Masatoshi Oba

Low-Resonant-Frequency Micro Electret Generator for Energy Harvesting Application

A vibration-driven electret generator has been developed for energy harvesting applications. By using parylene as the spring material, a low-resonant-frequency MEMS generator is realized. Electrostatic levitation is adopted for the gap control. Large in-plane amplitude of 0.5 mm at the resonant frequency as low as 21 Hz has been achieved. We also demonstrate electret-powered operation of LED using a low-power-consumption impedance conversion circuit.

Power output enhancement of a vibration-driven electret generator for wireless sensor applications

We developed a compact vibration-driven electret generator that excelled at a power output. It succeeded in the operation of wireless sensor modules only on electricity from electret generators. This electret generator can supply enough power to operate a wireless sensor module without an external power source. It was necessary for enabling this operation to enhance the power output of the electret generator. We enhanced the power output by decreasing the parasitic capacitance. To decrease the parasitic capacitance, we fabricated a collector substrate using concave electrodes. We decreased it from 25 to 17 pF. As a result, the power output from our generator was enhanced from 40 to 100 µW considerably at an acceleration of 0.15 g (1.47 m s−2) and a resonance frequency of 30 Hz.

An RF MEMS switch for 4G Front-Ends

OMRON developed a practical single pole double throw (SPDT)-structured RF-MEMS switch for 4G Front-Ends of next generation mobile handsets. This RF-MEMS switch has not only a very low insertion loss of less than 0.25dB and a high isolation of more than 30dB up to 3GHz but also high linearity and very low harmonic generation. The switch achieves small size by using Through Silicon Via (TSV) structure. And also we demonstrate 3V driving switch by integrating a charge pump IC.

Large-Area Growth of In-Plane Oriented (1120) ZnO Films by Linear Cathode Magnetron Sputtering

(1120) textured ZnO films are good candidates for shear-mode piezoelectric devices. In the previous deposition techniques of these films, there have been two problems related to their practical application. These problems are as follows: (i) highly oriented films can be obtained only in a small area and (ii) the crystallite c-axis of in the films is radially oriented in the substrate plane. To resolve these problems, the sputtering deposition technique using a linear cathode has been proposed. The in-plane and out-of-plane orientations of the films were quantitatively determined by pole figure analysis. As a result, we have demonstrated the formation of in-plane unidirectionally oriented (1120) ZnO films over the entire area of 4-in. silicon wafers.

Micro mirror arrays for improved sensitivity of thermopile infrared sensors

This papera reports an improved method for higher sensitivity of the thermopile infrared sensors. To increase the sensitivity of thermopile infrared sensors, the thermopile infrared sensors were bonded to the micro mirror arrays (MMA) which focused the infrared radiation in the infrared absorber. As the result, 4-pair thermopiles have demonstrated 220V/W to 350V/W under the pressure of 1Pa atmospheres, thus they are 1.6 times higher sensitivity than without MMA. The fabrication method of MMA is using etching depth difference of DRIE which depends on the aspect ratio with different size mask openings and isotropic RIE.

Thermopile infrared array sensor for human detector application

This paper reports the design of thermopile infrared sensor for human detector application. Sensitivity and response time of thermopile infrared sensor element are important for human detector application. In order to fulfill the specification, we developed S-shaped structure for thermopile infrared sensor element and fabrication process of chip scale vacuum package for mass production of the thermopile infrared sensors. As the result, 140V/W sensitivity and 17msec response time of the thermopile infrared sensor element are achieved. The thermopile infrared sensor is all fabricated by CMOS processes.

Smart Bumpless Bonding for MEMS - IC Vertical Integration

In the future ubiquitous network era, it is desired that more accessible health monitoring for human and objects by mounting sensor device into portable equipment such as mobile phone and PDA. However, conventional MEMS packaging technology is becoming difficult to meet its desire. Small and package-less 3D sensing module, which consist of MEMS and IC chips bonded by surface activated bonding (SAB), and is shown in Fig.1 solves this problem. In the case of MEMS part such as accelerometer needs vacuum package, vacuum sealing is accomplished by bonding IC wafers on both sides. Therefore, conventional vacuum package is unnecessary, and high performance in small volume is realized. This paper reports ‘Bumpless bonding’ which bond sealing parts for vacuum sealing and electrodes for electrical connection simultaneously by SAB. The plasma CVD SiO2 is utilized to realize vacuum sealing as sealing material. Because flat surface SiO2 layer should be deposited on accomplished IC wafer in low temperature, besides, the SiO2 should have enough flatness level for vacuum sealing by SAB. Metal projection is formed on the electrode and connected by compressive plastic deformation and SAB. In this paper, surface duplicated 2 layer TEG is fabricated, and experimental results to demonstrate its feasibility are reported. Enough bonding strength of sealing SiO2 and electrical connection by Au compressive plastic deformation were accomplished, therefore, its feasibility was confirmed. This development is supported by FINE MEMS PROJECT of New Energy and Industrial Technology Development Organization (NEDO).

Low power wireless human detector utilizing thermopile infrared array sensor

This paper describes the low power consumption wireless human detector which can monitor wide area. We have developed the S-shaped thermopile infrared sensor element by utilizing micro-electro-mechanical-systems (MEMS) technology. The developed thermopile infrared array sensor achieved high temperature resolution and fast response time. Number of human who exists in the detection area is simply detected by the human detection process using temperature outputs from the thermopile infrared array sensor.

Bump-less Wafer Level Bonding Experiment for Vertical Integration MEMS Device

In the future ubiquitous network era, it is desired that more accessible health monitoring for human and objects by mounting sensor device into portable equipment like mobile phone and PDA. But conventional MEMS packaging technology is becoming difficult to meet its desire. But usual assemble technology will not be able to follow the next generation needs for size and cost. Now, 3D integration technology (vertical integration) is the center of next generation packaging technology.