Slow down time by 1 quadrillion times. This is 1,000,000,000,000,000. At this rate what would normally take a femtosecond takes a second. We attempt to animate the behavior of electrons tunneling from a insulating barrier between two metal electrodes. The current at 1 mA is about 6 electrons per femtosecond, so that's about 6 electrons per second in our slowed down time. Roughly half the time instead of an electron popping out of the barrier on the positive voltage side a hole pops out on the negative side. The speed of these electrons is the Fermi velocity which is about 2 nm/fs in aluminum which is our favorite metal.
$$ v_{fermi}(Al) = 2\times 10^{8} \textrm{cm/s} $$ $$ 2\times 10^{8} \textrm{cm/s}\left(\frac{10^{7} \textrm{nm}}{1 \textrm{cm}}\right)\left(\frac{1 \textrm{s}}{10^{15} \textrm{fs}}\right) $$ $$ = 2 \textrm{ nm/fs} = 2 \textrm{ pm/as} = 2 \mu \textrm{m/ps}; $$
$$ I = 1 \textrm{mA} = $$ $$ 10^{-3} C/s\left(\frac{1 \textrm{e}^-}{1.602\times 10^{-19}\textrm{C}}\right)\left(\frac{1 s}{10^{15} fs}\right) $$ $$ \approx 6.25 \textrm{ e}^{-}\textrm{/fs} $$ $$ \tau = \frac{1}{I}\left(\frac{20 \textrm{ frames}}{1 \textrm{fs}}\right) $$ $$ \tau \approx \frac{3.2 \textrm{ frames}}{I [mA]} $$