Contact Conductance Quantization in a MEMS Switch

Abstract

When the dimensions of a metallic conductor are much smaller than the mean free path of the electrons and become comparable to the Fermi wavelength, the absence of scattering results in ballistic electron transport and the conductance becomes quantized. In this paper we present original experiments carried out in air at room temperature on MEMS switches actuated by a nanoindenter apparatus. The current and voltage curve across contact electrodes were monitored and recorded continuously while opening the switch at an extremely low speed. Instead of a linear conductance curve, the presence of quantized conductance plateaus lasting up to hundreds of µs have been observed just before the separation of the two contact members. The conductance plateaus are close to integer multiples of the conductance quantum G 0 =2e²/h. These results are consistent with theoretical predictions for quantum ballistic transport in atomic-sized contacts and show that a quantum phenomenon can easily be observed in a basic MEMS switch under ambient conditions. The influence of the nature of the contact material and current as well as the deviation between the experimental results and exact values are reviewed and discussed.

If holm had used a Scanning Tunneling Microscope: What the nanoscientists are teaching us about electrical contacts

“…From an electrical contact perspective, at this point the electron transfer shifts from tunneling to direct metal-to-metal even if this nanowire is only a few atoms in diameter. There is evidence that the current carrying capability of these nanowires is extraordinarily high (on the order of 10 8 A/mm 2 ) [29][30][31]. Ψ When asperities separate, "jump out" occurs and contact continues with a thin nanowire of only a few atoms in diameter prior to breaking.…”

“…Theoretical analyses of Au [103], as well as Ag, Pt, and Ni [104] nanocontacts, uses molecular dynamics to show the electronics transport channels form and close during stretching and relaxation. The role of conductance quantization has been studied primarily in relation to Micro-electromechanical Systems (MEMS) switches [30], but it is noted in [29,105] that the conductance quantization is a rather general phenomenon associated to the breakage of macroscopic and microscopic contacts. As noted above, these quantum contacts have superconducting capability with current densities on the order of 10 8 A/mm 2 .…”

A review of micro-contact physics for microelectromechanical systems (MEMS) metal contact switches

“…Unlike Timsit, Poulain et al examined quantized conductance experimentally with micro-contacts test apparatus for breaking contact in such a way that the dimensions of the conducting members of the micro-contact were much smaller than the mean free path of an electron [32]. The team found that by using a micro-switch and a nanoindentor, they were able to witness quantized conductance plateaus before separation of the two contact members.…”

“…The team found that by using a micro-switch and a nanoindentor, they were able to witness quantized conductance plateaus before separation of the two contact members. The conditions for observing the quantized conduction phenomena are an extremely low switch opening speed and a current limitation near 150 μA [32]. Upper and lower micro-contacts made of Au as well as micro-contacts made of Ru-Ru were tested.…”

“…The plateaus were consistent with theoretical predictions for quantum ballistic transport in atomic-sized contacts. The work showed that a metallic bridge formed during contact separation, in the last stage of contact break, and consisted of only a few atoms similar to a nanowire or waveguide thus revealing the wave character of the electrons [32]. The team observed that reproducibility of the results was difficult due to the fact that the elongation of the atomic-sized bridge is difficult to control and was strongly related to atomic arrangements [32].…”