What Is a MEMS Gyroscope?

MEMS sensors, or microelectro mechanical systems (Microelectro Mechanical Systems), are multidisciplinary, cutting-edge research areas developed on the basis of microelectronic technology. After more than 40 years of development, it has become one of the major scientific and technological fields that the world has noticed. It involves a variety of disciplines and technologies such as electronics, mechanics, materials, physics, chemistry, biology, medicine, and has broad application prospects. As of 2010, more than 600 units around the world were engaged in the development and production of MEMS. Hundreds of products including micro pressure sensors, acceleration sensors, micro inkjet print heads, and digital micro mirror displays have been developed. Among them, MEMS sensors account for a considerable proportion. MEMS sensors are new types of sensors manufactured using microelectronics and micromachining technologies. Compared with traditional sensors, it has the characteristics of small size, light weight, low cost, low power consumption, high reliability, suitable for mass production, easy integration and intelligentization. At the same time, the feature size on the order of micrometers makes it possible to perform functions that some traditional mechanical sensors cannot achieve.

1. Medical application

MEMS sensors are used in non-invasive fetal heart detection. Detecting fetal heart rate is a very technical task. Because the fetal heart rate is very fast, between 120 and 160 times per minute, using a traditional stethoscope, even only ultrasound Doppler with magnification It is difficult to measure accurately with manual counting. The digital Doppler fetal heart rate monitor with digital display function is expensive and only used by a few large hospitals. It cannot be popularized in small and medium hospitals and the vast rural areas. In addition, the ultrasonic vibration wave has a great adverse effect on the fetus. Although the detection dose is very low, it also belongs to the category of destructive detection, and is not suitable for frequent and repeated inspections and home use.

Based on VTI's MEMS acceleration sensor, a non-invasive fetal heart detection method is proposed. An easy-to-learn, intuitive and accurate clinical diagnosis between fetal heart rate stethoscope and Doppler fetal monitor is developed. Auxiliary instruments.

The fetal heart rate is converted into an analog voltage signal by an acceleration sensor, and the difference is amplified by an instrument amplifier for preamplification. Then perform a series of intermediate signal processing such as filtering, and use the A / D converter to convert the analog voltage signal into a digital signal. Input to the single-chip microcomputer for analysis and processing through the optical isolation device, and finally output the processing result.

Based on MEMS

1.Micro-mechanical pressure sensor

Micromechanical pressure sensor is the earliest micromechanical product developed, and it is also the most mature and earliest industrialized product in micromechanical technology. From the perspective of signal detection methods, micromechanical pressure sensors are divided into two types: piezoresistive and capacitive, and are manufactured based on bulk micromachining technology and sacrificial layer technology. From the perspective of the structure of the sensitive membrane, there are a variety of structures such as round, square, rectangular, and E-shaped. The piezoresistive pressure sensor has an accuracy of 0.05% to 0.01%, an annual stability of 0.1% / FS, a temperature error of 0.0002%, a withstand voltage of several hundred MPa, and an overvoltage protection range of 20 times the sensor range Above, and can perform full temperature compensation over a wide range. At present, the main development directions of micromechanical pressure sensors are as follows.

(1) Integrate sensitive components with signal processing, calibration, compensation, microcontroller, etc. on a single chip to develop an intelligent pressure sensor.
(2) The sensitivity of the pressure sensor is further improved, and a low pressure micro-pressure sensor is realized.
(3) Increase the working temperature and develop high and low temperature pressure sensors.
(4) Development of resonant pressure sensors.

2.Micro acceleration sensor

Silicon micro acceleration sensor is the second micro mechanical sensor to enter the market after micro pressure sensor. Its main types are piezoresistive, capacitive, force-balanced and resonant. The most attractive of these is the force-balance accelerometer, whose typical product is the AGXL50 model reported by Kuehnel et al. In 1994.
A lot of work has been done on the development of micro acceleration sensors in China, such as the piezoresistive micro acceleration sensor developed by Xidian University and the resonant micro acceleration sensor developed by Tsinghua University Microelectronics. The latter uses resistance thermal excitation and piezoresistive bridge detection. Its sensitive structure is in the form of a highly symmetrical 4-angle support mass. Four resonant beams are made between the 4 sides of the mass and the support frame for signal detection.

