Jun Terada

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 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.

A wireless sensor-network system with a dynamically programmable sensor interface

A wireless sensor-network system has been developed that achieves a compact and flexible sensing node. Allocating most of the sensing-control block to a remote host enables miniaturization of a node, which contains necessary minimum function blocks. The sensor configuration is determined by the host to meet system needs and sent to a node as a command with a radio-frequency transmitter. The bit rate is high enough to send sensing data and receive commands. The prototype of a node occupies 22.5 cm/sup 3/ and consumes 150 mW the active mode and operates with a 2 MHz bit rate using a 315 MHz carrier frequency.

A Capacitive Sensing Scheme for Control of Movable Element with Complementary Metal-Oxide-Semiconductor Microelectoromechanical-Systems Device

In this paper, we describe a new capacitive-sensing scheme that detects the displacement of a movable structure for the control of a microelectoromechanical-systems (MEMS) device stacked on a complementary metal–oxide–semiconductor (CMOS) LSI. The problem is that the small capacitance of the air gap between the movable element and a sensor plate needs to be detected in spite of the large parasitic capacitance caused by LSI interconnections. The solution is a sensing circuit that features a shield plate and a ramp detection circuit. The shield plate separates the sensed capacitance from the parasitic capacitance. A ramp detection circuit enhances the detection sensitivity using a gradient signal generated by the parasitic capacitance. To check the effectiveness of the scheme, a sensing circuit and a MEMS variable capacitor were fabricated in a 0.6-µm CMOS process and a MEMS process. This scheme enhanced the sensitivity, which is the ratio of the output voltage to the sensed capacitance, by a factor of six. These results demonstrate that this scheme is suitable for the control of a CMOS-MEMS device.

A 4th-order local-feedforward D/A converter that prevents limit-cycle oscillation

Limit-cycle oscillation in noise-shaping D/A converters is one of serious problems because it interrupts their noise-shaping operation. We propose a new noise-shaping structure that prevents limit-cycle oscillation. We have used this structure in an audio D/A converter that we fabricated. The measured result shows that limit-cycle oscillation is prevented and noise-shaping operation is maintained even when the input data is real zero. This D/A converter achieves the S/N+THD of 101 dB.

A 1-V Cyclic A/D Converter Using FD-SOI Sample/Hold Circuits for Sensor Networks

A cyclic A/D conversion circuit technique for sensor networks has been developed using 0.2-μm CMOS/FD-SOI technology. The FD-SOI analog switches can lower the supply voltage without degrading accuracy because of their negligible body effect. The proposed A/D converter achieves operation at the supply voltage of 1 V or less and can handle a sampling frequency ranging from 8 Sps to 8 kSps with a new clocking technique.

A 2-Mb/s, UHF-band, wireless sensor node for real-time multi-point sensing

A 2-Mb/s, UHF-band wireless sensor node constructs a network capable of high-speed data collection from multiple sensing points. A relatively high data-rate of 2 Mb/s ensures TDMA-based real-time sensing in a network of a maximum of 63 sensor nodes. Using a carrier frequency in the UHF band simplifies the RF section in the node and thus saves area and power. 1-V CMOS/SOI technology integrates some of the transceiver circuit on a silicon die and further reduces node area and power. A battery-operated, prototype circuit board occupies only 6.5 cc and demonstrates wireless sensing of multiple nodes.