MEMS APPLICATIONS

MEMS applications

RF MEMS Technology

Introduction

Integration of Micro-electromechanical as micron-scale devices, typically with moving parts, MEMS are built using fabrication techniques that are commonly used in microelectronics: depositing and then etching, via photolithography, very thin layers of different materials over silicon or gallium arsenide substrates. For radio frequency, or RF, applications, metal layers are preferred over other materials because of its higher conductivity. Mechanical design plays an important role in the design of an RF switch, as do RF design and materials science. The integration of components such as switches with the RF chip yields higher value for basic circuits required for advanced telecom systems applications, such as voltage-controlled oscillators-- an electronic circuit that supplies a frequency output proportional to its input voltage-and phase-locked loop circuits, which lock in the frequency and signal by detecting their phase shift.Discussion

The integration of mechanical sensors, elements, electronics and actuators on a silicon substrate by utilizing the phenomena of fabrication technology constitutes the MEMS. While micromechanical components may be fabricated by using the "micromachining" processes in which selective parts of the silicon wafer are either etched away or structural layers are systematically added to form the electromechanical and mechanical devices, electronics are primarily fabricated. One example of where mechanical design can influence device performance is an electro-statically actuated RF switch. MEMS-based switches are fabricated with low-loss metallic structures, or low-resistance materials-good conductors, such as gold, copper, or silver-that are required for a low-resistance line that does not distort or attenuate the signal. This, by any means is a significant advancement in the field of semiconductor bases electronics.

Low-loss metallic structures achieve lower insertion losses-sort of a natural degradation of the signal quality due to various physical factors-and higher linearity, the faithfulness with which an output signal reproduces an input signal. The actuation of the switch may be electrostatic or electromagnetic, and each kind has its advantages and disadvantages. The advantage of an electrostatic actuation is that there is no current consumption; its drawback is that it requires higher actuation voltage, typically greater than 10 volts. The advantage of electromagnetic actuation is lower voltage; however, this is offset by significantly higher current consumption. Electromagnetic actuation also introduces slightly more processing complexity because of the use of magnetic thin films (Mishra & Alex, 2009). Electrostatic switches offer the most promise as configuration switches, where low power consumption is a key factor in increased battery life. For this application, the switch permits the selection of the frequency range in which the device will operate. Power consumption of the switch should be as low as possible, while switching speed is less of an issue.

In a membrane-based RF switch, the operation relies on a thin membrane that is pulled down by electrostatic force. The switch has a signal line that is interrupted between the input and the output. A rigid membrane hangs over the signal line, separated by an air gap. The membrane is attached to the substrate by springs. When the membrane is in its equilibrium position, the output signal ...