Carbon Nano-Switches for Low-Leakage Circuit Applications

K.M. Milaninia, C.E. Schmitt, A.I. Akinwande, A.P. Chandrakasan, and M.A. Baldo

Sponsorship: FCRP IFC, DARPA

Nanoelectromechanical switches (NEMS) exhibit minimal leakage current in the off state. Consequently, they may find application in low power electronics. This work focuses on the fabrication of a vertically oriented nano-switch using a carbon fiber or nanotube as the active component. The device schematic is shown in Figure 1, and Figure 2 shows an SEM image of the self-aligned fabrication process used to create the nano-switch [1]. The device consists of a carbon nanotube/fiber grown directly on a highly doped silicon substrate between two contacts which are electrically isolated from the substrate by an insulator. The device is actuated when a voltage is applied between the substrate and one of the contacts. This causes the nanotube to be pulled into and eventually make physical contact with one of the contacts and allows current flow between the substrate and the contact.

One of the primary benefits of the nano-switch is that it has extremely low leakage current because a physical gap separates the nanotube from the contact during the off state. One possible application that takes advantage of the reduced leakage is power gating idle circuit blocks. The nano-switch is connected as a header switch between the power supply and the load circuit. During normal operation, the nano-switch acts as a short circuit and power is supplied to the load circuit. When the circuit is not in use, the nano-switch is opened and the supply voltage is disconnected to reduce power consumption. This technique is similar to power gating with a high threshold CMOS device, but the nano-switch provides extra power savings because it has even less leakage current.

A test chip has been designed to quantify the power savings of the nano-switch for this power gating application. The chip also implements proof-of-concept SRAM and reconfigurable interconnect circuits that explore other potential benefits of the nano-switch.

Figure 1: Left) Schematic of a vertically oriented carbon nano-switch. Right) Carbon nano-switch upon actuation using an applied voltage between the substrate, i.e. tube, and a contact.		Figure 2: SEM image of a carbon nano-based field emitter produced by the self-aligned fabrication process [1].

References

[1] Chen, L.-Y., Velasquez-Garcia, L. F., Wang, X., Teo, K., Akinwande, A. I., “A Micro Ionizer for Portable Mass Spectrometers using Double-gated Isolated Vertically Aligned Carbon Nanofiber Arrays,” IEDM 2007.