# Artificial Intelligence Applications for MEMS-Based Sensors and Manufacturing Process Optimization
## 2 MEMS Background
### MEMS Components  
As can be seen from Figure 4, MEMS are not only sensors; MEMS components can be subdivided into four categories, (1) microelectronics, (2) microactuators, (3) microsensors, and (4) microstructures, which are integrated into a single chip. Microsensors sense the physical parameters and detect changes in stimuli, such as pressure, temperature, motion, mass, light, etc. The microelectronics then process and analyze the collected information, which sends the signal to the microactuators. Upon receiving the signal, the microactuators respond and provide outputs as a change in the environment. MEMS components are packaged together with an application-specific integrated circuit (ASIC), which acts as an electrical interface among the components to send and receive analog and digital information. This makes the calibration and packaging processes quite complicated. As discussed so far, MEMS technology and related components are diverse, and the discussion of this paper is limited to only MEMS-based sensors. Types of MEMS Sensors and Applications  
Based on the received responses and measured quantity, the microsensors used in MEMS can be broadly divided into different types, such as physical, chemical, and biological. Table 1 shows a high-level classification of the microsensors used in MEMS-based systems [19] based on the received signal. MEMS sensors can be classified in many ways, such as application area, adaptation rate, popularity, MEMS structure, etc., but this is not  
Figure 3: MEMS Manufacturing Process. in the scope of this paper. The most common form of application and adaptation will be discussed for simplicity. Popular MEMS sensor types according to application:  
* Accelerometers
* Gyroscopes
* Pressure sensors
* Temperature sensors
* Inertial Measurement Units (IMU)
* Proximity sensors etc. Most common MEMS inertial sensors consist of accelerometers and gyroscopes. It will be later seen, in Section 4, that the contributions made in MEMS inertial sensors are pretty impressive. We will briefly discuss the working principle of the most important types, such as accelerometers and gyroscopes. This will help understand the problem's complexity and the contribution made by researchers using AI. In general, accelerometers can be divided into two categories based on the response type, such as (1) AC-response and (2) DC-response. AC-response accelerometers consist of piezoelectric elements for sensing. Thus, they are also known as piezoelectric accelerometers. The piezoelectric element \"displaces\" a charge when the accelerometer experiences acceleration, resulting in an electrical output proportional to acceleration. DC-response accelerometers can be of two types: piezoresistive (mainly used for low-range devices) and capacitive (high accuracy and sensitivity). They make use of MEMS fabrication technology, which scales to big-volume applications and lowers the cost of production. The advantages of using a MEMS-based accelerometer over a piezoelectric accelerometer are (i) active self-test, (ii) can measure both dynamic and static movement, (iii) generates precise velocity and displacement information, (iv) excellent bias stability and minimal noise, etc. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sensor Types** & **Input Signal Type** & **Measured quantity** \\ \hline \multirow{2}{*}{Physical} & Mechanical, Electric, Magnetic, & Acceleration, Force, Pressure, Charge, \\  & Optical, Thermal, etc. & Magnetic field \\ \multirow{2}{*}{Chemical} & Gas, Humidity, etc. & Toxic gases, Flammable gases, pH, H+, \\  & & Metallic ions, etc. \\ \multirow{2}{*}{Biological} & Enzyme, Immuno, etc. & Glucose, Lactic acid, Protein, \\  & & Virus, etc. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Microsensor Classification. Figure 4: MEMS Components Overview. The most commonly used MEMS accelerometer is the capacitive type, which is the cheapest and smallest. The accelerometer can be a single-axis, where acceleration is measured or a multi-axis, where the orientation of gravity is measured as well.