Sensors and actuators are an important part of the IoT system. The intelligent sensor constitutes the sensing layer of the Internet of Things system and is the most direct system unit for data acquisition in the IoT system. An independently working IoT terminal is generally composed of a sensor, a data processing unit (processor plus memory), a power management unit, and a wireless communication unit. In such a terminal, the data collected by the sensor is processed by the data processing unit and transmitted to the cloud by the wireless communication system to realize connection with the entire network. Sensor requirements for IoT applications include: device miniaturization, functional integration, low cost and mass manufacturing. Among them, low cost and mass manufacturing are directly related. The MEMS technology derived from silicon-based integrated circuit manufacturing technology can meet the above requirements and become the mainstream production technology of micro-sensor technology in the Internet of Things era. Figure 1 Four system units of the IoT terminal Widely used MEMS MEMS is an abbreviation for Micro-Electro-Mechanical System. It has two characteristics: one is that the device size is on the order of micrometers or nanometers; the other is that there is usually a suspended moving part to achieve sensing or transmission functions, such as the cantilever beam in Fig. 2. When the motion state of the cantilever beam changes, the designed electromechanical coupling device converts the mechanical motion into an electrical signal. There are many methods of electromechanical coupling. For example, by forming a cantilever beam and a lower electrode into a capacitor, the output voltage signal can be obtained to obtain information about the cantilever beam motion. A variety of sensors can be fabricated by attaching a film material capable of sensing the external environment to the cantilever beam, that is, a sensitized layer. For example, sensors that sense motion are used to detect pressure, acceleration, direction of motion, distortion, flow, wind, and the like. A MEMS microphone that senses sound waves is a very common acoustic sensor that is widely used in mobile phones and mobile terminals. A photosensitive layer is attached to the MEMS, which converts light into heat and changes the shape of the cantilever beam to form a photosensitive sensor, an infrared sensor, and the like. Figure 2 Schematic diagram of MEMS device structure MEMS technology can also manipulate the movement of the cantilever beam with electrical signals to make actuators such as micromotors, microswitches, micropumps, inkjet printheads, and the like. A widely used MEMS speaker in a mobile phone is a typical actuator. MEMS can also be used to make electronically controlled optical devices such as micromirrors, micro-projections, and micro-light gates for optical systems. There is also a class of devices fabricated using MEMS technology, which utilizes the mechanical resonance function of the cantilever beam to form a high-frequency filter, which is expected to replace the surface acoustic wave filter. In addition, there are energy harvesting devices that use moving parts to convert mechanical kinetic energy into electrical energy and store them. The MEMS sensor as a product appeared later. In the 1980s, the silicon cantilever structure was packaged on glass to make the first MEMS sensor for engine control. In the 1990s, MEMS accelerometers began to be used in automotive airbags; in addition, MEMS pressure sensors began to be used in sphygmomanometers; inkjet printheads made with MEMS technology were used in printers, becoming the first widely used consumer. MEMS-like actuators. Between 2000 and 2010, MEMS sensors and actuators were greatly promoted, with tire pressure sensors for measuring tire pressure, gyroscopes for monitoring horizontal and vertical motion of cameras and mobile phones, microphones and speakers based on MEMS technology, and MEMS. Switch, infrared image sensor, fingerprint recognition sensor and other products. Since 2010, driven by the demand for IoT technology , various MEMS sensors and actuators have been widely used in the fields of wearable systems, virtual reality products, smart homes , smart phones, smart manufacturing, automobiles and autopilots. (Figure 3), the product includes a variety of motion sensors and actuators, gas/humidity/photosensors, infrared imaging sensors, and more. There are more than a dozen MEMS device products for smartphones only, including 9-axis inertial sensors, MEMS microphones, RF MEMS, barometers, temperature and humidity sensors, gas sensors, autofocus actuators, optical MEMS, and more. Energy harvesters, infrared imaging sensors, ultraviolet sensors, ultrasonic sensors, etc. may also be introduced in the future. Figure 3 Rapidly growing MEMS sensor and actuator applications CMOS-based manufacturing technology MEMS manufacturing technology is derived from CMOS integrated circuit fabrication technology. Over the past 50 years, CMOS integrated circuit manufacturing technology has developed rapidly, becoming the finest and most complex manufacturing technology ever. In terms of device size, the 1 micron line width from the 1970s has been reduced to the present. The 20 nm line width makes the number of devices per unit silicon substrate area greatly improved. In terms of device graphics, the process capability of CMOS technology far exceeds the needs of MEMS device manufacturing. It can be said that CMOS integrated circuit manufacturing technology has laid a very solid foundation for MEMS manufacturing. On the other hand, the MEMS manufacturing process has its own characteristics different from that of CMOS manufacturing. First of all, it is a unique cantilever beam forming process. There are currently two types of cantilever beam forming processes available, one using a sacrificial layer process and the other using a wafer bonding process. Figure 4 (left) shows a schematic diagram of the process of forming a cantilever beam using a sacrificial layer process. Specifically, a sacrificial layer such as a silicon dioxide layer, a structural layer, or a polysilicon layer is deposited on the surface of the silicon substrate. Then, a special process involves exposing the sacrificial layer by CMOS patterning processes such as photolithography, etching, chemical mechanical polishing (CMP), and etching the absorption layer with a chemical solvent (wet method) or chemical vapor (dry method). , the structural layer is suspended to form a cantilever beam. Figure 4 (right) shows a schematic flow diagram of a cantilever beam formed by a wafer bonding process. Specifically, a cavity under the cantilever beam is formed on the silicon substrate, and the surface of the structural layer wafer is downwardly bonded to the substrate wafer. The thinning technique is then used to thin the structured wafer from the back side, leaving only the thickness required to meet the requirements of the