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

Abstract

We propose and demonstrate the operation of a monolithic field-effect-transistor-amplified magnetic field sensor device, in which a tunnel-magnetoresistive ͑TMR͒ 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. © 1999 American Institute of Physics. ͓S0003-6951͑99͒04431-9͔Magnetic field sensors with improved sensitivity at room temperature are highly desirable for a variety of applications, perhaps most notably in future magnetic data storage systems. Approaches for amplification of response based on incorporation of sensor materials into electronic device structures have been developed for a variety of sensor applications. In the spin-valve transistor, 1 a giantmagnetoresistive thin film is incorporated as the base layer in a metal-base transistor. A field-dependent base transport factor then leads to amplified collector current response in the transistor. However, the fabrication of these devices requires vacuum metal bonding, and lithographic processing is difficult. Another approach for amplification of a sensor signal is the incorporation of the sensor material within the gate structure of a field-effect transistor ͑FET͒; this concept has been demonstrated in FET-based chemical and gas sensors in which gas or ion adsorption or absorption in the gate structure results in a shift in transistor threshold voltage and, consequently, amplified response in the transistor channel conductance or subthreshold current. 2,3 In this letter, we describe the design, fabrication, and demonstration of a transistor-amplified magnetic field sensor in which a granular tunnel magnetoresistive ͑TMR͒ Co x (SiO 2 ) 1Ϫx thin film is incorporated within the gate of a p-channel Si metal-oxide-semiconductor-field-effect transistor ͑MOSFET͒ as shown in Fig. 1. The basic concept is, however, applicable to any FET, as well as other magnetoresistive materials in which stored charge associated with electrical current flow is present. The sensor device was fabricated employing a nonself-aligned process acceptable because of the large device dimensions (50 mϫ1000 m gate͒. The source and drain regions were formed by boron diffusion into an n-type Si wafer (N D ϳ2ϫ10 15 cm Ϫ3 ) with a patterned oxide mask. The 20 nm lower gate oxide was formed by dry thermal oxidation, and Al ...

Characterization and analysis of a novel hybrid magnetoelectronic device for magnetic field sensing

“…The detailed device fabrication process is given in Ref. 8. Previous reports have shown that the Co/SiO 2 film deposited under these conditions consists of Co clusters with an average diameter of about 4 nm embedded in a SiO 2 matrix.…”

“…Specifically, the observation of charge storage with retention times of up to several minutes in discontinuous magnetic metal/insulator multilayer structures 7 led to the design and demonstration of a novel monolithic field-effect-transistor-amplified magnetic field sensor. 8 In this device, a granular tunnel-magnetoresistive ͑TMR͒ thin film was incorporated within the gate structure of a p-channel metal-oxide-semiconductor field-effect transistor ͑MOSFET͒. The design allows for relatively simple fabrication and monolithic integration with other semiconductor components for increased sensitivity and functionality.…”