Superconducting films grown by activated reactive evaporation for high frequency device applications

123 films were grown on MgO substrates by activated reactive evaporation (ARE). In situ post deposition cooldown was optimized at low oxygen pressure to yield films with mirror-smooth surfaces with T sub(c)(0) = 86 K, transition width < 2 K and J sub(c) at 77 K = 10 super(5) A cm super(-2). Surface resistance (R sub(s)) at 60 K and 100 GHz was extremely low and comparable to R sub(s) of films grown by laser ablation on LaA10 sub(3). A film patterned into a bandpass filter showed a Q that was nearly an order of magnitude higher than that for a gold film at 92 GHz and < 50 K.