped and ϵ cclamped were 141 and 65, ϵ aunclamped and ϵ aclamped were 4300 and 2000, respectively.

Ultra-fine trench circuit on polymer film

As electric equipment decreases in size and height and increases in functionalities from day to day, high-density, fine circuits are required more than ever before. According to ITRS, its requirement for trace width/spacing of a printed circuit board will reach less than 10 μm/10 μm in 2014. However, it is difficult to fabricate such fine circuits on an organic substrate using current processes such as a semiadditive process and a subtractive process. So several new processes are suggested for fabricating such fine circuits [1]. This paper focuses on the first demonstration of an ultrafine circuit with a new process, both of which we developed. The circuit fabricated with our new process has trench-shaped traces buried in the insulating layer. The aspect ratio of the trace cross-section is more than 1, namely, the thickness of the trace is greater than the width. The minimum width of the conductor is 2 μm, the minimum spacing between the conductors is 2 μm and the maximum aspect ratio is more than 3. The fabrication process consists of trench-forming on a surface of polymer film and trench-filling by copper plating. Owing to a buried conductor structure, the adhesion of the trace to the polymer film is fairly good without roughening of the surface. No delamination occurred while bending of film and even after a thermal shock test. The adhesion and electrical continuity of the trace was verified by a 3-cycle-reflow test performed after the circuit board was let stand in 85 °C, 85 %Rh for 168 hours, and a thermal shock test in temperatures between -65 °C and 125 °C for 1000 cycles. No visual failure was observed, and the variation of continuity resistance was small. The surface smoothness of the trace is an advantage of this trench circuit for high-speed signal transmission. The trench circuit also shows good insulation and high resistance to electrochemical migration due to a buried trace structure. The insulation resistance between the 5 μm-wide comb traces spaced every 5 μm kept higher than 10M ohms for 336 hours in an unsaturated pressure cooker bias test under the conditions of 135 °C, 85 %Rh, 5V. Furthermore, micro via holes were able to be formed in the insulation layer simultaneously with the trench circuit. Manufacturing of multi-layer test vehicle with this trench circuit and via is finishing.

Polyimide Multi-Layer Substrate for High-Density Semiconductor Package

We have developed a polyimide multi-layer substrate for semiconductor package. Interstitial via holes filled with conductive paste make the electrical connection in any layers in the multi-layer substrate to realize high-density wiring. The substrate shows reliable resistance to moisture and heat. Use of polyimide film make the substrate considerable thin compared to the conventional method using glass-epoxy. The present multi-layer substrate can be applied to a promising interposer for high-density semiconductor such as multi-chip module and stacked chip.Copyright

Influence of recrystallization on the outgassing characteristics of copper

Disk specimens were prepared from high‐purity copper and oxygen‐free copper, which had a residual resistance ratio (RRR; p298 K/p4.2K) of 5450 and 207, respectively, and thermal desorption spectroscopy (TDS) measurement was applied for evaluating outgassing characteristics of those. For these types of pure copper, outgassing was encouraged by primary and secondary recrystallization. Particularly, the TDS spectra of H2, CO, CH4 and CO2, obtained from an as‐rolled specimen of the high‐purity copper, exhibited sharp peaks at the primary recrystallization stage. The outgassing characteristics of these pure copper depended on their recrystallized textures, so the amount of outgassing became lower with growing of recrystallized grains. With the high‐purity copper, whose recrystallized grains were grown even by low‐temperature annealing, secondary recrystallization progressed more rapidly than that with the oxygen‐free copper.

Ultrathin WLP Die Embedded Polyimide Multi-Layer Wiring Board

We have developed an ultrathin IC-embedded polyimide multi-layer wiring board utilizing a wafer level packaging (WLP) technology. The IC die is wafer level packaged with no solder bump (i.e. just copper land), thinned less than 100 micron and then sandwiched between multi-layer printed wiring boards composed of thin polyimide films with the thickness of several tens of microns used in standard flex boards. Therefore, the realized embedded board has a very thin structure, e.g. the thickness of a 4 layers board with 1 die embedded is 220 micron. For the electrical connection between circuit layers including redistribution layer of the embedded die, the means employed in our standard wiring board process is applied. The electrical connection is made by the conductive paste, which consists of several kinds of metal filler and resin adhesive and makes alloy between copper of circuit layer thorough pressing and heating processes. The alloying feature of the paste assures the robustness of the connection. The re...