In the past 10 years, technologies such as smartphones, smart watches, and drones have rapidly entered our lives, and in the next 10 years, various wearable devices, IoT devices, robots, autonomous driving, etc. will be integrated into our lives.
As one of the cornerstones of these technologies, sensor technology is driving the development of technology, and these technologies are also redefining the need for future sensor technology: smaller, more integrated, smarter, and lower power consumption......
In the future, what technologies will promote the development of sensors? This article summarizes the eight key technologies for sensor development, which may be inspiring.
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1. Sensing technology with new principles and new effects
Sensors are the crystallization of many high-tech, is the result of the intersection of many disciplines, we are based on a variety of physical, chemical, biological effects and laws, the development of force-sensitive, thermal, light-sensitive, magnetic and gas-sensitive and other sensitive components, the formation of today's global as many as more than 26,000 types of sensors.
Therefore, the development of sensitive elements and sensing elements with new principles and new effects, and the development of new sensors, is an important way to develop high-performance, multi-functional, low-cost and miniaturized sensors.
Taking inertial sensors as an example, inertial sensors are sensors that apply inertial principles and measurement technology to detect and measure acceleration, tilt, shock, vibration, rotation and multi-degree-of-freedom (DOF) motion, and an inertial system composed of accelerometers and gyroscopes can realize real-time monitoring of carrier position and motion information.
Different types of gyroscopes are driven by different physical principles, such as mechanical dry, liquid floating, semi-liquid floating, air float angular rate gyroscope, flexible angular rate gyroscope, MEMS silicon, quartz angular rate gyroscope (including hemispherical resonant angular rate gyroscope), etc., mainly using the Coriolis effect (refers to a phenomenon in which an object moving in a rotating coordinate system is deflected (Coriolis force is proportional to the input angular rate).
Sensor technologies such as fiber angular rate gyroscopes and laser angular rate gyroscopes mainly use another principle: the Sagnac principle, also known as the Sagnac effect (the phase difference is proportional to the input angular rate).
These new principles and effects play a key role in promoting the development of sensing technology and opening up more sensor applications.
At the same time, interdisciplinary new technologies also play an important role in the development of sensing technology. For example, in MEMS sensors, high-performance application-specific integrated circuits (ASICs) can integrate thousands of transistor circuits into a single chip, reducing the impact of environmental factors and parasitic parameters on sensor performance and greatly improving the accuracy of MEMS sensors.
▲MEMS acoustic sensor structure diagram (from Goertek micro prospectus)
Quantum sensors are one of the important application scenarios of quantum technology, and the National Science and Technology Council (NSTC) of the United States has previously released a national strategy on quantum sensors, "Putting Quantum Sensors into Practice"
Using the relevant effects in quantum mechanics, quantum-sensitive devices can be designed and developed, such as resonant tunnel diodes, quantum well lasers and quantum interference components, which have the advantages of high speed (1000 times faster than electronic sensitive devices), low power consumption (1000 times lower energy consumption than electronic sensitive devices), high efficiency, high integration, economic reliability and so on.
The development of nanoelectronics will also cause a new technological revolution in the field of sensing technology. The use of nanotechnology to make the sensor, the size is reduced, the accuracy is improved, the performance is greatly improved, the nano sensor is standing on the atomic scale, which greatly enriches the theory of the sensor, promotes the production level of the sensor, and broadens the application field of the sensor.
2. Sensor miniaturization and chip technology
Sensor miniaturization and chip technology, mainly including MEMS process and a new generation of solid-state sensor microstructure manufacturing process, among which MEMS process has been widely used in sensors.
Microelectromechanical systems (MEMS) are microsystems or devices that integrate micromechanisms, microsensors, microactuators, control circuits, signal processing, communications, interfaces, and power supplies, and are technologies for designing, processing, manufacturing, measuring and controlling micro/nano materials.
MEMS materials include functional materials (usually semiconductor materials with silicon as the main body), structural materials (such as piezoelectric materials, supermagnetostrictive materials, photosensitive materials, etc.) and smart materials (mainly shape memory alloys).
