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Sensor Technology on the Red Planet

Nick Depperschmidt, Director of Content
IoT Today

If you want to know when your products will break, take them into space. Better yet, send them to Mars. With massive temperature swings, dust storms and radiation, Mars is the ultimate testing ground for technology. Who knows, if built right, maybe Mark Watney will use it to survive on the Red Planet in 2035.

Mars-Valles_MarinerisAll joking aside, how would one even produce sensors robust enough to survive on Mars? Having your own wafer fab to build low volume, custom sensor technology is a good start. And that is how Sensitec is building MagnetoResistive (MR) sensors for the most demanding applications, both on and off the planet.

While working with Germany Trade and Invest (GTAI) and the Rheinland-Pfalz Ministry of Economic Affairs, the editorial staff at IoT Today got a sneak peek into Sensitecs facility in Mainz, Germany. Housed in a building that was previously used to manufacture storage technology for IBM, Sensitec has taken the old wafer fab and retrofitted it to produce MR sensors worthy of Outer Space. There they produce around 3,000 wafers a year, and their technology is currently in use on the Curiosity Rover.

The technology for MR sensors was born from read-heads for hard drives that are applied with read film techniques. These MR sensor chips and the corresponding microsystems are the basis for the measurement and control of magnetic, electrical and mechanical parameters. At the heart of each sensor is a chip, comprising single nanometer-thin layers or stacks of layers that change their electrical resistance under the influence of an external magnetic field.

The term Magneto Resistive is a collective term for sensors based on a range of different, but related physical principles. All MR effects have in common that the electrical resistance of the sensor changes due to the influence of a magnetic field. By adept arrangement of the sensor structure of the sensor quite different tasks can be solved, for example, to sense a magnetic field angle, magnetic field strength or a magnetic field gradient.

MagnetoResistive Effect
The MagnetoResistive Effect (MR-Effect) has been known for 150 years. However, its use in sensor applications was first made possible through the development of thin-film technology some 30 years ago. Since this time, MR sensors have consistently opened up new application fields in magnetic field measurement, be it in an electronic compass, in path or angle-measuring systems, or in small potential-free current sensors.

Anisotropic MagnetoResistive Effect
TheAnisotropic MagnetoResistive (AMR)effect was discovered by Thomson in 1857 and occurs in ferromagnetic materials, whose specific impedance changes with the direction of the applied magnetic field. The resistance change is in the order of a few percent and this effect can be used even for very weak magnetic fields.

Tunnel MagnetoResistive Effect
TheTunnel MagnetoResistive (TMR) effect, discovered by Julliere in 1975, occurs in layer systems consisting of at least two ferromagnetic layers and a thin isolation layer. The tunnel resistance between both layers depends on the angle of both magnetization directions.

Giant MagnetoResistive Effect
TheGiant MagnetoResistive (GMR) effectwas first discovered in 1988 by Fert and Grnberg, who were awarded with the Nobel Prize for Physics in 2007 for this achievement. This effect occurs in layer systems with at least two ferromagnetic layers and a single non-magnetic, metallic intermediate layer. If the magnetization in these layers is non-parallel, the resistance is larger than if the magnetization is parallel. The difference may reach up to 50 percent, thus the name giant. The change in resistance does not depend on the direction of the current. The characteristics of GMR sensors can be modified by stacking several layers with different properties and magnetizations. This allows the characteristic curve to be targeted on the specific requirements of a particular measurement application.

Colossal MagnetoResistive Effect
In 1993 von Helmholt et al discovered theColossal MagnetoResistive (CMR) effect. This effect occurs in perowskitic, manganese based oxides, which change their resistance in the presence of a magnetic field. Of all the known physical effects, by which a solid changes its properties due to magnetism, MR technology has particularly interesting and convincing advantages. The MR effect enables weak magnetic fields to be detected and delivers a signal with an excellent signal-to-noise relationship.

Sensitec FabAt Sensitec, sensors based on the AMR and GMR-effects are in series production. The first TMR-sensors are now under development. CMR-technology is still at the pre-industrial research stage.

Some of the advantages of MR sensors are: high accuracy, high resolution, high bandwidth to detect magnetic fields, reliability, wear free, galvanic separation and isolation, robustness, high sensitivity, and they are energy efficient and easy to integrate.

This robust sensor technology is then modified and adapted for industrial and automotive environments to help measure angle, path, electrical current, magnetic field, and more. These can then be used to accurately track, monitor, control and identify devices in the field.

Sensitec AMR and GMR-sensors are in use everywhere, where movement is being controlled and steered, where paths, angles, positions, electric or magnetic fields are measured and detected. Whether it is in a more than 200C, 10 km deep bore hole for geological research, or on the surface of Mars, -120C and 400 million km away, or in the steering mechanism of a car or in the object lens of a professional film camera.

This is all possible because from the chips design to its production, it all happens from a single source. This allows the sensor to be have customized measurement scales and integrated processing electronics for specific applications.

So when were ready to deploy a fleet of automated, autonomous rescue vehicles for Park Rangers at Valles Marineris, maybe the stranded hikers will be getting home because of Sensitec.

For more information please visit www.sensitec.com

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