Nanoscopic Electrostatic Drive – electrostatic MEMS bending transducer

© Fraunhofer IPMS
NED based Inchworm Drive.

Micromachined systems are the key to the miniaturization of components and devices, without which no fast-growing technical sector can survive. These include sound transducers for audio applications, transducers for ultrasound applications, drives for microscopic pumps or valves, micromirrors and optics for beam guidance and beam shaping of light of various wavelengths, and miniaturized varactors for signal amplification and adaptation of electrical antenna networks.

The micromachined systems enable components that have a significantly smaller installation space than previously known. At the same time, the requirements for the lowest possible energy consumption of such components have increased. In the future, these components will be installed in Internet-enabled and ultra-mobile devices characterized by long battery life. Radio interfaces and processors play a key role in determining the energy requirements of such systems. Since the space for the energy supply in such devices is very limited, all components have to manage with a very small energy budget.

This also means that actuator principles are required for micro- and nanomechanical systems that are characterized by low space and energy requirements. The business unit "Monolithic Integrated Actuator and Sensor Systems" (MAS) is developing electrostatic bending actuators for this purpose, which operate according to the bimorph principle. The Nanoscopic Electrostatic Drives, NED for short, are realized in MEMS technologies and are suitable for a wide range of applications.

Functionality of Nanoscopic Electrostatic Drives (NED)

NED is a novel MEMS actuator principle. A beam-shaped actuator consists of at least two electrodes standing in relation to each other, which are electrically separated from each other by gaps up to a few 10 nm thin. By applying a control voltage, an electrostatic field is generated between these electrodes, resulting in large attractive forces between the electrodes. Suitable geometries and topographies of the bar-shaped electrodes in turn transform these forces into lateral forces. From a technological point of view, there are two basic types of NED actuators. Vertical NED (V-NED) actuators move out of the chip plane and lateral NED (L-NED) actuators move within the chip plane. A distinguishing feature is that the deflection of an actuator is much larger than the electrode gap. This means that large deflections can be realized with low control voltages and thus extremely low energy requirements are possible.

NED advantages

Low power consumption → low capacitance, small reactive currents and low control voltages enable the use of energy-efficient driver circuits and thus result in low power consumption of the overall system
CMOS compatibility → integration of actuators with CMOS circuits, RoHS compatibility.
Alternative to functional ceramics → NED bending actuators replace functional ceramics such as PZT, which are currently exempt from the RoHS directive
High number of degrees of freedom →

Instead of a beam shape, the NED actuator can be designed as a rotationally symmetric plate. This gives an actuator plate that curves spherically.
Suitable electrode topographies or geometries can be used to deflect the actuators in a positive or a negative direction. A combination of topographies or geometries or an arrangement of the actuator cells on both surfaces of the bending actuator allows movements in both directions (bidirectional).
A tilting motion can be generated by two mechanically coupled NED actuators. If several NED actuator pairs are suitably connected, linear movements are possible.
The NED actuators can be cascaded to further increase the deflection (Rainbow configuration) or force (Parallel configuration), for example.

Nanoscopic Electrostatic Drive – electrostatic MEMS bending transducer