This paper presents a review of silicon micromachined accelerometers and gyroscopes. Following a brief introduction to their operating principles and specifications, various device structures, fabrication, technologies, device designs, packaging, and interface electronics issues, along with the present status in the commercialization of micromachined inertial sensors, are discussed. Inertial sensors have seen a steady improvement in their performance, and today, microaccelerometers can resolve accelerations in the micro-g range, while the performance of gyroscopes has improved by a factor of 10/spl times/ every two years during the past eight years. This impressive drive to higher performance, lower cost, greater functionality, higher levels of integration, and higher volume will continue as new fabrication, circuit, and packaging techniques are developed to meet the ever increasing demand for inertial sensors.

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Micromachined inertial sensors

There are growing concerns over the environmental, climate, and health impacts caused by using non-renewable fossil fuels. The utilization of green energy, including solar and wind power, is believed to be one of the most promising alternatives to support more sustainable economic growth. In this regard, lithium-ion batteries (LIBs) can play a critically important role. To further increase the energy and power densities of LIBs, silicon anodes have been intensively explored due to their high capacity, low operation potential, environmental friendliness, and high abundance. The main challenges for the practical implementation of silicon anodes, however, are the huge volume variation during lithiation and delithiation processes and the unstable solid-electrolyte interphase (SEI) films. Recently, significant breakthroughs have been achieved utilizing advanced nanotechnologies in terms of increasing cycle life and enhancing charging rate performance due partially to the excellent mechanical properties of nanomaterials, high surface area, and fast lithium and electron transportation. Here, the most recent advance in the applications of 0D (nanoparticles), 1D (nanowires and nanotubes), and 2D (thin film) silicon nanomaterials in LIBs are summarized. The synthetic routes and electrochemical performance of these Si nanomaterials, and the underlying reaction mechanisms are systematically described.

Silicon-based Nanomaterials for Lithium-Ion Batteries - A Review

Photoplethysmography and its application in clinical physiological measurement

A strain sensor has been fabricated from a polymer nanocomposite with multiwalled carbon nanotube (MWNT) fillers. The piezoresistivity
of this nanocomposite strain sensor has been investigated based on an improved three-dimensional (3D) statistical resistor network
model incorporating the tunneling effect between the neighboring carbon nanotubes (CNTs), and a fiber reorientation model. The
numerical results agree very well with the experimental measurements. As compared with traditional strain gauges, much higher sensitivity
can be obtained in the nanocomposite sensors when the volume fraction of CNT is close to the percolation threshold. For a small
CNT volume fraction, weak nonlinear piezoresistivity is observed both experimentally and from numerical simulation. The tunneling
effect is considered to be the principal mechanism of the sensor under small strains.

Tunneling effect in a polymer/carbon nanotube nanocompositestrain sensor

Semiconductor Physics: A Summary The Hall Effect Hall Elements: Theory of Operation Hall Elements as Magnetic Sensors Magnetic-Sensitive Field-effect and Bipolar Devices Applications of Hall Magnetic Sensors Hall Devices as a Means for Characterising Semiconductor Materials

Hall effect devices

In this paper, we present the vacuum-sealed vibrating gyroscope using silicon bulk micromachining technology. The size of the device is 12×12×1.4 mm 3 . Two glass substrates hold the silicon sensing part. The sensing part is encircled with the silicon frame which forms hermetic seal with the glass substrates. From the results of initial testing, we obtain an angular rate detection sensitivity of approximately 8.9 μV/(° s −1 ), a nonlinearity of 1.25% FS and a detection resolution of approximately 0.2° s −1 at 1 Hz BW. Additionally, we show the detection characteristics of the two orthogonal components of the applied angular rates simultaneously.

Disk-shaped bulk micromachined gyroscope with vacuum sealing

We present design methodology, fabrication process and characterization of a dual-axis MEMS galvano-mirror with double gimbal structure. In the device, soft torsion beams are made of the photosensitive epoxy resin, SU-8, in order to obtain large-deflection angle for small driving power. In this paper, we present characteristics of the inner and outer mirrors for dynamic and static operation, and also test results for stability. The tilt angle of the mirror for applied static current is about 0.1°/mA. Maximum deflection angle at resonant operation was measured to be over than ±40°.

Dual-axis MEMS mirror for large deflection-angle using SU-8 soft torsion beam

Micro electro mechanical systems (MEMS) technology has developed considerably in recent years and many sensors utilizing this technology are available in the market. MEMS technology enables miniaturization, mass production, and cost reduction of many sensors. In particular, MEMS inertial sensors that include an acceleration sensor and an angular velocity sensor (gyroscope, or simply ldquogyrordquo) are the most popular devices. Applications of inertial sensors have now extended into the field of networked sensing systems. In this presentation, we will describe current MEMS inertial sensors and their applications.

MEMS inertial sensors and their applications

In this paper, we present an MEMS gyroscope with double gimbal structure. The device has inner- and outer-gimbals with independent coils (inner- and outer-coils), and the gimbals are perpendicularly supported by torsion bars. In the parallel magnetic field, the reference vibration of the inner-gimbal is introduced by electromagnetic force from the inner-coil and displacement of the outer-gimbal by the Coriolis force is detected by electromotive force at the outer-coil. The device has no critical parts such as narrow gaps or comb drivers, and it requires less accurate alignment of the magnetic field. Since the device can operate in atmospheric pressure, a hermetic seal is not required. For stable operation, the device was combined with a semi-digital control circuit. The circuit has an overtone PLL oscillator, time-shared driving/detecting logic, a kind of adaptive band pass filters. The system showed excellent performance for angular rate detection. Additionally, the characteristics of the device operating in vacuum were also examined.

Design, fabrication and operation of MEMS gimbal gyroscope☆

This paper describes the fabrication of MEMS-based electromagnetic energy harvesters for scavenging energy from the ambient vibration. The novel energy harvester is fabricated by bonding a vibrator with embedded micro-magnets and a stator with integrated microcoils. The micro-magnets are formed by using sputtering deposition of NdFeB/Ta multilayered magnetic films with a thickness of 10 µm and silicon molding techniques. High-aspect-ratio silicon micro-springs are fabricated using deep reactive ion etching to achieve large vibration amplitude. The microcoils fabricated by electroplating processes are serially connected for multiplication of the output voltages from individual magnet-coil units. The energy harvester is successfully fabricated and wire-bonded for characterization. The maximum voltage output of the energy harvester at 115 Hz is approximately 2 mV, which corresponds to a power density of 1.2 nW cm−3. The performance of the energy harvester could be greatly improved by protecting the micro-magnets from oxidation and decreasing the spacing between the vibrator layer and the stator layer.

https://iopscience.iop.org/article/10.1088/0960-1317/21/9/095014/pdf

Kazusuke Maenaka

Papers

Disk-shaped bulk micromachined gyroscope with vacuum sealing

Dual-axis MEMS mirror for large deflection-angle using SU-8 soft torsion beam

MEMS inertial sensors and their applications

Design, fabrication and operation of MEMS gimbal gyroscope☆

Fabrication of a vibration-driven electromagnetic energy harvester with integrated NdFeB/Ta multilayered micro-magnets