How to achieve nanotesla resolution with integrated silicon magnetotransistors

Dual-collector magnetotransistors with large current gain beta /sub F/>>1, have been developed for the detection of magnetic fields in the nanotesla range. Although the magnetic response associated with such structures is very low ( Delta I/sub c//I/sub c/<0.1/T), there is a strong positive correlation between output collector noise voltages. Consequently, very large signal-to-noise ratios are obtained resulting in high resolution (B/sub min/ approximately 189 nT/ square root Hz at 10 Hz) at low operating current (I/sub c/<1 mA). Noise measurements performed for a variety of devices show that the limitations associated with resolution of such field strengths will not be imposed by the sensing device, but rather by the in situ amplification circuitry fabricated in standard IC technologies. Although the nanotesla magnetotransistor device discussed is fabricated in bipolar technology, a device with similar characteristics can just as well be fabricated in CMOS technology by placing the collectors in the substrate.<>