The significance of developing giant magnetoresistance (GMR) magnetic field sensor chips

"Science and technology are the primary productive forces." The development of science and technology always promotes the rapid progress of human civilization. When mankind entered the late 1920s, a new discipline, magnetoelectronics, emerged from the comprehensive development of science and technology. It absorbs the essence of the latest scientific and technological development, integrates the strengths of magnetism and microelectronics, develops what it cannot do, and opens a new chapter for the development of human technological civilization.

1. Introduction to the giant magnetoresistance effect

Magnetoelectronics is an interdisciplinary subject that mainly studies the transport characteristics of spin-polarized electrons within the mesoscopic scale and the electronic devices designed and developed based on these unique properties and working under new mechanisms. Its research objects include spin polarization, spin-related scattering, spin relaxation of current-carrying electrons, and related properties and applications.

Electrons are both charge carriers and spin carriers. Microelectronics, which mainly studies, controls and applies the transport characteristics of different numbers of electrons and holes (i.e., majority carriers and minority carriers) in semiconductors, is one of the greatest creations of mankind in the 20th century. But here the spin state is not considered, the electron transport process is only controlled by the electric field using its charge. Can the electron spin be used to manipulate its transport process? This is exactly the main content of magnetoelectronics. The study

of giant magnetoresistance effect is an important part of magnetoelectronics. The magnetic field acts on the spin of the conductive electrons in the magnetic multilayer film, resulting in a large change in the film resistance. This change can be reflected by measuring the resistance or in the form of voltage. According to this feature, it can be applied in many fields.

2. Application of giant magnetoresistance effect

Science and technology serve mankind. Only when science and technology are combined with applications can they play the role of "primary productive force" and have strong vitality at the same time. The emergence of magnetoelectronics is the result of the promotion of huge application prospects, and it has been serving applications since its inception. Up to now, the research of magnetoelectronics is still going on vigorously around the world, and its application has developed to many fields such as computer heads, giant magnetoresistance sensors , and magnetic random access memory. With further research and understanding of the principles of CMR and TMR, it will surely open up broader application prospects. In view of the novelty and complexity of magnetoelectronics technology, research on magnetoelectronics is still ongoing. Its application is currently limited to the scope of giant magnetoresistance (GMR). The following is a more detailed introduction to this. Its new applications are changing with each passing day, so please wait and see. 1. Application of giant magnetoresistance (GMR) sensors 1) GMR magnetic field sensors can be used for navigation and vehicle monitoring systems on highways The earth is a large magnet. The magnetic field on the surface of the earth is about 0.5Oe. The geomagnetic field is parallel to the surface of the earth and always points to the north. GMR film can be used to make an advanced compass for detecting the geomagnetic field. When a GMR magnetic field sensor that can simultaneously detect the X and Y direction components of the magnetic field in the plane is fixed on a vehicle, the angle between the instantaneous heading and the Earth's North Pole can be determined by the relative change of the X and Y direction voltages of the GMR sensor. Figure 3 shows the specific working principle of this sensor. The GMR magnetic field sensor changes its angle with the geomagnetic field as the direction of the ship changes. Relatively speaking, it can also be equivalent to the direction of the geomagnetic field changing. We have developed an integrated GMR sensor that can detect the X and Y direction components of the magnetic field. This sensor can be used as a compass and as a navigation device in various vehicles. NVE in the United States has used GMR sensors in vehicle traffic control systems. We know that various vehicles (objects) have their own characteristic magnetic field distribution in the outside world. By using GMR weak field sensors, the magnetic field distribution of various vehicles can be detected and the model of the vehicle can be determined. GMR sensors can not only detect the status of stationary vehicles and be used for traffic control at traffic lights and monitoring of parking positions in parking lots, but also detect the status of moving vehicles. Specifically, GMR sensors placed on the side of the highway can count and distinguish vehicles passing through the sensor. If two GMR sensors are placed separately at the same time, the speed and length of the passing vehicle can also be detected. Of course, GMR can also be used in toll booths on highways to achieve automatic control of tolls. In addition, sensors with high sensitivity and low magnetic field can be used in aviation, aerospace and satellite communication technology. As we all know, in the military industry, with the development of wave absorbing technology, military objects can be concealed by covering a layer of wave absorbing material, but they will generate magnetic fields anyway, so hidden objects can be found through GMR magnetic field sensors. Of course, GMR magnetic field sensors can be used on satellites to detect objects on the earth's surface and the distribution of mineral deposits underneath.

