Artificial tunnel barriers produced by cryogenically deposited Al2O3

Abstract
Electron beam evaporated sapphire has been used to form tunnel barriers on substrates cooled to near 77 K. Ni/Al2O3/Al junctions show tunneling characteristics comparable with those obtained by plasma oxidation of Al and the subsequent deposition of Ni. The deposited Al2O3 barriers are stable and usually have insignificant leakage currents. The barrier heights are about 2.5 eV, and Al2O3 does not degrade the spin polarization of tunnel currents (as does oxidized amorphous Si). Au/Al2O3/Al junctions were made with good superconducting tunneling characteristics and with leakage less than 1%. Even Au/Al2O3/Au junctions apparently exhibit good tunneling characteristics.