Differential amplification magnetic sensor

Abstract

The differential amplification magnetic sensor (DAMS) comprises a rectangular Hall device and two transistors. These three elements are not only integrated as a monolithic IC, but are also made smaller by using the Hall region as the common base of the transistors, the collectors of which are used to isolate the Hall region from the substrate. Relations between electromagnetic characteristics of the DAMS and impurity atom density and effective thickness of the Hall region are analytically described, assuming a simplified model. Numerical calculation shows that a magnetic sensitivity of higher than 10 V/kG (with a load resistance of 10 kΩ) and a noise-equivalent magnetic flux density of less than 0.1 m/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> can be obtained when the effective thickness of the Hall region and its impurity atom density are well designed. Two types of test samples were fabricated. One, made by triple diffusion, had a Hall region with impurity atom density of 8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> and effective thickness of 3.2 µm; the other, made by diffusion and epitaxial growth, had values of 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> and 3.3 µm, respectively. These prototypes were found to have magnetic sensitivities of 0.5 V/kG and 12 V/kG (with load resistances of 100 kΩ), respectively, when exposed to static magnetic fields. The constancy of the magnetic sensitivity is better than ten percent for magnetic flux densities below 2 kG.