  We show that the electric field driven surface instability of visco-elastic
films has two distinct regimes: (1) The visco-elastic films behaving like a
liquid display long wavelengths governed by applied voltage and surface
tension, independent of its elastic storage and viscous loss moduli, and (2)
the films behaving like a solid require a threshold voltage for the instability
whose wavelength always scales as ~ 4 x film thickness, independent of its
surface tension, applied voltage, loss and storage moduli. Wavelength in a
narrow transition zone between these regimes depends on the storage modulus.