Navigation principle of magnetic field sensor

2) GMR magnetic field sensors can be used to detect DC and AC currents and used as isolators and feedback systems in electronic circuits (switching power supplies ). It is well known that a magnetic field will be generated around a current-carrying conductor, and the strength of the magnetic field is proportional to the magnitude of the current. If a GMR magnetic field sensor and a toroidal soft magnetic flux collector are placed near a current-carrying conductor, the current passing through the conductor can be measured by the output voltage of the GMR sensor. We have used antiferromagnetically coupled FeNi/FeCo/Cu multilayer films and integrated permanent magnetic films as bias fields, and developed a Wheatstone bridge sensor with a linear measurement range of plus or minus 200Oe. This sensor can detect DC and AC currents up to 10,000 amperes. There are currently three methods for detecting current: the resistor short-circuit method, which has the disadvantage of introducing a voltage drop and that this method cannot provide isolation between the upper and lower levels. The current converter is based on Ampere's theorem, but it is only used to detect DC. GMR magnetic field sensors can not only detect DC and AC but also ensure isolation between the upper and lower levels. With the development of semiconductor integration technology, GMR thin film sensors and integrated circuit boards have been combined to achieve miniaturization and integration, improve sensitivity and reduce costs. In addition, the current detection principle has been used as an isolator, switching power supply and brushless DC motor system. The isolator mainly converts the primary signal under high voltage and high current conditions through voltage/frequency conversion and transmits it to the next level, and then converts it into a voltage or current signal through frequency/voltage in the next level, so that the upper and lower levels do not interfere with each other. This isolator that detects the size of the current has been adopted by a company in Portugal. As for the switching power supply, we have developed a GMR magnetic field sensor that can detect micro-ampere-level AC and DC and detect magnetic fields in the range of plus or minus 20Oe by depositing the spin valve multilayer film twice. And in cooperation with a university in Spain, this sensor has been successfully used in the switching power supply circuit as a feedback system, which can improve its frequency output characteristics up to 1MHz. As for the application in brushless DC motors: As we all know, brushed DC motors use contact carbon brushes or metal sheets as commutators to power the rotor. This contact commutator has a very bad effect on the motor due to friction, such as short service life, loud noise, sparks, and interference electromagnetic waves. If the GMR sensor is used to replace the friction commutator of the motor, the impact caused by brush friction can be avoided, and the purpose of high-speed rotation of the motor and its speed regulation and stabilization can be achieved. Therefore, its stability and reliability are very high. In addition, this brushless motor has a large torque-to-weight ratio and a good linearity of speed-torque characteristics. Figure 4 shows the schematic diagram of measuring current.

3) GMR sensors can be used to measure tiny displacements and their related applications.

The principle of GMR magnetic field sensors to detect the displacement of the measured object is to use a permanent magnet as a reference. The movement of the reference relative to the magnetic sensor is equivalent to the movement of the magnetic sensitive device in a uniform gradient magnetic field. Therefore, the output of the magnetic field sensor reflects the displacement of the magnetic field sensor or the permanent magnet. Figure 5 shows a cylindrical magnetic steel and the magnetic field distribution around it. We have developed a magnetic field sensor that can detect displacement in the X-Y direction at the same time. Due to the use of integrated technology, the magnetic field sensor can be miniaturized and the accuracy is improved. This sensor has been successfully used in the control system of robots and manipulators, making them intelligent and able to pick up and place objects. In addition, the robot has the function of identifying objects. This displacement sensor can also be used in elevators and corresponding lifting systems as control systems. In addition, GMR displacement sensors can be used to transform some traditional industrial instruments to expand their application range. For example, a float flowmeter is a widely used non-electrical instrument. If a magnetic float is used instead and a GMR magnetic displacement sensor is used externally, a digital displacement sensor with voltage output can be made. In automobile engines, in order to achieve electronic ignition, a precise and sturdy displacement sensor is often needed to measure the exact rotation angle of the engine main shaft and determine the ignition time. Hall elements were used in the past, but now they can be completely replaced by GMR, thereby increasing the operating temperature range and reducing the intensity of the magnetic field triggered by the magnetic field. GMR displacement sensors can also be used on precision machine tools to improve the accuracy of mechanical processing. The movement of the piston in the cylinder can also be detected by the GMR displacement sensor.

