Applicability and considerations of MRAM in external magnetic field environments

 
1. Basic Concepts Regarding External Magnetic Field Tolerance of MRAM​

As a prerequisite, Renesas Electronics Corporation has defined the following upper limits on the external magnetic field on the surface of MCUs to ensure the safe use of MRAM-equipped MCUs.

 
2. Are you concerned about the effects of external magnetic fields?

Because MRAM stores data based on the magnetization state of its magnetic tunnel junction (MTJ), a strong external magnetic field can affect the recorded data.

Looking at this point alone, it's easy to mistakenly think, "Does this mean it can't be used near motors or inductors?" However, for the design of typical industrial equipment and embedded devices, there's no need to worry excessively.

3. What is the actual magnetic field strength around a motor inductor?

Renesas Electronics Corporation conducted a field measurement survey of magnetic flux density targeting components that generate magnetic fields, such as motors and inductors, in order to confirm whether MRAM-equipped MCUs can be used in actual application environments.
 

Conclusion ①: The magnetic field around the motor is quite small.

For permanent magnet synchronous motors (PMSM motors), regardless of size, the casing itself functions as a magnetic shield, both when the motor is alone and during operation, resulting in a magnetic field leakage to the outside of a few gauss or less. This level of magnetic field has virtually no effect on the operation or data retention of MRAM.

Because leakage magnetic fields reduce efficiency, motors are designed to minimize them. Furthermore, many products use iron casings to further reduce magnetic field leakage to the outside.
Therefore, MRAM can be used without problems in common configurations such as motor control equipment, inverters, and industrial PLCs.

*For detailed survey results, please refer to "What is Next-Generation Memory MRAM? Chapter 3: Verification Data."
 
Conclusion ②: The effect of the inductor is also limited.

An investigation was also conducted into inductors used in power supply circuits.
Even when a large current flows, the magnetic flux is confined inside the core, resulting in a very small magnetic field leaking to the outside.

In actual measurements, even with a gapped inductor, the leakage magnetic field remained at a maximum of about 10 gauss, which was not at a level that would affect the operation of the MRAM.
Therefore, MRAM can be used without practical problems even in the vicinity of typical power supply circuits and power conversion circuits.

moreover, Sagami Electric Co., Ltd. Power inductor CVK2522H-5R4M And, for ferrite core inductors of equivalent size and inductance value, the difference in core material 2 We also obtained the results of the magnetic flux density survey of the patterns. These inductors all share the following characteristics:
・Closed magnetic circuit structure
• External dimensions are approximately 20mm class
• High-current inductor (CVK2522H So, the allowable DC superimposed current (A) but 100A)
 

Furthermore, its high-density winding structure achieves both low DCR and high current handling capabilities, making it a suitable power inductor for applications requiring high current, such as car audio and power modules.

Even in such power inductors, 100A Under the conditions of applying the current, CVK2522H (Metalcore) is number mm To what extent, the ferrite core is approximately 0.5mm Maintain distance By doing so, the magnetic flux density 200 Attenuation below Gaussian density It has been confirmed that this will happen.

These evaluation results serve as an example demonstrating that even in circuit designs using high-current inductors, there are very few cases where the magnetic field tolerance of the MRAM is exceeded, unless the MCU with built-in MRAM is placed in extremely close proximity.

*For detailed survey results, please refer to "What is Next-Generation Memory MRAM? Chapter 3: Verification Data."
 
4. What is the relative position of the magnetic field source and the MCU in actual applications?

Renesas Electronics Corporation confirmed the placement relationship between magnetic field sources (motors, inductors, magnets, etc.) and control MCUs based on actual application configurations. As a result, in many applications, the magnetic field sources and MCUs were placed sufficiently far apart for structural reasons. Therefore, even when MRAM is built into the MCU, the effect of the magnetic field is considered to be practically negligible.

 
4.1 General placement trends in home appliances and industrial equipment

In common home appliances such as air conditioners, washing machines, and refrigerators, the drive components, including motors, fans, and pumps, and the circuit board containing the control MCU are physically separated within the casing.
In these products, it is common practice to design the control board to be located several centimeters or more away from the drive unit for vibration countermeasures, heat dissipation, and wiring purposes.

