Browse Prior Art Database

# An Active Magnetic Sensor

IP.com Disclosure Number: IPCOM000037923D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 1 page(s) / 11K

IBM

## Related People

Fang, FF: AUTHOR [+2]

## Abstract

An active magnetic sensor using sensing of Hall voltage is made up of two transistors with common emitter and base (EBC1 and EBC2 in FIG. 1). The sensitivity of this magnetic sensor is calculated as follows:

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An Active Magnetic Sensor

An active magnetic sensor using sensing of Hall voltage is made up of two transistors with common emitter and base (EBC1 and EBC2 in FIG. 1). The sensitivity of this magnetic sensor is calculated as follows:

Let the Hall-field be EH and EH = RH*J*H, where RH is the Hall constant, J is the base bias current density, and H is the magnetic field perpendicular to both bias current and the plane of the emitter-base junction.

Thus, the Hall voltage is VH = EH*L = (RH*J*H) * L, where L is the distance between the two collectors.

In the base region, RH = 1/(q*p), J = Ib/ (wb*L), where q is the electronic charge, p is the base doping density, wb is the base width, and Ib is the base bias current.

Accordingly, the Hall voltage VH = Ib*H/ (q*p*wb).

Interestingly, VH is independent of L or the distance between the collectors for constant bias current. Letting the base doping (p) be 1E18 1/cm3, wb be 100 nm, and Ib be 10 mA, we obtain a Hall voltage with a sensitivity of 62.5 mV/1000 gauss for silicon and 10 mV/10 gauss for GaAs, or one order of current difference between the collectors. With lithography at 1 um level, it is possible to make such a sensor with an L (the distance between collectors) of 10 um, which is the track width of a magnetic disk.

Disclosed anonymously.

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