3.Micromechanical gyroscope

Angular velocity is usually measured using a gyroscope. Traditional gyroscopes measure the angular velocity by using the characteristics of a high-speed rotating object to maintain its angular momentum. This kind of gyroscope has high accuracy, but it has a complicated structure, short service life, and high cost. It is generally only used for navigation, and it is difficult to apply it in general motion control systems. In fact, if it is not limited by cost, the angular velocity sensor can have broad application prospects in fields such as automobile traction control systems, camera stabilization systems, medical instruments, military instruments, sports machinery, computer inertial mice, and military. Common micro-mechanical angular velocity sensors include a dual gimbal structure, a cantilever beam structure, a tuning fork structure, and a vibration ring structure. However, the accuracy of the realized micromechanical gyroscope is less than 10 ° / h, which is far from the 0.1 ° / h required by the inertial navigation system.

4. Micro-flow sensor Micro-flow sensor is not only small in size and can reach a very low measurement level, but also has a small dead zone capacity and short response time, which is suitable for precise measurement and control of microfluidics. Micro-flow sensors researched at home and abroad can be divided into three types: thermal (including thermal conduction and thermal time of flight), mechanical and resonant based on the working principle. The valve disc type micro flow sensor designed by the Department of Precision Instrument of Tsinghua University converts the flow rate to the bending stress on the beam surface through the valve disc, and then the flow signal is detected by the pressure sensitive bridge integrated on the valve disc. The chip size of this sensor is 3.5mm × 3.5mm, and the linearity is better than 5% under the gas flow rate of 10ml 200ml / min.

5.Micro gas sensor

According to different materials, micro gas sensors are divided into silicon based gas sensors and silicon micro gas sensors. The former uses silicon as a substrate and the sensitive layer is a non-silicon material, which is the mainstream of current micro gas sensors. Micro gas sensors can meet people's requirements for integrated, intelligent, and multifunctional gas sensors. For example, the sensitive performance of many gas sensors is closely related to the operating temperature, so heating elements and temperature detection elements must be made at the same time to monitor and control the temperature. MEMS technology makes it easy to make the gas sensing element and the temperature detecting element together to ensure the excellent performance of the gas sensor.

Resonant gas sensors do not need to heat the device, and the output signal is a frequency quantity, which is one of the important directions for the development of silicon micro gas sensors. A micro-structured gas sensor proposed by Peking University Microelectronics is composed of a silicon beam, an excitation element, a vibration measurement element and a gas-sensitive film. After the silicon beam is placed in the measured gas, the sensitive film on the surface adsorbs gas molecules to increase the mass of the beam and reduce the resonance frequency of the beam. In this way, the concentration value of the gas can be obtained by measuring the resonance frequency of the silicon beam. The detection experiment of NO ₂ gas concentration shows that there is better linearity in the range of 0 × 10 1 × 10, the concentration detection limit reaches 1 × 10, and when the operating frequency is 19kHz, the sensitivity is 1.3Hz / 10. German M.Maute et al. Coated a polymer PDMS on the surface of a SiNx cantilever to detect hexane gas, and obtained a sensitivity of -0.099Hz / 10.

6.Micro-mechanical temperature sensor

Compared with traditional sensors, micromechanical sensors have the characteristics of small size and light weight, and their inherent thermal capacity is only 10J / K 10J / K, which makes them have incomparable advantages in traditional temperature sensors in temperature measurement. Developed a silicon / silica double-layer micro-cantilever temperature sensor. Based on the differences in thermal expansion coefficients of silicon and silicon dioxide, the deflection of the beam is different at different temperatures, and its deformation can be detected by a pressure-sensitive bridge located at the root of the beam. Its nonlinear error is 0.9%, hysteresis error is 0.45%, repeatability error is 1.63%, and accuracy is 1.9%.

7.Other micromechanical sensors

The use of micromachining technology can also realize a variety of other sensors, such as the resonant fluid density sensor designed by PeterE and others at Chalmers University in Switzerland, the force balance micromechanical vacuum sensor developed by Zhejiang University, and the vibrating beam micromachine developed by Hefei Intelligence of the Chinese Academy of Sciences. Force-sensitive sensors, etc. ^[2]

1. MEMS gas flow sensor: high accuracy, wide detection flow range, suitable for flow measurement of various needs.

2. MEMS pressure sensor: MEMS pressure sensor with small performance deviation.

3, MEMS non-contact temperature sensor: can detect the stationary human body, high sensitivity human body induction sensor.

4, MEMS switch: high frequency, small, long life MEMS switch.

China's research in the field of MEMS sensors is relatively late, but it has become an indispensable force. Under the premise of the synergistic pattern of the innovation bodies of some patent rights in China, increasing government investment in science and technology can not only eliminate the financial blockade in the development of technological innovation, It also helps to guide the consciousness of technological innovation of enterprises or units, thereby improving the efficiency of China's innovation drive and promoting the rapid and stable development of the economy ^[3] .

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