Push-pull bridge sensor using SDT junctions without shields

Summary form only given. The most likely application areas for spin dependent tunneling (SDT) materials include magnetic field sensors, galvanic isolators, MRAM, and possibly read heads. For the first two applications, it is customary to use a Wheatstone bridge design with four legs of SDT resistors. For galvanic isolators using a planar coil to generate the magnetic field, it is natural to form a push-pull configuration with all four resistors active, with a uniform magnetic structure over a whole wafer. For a magnetic field sensor, however, achieving a bridge output has been traditionally done with the helps of a soft magnetic shield to null out two of the resistors as in GMR devices. Therefore, only two legs of resistors are active. The primary drawback for the design is a 50% reduction of the output signal compared with a push-pull configuration. There are additional processing complications as well as undesirable effects from the shields. Here we present a push-pull design of SDT magnetic field sensors without using a magnetic shield. The design makes a unique use of the synthetic antiferromagnetic sandwich of FM1/Ru/FM2, and takes the form of a push-pull SDT bridge.