Micro Electro Mechanical System (MEMS) is a technology of micrometer-scale devices. MEMS is a combination of actuators, sensors, mechanical elements and electronics on a common substrate using IC process sequences and these are used in different applications, such as display technologies, sensor systems and optical networks. MEMS are very attractive for different applications because of their size and weight. The size of the MEMS ranges from micrometers to millimeters.
These can be found in many systems ranging from automotive, embedded system electronics, communication, to medical applications. Modern MEMS devices include BP sensors, projection display chips, accelerometers for airbag sensors, computer disk drive Read and Write heads, optical switches, and micro valves. These products are all manufactured in high commercial volumes. These MEMS systems have the capability to control and sense on a micro scale and cause effect on the macro scale. In recent years, RF MEMS switch has become one of the fast intensifying technologies. This technology offers incredible advantages over silicon switching devices and GaAs.
RF MEMS Switches
The RF MEMS switches are frequently used in Microwave and Radio Frequency communication devices, such as transmitters and receivers, mode selection switch, antenna switch, etc. These switches are the unambiguous micro mechanical switches that are intended to operate at RF to mm wave frequencies, which mean 0.1 to 100 GHz. RF MEMS have many advantages over electrical switches like GaAs, FET diodes, PIN diodes, etc. They consume low power and possess properties like low insertion loss, linearity, reliability, affordability, power handling and high isolation rates. The properties of MEMS include low weight, small size and insertion loss but temporarily they have challenges such as high actuation voltage, slow speed, etc.
RF MEMS switches are micro-machined systems that use a mechanical faction in the Radio Frequency transmission line to attain a short circuit or an open circuit. These switches are categorized by actuation method. There are two types of forces used for the actuation of RF MEMS switches; they are electromagnetic and electro-static forces. The electrostatic force has a high actuation voltage, but has no current consumption. On the other hand, the electromagnetic force has a high current consumption and low actuation voltage. The electrostatic switches are most common switches and are of two kinds: series and shunt. The electromagnetic switches are used in the mm-wave and microwave regions.
As a series and shunt switches, Ohmic and Capacitive coupling switches can be used. Usually Ohmic switches are used in serial mode, while the shunt switches are preferred as capacitive coupling switches. When the switch is actuated, Series switch is primarily disconnected and gets connected and when a required voltage is applied, the shunt switch is primarily connected and gets disconnected. A series contact switch is shown in the above figure.
In series contact switch, the signal transmission line is off, it means, when the switch membrane is pulled down, the signal passes the line and the conductor touches both the sides of the transmission line. But the reliability and insertion loss are the issues to be noted. In the capacitive shunt switch, the transmission line is normally on – a dielectric layer is laid between the transmission line and the switch membrane. When a membrane is pulled down it forms a parallel plate capacitor. The RF signal conducts to the ground by the use of a capacitor. If a DC voltage is applied to both the ends of the switch, the switch will get charged differently, and an electrostatic force will be generated. This force causes the switch to close between the two areas. This permits the RF power to flow through the switch, but it doesn’t allow the electricity to flow through this due to the dielectric layer, and also the switch opens back when the voltage is turned off.
RF MEMS Switch Circuit
This RF MEMS switch circuit uses an integrated structure for the DC ground pin9 on the input side and RF ground on the output side. A relay drive circuit uses high-side switches Vcont_1 and Vcont_2 to turn the operating voltage on and off. This MEMS switch is an electrostatic drive type. To turn off the switch on the primary side, the charge accumulated should be discharged. Set up a discharge circuit in the switch drive circuit to turn off the switch. If there is no discharge circuit, then the switch will not be turned off. This MEMS switch is designed in such a way that the actuator operates at a high speed. Due to this, the time constant of the drive waveform may affect the life performance of the switch, so that the operating input pins (V_cont1 and V_cont2) is less than 10us and greater than 0.5us, respectively. The operating voltage must be reserved in the range of 34V+5% or 34V-5% including ripple.
In the year 1990, MEMS was developed in ICs as sensors. The Control functions and actuators are fabricated in silicon – and, for the invention of MEMS devices – micromachining is used as a fundamental technology. The Micro Electro Mechanical Systems is a process technology, used to build tiny integrated systems that combine electrical and mechanical components. MEM works on micro-scale technology and performs a number of functions like the conversion of physical parameters into electrical, mechanical and optical signals; and actuation sensing functions.
Essentially, MEMS consists of micro-sensors, microelectronics, micro-actuators and microstructures, all integrated onto the silicon chip. Micro sensors detect the changes in the systems’ environment by determining the electromagnetic information. Microelectronics route this information and signal the micro actuators to generate and respond some form of the changes to the environment. However, the MEMS is not just about making things out of silicon, it is a fabrication technology; a prototype for creating and designing complex devices.
Accelerometer, an electromechanical device, is used to measure acceleration forces. The forces can be static or dynamic. There are many types of accelerometers developed in the scientific literature. The majority of the accelerometer is based on piezoelectric crystals, but they are too clumsy and big. Therefore, small MEMS accelerometers are developed.
The first MEMS accelerometer was developed in the year 1979 at Stanford University, but the developmental work took many years. In 1990s, automotive airbag industry had invented MEMS accelerometers; since then there have been unique applications and features associated with them ranging from hard disk security on laptops to game controllers. MEMS accelerometers have immensely enabling technology with an enormous profitable potential. They provide robust sensing, compact and low power. Nowadays Accelerometers are being built into many personal electronic devices such as gaming devices and media players. Accelerometers are used in smart phones as a tilt sensor for tagging the orientation of the photos taken with a camera.
Applications of MEMS
MEMS in Consumer Appliances
- Phones and tablets
- Remote control and gaming devices
- Notebooks and Ultra books
MEMS in Wireless Applications
- Pedometers and watches
- Barbells and Tread Mills
- MEMS in home appliances
- Car Garages and Home Automation Systems
- White Goods
- Electric, Gas or Water Meters
- MEMS in Cars
- Navigation and safety
MEMS in Industrial Applications
- Automation and Robotics
- Monitoring of industrial equipments
- Monitoring and Parcel Tracking
- Building Monitoring
- Geo Phones and Seismic Exploration
MEMS in Medical Applications
- Implantable Medical devices
- Concussion detection in sports
- Motion detection and body motion reconstruction
- Wheel chairs and health care
- Instrument guidance surgery
This is all about the RF MEMS Switches and their working abilities, which can be used in different applications such as Wireless devices, Home appliances, Medical equipment, Industrial and consumer appliances, etc. We hope that our readers after spending their valuable time might have got some valuable insights from this article. Furthermore, for additional information about this topic, you can comment in the comments section below.