Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
2002-06-19
2003-07-29
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C324S247000, C033S35500D, C338S03200R, C360S324200, C428S900000
Reexamination Certificate
active
06600314
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tunneling magnetoresistive effect device, such as a geomagnetism sensor for magnetic field measurement or navigation, and a direction sensor system using the device.
2. Description of the Related Art
Examples of conventional magnetism sensors include magnetoresistive effect devices (MR devices), magnetism impedance devices (MI devices), flux gate sensors, and semiconductor Hall effect sensors. Among these sensors, MI devices, which have been developed only recently, can constitute thin-film and small-sized Ml sensors, and therefore are expected to be improved even further. An MI device can also sense a magnetic field strength from a change in the magnetic field of high-frequency impedance, when high-frequency electric current is applied to the MI device.
In addition to those magnetism sensors, tunneling magnetoresistive effect devices (TMR devices) have been recently developed. A TMR device has a plurality of magnetic thin-film layers, with an insulating layer being interposed in between. In such a TMR device, electrons are transmitted through the insulating layer by a tunneling effect, while maintaining the spin. Here, a magnetic field is sensed based on the tunnel permeability coefficient that is changed with the magnetized state affected by the tunneling effect. Having a very high magnetic field sensitivity, a ferromagnetic tunneling effect can be effectively used in a HDD magnetic reproducing head for reproducing very high-density magnetic recording media. Also, such a ferromagnetic tunneling effect can be used in a magnetic field measuring device for motors, a magnetism sensor such as a geomagnetism sensor for navigation, or a magnetic solid-state memory device that is generally referred to as MRAM.
Japanese Laid-Open Patent Application No. 11-161919 (Japanese Patent No. 3004005) discloses such a TMR device that achieves an improved magnetostatic interactive operation.
Japanese Laid-Open Patent Application No. 5-157566 discloses a general MR device that is used in a direction indicator. To realize a higher magnetic field sensitivity and hysteresis, an auxiliary magnetic field is generated in the MR device.
In Japanese Laid-Open Patent Application No. 11-161919 (Japanese Patent No. 3004005), however, the magnetostatic interactive operation is improved by the lamination structure of the layers, which is not an essential solution and leads to higher production costs.
Also, to produce a direction sensor, it is not desirable to increase the sensitivity by generating an auxiliary magnetic field in an MR device.
In view of these facts, the conventional magnetism sensors are not effective enough in terms of size, weight, costs, and sensitivity, and should be further improved.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a tunneling magnetoresistive effect device that is small and light, and has a high sensitivity.
Another object of the present invention is to provide a direction sensor system that can increase the precision in sensing geomagnetism by virtue of the above tunneling magnetoresistive effect device, and can be effectively used in a navigation system or the like.
The above objects of the present invention are achieved by a tunneling magnetoresistive effect device that includes: a soft magnetic layer for assisting magnetic field sensing operations, the soft magnetic layer being stacked on a surface of a substrate; a first spin polarization layer that is stacked on the soft magnetic layer, and has a higher coercive force and a higher spin polarization rate than the soft magnetic layer; a tunneling layer that covers the soft magnetic layer and the first spin polarization layer, and is made of an insulating material or a dielectric material; and a second spin polarization layer that is stacked on the tunneling layer, and corresponds to the first spin polarization layer. In this tunneling magnetoresistive effect device, a magnetism sensing unit is formed by the lamination structure consisting of the soft magnetic layer, the first spin polarization layer, the tunneling layer, and the second spin polarization layer. The thickness of the first spin polarization layer is smaller than the thickness of the tunneling layer or 2 nm, whichever is smaller.
Since any tunneling magnetoresistive effect device is manufactured by a thin-film formation technique, the size and weight of the device can be sufficiently reduced. Also, as the thickness of the first spin polarization layer having a higher coercive force and a higher spin polarization rate than the soft magnetic layer, on which the first spin polarization layer is stacked, is adjusted so as to achieve both a low coercive force and a desirable TMR ratio, the sensitivity for a magnetic field can be sufficiently increased. The soft magnetic layer may be located either at the top or at the bottom of the device.
In the above tunneling magnetoresistive effect device, the thickness of the soft magnetic layer is 10 or more times greater than the total thickness of the tunneling layer and the first spin polarization layer.
With the thickness of the soft magnetic layer being 10 or more times greater than the total thickness of the tunneling layer and the first spin polarization layer, the TMR ratio can be further increased, and the coercive force of the device can be further reduced.
In the above tunneling magnetoresistive effect device, the area of a non-junction part of the soft magnetic layer is 10 or more times greater than a junction area through which tunnel current flows. The junction area is defined by the soft magnetic layer, the first spin polarization layer, and the tunneling layer.
With the area of the soft magnetic layer excluding the junction part being 10 or more times greater than the area of the tunnel-current flowing junction area, the coercive force of the device can be further increased, while the TMR ratio remains unchanged.
The above tunneling magnetoresistive effect device may further include a high permeability layer that is placed in the vicinity of the magnetism sensing unit, and is connected to the soft magnetic layer.
Since the high permeability layer connected to the soft magnetic layer is located in the vicinity of the magnetism sensing unit, the high permeability layer can function as a magnetic flux sink, and thus further increases the sensitivity of the device.
The above tunneling magnetoresistive effect device may further include a bulk magnetic member that is placed in the vicinity of the magnetism sensing unit.
The bulk magnetic member can achieve a much lower permeability and a much lower coercive force than a thin magnetic film. Also, the bulk magnetic member characteristically tolerates a large amount of magnetic flux. With this bulk magnetic member being located in the vicinity of the magnetism sensing unit, the sensitivity of the device can be further increased.
The above tunneling magnetoresistive effect device may alternatively include a bulk magnetic member that is placed on the high permeability layer.
As the bulk magnetic member is formed on the high permeability layer that is located in the vicinity of the magnetism sensing unit, the sensitivity of the device can be further increased.
In the above tunneling magnetoresistive effect device, the soft magnetic layer may have a lamination structure that has a plurality of soft magnetic films stacked on a non-magnetic layer.
As the soft magnetic layer is formed by the lamination structure that has a plurality of soft magnetic films stacked on a non-magnetic layer, the formation of reflux magnetic domains can be prevented. Accordingly, the device causes less noise and enables higher frequency operations (i.e., high-speed sampling operations). Thus, the device capacity can be further increased.
In the above tunneling magnetoresistive effect device, the soft magnetic layer may have a circular shape or a ring-like shape in a plan view.
As the soft magnetic layer has a circular (or oval) shape or a ring-like shape in a plan view, the mag
Ricoh & Company, Ltd.
Strecker Gerard R.
LandOfFree
Tunneling magnetoresistive effect device and direction... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Tunneling magnetoresistive effect device and direction..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Tunneling magnetoresistive effect device and direction... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3060832