Tomomi Sakata

Reflection-type 2×2 optical waveguide switch using the Goos–Hänchen shift effect

We have designed a structure for a 2×2 silica-based optical waveguide switch that is based on a thermocapillarity effect. This switch can use the reflection walls on both sides of the slit, because the Goos–Hanchen shift effect was taken into account when the structure of the waveguides and the slit was designed. This switch can provide a cross/bar function through a single element, and the measured reflection losses in the reflection walls on both sides of the slit were consistent. The loss was comparable to the insertion loss of a Mach–Zender-interferometer-type thermo-optic switch.

Improvement of switching time in a thermocapillarity optical switch

A switching time of 6 ms is achieved in a thermocapillarity switch by lowering the viscosity of the refractive-index-matching oil and improving the switch design. Further improvements would result in sub-ms switching time in this switch.

128×128 three-dimensional MEMS optical switch module with simultaneous optical path connection for optical cross-connect systems

A 128×128 three-dimensional MEMS optical switch module and a switching-control algorithm for high-speed connection and optical power stabilization are described. A prototype switch module enables the simultaneous switching of all optical paths. The insertion loss is less than 4.6 dB and is 2.3 dB on average. The switching time is less than 38 ms and is 8 ms on average. We confirmed that the maximum optical power can be obtained and optical power stabilization control is possible. The results confirm that the module is suitable for practical use in optical cross-connect systems.

Monolithic Integration Fabrication Process of Thermoelectric and Vibrational Devices for Microelectromechanical System Power Generator

This paper describes a fabrication process to integrate different types of energy-converting microelectromechanical system (MEMS) devices for a power generator. MEMS structures and a fabrication process for the monolithic integration are proposed for the purpose of accumulating small amounts of energy from various surrounding environments. For the MEMS power generator, thermocouples and movable plates are simultaneously fabricated in thick-film formation processes with deep reactive ion etching of silicon and gold electroplating. The fabricated thermoelectric devices of gold and silicon produced voltages in accordance with the temperature difference at the thermocouples. The vibrational devices with gold movable plates resonated with external vibrations. These results confirm that the monolithic integration process of MEMS devices can be established for harvesting thermal and vibrational energies from their surroundings.

Novel Structure and Fabrication Process for Integrated RF Microelectromechanical-System Technology

This paper describes a novel structure and fabrication process for the integration of several types of RF microelectromechanical-system (MEMS) device, such as switches and varactors having different structures. It also describes an encapsulation technique suitable for the integrated devices to protect movable parts during packaging. An adaptable multilayer structure and its fabrication process, which includes planarization with photosensitive polyimide, are proposed for integration. A capsule structure fabricated using spin-coating film transfer and hot-pressing technology is also proposed for protection. Several types of RF MEMS device were simultaneously fabricated on the same substrate using these techniques. The results confirm that these techniques will pave the way for the development of single-chip RF transceivers with integrated RF MEMS devices.

A Fingerprint Sensor with Impedance Sensing for Fraud Detection

A fingerprint sensor that integrates fraud detection and fingerprint sensing to prevent spoofing with a fake (artificial) finger is presented. Fingerprint identification using capacitive fingerprint sensing provides small user-authentication systems. For systems that need a higher level of security, fraud detection, which determines whether the sensed finger is alive or not, is necessary. Integrating fraud detection capability into a capacitive sensor is important because attempted fraud has to be detected at the same time that the fingerprint is captured. Various methods that use information about a finger, such as its electrical characteristics, optical characteristics or elastic characteristics, have been tried. Impedance-sensing is suitable from the viewpoint of using electrical signals. An impedance-sensing circuit should not increase the chip size nor degrade the quality of the captured fingerprint image. To meet these requirements, we propose an impedance-sensing scheme built into a capacitive sensor and implemented as a circuit and electrode without changing the chip size.

Novel MEMS power generator with integrated thermoelectric and vibrational devices

This paper describes a novel concept of an integrated power generator chip that utilizes environmental temperature differences and vibrations as power sources. In the concept, thermoelectric devices produce voltage by the Seebeck effect and vibrational devices produce electrostatic energy from the external kinetic energy of vibration. A monolithic fabrication process for these microelectromechanical systems (MEMS) devices is proposed based on the seamless integration technology (SeaiT) consisting of thick-film forming processes with deep reactive ion etching (DRIE) of Si, electroplating of gold and ashing of a sacrificial layer. The fabricated thermoelectric devices generated its voltage outputs under temperature difference. The vibrational devices were also evaluated by applying an ac voltage which showed its resonant frequency characteristics. The integration of the different types of power generation paves the way for utilizing small amounts of energy from human and environmental sources.

Electrically separated two-axis MEMS mirror array module for wavelength selective switches

A novel two-axis MEMS mirror array module for wavelength selective switches feature a new electrode structure that reduces electrical interference between adjacent channels. The fabricated 50-channel mirror module has good characteristics satisfying system requirements.

Surface Cleaning of Gold Structure by Annealing during Fabrication of Microelectromechanical System Devices

We describe a technique for cleaning a gold surface using a dry process during the fabrication of microelectromechanical system (MEMS) devices. After exposure to oxygen plasma for ashing of the organic contaminants or etching of a sacrificial-layer film, the gold surface is oxidized. On such an oxidized surface, there are different incubation periods at different places, which give rise to nonuniform thickness in electroplating as well as in electrodeposition. A surface analysis by X-ray photoelectron spectroscopy (XPS) revealed that annealing at a temperature of over 260 °C causes oxygen to desorb from the gold oxide. The application of this cleaning technique before electroplating or electrodeposition leads to uniform growth.

Impedance-Sensing Circuit Techniques for Integration of a Fraud Detection Function Into a Capacitive Fingerprint Sensor

This paper describes techniques for an impedance-sensing circuit integrated into a capacitive fingerprint sensor to prevent spoofing with a fake finger. We have reported a sensor chip with an embedded impedance-sensing function. We proposed an impedance-sensing circuit that features current-to-voltage con- version using a unity gain buffer. Here, the design of the sensing circuit is discussed. The detectable impedance range and the sensitivity are analyzed within the impedance range for various human fingers. A test chip with the proposed circuit was fabricated using 0.5-μm CMOS/sensor processes. The results confirm that the difference in impedance between a real finger and a fake finger is detected without any degradation of the original characteristics of the fingerprint sensor chip.