A monolithic field-effect-transistor-amplified magnetic field sensor

We propose and demonstrate the operation of a monolithic field-effect-transistor-amplified magnetic field sensor device, in which a tunnel-magnetoresistive (TMR) material is incorporated within the gate of a Si metal-oxide-semiconductor-field-effect transistor. A fixed voltage is applied across the TMR layer, which leads charge to build up within the gate. Applying or changing an external magnetic field causes a change in the charge within the TMR layer and, consequently, a shift in the transistor threshold voltage, which leads to an exponential change in subthreshold current I-DS sub and a quadratic change in saturation current I-DS sat. The application of a 6 kOe magnetic field at room temperature leads in our device to an absolute change in I-DS sub three times as large and in I-DS sat 500 times as large as the corresponding change in current through the TMR layer alone. The relative change in I-DS sub is a factor of four larger than that in the current through the TMR layer. (C) 1999 American Institute of Physics. [S0003-6951(99)04431-9].