Multi-axis magnetic sensors or magnetometers, such as three-axis magnetic sensors, are particularly desirable for modern electronic compass applications. However, such devices are usually unable to sense magnetic flux from all three orthogonal axes. For example, conventional magneto-resistive (MR) sensors, such as AMR (anisotropic MR) sensors, GMR (giant MR) sensors, TGMR (tunneling GMR) sensors, and the like, can detect magnetic flux that is parallel to the device plane but cannot detect flux that is perpendicular to the device plane. On the other hand, Hall-effect sensors can sense magnetic flux that is perpendicular to the device plane, i.e., along the Z axis, but cannot sense magnetic flux parallel to the device plane, i.e., in the XY plane.
There are many known approaches to fabricate a magnetic sensor with three-axis sensitivities. One approach is to package a Z axis sensor of the same technology as the X and Y axis sensors in orthogonal disposition to the two-axis XY sensors. Another approach uses two types of sensor technologies that are disposed on a common die with one constructed to sense vertical magnetic flux signals and the other constructed to sense horizontal magnetic flux signals. Multi-axis sensitivities can also be achieved by building sensors on a sloped surface. A further approach uses a magnetic concentrator that is adapted to convert signals along one axis to an orthogonal direction so that magnetic flux from all three axes can be detected using the same technology.
However, there are disadvantages associated with each of the known approaches. For example, combining a Z axis magnetic field sensor, whose sensing direction is perpendicular to the device (XY) plane, with an X or Y axis magnetic field sensor(s) requires one or more additional packaging steps in order to install the Z axis magnetic field sensor vertically without significant angle variation. The additional packaging steps add significant cost to the whole product manufacturing process. Furthermore, variation in the positioning angle complicates signal processing since cross-talk signals from the XY plane are introduced if the Z axis magnetic field sensor in not perfectly vertical.
Hall-effect sensors, which can sense magnetic flux from a direction that is perpendicular to the device (XY) plane, can be built on a common die with two-axis MR sensors; however, the different Hall-effect and MR technologies require different processing steps and resultant fabrication complexity.
Sensors that are disposed on a sloped surface can detect magnetic flux signals that are parallel and perpendicular to the device (XY) plane, but with the disadvantage of a complicated manufacturing process. For example, typical fabrication steps, including film deposition, photolithographic, etch patterning and the like on sloped surfaces, are much more difficult than on planar surfaces, especially as device dimensions become smaller and smaller.
A magnetic concentrator can convert magnetic flux signals along one direction to signals along another direction and can also improve sensitivity through flux signal amplification. However, known concentrator configurations complicate signal processing because of cross-talk which can affect the sensing units.
Therefore, it would be desirable to provide a multiple-axis magnetic sensor or magnetometer having a magnetic concentrator that is less affected by cross-talk.