4) GMR angular displacement and angular velocity sensor and related applications

In order to measure the size of the rotation angle of an object, it is often possible to detect the change in the direction of the magnetic field caused by the rotation of the magnet relative to the fixed GMR magnetic field sensor. The GMR magnetic field sensor we developed can detect the direction and size of the magnetic field in the plane and can detect the rotation angle of the magnet relative to it. When a magnet is fixed to the edge of a rotating wheel and the GMR magnetic field sensor is fixed next to the wheel and keeps a certain distance, the reference magnet rotates with the wheel. Every time the wheel rotates a circle, a voltage pulse output is generated. Figure 6 shows the schematic diagram of the angular velocity sensor. We have developed a digital spin valve GMR magnetic sensor dedicated to measuring angular velocity, that is, rotation speed, using integrated technology. The magnetic sensor can detect angular velocity in various situations. This type of GMR magnetic field sensor can be used in various remote meter reading systems, including digital processing of gas, water, and electricity meters. With the improvement of the automation level, the demand for various digital instruments is increasing. We have established contact with Liaoning Wanheng Technology Co., Ltd. The company needs a large number of digital GMR magnetic sensors for application in remote meter reading systems. In the automobile (motorcycle) industry, GMR magnetic field sensors can be used in the braking system (ABS) to detect the angular velocity and then play a braking role. my country will soon join the World Trade Organization (WTO), so the development and use of explosion-proof braking systems for automobiles (motorcycles) is indeed imperative. As for the motor industry, in order to obtain a stable speed working state, the speed measurement and control requires the use of GMR sensors to measure the angular velocity and obtain a stable angular velocity output through the feedback system. At the same time, GMR angular velocity sensors can also be used in the washing machine industry. With the improvement of computer storage density, the requirements for servo systems are also increasing, and the accuracy of disk speed control is also increasing, so magnetic field angular velocity sensors will be used in this field. In addition, GMR thin film materials can be used to develop magnetic encoders for various purposes. The advantages of magnetic encoders are that they are not easily affected by dust, condensation, and influence, and are not sensitive to humid gases and pollution. At the same time, their structure is simple and compact, they can operate at high speed, and their response speed is fast (nanosecond level). They are smaller in size than optical encoders, and their cost is lower. They are easy to integrate multiple components accurately, and are easier to form new functional devices and multifunctional devices than using optical components and semiconductor Hall magnetic sensors. Due to the above advantages, the application of magnetic encoders in the field of high-precision measurement and control has been increasing in recent years, and its market demand has increased by 20-30% each year. Under the requirements of high speed, high precision, miniaturization, integration and long life, in the fierce market competition, magnetic encoders have unique advantages with their outstanding characteristics and have become the key to the development of high technology.

5) GMR medical and biomagnetic field sensors

There are various forms of mechanical motion in the human body, which are the premise and guarantee for the body to complete necessary physiological functions. Therefore, the detection of these biomechanical motions is of great significance to both basic medicine and clinical medicine. In the past, the development of medicine was limited to this aspect because it had to use large, high-power and expensive superconducting quantum magnetometers. The emergence of highly sensitive and integrated GMR magnetic sensors has provided convenience for the non-contact detection of these mechanical motions and lesions, and promoted their development. The following introduces several special applications in this regard. The principle of magnetic biosensors is shown in Figure 7: First, various cells, proteins, antibodies, pathogens, viruses, and DNA can be marked with nanoscale magnetic particles, that is, these detected objects are first magnetized, and then their specific locations are detected with highly sensitive GMR magnetic field sensors. This can also be used in medical and clinical analysis, DNA analysis, environmental pollution monitoring and other fields. Highly sensitive GMR sensors can also be used in high-precision instruments and equipment used for electroencephalograms, cardiographs, etc. to diagnose problems similar to brain tumor lesions. GMR magnetic field sensors can be used to detect eye movement and eyelid movement, which helps to quantitatively evaluate and study drowsiness and visual fatigue, and diagnose certain ophthalmic diseases.

