The development history and main routes of MEMS inertial sensors

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The development history and main routes of MEMS inertial sensors

Posted Date: 2024-01-28

Author: Ding Henggao

This article comes from part of the abstract of the latest signed paper written by Ding Henggao, an academician of the Chinese Academy of Engineering and a general of the Chinese People's Liberation Army, published in 2023. Academician Ding Henggao is the only two "general academicians" in my country who hold two titles at the same time. .

This article is compiled based on many discussions between Academician Ding Henggao and relevant comrades in the inertial technology community over the years. It mainly discusses the great progress and future development of my country's MEMS inertial sensor technology in the past 30 years. Information shows that Academician Ding Henggao was born in 1931 and is 93 years old this year. He is still concerned about the development of my country's inertial technology. Academician Ding Henggao is not only one of the first academicians of the Chinese Academy of Engineering, but also a well-known expert in inertial technology and precision instruments in my country. As one of the founders of my country's strategic missile inertial technology, he is also the main promoter of the development of my country's inertial technology disciplines and the main advocate of China's MEMS and other micron and nanotechnology. See article details below.

This article is from "Navigation and Control". The relevant content may be deleted. Please subscribe to the journal to view the original text for the full content. "Navigation and Control" was founded in 2002. It is managed by China Aerospace Science and Technology Corporation and sponsored by Beijing Aerospace Control Instrument Research Institute. It is an academic publication that reflects the development status of inertial technology in the maritime, land, air, space and civil fields. It is my country's The authoritative publication in the field of inertial technology.

Ding Henggao, an expert in inertial technology and precision instruments, was born in Nanjing, Jiangsu Province in February 1931. He is a general of the Chinese People's Liberation Army and an academician of the Chinese Academy of Engineering. Graduated from the Department of Mechanical Engineering of Southeast University (now the School of Mechanical Engineering) in 1952. He has successively served as Director of the Commission of Science, Technology and Industry for National Defense, member of the Presidium of the Chinese Academy of Engineering, Honorary Chairman of the Chinese Astronautical Society... and other positions. Ding Henggao is one of the founders of my country's strategic missile inertial technology, the main promoter of the development of my country's inertial technology discipline, and the national advocate of micron and nanotechnology. He has long been engaged in the development of gyroscopes, accelerometers, and inertial platform systems for guided weapons.

In the past thirty years, MEMS inertial sensor technology has made great progress and has been widely used in human life, industry, and high-end equipment. This article outlines the development history and main routes of MEMS inertial sensors in my country, and takes vehicle assisted driving as an example. It summarizes the rapid development and typical applications of MEMS inertial sensing technology at home and abroad, and concludes that MEMS inertial sensors are moving toward high reliability and integration. Accelerate development in the direction of modernization, high integration and intelligence.

Preface P

In mid-November 1994, the first "National Academic Conference on Nanoscience and Technology" determined the proper academic term "micron nanotechnology".

During the "Ninth Five-Year Plan" period, our country regarded the development of high-performance MEMS inertial sensors as a strategy for developing military micron and nanotechnology, and carried out technical research closely around the needs of Miniature Inertial Measurement Units (MIMU).

In the blink of an eye over the past thirty years, MEMS inertial sensors have moved from laboratory exploration and research to engineering applications. Great progress has been made in technology and products, and they have been widely used in consumer electronics, vehicle navigation, the Internet of Things, industrial equipment, and high-end equipment. application.

Development status and achievements

1.1 High-performance MEMS inertial sensor products have been widely used

Currently, the global market for high-performance MEMS inertial sensor products is highly concentrated, with market shares dominated by Honeywell, Analog Devices, and Northrop Grumman. The core indicators of domestic high-performance MEMS gyro products can be matched by giants such as international companies, with a share of 50%. Honeywell has achieved domestic independent production. Although the market penetration rate needs to be further improved, it has solved the problem of "stuck neck" in equipment application. question.

The main solutions for the exploration and research of MEMS gyroscopes include: mass vibration gyroscope, tuning fork gyro, four-mass gyroscope, ring gyroscope, etc. The main solutions for the exploration and research of MEMS accelerometers include: seesaw accelerometer, sandwich accelerometer, and comb-tooth accelerometer. and resonant beam accelerometers, etc.; the Top-Down method is used to manufacture the sensitive structures of gyroscopes and accelerometers based on bulk silicon technology.

Through technology introduction and other means, a 6-inch silicon-based standard manufacturing process platform has been established, which has improved the processing level and ensured the dimensional accuracy of mechanical parameters such as aspect ratio, verticality, bottom undercut, etc., thus greatly improving the understanding of designers. level.

At the end of 2011, China developed a MEMS+ASIC two-piece system-in-a-package (SiP) gyroscope and accelerometer based on a ceramic shell. In 2019, high-performance MEMS gyroscopes and MEMS accelerometers will achieve large-scale mass production. At this point, China has mastered the main technical aspects of MEMS inertial sensor design, manufacturing, packaging and testing, and has the ability to develop high-performance MEMS inertial sensor products.

1. 2 Be the first to apply MEMS inertial sensors to intelligent assisted driving

The basic requirements for positioning systems for intelligent assisted driving and autonomous driving are high accuracy, high reliability, and high availability, and they also need to meet functional and safety requirements. Relying solely on GNSS positioning is risky in complex environments and extreme weather conditions, while inertial navigation becomes an effective safety redundancy. Compared with laser gyroscopes and fiber optic gyroscopes, MEMS inertial sensors have irreplaceable advantages in terms of volume, quality, power consumption, price, and lifespan. However, compared with laser gyroscopes and fiber optic gyroscopes, the bias stability index of MEMS inertial sensors is far behind, about 2 to 3 orders of magnitude.

