Takashi Katsuki

A compact and high optical transmission SAW touch screen with ZnO thin-film piezoelectric transducers

A compact and high optical transmission touch screen has been developed using surface acoustic waves (SAWs) oscillated by ZnO thin-film piezoelectric transducers. It has a 98% optical transparency and a narrow frame of 1.4 mm. Therefore, it is ideally suitable for mobile devices, such as PDAs or cellular phones. Utilizing a single-phase transducer (SPT) constructed with a ZnO piezoelectric thin film sandwiched between a lower planar electrode and a comb-type electrode enabled us to reduce the ZnO film thickness to 1/20. The peculiarity of the ZnO transducer is using the local maximum of the electromechanical coupling factor with the SPT structure. It has been found that the hillocks on the lower electrode extremely affects the insertion loss and their suppression can improve the ZnO transducer quality. It is very helpful to introduce our own index, the area ratio of hillocks, to determine whether an aluminum alloy is suitable for the ZnO thin-film transducer or not. This paper describes the ZnO thin film we developed for the new SAW touch screen.

A highly reliable single-crystal silicon RF-MEMS switch using Au sub-micron particles for wafer level LTCC cap packaging

This paper presents a small packaged, reliable and low-voltage driven RF-MEMS switch for wireless communication. We developed novel fabrication process of an RF-MEMS switch using a PZT actuator without a backside cavity to realize wafer-level-packaging (WLP). We also developed organic-free WLP process using sub-micron Au particles simultaneously to contact electrically and to seal hermetically with a low temperature co-fired ceramics (LTCC) wafer as a cap on a multilevel height RF switch. As a result, we obtained a small packaged SPST switch, which is in the small size of 1.4 × 0.9 × 0.8 mm. The RF-MEMS switch operated keeping a low contact resistance (<;3 Ω) up to 1 billion cycles at a low-power condition (DC 1 mW).

Imaging optical system using a pair of replicated binary micro-Fresnel-lens arrays

An imaging optical system with a short conjugate length (6.6 mm) was designed and fabricated using a pair of replicated binary micro Fresnel lens arrays. Two aperture arrays were placed between the lens arrays to prevent crosstalk images from adjacent lenses in the array. Our imaging optical system also has an off-axis configuration to eliminate the adverse effects of the zero-diffraction order light that is inevitable with diffractive optical elements. First, binary lens arrays were fabricated on a 0.5 mm thick quartz substrate by sub-micron photolithographic and reactive ion etching techniques, and the imaging optical system was constructed from these quartz binary lens arrays. In reading experiments, that quartz lens imaging optical system exhibited an excellent modulation transfer function value of 73% for an 8 line/mm test pattern. Then, replicated binary lens arrays were fabricated on a 0.5 mm thick polycarbonate substrate by employing a photopolymerization (2P method) replication process from a Ni stamper. This Ni stamper was fabricated by electroplating a quartz lens substrate, which was the original master. Then the replicated lens imaging optical system was constructed and also exhibited a good MTF value in reading experiments.

A sticking-free and high-quality factor MEMS variable capacitor with metal-insulator-metal dots as dielectric layer

This paper describes a novel design of a MEMS variable capacitor with high operating reliability and high quality factor. Metal-Insulator-Metal (MIM) dots between a fixed electrode and a movable electrode in a variable capacitor is proposed. A Fabricated MEMS capacitor was operated one billion or more times without sticking. It demonstrated a high quality factor of 200 at 0.5 pF. It was experimentally confirmed that MIM dots effectively achieve a sticking-free and high-quality-factor MEMS variable capacitor.

Effect of frequency in the 3D integration of a PZT-actuated MEMS switch using a single crystal silicon asymmetric beam

This paper presents the effect of frequency of radio frequency microelectromechanical system (RF MEMS) 3D integration with an actual device. A piezoelectric transducer (PZT)-actuated RF MEMS switch that uses a single crystal silicon asymmetric beam was designed, fabricated, and evaluated. We successfully drove a stiff beam (with spring constant >; 2,000 N/m) despite a low voltage (<;15 V). The switch lifetime was 4 × 107 cycles at low contact resistance and more than 1 × 109 cycles for the PZT actuator. The overall insertion loss and isolation were -0.3 dB and -25 dB, respectively, up to 5GHz. The effect of frequency of 3D integration was simulated with an RF MEMS switch and a ground plane placed over it. We discovered that a 3D IC comprising a control IC and an RF MEMS switch with a distance of more than 80 μm was successfully integrated.