Nanoelectromechanical relay
A nanoelectromechanical (NEM) relay is an electrically actuated
A typical NEM Relay requires a potential on the order of the tens of volts in order to "pull in" and have contact resistances on the order of gigaohms. Coating contact surfaces with platinum can reduce achievable contact resistance to as low as 3 kΩ.[1] Compared to transistors, NEM relays switch relatively slowly, on the order of nanoseconds.[2]
Operation
A NEM relay can be fabricated in two, three, or four terminal configurations. A three terminal relay is composed of a source (input), drain (output), and a gate (actuation terminal). Attached to the source is a
The nonlinear nature of the electric field, and adhesion between the beam and drain cause the device to "pull out" and lose connection at a lower voltage than the voltage at which it pulls in. This hysteresis effect means there is a voltage between the pull in voltage, and the pull out voltage that will not change the state of the relay, no matter what its initial state is. This property is very useful in applications where information needs to be stored in the circuit, such as in static random-access memory.[1]
Fabrication
NEM relays are usually fabricated using
NEM relays can be fabricated using a back end of line compatible process, allowing them to be built on top of CMOS.[1] This property allows NEM relays to be used to significantly reduce the area of certain circuits. For example, a CMOS-NEM relay hybrid inverter occupies 0.03 µm2, one-third the area of a 45 nm CMOS inverter.[5]
History
The first switch made using silicon micro-machining techniques was fabricated in 1978.[6] Those switches were made using bulk micromachining processes and electroplating.[7] In the 1980s, surface micromachining techniques were developed[8] and the technology was applied to the fabrication of switches, allowing for smaller, more efficient relays.[9]
A major early application of MEMS relays was for switching radio frequency signals at which solid-state relays had poor performance.[10] The switching time for these early relays was above 1 µs. By shrinking dimensions below one micrometer,[11] and moving into the nano scale, MEMS switches have achieved switching times in the ranges of hundreds of nanoseconds.[5]
Applications
Mechanical computing
Due to transistor leakage, there is a limit to the theoretical efficiency of CMOS logic. This efficiency barrier ultimately prevents continued increases in computing power in power-constrained applications.[12] While NEM relays have significant switching delays, their small size and fast switching speed when compared to other relays means that mechanical computing utilizing NEM Relays could prove a viable replacement for typical CMOS based integrated circuits, and break this CMOS efficiency barrier.[3][2]
A NEM relay switches mechanically about 1000 times slower than a solid-state transistor takes to switch electrically. While this makes using NEM relays for computing a significant challenge, their low resistance would allow many NEM relays to be chained together and switch all at once, performing a single large calculation.[2] On the other hand, transistor logic has to be implemented in small cycles of calculations, because their high resistance does not allow many transistors to be chained together while maintaining signal integrity. Therefore, it would be possible to create a mechanical computer using NEM relays that operates at a much lower clock speed than CMOS logic, but performs larger, more complex calculations during each cycle. This would allow a NEM relay based logic to perform to standards comparable to current CMOS logic.[2]
There are many applications, such as in the
Field-programmable gate arrays
The zero leakage current, low energy usage, and ability to be layered on top of CMOS properties of NEM relays make them a promising candidate for usage as routing switches in
See also
References
- ^ S2CID 24310991.
- ^ ISBN 9781424428205. Retrieved 29 October 2014.
- ^ S2CID 8905826.
- S2CID 41011570.
- ^ S2CID 41342836.
- S2CID 31025130.
- S2CID 15378788.
- doi:10.1109/5.704260.
- S2CID 111117216.
- S2CID 110197804.
- .
- S2CID 15037515. Retrieved 29 October 2014.)
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: CS1 maint: multiple names: authors list (link - S2CID 206527731.
- S2CID 1081387.