Yusuke Aoki

Evaluation of C15TCNQ Langmuir-Blodgett Ultrathin Films on Aluminum Thin Films by Attenuated Total Reflection Measurements

The attenuated total reflection (ATR) properties of C15TCNQ Langmuir-Blodgett (LB) ultrathin films deposited on the Al thin films about 20 nm thick were measured in order to evaluate the actual structure. The C15TCNQ LB ultrathin films were prepared by the vertical dipping method, using two deposition processes. The dielectric constants and the thicknesses of these deposited LB films were theoretically calculated from the ATR curves, taking into account the presence of the natural oxide layer on Al. It was considered that Z-type LB films were obtained when the deposition of each monolayer was carried out only as the substrates were withdrawn. In contrast, when monolayers were deposited during both upward and downward movements of the substrates, the resulting LB films were considered to be not perfect Y-type, but partially Z-type.

Fabrication of Surface Acoustic Wave-Semiconductor Coupled Devices Using Epitaxial Lift-Off Technology

In this paper, we report the results of a study on the fabrication process of surface acoustic wave-semiconductor coupled devices, using epitaxial lift-off (ELO) and thin-film bonding technology. In order to realize a rugged bonding interface between the semiconductor film and piezoelectric substrate, we studied the 1) optimum conditions controlling stress in GaAs films, 2) reduction of releasing time for GaAs films, 3) and enhancement of bonding force between the film and LiNbO3 substrate. The experimental results clarified that these process improvements were effective for fabricating functional devices with the AlGaAs/LiNbO3 structure.

Design on semiconductor coupled SAW convolver

This paper presents results of a design study on a semiconductor coupled surface acoustic wave (SAW) convolver in which bi-directionally propagating SAWs, on a piezoelectric substrate with a high coupling coefficient, couple with bonded semiconductor diodes through multistrips. To obtain convolution signals with a high efficiency, we adopted a diode-balanced bridge structure for the nonlinear operation. We also found that the tapping pitches of the multi-strip electrodes have robustness against operation frequency variation and temperature-dependent variation on the delay of the SAW. We verified the effectiveness of the device in. a circuit simulation and an experiment on a test circuit, which was fabricated by using an epitaxial lift-off film-bonding process.

Photoresponse on Surface Acoustic Wave Devices with Compound Semiconductor and LiNbO3 Structures

We studied the photoresponse on a surface acoustic wave (SAW) device coupled with AlGaAs film. The experimental results indicate that the transferred carriers by SAW are optically generated electrons rather than optically generated holes. The electric field due to SAW propagation reduces the recombination of the optically generated electrons and holes. We were able to observed a modulated SAW signal due to the nonlinear interaction between SAW and optically induced carriers. The photoresponse due to the interaction between SAW and optically induced carriers shows a high sensitivity for the light intensity. The main results are (1) the control of SAW by optically induced carriers, and (2) the control of the optically induced carriers by SAW. We expect that the characteristics of the photoresponse will be applicable to the fabrication of functional optical-SAW coupled devices.

Electrical Insulating and Heat-Resistive Properties of PDMS-TEOS Hybrid with Different Molar Ratio of TEOS to PDMS

The hybrids prepared from polydimethylsiloxane (PDMS) and tetraethoxysilane (TEOS) have been well known to be rubbery hybrid materials. In this report, the authors have investigated the electrical insulating and heat resistive properties of the hybrids by changing the molar ratio of TEOS to PDMS. The electrical insulating properties are evaluated by volume resistivity and AC breakdown strength at room temperature. The resistivity is about 1013 Ω · m and AC breakdown strength is about 25 kV/mm irrespective of the molar ratio. Heat-resistive properties are evaluated by the weight loss after keeping for 480 h at 200°C in air. The weight loss becomes smaller as the TEOS content increases, and it is less than 3%. It has been clarified that the hybrids have good electrical insulating and heat-resistive properties.

