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Method for extending the GMR Dynamic Range and Coping with Back-Bias Applications

IP.com Disclosure Number: IPCOM000146912D
Original Publication Date: 2007-Mar-25
Included in the Prior Art Database: 2007-Mar-25
Document File: 3 page(s) / 211K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

The use of a GMR-based (Giant Magneto Resistive) sensor along with a Back-Bias application leads to the problem of its limited dynamic range. For this kind of application, the high sensitivity of a GMR-based sensor strongly comprises the system functionality, especially when mechanical tolerances are also taken into account. Therefore, it is of high interest to extend the GMR dynamic-range and make it suitable for back-bias applications. In Fig. 1 it is shown that the limited dynamic range constitutes a severe critical factor. The relationship describing the magneto resistive effect can be expressed by the formula: in which S represents the MR-sensitivity and R0 the nominal value for B=0. In theoretical cases, the GMR characteristic is centered at B=0. In real cases, especially in the context of back-bias applications, the external field has a non-zero DC component, which is indicated as B0. It is clear, that for large values of B0 the GMR element approaches its saturation region. As a primary effect, the linear relationship R~B vanished, making the element totally useless.

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Method for extending the GMR Dynamic Range and Coping with Back-Bias Applications

Idea: Dr. Francesco Maone, AT-Villach; Tobias Werth, AT-Villach

The use of a GMR-based (Giant Magneto Resistive) sensor along with a Back-Bias application leads to the problem of its limited dynamic range. For this kind of application, the high sensitivity of a GMR- based sensor strongly comprises the system functionality, especially when mechanical tolerances are also taken into account. Therefore, it is of high interest to extend the GMR dynamic-range and make it suitable for back-bias applications.

In Fig. 1 it is shown that the limited dynamic range constitutes a severe critical factor. The relationship describing the magneto resistive effect can be expressed by the formula:

        B S R
x R
r

+

()= 0

in which S represents the MR-sensitivity and R0 the nominal value for B=0. In theoretical cases, the GMR characteristic is centered at B=0. In real cases, especially in the context of back-bias applications, the external field has a non-zero DC component, which is indicated as B0. It is clear, that for large values of B0 the GMR element approaches its saturation region. As a primary effect, the linear relationship R~B vanished, making the element totally useless.

In order to reduce the impact of B0 on the GMR response, the only solution will be represented by an extension of the dynamic range D=2Bm. Although possible through technology changes, this will not be a practicable way, since it would demand a costly new technology development.

It is therefore proposed to extend the GMR dynamic range through a series-connection of properly magnetized and shaped GMR elements. It is well know that the constitutive law of a GMR element can be shifted by means of using an appropriate "magnetic writing procedure" or by exploiting the form- anisotropy. This is achieved by assuming that it is possible to have two different elements centered at +B0 (see Fig. 2). In formulas this means:

-

+

      =
+ =
.

The dynamic range of this setting is twice as big as the one of a single element.

In the former analysis an ideal case...