Magnetic sensors for automotive applications

Magnetic sensors offer several key advantages: they allow contactless and, consequently, wear-free measurement of mechanical quantities like angle of rotation and angular speed. They are robust and inexpensive to manufacture. As one example of magnetic sensors in production at Robert Bosch GmbH, the steering wheel sensor LWS3 is shown, developed for the electronic stability program (ESP), which prevents vehicles from spinning. We recently demonstrated, that the inherent limitation of the AMR-effect to an 180 degrees angular range can be overcome by using a switchable magnetic field generated inside the sensor element. For a new generation of magnetic sensors, the technology of giant magneto-resistance (GMR) thin film systems promises several advantages Like larger working distances, more precise angular position measurement in a wider range (up to 360 degrees), smaller and therefore cheaper sensor chips and economic system solutions due to the higher signal output. A GMR multilayer system of CoCu/Cu was developed, which fulfills the requirement of having no hysteresis in the magneto-resistive characteristics. On the other hand, research is still going on for sensitive GMR layers, which are stable at temperatures of 200 degreesC (or more) for long time periods of at least 500 h. Thin film systems of spin valve type, used in read heads for disc drives, have been thoroughly evaluated about whether they can be used in sensors for automotive applications. The great challenge is to generate GMR thin film systems which cover a much wider range of features than the existing technologies of Hall and AMR and which can be produced at lower cost. Only versatile GMR sensors will lead to high production volumes, which are needed for a cost efficient fabrication as in other modem micro technologies. (C) 2001 Elsevier Science B.V. All rights reserved.