Electrical Treeing Characteristics in Polydimethylsiloxane-Based Organic-Inorganic Hybrid Materials

Electrical treeing characteristics of hybrid materials made from titanium alkoxide Ti(OCH2CH(C2H5)C4H9)4 and alkoxysilane-terminated polydimethylsiloxane (PDMS) in different TA/PDMS ratio was investigated. The development of AC tree of sample was mounted on a glass substrate with needle electrode was observed by CCD camera and computer. The tree inception voltage increased and tree growth speed decreased with increase in TA/PDMS ratio of the hybrid. It is suggested that the variation of crosslinking density and homogeneity of dispersion of silica clusters influenced on their tree propagation characteristic. We found that the hybrid made from the alkoxysilane-terminated PDMS and TA has good electrical insulating property compared with conventional PDMS-based hybrid materials and silicone rubber.

Electrical Insulating and Heat-Resistive Properties of Organic-Inorganic Hybrid Materials Made from Alkoxysilane-Terminated Polydimethylsiloxane

Hybrid materials made from titanium alkoxide (TA) (Ti(OCH2CH(C2H5)C4H9)4) and alkoxysilane-terminated polydimethylsiloxane (PDMS) in different TA/PDMS ratio was prepared and characterized. Gel fraction, mechanical strength, dielectric strength and thermal endurance of hybrids made from TA and alkoxysilane-terminated PDMS increased more than that of conventional hybrids made from silanol-terminated PDMS. Tensile strength, dielectric strength, and thermal endurance were improved with increase in TA/PDMS ratio. These results suggest that utilizing alkoxysilane-terminated PDMS and TA as raw material is useful for improving the electrical insulating property, thermal endurance, and mechanical property of PDMS-based hybrids.

Bonding Technology of Semiconductor Film on Piezoelectric Substrate Using Epitaxial Lift-Off Technology

In this paper, we report the results of a study on the basic problems of the mass production of epitaxial liftoff (ELO) film bonding technology. We propose a new releasing method for a large number of semiconductor films using polyimide to protect the semiconductor films. We investigated the basic process conditions and successfully released a large number of stripe shaped GaAs films. We also studied the heating method for enhancing the bonding strength between a small-sized semiconductor film and a piezoelectric substrate. We investigated the effect of migration of water molecules from the bonding interfaces using microwave and laser irradiation. We estimated the crystallinity of semiconductor films by X-ray diffraction. The results clarified that these processes were effective in improving mass productivity on the fabrication technology of surface acoustic wave (SAW)-semiconductor coupled devices.

Preparation and Characterization of Highly Heat-Resistant Organic–Inorganic Hybrid Materials Made from Two-Component Polydimethylsiloxane

Organic–inorganic hybrid materials made from polydimethylsiloxane (PDMS) have been studied as encapsulation materials for high-power devices because of their high dielectric strength, high heat resistance, and flexibility when compared to conventional elastomers. To improve the heat-resistant property, hybrid materials made from two PDMS components, PDMS terminated with silicon alkoxide Si5O4(OC2H5)12 (A-PDMS) and PDMS terminated with ethyl-acetoacetate-modified titanium alkoxide Ti(OCH2CH(C2H5)C4H9)4 (T-PDMS), were prepared. We found that the heat-resistant property of a hybrid material could be improved by adjusting the molar ratio between A-PDMS and T-PDMS. After heat treatment at 250°C for 1,000 h, the hardness and weight loss of the hybrid material made from A-PDMS and T-PDMS were under 60 degrees (on an Asker C durometer) and under 5.0%, respectively. The excellent long-term thermal stability of the hybrid material made from A-PDMS and T-PDMS can be attributed to the improved homogeneity of inorganic clusters and the decrease in unreacted functional groups in hybrids by using T-PDMS as a raw material.

Simulation Study on Semiconductor Coupled Surface Acoustic Wave Convolver through a Multi-Strip Electrodes

This paper presents results of simulation study on a semiconductor coupled surface acoustic wave (SAW) convolver, in which the propagating SAW on a highly coupling coefficient piezoelectric substrate, couples with a bonded semiconductor diodes through multi-strip electrodes. We focus our study on a relatively wide band device which is the main feature of a highly efficiency device. By using a simple analysis and circuit simulator, based on the simulation program with integrated circuit emphasis (SPICE), we clarified the effect of device parameters, such as the shape of multi-strip tapping electrodes, characteristics of diode, impedance matching condition, kinds of transmission code and electro-mechanical coupling coefficient of SAW, on the device performances. We discussed the phenomenon, which cause the degradation, focusing on the frequency domain. We also clarified the essential problems of second order effect on the wide bandwidth device, which should be solved.