Benedetto Vigna

Optical detection of the Coriolis force on a silicon micromachined gyroscope

In this paper, we report on the optical characterization of a micromachined gyroscope prototype for automotive applications, by means of feedback interferometry. In order to directly detect the rotation-induced Coriolis force, we have developed a compact and stable interferometric setup, which has been positioned inside a small vacuum bell, mounted on a rotating table. By this setup, which has a noise limit of the order of 10/sup -11/ m/(Hz)/sup 1/2/, we have measured the gyro responsivity curve, demonstrating the feasibility of the optical interferometric detection of the in-plane response of a MEMS sensor. In addition, we have carried out the full mechanical characterization of the device at different pressures, and we have performed the matching of the gyro resonance frequencies by the interferometric monitoring. Our gyro had a resonance frequency of 3986 Hz for both axes after tuning; at a pressure of 7 10/sup -2/ torr, the quality factor were Q=18000 for the driving axis and Q=1800 for the sensing axis, while the measured responsivity was 7 10/sup -10/ m/(/spl deg//s). The optical characterization represents an important feedback to the designer and is especially powerful in the case of prototypes for which the on-board electronics is not yet available.

Tri-axial MEMS gyroscopes and Six Degree-Of-Freedom Motion Sensors

Only six years passed since the dawn of the Motion Sensors Era in the Consumer market and now the world of MEMS Motion Sensors is completely different. Till end of first Half of 2010, when STMicroelectronics did a bold step in the production of MEMS gyroscopes, accelerometers were the most pervasive motion sensor, but today also gyroscopes are widely spread in the consumer market and known to the wide public. Combinations of these two inertial products, also known as Six Degree-Of-Freedom Motion Sensors, are starting to appear in the market and most likely they will coexist with standalone accelerometers and gyroscopes, depending on customer needs in terms of compactness and performances. This paper reports the details of an innovative tri-axis silicon MEMS vibratory gyroscope that fulfills the pressing market requirements for low power consumption, small size, slim requirements, high performances and low cost, and it addresses also the recent trends of the Six Degree-Of-Freedom Combos. More intuitive user interface has been the key application driving the adoption of the Motion Sensors in the Mobile Phones and Remote Controllers, Personal Computers and Tablets, Games and Portable Multimedia Players. Image Stabilization, Context Awareness, Location Based Services and Remote Monitoring are the new emerging applications that will continue to drive the adoption of Motion Sensors in the market segments mentioned above as well in new ones, still unknown to most of the people.

IF MEMS filters for mobile communication

For the past few years, the mobile phone market has been facing fast growth. However, the first generations of mobile telecommunications were based on several different standards over the world, and even at the time major operators negotiate for the third generation licenses, it seems UMTS, CDMA2000 and TD-SCDMA cannot achieve one single standard. A great challenge would be to develop flexible, re-configurable mobile phone handsets that could switch from one standard to another. To do so, MEMS technology is expected as a promising solution to provide tiny, low-consumption tunable components. Moreover, enhancing MEMS technologies to be compatible with IC processing, a novel architecture can be used for a MEMS-based transceiver that could reach the ultimate goal of a fully-integrated single-chip system. Indeed, it has been recently demonstrated that every off-chip, bulky, and expensive passive component present in a typical superheterodyne transceiver front-end could be advantageously replaced by an RF-MEMS counterpart. For example, micro-mechanical resonators could avoid the use of ceramic, SAW, and quartz off-chip resonators to allow low-loss filtering, mixing and carrier generation. But that kind of micro-scale resonators requires high quality factor and temperature stability to achieve highly selective filtering and low phase-noise frequency references. So, to demonstrate this ability, resonators and filters with center frequency up to 300 MHz were designed, and for their fabrication, two processes have been undertaken: an epitaxial thick-film polysilicon industrial technology and a thin-film polysilicon-based technology made compatible with a CMOS-SOI technology.

