Technology of MEMS
This blog is written by Harish Chaudhari along with Hemant Chaudhary, Yash Dabhade and Atharva Dandapur.
What is MEMS ?
The semiconductor material has brought a huge change in the field of electronics. It has made possible the invention and discovery of many number of new sensors and electronic devices. Along with the coming new years, there is a miniaturization of these mechanical and electro-mechanical devices. All this has become possible due to technology called “MEMS”. The word MEMS stands for Micro-Electro-Mechanical Systems that can be defined as the process of miniaturization of mechanical and electro-mechanical devices that are made using the method of microfabrication that is assembly of micro devices at micro scale. The physical dimensions of MEMS can vary from nearly one micron to a few millimetres.
Elements of MEMS
MEMS consists of arts such as microsensors, microprocessors, microactuators and other miniaturized parts that processes data. All these components are fabricated on a small chip called as integrated circuits (ICs) that contains thousands of diodes, gates and transistors on it.
Microsensors and microactuators are categorized as transducers which are defined as the devices that convert energy from one form to another. Microsensors are very small sensors that senses non electrical physical quantity such as force, pressure, displacement, temperature etc. and converts it into an electrical signal. Microactuators are also micro scale level components that supplies and transmits a measured amount of energy and hence performs mechanical motion for the operation of system. This can be actuated by using different methods such as by using hydraulic oil or pneumatic power, electromagnetic forces etc.
Applications of MEMS
There are numerous applications of MEMS and are increasing day-by-day to decrease the space as well as weight and to minimize the components. These devices are widely used in everyday products such as Smartphones (microphones, gyroscope, magnetometer), Wearable devices (accelerometers, heart rate sensors), Automotive (pressure, flow, acceleration sensors) and many other applications.
Some of the applications are:
Accelerometers are used in cars which measures proper acceleration.
MEMS gyroscopes are used in ships, aeroplanes, 2-wheeler and 4-wheeler, drones etc. for orientation and navigation.
An inertial measurement unit (IMU) measures linear and angular acceleration by using a accelerometer and gyroscope in a combination. It can also include a magnetometer and a pressure sensor to provide information about 3-D orientation and yaw, pitch, roll. This is used in smartphones and tablets, virtual reality and gaming, robotics and vehicle testing etc.
MEMS microphones in devices such as laptops and smartphones.
Pressure sensors which are used to detect pressure of a system.
Similarly, it is used now in almost every sector that includes medical science, biotechnology, communication systems etc.
Materials used for MEMS manufacturing
· Silicon: Silicon is used in most of the cases to make ICs in the modern industries. First reason for its more use is that it is a semiconductor material which can act like a conductor at moderate temperatures and insulators at a low temperature. Second reason being that it is abundantly available on the earth.
· Metals: Metals can also be used to create MEMS elements. Metals do not have that advantages that silicon possess but metals have very high reliability. Some metals commonly used for MEMS are aluminium, copper, titanium, nickel, gold, silver, platinum, tungsten, chromium etc.
· Polymers: MEMS devices can be made using polymers such as injection molding or stereolithography in huge volumes with a great variety of material characteristics.
· Ceramics: These materials have a high electrical conductivity and large elastic modulus. They also shows pyroelectric and piezoelectric properties which makes sensors sensitive to normal and shear forces.
Manufacturing methods for MEMS
· Lithography: It is the transfer of a pattern into a photosensitive material by selective exposure to a radiation source such as a light. A photosensitive material is a material that experiences a change in physical properties when exposed to a radiation source. So, when a photosensitive material is selectively exposed to radiation, the pattern of radiation is transferred to the material. This exposed region can be removed by providing a mask for underlying substrate. This method is particularly is known as photolithography. There are also many other types of lithography which depends on the type of light or radiation used: Electron beam lithography, Ion beam lithography, X-ray lithography etc.
· Etching: Etching is used to chemically remove the layers from the surface of a wafer during microfabrication. There are two basic categories of etching process:
Wet etching and Dry etching
The etching process that involves using liquid chemicals or etchants to take off the substrate material is called as wet etching. In dry etching which is also known as plasma etching, plasmas or etchant gases are used to remove the substrate material.
Advantages of MEMS
· MEMS devices operate on a very low power.
· When produced in mass quantities, they can result in very low cost units.
· MEMS sensors have extremely high sensitivity and accuracy.
· MEMS actuators can work at any high speed as desired by the user.
· They can be used with microelectronics to achieve embedded mechatronics system.
Disadvantages of MEMS
· They are much expensive while doing research and development of any new MEMS device.
· The cost of MEMS devices are very high if used in low quantity.
· Skilled persons are required for their manufacturing and produce.
· Their design is much complex as compared to conventional systems.
Conclusion: This article gives basic idea or introduction of MEMS. Its applications in daily life is discussed. Further, the components of MEMS and the manufacturing technology of MEMS for microfabrication are discussed.
References
[1] https://engineeringproductdesign.com/mems-micro-electro-mechanical-system/
