Electrical breakdown spots in metal-aluminum oxide-metal structures

Metal-aluminum oxide-metal structures are prepared by evaporation in vacuum on silicon wafers using Au, Cu or Pd on top and Al as bottom electrode. The aluminum oxide layer is deposited by electron beam evaporation with a thickness of 200 nm. The diameter of the top electrode is varied between 0.1 and 1.9 mm. Capacitance measurements reveal a relaxational dielectric permittivity as expected for aluminum oxide. Applying ramp voltages results in single breakdown spots on the electrode before the structure finally becomes conductive. The breakdown spots, as characterized with an AFM, are in the form a crater, reaching 500 nm into the silicon. However, for the smallest electrode, the calculated electrostatic energy stored in the capacitance is not high enough to form the craters.