Motion MEMS and Sensors, Today and Tomorrow

Only 6 years passed since the dawn of the Motion Sensors Era in the Consumer market and now the world of MEMS Motion Sensors is completely different and it’s going to change even more in the future. If 2006 was the year of the Accelerometer adoption by NintendoTM in the WiiTM Controller, 2010 was the year of the Gyroscope adoption by Smartphone manufacturers. And in both cases STMicroelectronics triggered the big volume production of those two micro-machined devices, previously known only by automotive customers and used only for active and passive safety applications. Moreover nowadays combinations of these two inertial products, also known as Six Degree-Of-Freedom Motion Sensors 6XDOF, are starting to appear in the market and most likely they will coexist with standalone accelerometers and gyroscopes, depending on customer needs in terms of compactness and performances. This paper reports the details of an innovative tri-axis silicon MEMS Coriolis’ gyroscope that fulfills the pressing market requirements for low power consumption, small size, slim form factor, high performances and low cost, but it addresses also the recent trends of the Six Degree-Of-Freedom 6XDOF and Nine-Degree-of-Freedom 9XDOF systems, realized by integrating the 6XDOF with a compass.

Polysilicon Failure Stress and Young’s Modulus Evaluation in MEMS Devices

The main object of the paper is the implementation of two different approaches for the estimation of the modulus of elasticity and of the failure strain/stress in micro machined structures manufactured of epitaxial polycrystalline silicon (15 μm thick film). The micro-test-structures are produced using a standard THELMA process becoming an integral part of a MEMS actuator of comb-finger type. The micro-motor is designed to develop electrostatic in plane forces of desired intensity when fed by suitable electric potential difference.© 2003 ASME

Optical characterization of micro-electro-mechanical structures

In this paper, semiconductor laser feedback interferometry is applied to the characterization of vibrating mass microsensors, such as gyroscopes and accelerometers. Complete characterization of such devices with this technique includes the identification of the vibration modes and the measurement of the resonance curves of the different axes, the determination of resonance frequency, quality factor and the actuation efficiency as functions of different parameters such as pressure. In the case of a gyroscope, tuning of the driving and of the sensing axes can be also performed, as well as the measurement of the Coriolis force. Thanks to its very simple optical implementation, feedback interferometry provides a viable alternative to the standard electrical measurements, and is especially useful for the characterization of prototypes, for which a dedicated electronics circuit is not yet available.

A Low-g 3 Axis Accelerometer for Emerging Automotive Applications

A 30 µg/sqrt(Hz) resolution MEMS based low-g 3-axis accelerometers targeted for emerging automotive application is presented. The device is composed by 2-dice in a single package: the sensing element and the processing IC. The sensing element is realized with an epitaxial micro-machining process (ThELMA™) while the IC uses a 0.5 μm BICMOS process. The IC amplifier is able to detect capacitive changes as low as 10 aF (10·10−18 F) and the device is able to provide both an analog and a digital output. Moreover it has very good linearity and very low cross talk between the sensing axes thanks to a design that fits very well the ST micro-machining process ThELMA. Finally, the proposed interface accelerometer is factory-trimmed to ensure repeatable performance without production-line adjustments in the end product

Application of MEMS-based rotational accelerometers to vibration suppression in hard disk drives

A MEMS-based rotational accelerometer has been recently developed by STMicroelectronics. This paper reports the preliminary results of its application to the reduction of vibration effects on a commercial Hard Disk Drive. Experimental results show that even with a simple feed-forward compensation, self-induced and external vibrations effects are greatly reduced up to 200 Hz.

Autonomous vehicles: A playground for sensors

The automotive electronics market has increased steadily over the past several years even at times when the automobile market per se is not growing substantially. Indeed the per car electronics content is increasing at a fast pace. This is just the tip of the iceberg as we are entering the age of the “zero-accident car” with autonomous driving based on wireless and wired networks of powerful sensors (potentially including intelligent tires) and complex control algorithms implemented on a distributed computing platform. The key to this brave new world is the continuous evolution of the sensor component of the car electrical architecture. We will discuss the sensor design and manufacturing challenges to bring autonomous cars on the street. Albeit significant steps have been made in the technology base that sustains autonomous driving, massive algorithmic and integration problems loom here.

Smart systems for internet of things

Sensors add intelligence to systems which represent a broad class of devices incorporating functionalities like sensing, actuation, and control. They are the core of smart components and subsystems; then, the challenge in the realization of such smart systems goes beyond the design of the individual components and subsystems and consists of accommodating a multitude of functionalities, technologies, and materials to play a key role to augment our daily life.