Bistable nanoswitch
A non-volatile bistable nano-electromechanical switch is provided for use in memory devices and microprocessors. The switch employs carbon nanotubes as the actuation element. A method has been developed for fabricating nanoswitches having one single-walled carbon nanotube as the actuator. The actuation of two different states can be achieved using the same low voltage for each state.
1. A method of making a non-volatile, bistable nanoswitch device, the method comprising the steps of:
applying an insulating layer onto a substrate surface;
applying a metal mask onto the insulating layer;
applying a photoresist layer onto the metal mask layer;
using lithography to fabricate first, second, third, and fourth nanoscale terminal areas and first and second nanoscale channels in the photoresist, metal mask, and insulating layers, the terminal areas surrounding an insulating area containing the channels, the first and second terminal areas opposite each other and the third and fourth terminal areas opposite each other, the third terminal area connected to the first channel and the fourth terminal area connected to the second channel;
carrying out a wet etch to undercut the insulating layer;
applying a conductive layer onto the terminal areas, the channels, and the metal mask layer, whereby conductive terminals are formed in the terminal areas and conductive channels within the channels;
removing the metal mask layer, leaving conductive layer inside the terminal areas and channels; and
applying at least one single-walled or multi-walled carbon nanotube as an actuating element across the insulating area and across the first and second channels by a process comprising performing dielectrophoresis by applying a voltage between the first and second conductive terminals, wherein the nanotube provides electrical contact between the conductive layer of the first and second terminals.
2. The method of claim 1 , wherein the substrate comprises silicon and the insulating layer comprises silicon dioxide.
3. The method of claim 1 , wherein the metal mask layer comprises tungsten.
4. The method of claim 1 , wherein the photoresist layer comprises polymethylmethacrylate (PMMA).
5. The method of claim 1 , wherein the lithography process comprises E beam lithography of the photoresist layer.
6. The method of claim 1 , wherein the lithography process comprises etching of the metal mask and insulating layers.
7. The method of claim 1 , further comprising a wet etching step prior to the step of applying the conductive layer.
8. The method of claim 1 , wherein the conductive layer comprises gold, chromium, silver, or a combination thereof.
9. The method of claim 1 , wherein the actuation element comprises a single-walled carbon nanotube (SWNT).
10. The method of claim 9 , wherein the step of applying the SWNT comprises the steps of:
adding a liquid suspension of SWNT to the surface of the device to cover the conductive terminals and channels;
performing said dielectrophoresis by applying said voltage between the first and second conductive terminals; and
removing excess SWNT using a stream of gas, whereby one or more SWNT remains as the actuating element.
11. The method of claim 10 , wherein the step of performing dielectrophoresis comprises apply an AC voltage in the range from about 1 to about 5 volts at a frequency of about 1 MHz.
12. The method of claim 10 , wherein the tips of the dielectrophoresis electrodes are pointed and form an acute angle of about 30 degrees or less.
13. The method of claim 10 , wherein dielectrophoresis is performed using a phase shifter to provide an electrical field gradient at the ground electrode of opposite phase to that at the phase electrode.