Therefore, almost no one thinks that MEMS inertial sensors can be used to sense vehicle position information in unmanned driving systems. Many companies use a combination of fiber optic inertial navigation and satellites to conduct tests on vehicles and have achieved good results. However, the high price, low production efficiency and long production cycle make it difficult to apply this solution on a large scale on vehicles.

Under the strong traction of new domestic car-making forces, especially Xpeng Motors' intelligent assisted driving solution, domestic companies dared to be the first in the world and took the lead in trying the MEMS inertial sensor + GNSS combination on-board test, and achieved satisfactory results.

On the premise of ensuring product quality and product safety, building mass production and delivery capabilities for vehicle-mounted P⁃Box is the core key to achieving large-scale vehicle applications. Prior to this, no unit in the country had made a similar attempt.

Domestic companies have applied MEMS six-axis inertial sensors to intelligent assisted driving, pioneering a new path in the segmented track of vehicle positioning, and are at the forefront of the world.

1. 3 Consumer-grade MEMS inertial sensors emerge

As the world's largest electronic product production base, my country is consuming a quarter of the world's MEMS sensors. The demand and market are huge. However, at present, most of my country's MEMS sensors still rely on imports. Large IDM companies such as Bosch, ST, and TDK have strong technical and financial strength. They design their own sensors and produce their own sensor wafers. Their products have huge advantages in terms of price and performance.

Supply chain security issues also exist in the consumer sector. Against the background of domestic substitution, system manufacturers have a huge demand for MEMS gyroscopes and MEMS accelerometer products, and domestic companies have ushered in new development opportunities.

Direction of development

2.1 L3 and above autonomous driving requires safe, reliable, low-cost, and high-precision MEMS inertial sensors

At present, the global penetration rate of autonomous driving is mainly L1 and L2, while the penetration rate of L3~L5 is relatively low. Autonomous driving technology in the domestic passenger car market is mainly L2 level, and L3 level has not yet been implemented. According to ICV forecasts, the global autonomous driving penetration rate of L2 and above will show an increasing trend from 2023 to 2027. Among them, the L2/L2+ level is expected to have a penetration rate of 58% in 2027, and the L3 level is expected to have a penetration rate of 25% in 2027.

From L2 to L3, the safety of autonomous driving is very prominent. For example, when testing autonomous vehicles, 99.9% of the problems can be found in 150,000 kilometers of testing, but the remaining 0.1% of the problems may not be discovered and eliminated in 1.5 billion kilometers. solve. Multiply this 0.1% by the hundreds of millions of vehicles and kilometers driven on the road every year, and that is an astronomical figure. So, how do you make self-driving cars safer than airplanes? Functionally safe sensors with 99.9999% reliability are essential.

The market share of passenger cars priced above 300,000 yuan is very limited, so the installation rate of high-precision positioning products for passenger cars is around 1.8%. In the future, high-precision positioning products will definitely penetrate into cars priced at 200,000 yuan or even 100,000 yuan, and huge cost pressure will follow. Without affecting safety and quality, it is inevitable to reduce the cost of MEMS inertial sensors. The price should be very low, and the performance and reliability requirements are still very high.

2.2 Humanoid robots open up room for growth of MEMS inertial sensors

The MEMS inertial sensor can acquire the humanoid robot's MEMS IMU, which can monitor the real-time status, position information and movement trajectory of the humanoid robot, and maintain the posture balance of the humanoid robot in completing actions such as walking, running, and squatting. A single humanoid robot uses one or more MEMS IMUs, and the market space is vast. MEMS IMU is integrated with other sensors, such as stereo cameras, joint encoders, force and torque sensors, foot contact sensors, etc., to achieve data complementation, estimate the center of mass position, speed, direction, angular rate and angular momentum of the posture foot, and jointly determine the robot state Feedback and complete the next action, which can be used in scenarios such as squatting and standing, walking forward and backward, going up and down stairs, and avoiding obstacles.

2.3 MEMS inertial sensors move towards integration, fusion and intelligence

As the degree of integration becomes higher and higher, the cost of products will become more competitive, and chip integration may become the ultimate form of products. Advanced packaging technology, especially 3D stacking packaging technology, can combine multiple chips and integrate more sensor chips in a limited volume to achieve more complex and powerful functions.

The bias accuracy and scale error of the MEMS inertial sensor directly affect the accuracy of the trajectory calculation. Therefore, error analysis and compensation of inertial sensors are the main methods to improve positioning accuracy. With the continuous advancement and maturity of ASIC technology, the sensor's signal detection and processing circuit, closed-loop control circuit and computing unit will be highly integrated. Error compensation algorithms, self-calibration, self-calibration and functional safety algorithms will all run at the sensor chip layer. .

As the performance indicators of MEMS inertial sensors continue to improve, their size and power consumption continue to decrease, and their costs and prices continue to decrease, their application fields will continue to expand. While firmly occupying the consumer electronics market, it will keep pace with the development of artificial intelligence (AI) technology and be widely used in smart cars, humanoid robots, drones, and unmanned systems. Domestic universities, research institutes and innovative enterprises will surely gain opportunities for rapid development. Domestic MEMS inertial sensors will not only occupy the domestic market, but also occupy a place in the international market.

Review Editor: Huang Fei

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