Understanding Sub-20 nm Breakdown Behavior of Liquid Dielectrics

Nanoscale confinement of dielectric molecules is expected to influence their breakdown mechanism in applications such as nanoprobe based machining, molecular electronics, and other related technologies. This Letter presents the first experimental study of the breakdown of nonpolar, nonthiolated liquid dielectrics in the nanometer regime and develops a field emission assisted avalanche based approach to model such behavior. The studies show that dielectric breakdown in the sub-20 nm regime is independent of the cathode materials and is dominated by the electron emission and atomic cluster migration due to the “sub-20 nm scale confinement of the liquid dielectric.”

Figure 1

The breakdown characteristics of $n$-decane across 3 nm cathode-anode gap. Instabilities in the current-voltage curve start at a gap potential of about 4.8 V (dashed arrows), and at about 6 V (solid arrow) complete dielectric breakdown was measured. The recovery of dielectric strength was not complete until about 25–30 ms from the time voltage dropped below the initial instability voltage ($\sim 4.8\mathrm{V}$).

Figure 2

Paschen curves for the breakdown of $n$-decane across increasing gaps with a flat gold anode and etched W and Pt-Ir cathodes and for flat gold cathode and etched W anode. The linearly increasing electric field strength required for breakdown was measured to be about $1\times {10}^9\mathrm{V}/\mathrm{m}$, irrespective of the voltage polarity.

Figure 3

SEM micrographs of a tungsten cathode before and after breakdown. The end radius of the cathode increased from about 35 nm before breakdown (a) to a near flat end after breakdown (b) and the shank diameter increased by 15%. The inset in (b) shows the melting event captured for breakdown at 15 nm gap.

Figure 4

The simulation of the variation of the Townsend $\alpha$, the Townsend current ratio $E_T$, and the field avalanche current $I$ with the applied field for a 3 nm gap. The Townsend enhancement alone is not sufficient to explain the high current of tens of nanoamperes at breakdown.