The key technologies of the MEMS process include: deep reactive ion etching, LIGA technology, molecular assembly technology, bulk micromachining, surface micromachining, laser microfabrication and micro-packaging technology.
Among them, silicon micromachining technology is the mainstream technology of MEMS, it is a precision three-dimensional processing technology, is the core technology for the development of sensors, microactuators, microactors, micromechanical systems, has been successfully used in the manufacture of various microsensors and multi-functional sensitive element arrays, such as microsilicon capacitive sensors, microsilicon mass flow sensors, aerospace dynamic sensors, microsensors, automotive special pressure and acceleration sensors, environmental protection microchemical sensors, etc.
Deep Reactive Ion Etching (DRIE) is one of the important processes in MEMS structure processing, which is mainly used for the etching of polysilicon, silicon nitride, silica thin films and metal films, and is a microelectronic dry corrosion process.
LIGA technology, or photolithography, electroforming, and injection molding, is a method that uses deep X-ray etching to form deep three-dimensional microstructures through electroforming and plastic molding.
▲MEMS gyroscope structure
At present, in order to adapt to the development of MEMS technology, many new MEMS packaging technologies and processes have been developed, such as anodic bonding, silicon fusion bonding, eutectic bonding, etc. MEMS packages are typically divided into the following levels: die-scale, device-in-package, wafer-scale, monolithic, and system-in-package.
Single-chip packaging (SCP) belongs to the category of device-level packaging, which refers to the creation of a protective layer on a chip to shield vulnerable components and circuits to avoid adverse effects of the environment, and to make an active sensor/actuator path to achieve electrical contact with the outside to meet the technical requirements of the device in terms of electrical, mechanical, thermal and chemical aspects.
Multi-chip assembly (MCM) is a major breakthrough in electronic packaging technology, which belongs to system-in-package. MCM assembles two or more IC/MEMS chips or CSPs on a single circuit board to form a functional circuit board, that is, a multi-chip assembly, which provides signal interconnection, I/O management, thermal control, mechanical support, and environmental protection for each chip (building block) in the assembly. MCM has the ability to support multiple chips on the same substrate without changing the manufacturing process of the MEMS and circuits.
3. Integration technology of sensor array and multi-sensor parameter composite
Such integrated technologies include integrated process and multi-variable composite sensor microstructure integrated manufacturing process, multi-variable composite sensors for industrial control, etc., such as pressure, static pressure, temperature three-variable sensors, barometric pressure, wind, temperature, humidity four-variable sensors, microsilicon composite strain pressure sensors, array sensors.
Integration refers to the integration of a variety of sensing functions with data processing, storage, two-way communication, etc., which can fully or partially realize signal detection, conversion processing, logic judgment, function calculation, two-way communication, as well as internal self-testing, self-calibration, self-compensation, self-diagnosis and other functions, with low-cost, high-precision information collection, data storage and communication, programming automation and function diversification.
There are two kinds of sensor integration: one is to build multiple sensing modules on a chip through micromachining technology to form a linear sensor (such as a CCD image sensor), and the other is to make sensitive components with different functions on the same silicon wafer to make an integrated multi-functional sensor, with high integration, small size, easy to compensate and correct.
Micromachining technology and precision packaging technology have a significant impact on the integration of sensors.
Multi-sensor information fusion integrates sensor application technology, data processing technology, computer software and hardware technology and industrial control technology.
It uses computer technology to analyze, eliminate the redundancy and contradiction that may exist between multi-sensor information, complement it, reduce its inaccuracy, and obtain the consistent interpretation and description of the measured object, which has the advantages of fault tolerance, complementarity, real-time and economy.
4. Sensor digitization and intelligent technology
Intelligent technology and intelligent sensor signal wired or wireless detection, conversion processing, logic judgment, function calculation, two-way communication, self-diagnosis and other intelligent technologies, intelligent multi-variable sensors, intelligent power sensors and various intelligent sensors, transmitters.
