Sensors are widely used in modern systems to measure or detect physical parameters, such as direction, position, motion, force, acceleration, temperature, and pressure. While a variety of different sensor types exist for measuring these and other parameters, they all suffer from various limitations. For example, inexpensive low field sensors, such as those used in an electronic compass and other similar magnetic sensing applications, may comprise anisotropic magnetoresistance (AMR) based devices. In order to arrive at the required sensitivity and reasonable resistances that mesh well with complementary metal-oxide semiconductors (CMOS), the chip area of such sensors are generally in the order of square millimeters in size. Furthermore, large set-reset pulses from bulky coils of approximately 500 mA are typically required. For mobile applications, such AMR sensor configurations are costly, in terms of expense, circuit area, and power consumption.
Other types of sensors, such as magnetic tunnel junction (MTJ) sensors, giant magnetoresistance (GMR) sensors, and the widely used Hall effect sensors have been used to provide smaller profile sensors, but such sensors have their own concerns, such as inadequate sensitivity and the temperature dependence of their magnetic field response. To address these concerns, MTJ, GMR, and AMR sensors have been employed in a Wheatstone bridge structure to increase sensitivity and to reduce the temperature dependent resistance changes. Hall effect sensors have recently become competitive in this type of application through the development of high sensitivity silicon (Si) based sensors coupled with a thick nickel iron (NiFe) magneto-concentrator for amplification of the local magnetic field. These Hall effect devices typically employ the current spinning technique for optimal temperature response, resulting in a larger than desired CMOS footprint for the circuitry associated with the multiplexing between the various tap point functionality. For minimal sensor size, cost and high performance, MTJ sense elements are preferred.
As a result of the manufacturing process variations, low field Wheatstone bridge based magnetic sensors may exhibit a small yet variable residual offset. Temperature shifts, mechanical stress, and the aging of the device may cause small changes in this offset. Furthermore, conventional magnetic sensors have a sensitivity built into the device by factors such as sense layer thickness, shape, and flux concentrator geometry. Therefore, small variations in the manufacturing process may create variations in the sensor parameters and therefore create a need for the magnetic sensors be tested and calibrated for optimal performance.
As magnetic sensor size becomes smaller, the packaging and test costs begin to dominate the final product cost. For a magnetic field sensing solution that minimizes manufacturing costs, increasingly attention must be paid to minimization of test time and complexity. As packaging and final test are increasingly performed by contractors at remote locations with massively parallel testing systems, the large development and installation cost of specialized test apparatus to apply an external magnetic field for testing of sensor characteristics becomes prohibitive. An additional problem is that the magnetic environment may not be completely controlled on the production floor.
Accordingly, it is desirable to provide an inexpensive low field three axis sensor and method that provides on chip testing and calibration. Furthermore, other desirable features and characteristics of the exemplary embodiments will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.