Co-investigators Timothy Swager , Vladimir Bulovic
Nanoelectromechanical (NEM) switches are under investigation as complements to, or substitutes for, CMOS switches owing to their intrinsic quasi-zero static leakage, large ON-OFF conductance ratio, and high robustness in harsh environments. For most NEM contact switches, a trade-off between high actuation voltage and the risk of stiction failure seems inevitable due to the strong van der Waals attraction between contacts at the nanoscale. This attraction leads to unfavorable dynamic power consumption and decreased reliability. Through this research, we have developed a novel tunneling NEM switch, termed a “squitch”, based on a metal-molecule-metal junction whose tunneling gap can be modulated by compressing the molecule layer with electrostatic force created by a voltage applied between the metal electrodes. In contrast to conven- tional NEM contact switches, direct contact of squitch electrodes in the ON state is avoided by assembling a molecular spacer between the electrodes; the molecu- lar spacer acts to hold the squitch together and helps reduce hysteresis and the possibility of stiction failure.
A multi-terminal squitch has been demonstrated using a chemically-synthesized Au nanorod as a floating top electrode, and bottom Au electrodes patterned with electron beam lithography. With the help of a peeling technique that we have developed, Au electrodes are created with sub-nanometer roughness. The electrodes include two actuation gates recessed by several nanometers via a graphene sacrificial layer. By choosing molecules with appropriate chain lengths, we are able to define nanometer-wide electrode-to-nanorod gaps, which can be subsequently adjusted by a bias voltage applied between the gate electrodes. With a proper bias voltage, we can exponentially modulate the conduction current through a small variation of the gating voltage. The squitch has been experimentally demonstrated to exhibit low actuation voltage and hysteresis, which supports its prospects in ultra-low power logic applications.