A digital sensor consists of circuitry that regulates and processes signals and an interface for network communication. They are typically made in the form of modules, including sensors, DSPs (Digital Signal Processors), DSCs (Digital Signal Controllers) or ASICs (Purpose-Purpose Integrated Circuits), but they are also made in system packages or system-on-chips. There are typically three types of electronic components used to drive digital outputs: mechanical relays, transistors, and bidirectional FET devices.
Intelligent sensor refers to the sensor with anthropomorphic intelligence characteristics or functions developed by artificial intelligence technologies such as hardware softness, software integration, virtual reality, and soft measurement, and is also an active sensing system with independent detection and signal processing and conversion capabilities, self-testing, and communication functions.
The typical representative of smart sensors is high-performance smart industrial transmitters. For example, Yokogawa's EJA series intelligent transmitter, ABB's MV2000T series multi-function differential pressure/pressure transmitter, and Rosemount's 3095MV multi-parameter mass flow transmitter respectively use silicon resonant sensors, composite microsilicon solid-state sensors and high-precision capacitive sensors as sensitive components, with an accuracy of 0.1075%, high stability and reliability, and no need to zero adjustment within ten years.
5. Strong environmental adaptability technology of sensors
We know that sensors are ubiquitous from automotive to industrial, from medical to aerospace, from home appliances to test and measurement, and many industrial applications have high requirements for the environmental adaptability of sensors. For example, in 2004, the magnetoresistive sensors produced by a German company used in the Mars rovers Spirit and Opportunity can operate in temperatures ranging from +270°C to -133°C.
The strong environmental adaptability test of sensor products includes electrical safety experiments, failure analysis experiments, corrosive gas experiments, environmental performance experiments, material experiments, etc.
The advancement of sensor packaging materials and technology has made the sensor more and more adaptable to the environment.
Metal matrix composite packaging (AI/Si Cp) can realize the physical property design of the material by changing the type and arrangement of the reinforcement, or changing the alloy composition of the matrix, or changing the heat treatment process, or change the interface bond between the matrix and the reinforcement by changing the heat treatment process, so as to affect the thermal properties of the material. This type of material has a low coefficient of thermal expansion, which can not only match the coefficient of thermal expansion of electronic component materials, but also have high thermal conductivity and low density.
More than 90% of plastic encapsulation is made of epoxy resin, which has the advantages of mass production and reliability comparable to that of metal or ceramic materials. Vulcanized epoxy resins also have the characteristics of faster curing speed, lower curing temperature and moisture absorption, high moisture resistance and heat resistance.
Ceramic packaging uses adhesive or solder to mount one or more chips on a ceramic base plate or header, and uses flip soldering to bond with the ceramic-metal pattern layer, and then seals the package body with a suitable electrical connection.
Ceramics have a high Young's modulus, high insulation performance and excellent high-frequency characteristics, good reliability, plasticity and easy sealing, its linear expansion coefficient is very similar to that of electronic components, stable chemical properties and high thermal conductivity, and is used in multi-chip components, soldering arrays and other packages.
6. Wireless sensor network technology
Wireless sensor network (WSN) is a multi-hop ad hoc network system composed of a large number of stationary or moving sensors with sensing, wireless communication and computing capabilities, which can autonomously complete the specified tasks according to the environment.
A large number of sensors form a distributed and intelligent information processing system through the network, which can monitor, perceive, collect and analyze the events, phenomena and environment in the network coverage area in real time from a variety of perspectives and in a variety of modes, obtain rich and high-resolution information, process and transmit this information, and send it to observers.
Sensors, sensing objects, and observers make up the three elements of a wireless sensor network. A wireless sensor network (WSN) consists of a sensor unit, a controller, and a wireless communication module that enables functions such as data acquisition, short-range communication, data computing, and long-range wireless communication.
