Revolution sensors for automobiles can be used under high temperature condition. In particular, temperature near an engine room or a transmission can reach 150°C or more. Giant magnetoresistive (GMR) elements had not been used for automobiles until we put them into practical use, although they are suitable for the revolution sensing due to very sensitive to a magnetic field. It is because the GMR films were thought to have poor thermal stability. We have solved this problem by optimization of materials and proper annealing. Our GMR elements show very large MR ratio and small magnetic hysteresis that are proper characteristics for sensors, as well as good thermal stability over 2000 hours at 170°C. Monolithic integration of GMR elements to a signal processing IC enables more than ten times larger signal than that of semiconductor Hall elements. This paper also reports very high temperature (up to 200°C) detection ability of the GMR revolution sensor.
展开▼
