From Accelerometer To Gyro MEMS
Analog Devices (ADI) claims the world's first MEMS-based gyroscope. The company says that it is the first commercially available device to integrate both an angular rate sensor and signal processing electronics onto a single piece of silicon. This integration allows the iMEMS ADXRS gyro to be smaller, more accurate, more reliable, and more economical than other angular rate sensors in its class, says ADI. The gyro is mounted inside a 7x7x3mm ball grid array (BGA) package and consumes only 5mA of current at 5V. The gyro has a full mechanical and electronic self-test feature that can operate while the sensor is still active. The output is stable in the presence of mechanical noise up to 2000g over a wide frequency range.
The ADI gyroscopes are designed to measure the rate at which objects rotate. The devices do this by measuring the Coriolis effect that arises in rotating frames of reference. This effect deflects wind and plughole patterns to the right (left) in the Northern (Southern) hemisphere. The ADI device has two vibrating plates oscillating in anti-phase. Any deflection at right angles to the motion gives a measure of the rotation in the plane of the plates. By having the two plates, ADI can remove noise from shocks and other vibrations.
An ADI scientist claims a detectable deflection of 16Fermi (16fm or 0.00016Angstrom). Given that the effective radius of protons and neutrons is at the Fermi level, this is almost unbelievable. The name "Heisenberg" comes to mind. A request has been put in to ADI for further clarification of this figure.
Another incredibly small figure is in the detectable change in capacitance (12zeptoFarad or 12zF) used to derive the rotation measurement. A "zepto" is 10E-21 - and I had just got used to "atto" (10E-18), used in some recent short-time measurements. For reference, beyond "nano" (10E-9), we also have "pico" (10E-12) and "femto" (10-E15).
The information provided by gyros can be used to trigger automobile airbags during rollover, improve the accuracy and reliability of GPS/navigation systems and stabilise moving platforms such as automobiles, airplanes, robots, antennas and industrial equipment.
One company already using the ADI device is Fibersense Technology. Michael S Perlmutter, executive vice-president at Fibersense, explains: "Analog Devices' ADXRS gyro has a very low noise output which enables us to use it in many applications to augment GPS receivers where critical location information is required during temporary disruptions of GPS signals. In our product designs, reliability is critical and immunity to shock and vibration is a must. Competitive solutions were not able to match Analog Devices in terms of size, performance or reputation for MEMS reliability."
The ADXRS gyro is offered in two versions to accommodate different customer requirements for dynamic range. The ADXRS300 provides a dynamic range of 300degrees/second, and the ADXRS150 provides 150degrees/second. Both are priced at $30 per unit in thousand piece quantities. Samples are currently available and both products will be in full production by the end of 2002.
Franklin Weigold, vice president and general manager of ADI's Micromachined Products Division, says: "Using the iMEMS process, we can offer our customers a roadmap that will provide high quality, high performance gyros for as little as $10."
The iMEMS (integrated Micro Electro Mechanical System) process is a surface micromachining technology that ADI has used to make more than 100mn accelerometers since 1993.
