MEMS: Basic structures & Current Applications Presented by: Amit Kumar Sharma Amit Bansal Amit Goyal

What are MEMs? Micro Electro Mechanical Systems/Sensors. Machines fabricated at micro scale . The basic principles being that of Electrical and Mechanical machines. In the simplest terms miniaturization of electro-mechanical devices by application of semiconductor fabrication techniques.

MEMs

Microengine (Comb Drive Actuator) How they work… The light brown fingers are fixed to the substrate, and the black fingers are free to move.  By applying a voltage alternately to the top and bottom brown fingers, the electrostatic force causes the black structure to start to resonate.  A mass attached to the comb drive resonator can be made to translate

Microengine (Comb Drive Actuator)

Microengine (Comb Drive Actuator)

Microengine (Comb Drive Actuator)

Microengine (Comb Drive Actuator)

Microengine (Comb Drive Actuator)

Microengine (Comb Drive Actuator)

Microengine (Comb Drive Actuator)

Microengine (Comb Drive Actuator)

Microengine (Comb Drive Actuator)

Microengine (Comb Drive Actuator)

Microengine (Comb Drive Actuator)

Microengine (Comb Drive Actuator)

Microengine (Comb Drive Actuator)

Microengine (Comb Drive Actuator)

Microengine (Comb Drive Actuator)

Microengine (Comb Drive Actuator)

Microtransmission (Gears and Shaft) To increase the torque available from a rotary drive, a multi-layer microtransmission was developed. Output gear of a microengine, may be meshed with a linear rack to provide linear motion with a high degree of force.

Microtransmission (Gears and Shaft) contd. The transmission, shown, employs sets of small and large gears that mesh with each other to transfer power while providing torque multiplication and speed reduction .

Micromirror (Digital Micromirror Devices ) DMD's are large matrix (640 by 480 and higher) of tiny mirrors (16μm square mirrors with 1μm spacing between mirrors). DMD’s are used in smaller, lighter display devices having better resolutions.

Micromirror (Digital Micromirror Devices ) On a DMD consists of three physical layers and two "airgap" layers. The airgap layers separate the three physical layers and allow the mirror to tilt +10 or -10 degrees. When a voltage is applied to either of the address electrodes, the mirrors can tilt +10 degrees or -10 degrees, representing "on" or "off" in a digital signal.

APPLICATIONS

Three-axis accelerometer inertial sensors, examples of which are Analog Devices’ ADXL1508 and Motorola's XMMAS40GWB9. The primary application of these accelerometers is as airbag-deployment sensors in automobiles, but they are also being used as tilt or shock sensors The application of these types of accelerometers as inertial measurement units is limited by the need to manually align and assemble them into three-axis systems, the resulting alignment tolerances, their lack of on-chip A/D conversion circuitry, and their lower limit of sensitivity.

Three-axis accelerometer contd. For inertial measurement units (three-axis acceleration and three-axis rotation rate) were built using Sandia’s Integrated MicroElectroMechanical Systems (IMEMS) Technology. This system-on-a-chip is a realization of a full three- axis inertial measurement unit that does not require manual assembly and alignment of sense axes.

Screen size greater than 40 inches (101 cm) Projection TV Home theater system Screen size greater than 40 inches (101 cm)

Projection TV In a projector, light shines on the DMD. Light hitting the "on" mirror will reflect through the projection lens to the screen. Light hitting the "off" mirror will reflect to a light absorber. Each mirror is individually controlled and is totally independent of all the other mirrors.

The Future of Projection TV virtual reality

Microactuator Microactuator for HDD is developed to satisfy the growing needs for higher track density and higher performance of the future generation drives

Microactuator a micro-actuator attached between the slider and the suspension beam in order to move the slider with high speed and high accuracy.

Microactuator To achieve relative motion between the head and suspension, the device pictured below positions the rotor with tiny springs and generates forces between rotor and stator using electrostatic attraction.

Micromechanical Switches Low contact resistance. Low threshold voltage. High switching speed

Micromechanical Switches When a voltage is applied to the gate electrode, the beam is pulled down by electrostatic force until the switch closes. When the gate voltage is removed, the restoring force on the beam returns it to its original position.

Micromechanical Switches SEM micrograph of a completed three terminal switch. Low contact resistance. Low threshold voltage. High switching speed

Conclusion A technology involving micromachined devices embedded below the surface of a wafer, prior to fabrication of microelectronic devices, was developed and applied to build complex sensor systems on a single chip. A three-layer polysilicon process made possible intricate coupling mechanisms that link linear comb-drive actuators to multiple rotating gears. This technology has been used to build devices such as microengines, microtransmissions, and micromirrors. These devices were also combined to yield intricate mechanical systems-on-a-chip.

Conclusion The predominant technology at present state is surface micromachining, and current developments show that this trend will continue in the future. The other industries such as space, aeronautical, and automotive will continues to substitute the conventional sensors with the MEMS equivalents. The designer of electromechanical systems should pay attention to the availability of sensors and devices on the market. When possible, the choice have to fall on MEMS devices, as these are commonly cheaper, more accurate and reliable, and less cumbersome.