Magnetic sensors play an important role in many fields. As a well-known type of sensor, its development can be divided into the following stages, from the magnetic sensor based on the Hall effect to the magnetic sensor based on the anisotropic magnetoresistance effect. (AMR sensing), GMR sensing based on giant magnetoresistance, and TMR sensing based on tunnel magnetoresistance. Aside from Hall effect sensing, the most well-known type of magnetic sensing, what are the different technical characteristics of the three types of magnetic sensing: anisotropic magnetoresistance, giant magnetoresistance and tunnel magnetoresistance?

The most basic principles of the three can be said to be based on the most primitive magnetoresistance effect, that is, when a magnetic field is applied to a conductor carrying a current, the resistance value of the conductor will change significantly. The anisotropic magnetoresistance effect is that the magnetoresistance change in the material is related to the angle between the magnetic field and the current, and it involves the anisotropy of electron scattering in the S orbital and d orbital in the material. AMR sensing generally adopts a bridge structure, and the magnetoresistance ratio (ΔR/Rmin) is about 3%. AMR sensing has many applications in operation control applications, especially in vehicle-level operation control applications.

The giant magnetoresistance effect refers to the phenomenon that the resistivity of the magnetic material changes greatly when there is an external magnetic field compared to when there is no external magnetic field. Simply put, the magnitude of the decrease in the resistivity of a substance in a magnetic field under certain conditions is very large, which is called the giant magnetoresistance effect. The GMR sensor also generally adopts a bridge structure, and the magnetoresistance ratio is about 15%.

The tunneling magnetoresistance effect refers to the effect that the magnitude of the tunneling resistance in the ferromagnetic-insulator film-ferromagnetic material changes with the relative direction of the ferromagnetic materials on both sides. There are not many companies that master TMR sensing technology, and its advantages such as high sensitivity and large magnetoresistance effect are accompanied by a high technical threshold. The TMR sensor also adopts a bridge structure, and the magnetoresistance ratio is often greater than 50%.

AMR GMR TMR
Magnetoresistance ratio (ΔR/Rmin) 3 15 >50
Power consumption (mA) <10 <10 <0.01
Response time (ns) 10 10 0.1
Temperature drift (PPM/K) 3000 3000 400
Minimum size (mm) 1×1 1×1 0.5×0.5

(Comparison of three leading technology indicators)

AMR sensing ICs

Many big companies are doing AMR-based magnetic sensing. After all, AMR sensing plays an important role in vehicle-grade angle sensors that cannot be ignored. The choice here is NXP’s AMR sensing IC.

(Image source: NXP)

Take NXP’s AMR sensor as an example, this type of magnetic sensor can provide very low power consumption in addition to providing high-precision measurement. Automotive-grade AMR sensing ICs have an accuracy of ±1% over their entire temperature range and life cycle, which is currently the industry standard for AMR sensing.

As for how much the device is affected by parameter degradation and whether it is sensitive to magnet aging, it depends on each company. NXP’s AMR sensing integrates a magnetoresistive MR sensor bridge, a mixed-signal integrated circuit IC, and the required capacitors in a single package. Both integrated channels operate in a completely independent manner and are virtually immune to parameter degradation. The power consumption of the device not exceeding 10mA is also the leading level in the industry.
From the average level of the entire industry, due to the limitations of its technology, the parameters of resolution, response time, and temperature drift of first-class manufacturers are not much different. For example, ADI’s AMR is better in drift, and NXP’s AMR is significantly higher than its peers in temperature coverage.

GMR Sensing IC

Compared with AMR, there are fewer manufacturers that master GMR sensing. Infineon is one of the few manufacturers that masters AMR, GMR and TMR. We take Infineon as an example for the performance of GMR sensing.

(Source: Infineon)

Most of Infineon’s angle sensors integrate several technologies together. From the perspective of GMR technology alone, Infineon’s GMR sensors are very suitable for wide-angle range applications. Infineon’s GMR sensing can cover the full angle of 0-360°, and the magnetic field operating range covers 30mT to 50mT, and the resolution of 2mOe is also the standard of first-class GMR sensing in the industry.

The response of GMR sensing is not far from the response of AMR sensing, both are at the level of 10ns, and the power consumption is also at the level of 10mA. It’s worth noting that GMR sensing is generally the largest of these technologies in size, but Infineon uses an innovative stack-mount technology that combines two separate sensors in a standard and space-saving TDSO package, And the thickness is only about 1 mm, which achieves the same size level as AMR sensing.

TMR sensing ICs

TMR technology belongs to the highest threshold among these technologies, but its sensitivity and magnetoresistance effect are also the most advanced. Crocus’ TMR sensing represents the technical trend of TMR technology in the world.

(Image source: Crocus)

Crocus’ TMR sensing sensitivity range is up to ±50mT, and it can measure currents over 1000A. The current measurement range is greater than ±1000A. It can be said to be a rigid indicator of high-end TMR technology in the industry. Under the measurement range of ±20mT, the total error is less than 0.5%. The linearity of this level in TMR technology can be said to be the ceiling in the industry.

Compared with AMR and GMR, TMR sensitivity can be said to be an order of magnitude leading, and its temperature drift is more stable. In terms of response time, the first two are almost on the 10ns standard, and the response time of TMR is only 0.1ns. The size of the TMR sensor chip has always been a stumbling block for its expansion and application. At present, the minimum is 0.5×0.5mm, but most manufacturers cannot do it.

summary

It has excellent power consumption, sensitivity and response time within the measurement range of AMR sensing. For motion control applications, AMR sensing can provide this precise position measurement at a cost that manufacturers can accept. In addition to providing higher accuracy, GMR sensing has different advantages given by different manufacturers, which greatly broadens the application range of GMR sensing. As a technology that integrates various advantages, TMR magnetic sensor-based products will expand more applications in the field of smart homes and smart cars. From a technical point of view, no matter what kind of magnetic sensing technology is based on, how to make differences and advantages in package size, linearity, sensitivity, measurement range, measurement accuracy and cost, this is a more worthy of attention. In the final analysis, the development of materials and manufacturing level is the top priority.

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