Therefore, even if a localized magnetic field is generated near the motor or power supply circuit, it is unlikely to reach a level that would affect the device due to magnetic field attenuation with distance.

Figure 1: Positional relationship between the MCU board and the motor (drum-type washing machine)

 
4.2 Considerations regarding power supply units and inverters

Power supply devices such as power conditioners, server power supplies, and general-purpose inverters,
• Large inductor
·transformer
・High current wiring

These could be sources of magnetic fields.

However, these components are often positioned separately from the control circuit within the enclosure, with the MCU located several centimeters or more away. Based on actual measurements and structural verification, the magnetic flux density observed at the MCU location is kept below a few gauss, suggesting that the impact on the MRAM built into the MCU is minimal.

4.3 Motor-integrated and mechatronic integrated applications

In mechatronic applications such as robotic arms and AC servos, the motor and control circuit are housed in the same enclosure, so there are cases where the effects of magnetic fields must be considered.

However, in many products
The motor is enclosed in a metal casing.
- Structural components or partitions exist between the control board and the surrounding area.
For these reasons, the magnetic field originating from the motor directly MCU The cases in which this is affected are limited.
On the other hand, caution is required when using magnetic sensors. Typical magnetic sensors use magnets for magnetic detection. These magnets generate strong magnetic fields, so the magnet and MCU The number mm In configurations where the order is close, MCU Built into MRAM It may exceed the magnetic field resistance limit.

 
5. Cases requiring caution: When strong magnets are in close proximity.

Magnetic fields cannot be ignored in all cases.

As mentioned in Section 4, caution is needed when components that intentionally generate strong magnetic fields, such as "magnets for magnetic sensors," are placed near the MCU with built-in MRAM.

Magnetic sensors generate magnetic fields exceeding several thousand to 10,000 gauss near the magnet, which can exceed the magnetic field tolerance of MRAM at distances of a few millimeters.

Therefore, it is important to design layouts that do not place MRAM-integrated MCUs near magnets, and to consider placements and configurations that are less susceptible to magnetic field influences.

These findings can be summarized as follows:

• Near typical motor, inductor, and power supply circuits, MRAM It can be used without any problems.
- Due to the shielding effect of the enclosure and the distance attenuation of the magnetic field, MRAM The magnetic field to is sufficiently small.
The applicability of MRAM is determined by the magnitude of the magnetic field and its distance from the magnetic field source.
• In configurations that intentionally use strong magnetic fields, such as when powerful permanent magnets or magnets for magnetic sensors are in close proximity, design considerations may be necessary.

Future prospects of MRAM

 
MRAM is a memory technology that offers many advantages not found in conventional memory, such as high speed and non-volatility.

・High speed

- Non-volatile

-High reliability

・Low power consumption
　

In situations where these features are required simultaneously, MRAM demonstrates strengths that other memory types lack.

In particular, expectations for MRAM are increasing year by year in embedded devices where immediate system startup and reliable data retention are crucial, as well as in industrial applications with harsh environmental conditions.

In fact, recent market research reports also show that MRAM The market includes automobiles, industrial equipment, IoT edge AI It is positioned as a sector that is expected to continue growing, primarily for specific applications.
Mordor Intelligence According to the survey, MRAM The market 2026 From 2031 The average annual growth rate over the years (CAGR) 32.72% Grew up in, 2031 In that year, the market size was approximately 182.4 billion US dollars (USD 18.24 Billion It is predicted to reach ).

Figure 2: MRAM Market Size Forecast

(Reference: Mordor Intelligence, Magneto-Resistive RAM (MRAM) Market– Growth Trends and Forecast,https://www.mordorintelligence.com/industry-reports/magneto-resistive-ram-market)

Summary

In the future, as manufacturing technology advances and the range of compatible products expands, MRAM is expected to further increase its presence as a "memory with a clear purpose" that is chosen according to its intended use.

This type of memory will not only broaden the options for system design but also lead to the creation of new uses and applications, and will likely attract increasing attention in the future.

Specific analysis results under magnetic field conditions are described in detail in Chapter 3, "Verification Data."​
Also, if you would like to understand the basics, please refer to ​Chapter 1, "Basics."​

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