6) Application of GMR magnetic sensor in the detection of magnetic media and in magnetic ink counterfeit detection banknote counting machine

GMR magnetic field sensor can detect different magnetic media. In this application, the magnetic medium carries the information to be detected. The magnetic medium is composed of a non-magnetic substrate and a magnetic material, and the magnetic material is placed in the substrate or on the surface of the substrate. When the magnetic medium carrying information sweeps over the GMR magnetic field sensor, the specific information is detected. The output of the sensor depends on the performance of the magnetic medium, the distance of the working gap and the sensitivity of the sensor. At present, it is mainly used in the recognition of magnetic ink, the reading of magnetic coding, the detection of fine magnetic particles, and the identification of magnetic signatures of media.

7) GMR magnetic acceleration sensor

Acceleration sensor is a measuring device that determines the acceleration by measuring the inertial force of the accelerated moving object. According to Newton's law, the accelerated object has an inertial force, the magnitude of which is equal to the product of its mass and acceleration, and its direction is opposite to the acceleration direction. Due to the existence of this inertial force, the elastic sheet suspended in the accelerated system is bent, and the bending amount can be measured by the GMR magnetic sensitive device to obtain the acceleration of the system.


2. Application of GMR read heads in computer information storage

The new generation of hard disk read heads developed by using SPIN-VALVE GMR materials has increased the storage density to 56 billion bits/square inch at present (2000), and GMR heads have occupied 90 to 95 percent of the head market. Now the magnetic recording storage density has exceeded all storage methods. It is the use of GMR materials that has enabled the storage density to grow 3-4 times per year in recent years. With the acquisition of low-resistance and high-signal TMR, achieving a storage density of 100 billion bits/square inch will be the goal in the next one or two years.


3. Application of GMR in random access memory (MRAM)

A new computing random access memory chip is being developed using SPIN-VAVLE, TMR materials and semiconductor integration technology. Since the principle of setting the 0 and 1 states is derived from the hysteresis effect unique to magnetic materials, information will not be lost when the power is suddenly cut off. Semiconductor non-volatile memory uses extremely small capacitors to store information by storing a charge. If the power is cut off, the charge will be exhausted and the information will be lost. In addition, magnetic random access memory using GMR will be faster and cheaper than semiconductor non-volatile memory. IBM and Motorola in the United States and Philips, Siemens and INESC in Europe are stepping up research.


4. Application of GMR in various logic elements and all-metal computers

GMR materials can be used to develop magnetic diodes, triodes and various logic elements. Currently, magnetic GMR multilayer films and semiconductor materials are being integrated together, mainly using electron spin injection (SPIN-INJECTION) to develop new magnetic devices. All-metal computers will become possible.

III. Development prospects

Humans have created today's information age on semiconductor chips using the charge of electrons. Spin-polarized transport may bring humans another vast world. Magnetoelectronics gives humans dreams and hopes, but also gives us more and greater challenges. In fact, humans' understanding of spin-polarized transport is still at a very superficial stage, and the understanding of new phenomena and new effects that have emerged is basically a "patchwork" and semi-classical phenomenological theory. As an interdisciplinary subject between magnetism and microelectronics, magnetoelectronics will be a new field for condensed matter physicists and electronic engineering technicians to show their talents both in basic research and in application development. Magnetoelectronics

is a burgeoning cause, and its development will surely bring about further development of human technological civilization. Shenzhen Huaxia Magnetic Electronics Technology Development Co., Ltd. aims to establish a domestic development platform for magnetoelectronics, widely attract magnetoelectronics talents from home and abroad, promote the industrialization of magnetoelectronics in China, and develop and produce high-precision magnetoelectronics products such as magnetic random access memory and all-metal computers on the basis of magnetic sensor chip production, setting an example for the simultaneous development of new technologies and industrialization.