Dynamic low-frequency noise cancellation in quantum well Hall sensors (QWHS)

We show that the low-frequency noise of AlGaAs/InGaAs/GaAs quantum well Hall sensors (QWHS) can be cancelled using a method similar to the spinning current method. A two-phase permutation of the current biasing electrodes and the voltage sensing electrodes of the Hall cross is performed by a switching circuit made of field effect transistors (FET). A Hall cross and eight switching FETs are integrated on the same chip. This system yields to a noise reduction of 30 dB around 1 Hz. However, the noise floor, typically 140 nT/Hz in 8 μm devices, remains larger than the expected thermal noise, and is shown to be correlated with leakage current in the FET gates. For comparison, hybrid microsystems using a discrete QWHS and leakage-free CMOS switches were fabricated. They are shown to have a record noise level of 30 nT/Hz at 1 Hz at room temperature.