Capacitive Micro Accelerometer

Accelerometer, as the name suggests, are used to measure acceleration, and today’s science and technology requires inexpensive, fully functional, and large-scale processing and production of  accelerometer. In many fields, such as aerospace, machinery, and military industry, small and lightweight accelerometer are needed that can achieve many functions and are easy to test. The acceleration sensor integrated on the silicon chip has many advantages, micro acceleration sensor due to small and lightweight, conducive to mass production and other advantages, has been widely used in military, scientific measurement and other fields.

Micro accelerometer definition

Micro-electro mechanical systems (MEMS) are integrated miniature systems that combine electronic, mechanical, and other components, ranging in size from a few nanometers to micrometers, and are widely recognized in many fields. At present, micro acceleration sensor is one of the most widely used MEMS devices, which has the advantages of microfluidization, integration, intelligence, low cost, high performance and easy mass production. Applications range from smart phones, personal computers, the automotive industry and military defense. The micro-mechanical acceleration sensor based on MEMS technology has many advantages such as small size, light weight, fast start-up, low power consumption, easy integration, good reliability, strong anti-overload ability and low cost. According to the different types of sensitive signals, it can be divided into capacitive, piezoresistive and other micro acceleration sensors.

Structure and characteristics of capacitive micro-accelerometer

Capacitive micro acceleration sensor is the mainstream of MEMS acceleration sensor. Its basic structure is a capacitor composed of mass block and fixed electrode. When the mass block is displaced by acceleration, the capacitance pole area or distance is changed, and the acceleration is measured by measuring the capacitance. Capacitive micro accelerometers are the most common and mature products. The basic principle is to use the capacitor as a detection interface to detect the micro-displacement of the inertial mass due to the inertial force. The mass is supported by the elastic microbeam support on the substrate. One plate of the detection capacitor is generally disposed on the moving mass, and one plate is disposed on the fixed substrate. Figure 2 shows a typical sandwich-type flat capacitive micro accelerometer. Also, the capacitive micro accelerometer developed by AD uses a comb-tooth array capacitor as a detection interface. The capacitive micro accelerometer has high sensitivity and measurement accuracy, good stability, small temperature drift, low power consumption, and strong overload protection capability. It can realize feedback closed-loop control by using electrostatic force, which significantly improves the performance of the sensor.

For high-precision MEMS micro-accelerometers, performance stability is an important index of product quality. Under the same test conditions, such as temperature, humidity, etc., the repeatability of the same performance parameters of the device over a long period of time is called the stability of the device. Especially for capacitive MEMS micro accelerometers, due to changes in environmental factors or long-term storage, its zero drift and scale factors will change, thus reducing the accuracy of the device, resulting in long-term stability problems. Ericco introduced ER-MA-5,bias stability (Allan Curve)is 5μg, has the characteristics of small size, light weight, low energy consumption, can be widely used in vibration detection, attitude control, security alarm, consumer applications, motion recognition and state recording and other fields. The accelerometer is combined with a gyroscope and magnetometer to form an inertial measurement Unit (IMU).

At present, capacitive micro accelerometers have been gradually mature in the application of smart phone smart wearable medical and automotive industries. At the same time, with the continuous expansion of the market and technological upgrading, the application market of accelerometers continues to expand. Accelerometer application scenarios will have a broader space for development.

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