WSN integrates sensor technology, embedded operating system technology, distributed information processing technology, wireless communication technology, energy harvesting technology, low-power technology, routing protocol of multi-hop ad hoc network, positioning technology, time synchronization technology, data fusion and data management technology, information security technology, network transmission technology, the key is to overcome node resource constraints (energy supply, computing and communication capabilities, storage space, etc.), and meet the requirements of sensor network scalability and fault tolerance.
This technology was named by the Massachusetts Institute of Technology's (MIT) Technology Review magazine as one of the top 10 emerging technologies that will have a profound impact on the future of human life.
7. Sensor digital communication bus technology
Fieldbus technology is a set of computer technology, communication technology, integrated circuit technology and intelligent sensing technology in one of the emerging control technology, is installed in the manufacturing and process area of the field device and the control room between the digital, serial, multi-point communication data bus, is a fully digital, open, two-way transmission, multi-branch, multi-station communication system, is the integration of field communication network and control system.
▲Schematic diagram of intelligent sensing technology based on fieldbus
The key symbol of the fieldbus is to support all-digital communication, establish a high-reliability data communication line in the control site, realize the data communication between the intelligent sensors and between the intelligent sensor and the main controller, and turn a single scattered intelligent sensor into a network node.
Fieldbus intelligent sensors need to have the following functions: share a bus to transmit information, with a variety of calculation, data processing and control functions, so as to reduce the burden on the host; replace 4-20mA analog signal transmission, realize the digitization of the transmitted signal, enhance the anti-interference ability of the signal; adopt a unified network protocol, become the node of FCS, realize the information exchange between the sensor and the actuator; the system can be calibrated, configured, testing to improve system reliability, standardized interfaces with plug-and-play features.
Fieldbus smart sensors are the mainstream instruments for industrial process control systems of the future.
8. Application technology of sensors
The application technology of sensors refers to the general term for various technologies that apply sensors to downstream devices and scenarios, and sensors alone often do not play their due role.
These technologies include: signal processing and interface technology, noise reduction and anti-interference technology, display and adjustment instrument, measurement and error processing, sensor selection and installation adjustment technology, displacement, force, torque, load, speed, acceleration and other mechanical quantity detection technology, temperature, pressure, flow, level and other process quantity detection technology, humidity detection and gas analysis technology, detection, imaging and safety prevention technology, intelligent and automatic testing technology, proximity sensor, pressure sensor, induction synchronizer installation technology, infrared, Ultrasonic, microwave detection burglar alarm installation technology, etc.
For consumer applications, the main technical difficulty of sensor fusion is how to control the size of the product, reasonably test the performance of each sensor, control the yield rate of the entire chip, and reduce the cost.
For sensor fusion in industrial, military, automotive, medical and other fields, it is also necessary to consider how to ensure the accuracy and reliability under various working conditions, and use the characteristics of fusion to realize compensation and correction between sensors.
The internal noise of the sensor circuit includes the interference of electromagnetic components of the circuit board, low-frequency, high-frequency heat, semiconductor device shot transistors, resistors, integrated circuit noise, etc., and the external interference includes power supply, ground wire, long-line signal transmission, space electromagnetic waves, etc.
Therefore, in the circuit design, it is necessary to reasonably select low-noise semiconductor components according to different working frequencies, and select appropriate amplification circuits according to different working frequency bands and parameters.
epilogue
Although the sensor is small, it is behind the trillion-level market of industrial automation, robots, automatic driving, Internet of Things, etc., which is a key technology field that is truly related to the national economy and people's livelihood!
The 8 key common technologies of sensors in this paper are an important cornerstone for the development of sensing technology in the future, and through these technical directions, we can seize the leading position of industrial development and narrow the gap between sensor technology in mainland China and abroad.
But at the same time, we should pay more attention to the disconnection between technology and industry in the mainland sensing industry, that is, technology research and development in universities in research institutes, and the implementation of the development of the sensor industry is the majority of small and medium-sized sensor enterprises, how to combine the technology in the laboratory with the majority of small and medium-sized sensor enterprises, do a good job in technology industrialization, and sensor technology research and development is equally important.