cantilever beam. The cantilever beam is formed by a CMOS patterning process such as photolithography and etching. The difference between the two technical solutions is that the former process is relatively simple. In addition to the special steam etching equipment required for steam etching, the existing CMOS industrial equipment can be basically used, and the compatibility with CMOS manufacturing is good. The use of a wafer bonding process requires the use of wafer bonding equipment, so the technical complexity is relatively high, and thus some manufacturing costs are increased. Its advantage is the high quality and process consistency of the cantilever beam. In the sacrificial layer process, the structural layer is a polycrystalline silicon material formed by high temperature deposition, and stress is inevitably left in the layer. Thus, fluctuations in the film growth process conditions are liable to cause on-chip and inter-sheet uniformity problems, and even cause a decrease in yield. The structural layer formed by the bonding process is a single crystal material, and there is no stress caused by high temperature growth in the layer, and the consistency of the material properties is good, which greatly contributes to the improvement of the yield. Figure 4 Two process flow for fabricating MEMS cantilever beam structure Another aspect of MEMS processes that differ from CMOS processes is the special requirements of the former for packaging. For CMOS, when the device is interconnected to form a multilayer wiring, it can be packaged by side wire bonding, flip chip bonding, or multi-layer (2.5D/3D) package based on through-silicon via (TSV) technology. Then fill the package with a plastic package. For MEMS, the cantilever structure of the device must be able to move freely. Therefore, it is not possible to fill and package like CMOS. Instead, the capping method must be used to cover the components such as the cantilever beam with a cap. The material is not filled in the cap. In particular, sports MEMS devices require a vacuum to be maintained within the cap. Therefore, MEMS packaging brings a large process complexity and cost increase. In the single-chip capping process, the package occupies more than 70% of the MEMS manufacturing cost of the vacuum package. One way to reduce costs is to use wafer-level packaging, which is to design a cavity on a silicon wafer, form a cap wafer, and then cover the wafer onto the device wafer for wafer-level vacuum packaging. . In order to match the wafer level package, it is also necessary to consider the connection of the electrical leads. Figure 5 shows a schematic diagram of the structure of a MEMS device completed by wire bonding and wafer level packaging using silicon. Figure 5 Schematic diagram of MEMS device completed through through-silicon via and wafer-level package Opportunities and challenges MEMS technology has a very broad application prospect, especially in the era of the Internet of Things, only MEMS can meet the requirements of sensors and actuators for IoT applications. First, the size of MEMS fully meets the miniaturization requirements of IoT applications. Second, the compatibility of MEMS technology with CMOS technology makes it easy to meet the intelligent requirements of sensors and actuators in the Internet of Things. Using the same process line, the fabrication of CMOS integrated circuits and MEMS devices can be completed simultaneously, achieving heterogeneous integration of the two. Heterogeneous integration can be done by interconnecting and interconnecting the two on the same chip, or on different wafers, and then integrated into the same system in a 2.5D or 3D package. The third advantage is the advantage of MEMS in terms of energy loss. IoT applications require more power consumption than other application environments. The way MEMS is perceived and implemented makes it a device with lower power consumption and is most likely to be a technology that meets the power requirements of IoT. Another advantage is that it can meet the number of sensors/actuators required by the Internet of Things. Silicon-based integrated circuit technology can produce tens of thousands of MEMS sensors on a single wafer, while at the same time providing low manufacturing costs. Thanks to R&D investment in the development of CMOS manufacturing technology, equipment and process manufacturing technologies required for MEMS manufacturing already exist. It can be used for MEMS production with minor adjustments and development. In fact, the current production line for MEMS manufacturing in the world is mainly an 8-inch line that has been eliminated from the manufacture of CMOS mainstream products. These production lines can be used to meet the requirements of mass manufacturing, and the manufacturing cost of each MEMS can be reduced to meet the price requirements of consumer products. Due to the wide variety of applications in the MEMS market, the diversification of product production technologies has brought opportunities for SMEs. In particular, companies that have accumulated technology before will find opportunities in many markets and win rapid development. But on the other hand, the development of MEMS production technology and the growth of enterprises also face some special challenges. First of all, the MEMS market segmentation is prominent, making the total demand for a single product much smaller than that of integrated circuit products, while the investment in MEMS product production lines is relatively large, resulting in high investment risk and long return on investment, to a certain extent. Limit the development of MEMS industry and enterprises. To solve the difficulties of SMEs in industrial technology development and investor confidence, and to promote the agglomeration and development of national and local MEMS industries, a feasible measure is to establish a public technology research and development platform to provide process research and development and pilot services for SMEs. Strive to reduce the blindness of investment and enhance the ability of startups to generate. In recent years, the Institute of Microelectronics of the Chinese Academy of Sciences has established a complete MEMS process pilot line, using industry-standard production equipment to provide research and development services for enterprises, and achieved good social benefits. It is believed that through the joint efforts of the state, local and enterprises, the concept of cooperation between industry, academia and research will be able to overcome the difficulties encountered in industrial development, promote the rapid development of the MEMS industry, and timely meet the rapid growth of sensors and actuators in the development of Internet of Things technology. Demand. 950W Human Sensor PTC Fan Heater 950W Human Sensor Ptc Room Heater,Ptc Fan Heater,Ptc Tower Heater,Ptc Electric Fan Heater Foshan Shunde Josintech Electrical Appliance Technology Co.,Ltd , https://www.josintech.com