TlCaBaCuO films using e-beam evaporation with subsequent sintering and annealing that have critical current densities of at least several hundred kA/sq cm, critical temperatures over 100 K, and surface resistance better than that of gold at 77 K and 8 GHz. Processing techniques have been developed for making microwave passive elements and a four-terminal active device called the superconducting flux flow transistor (SFFT) for microwave applications. The techniques include contacting, dielectric, normal layer deposition, and controlled HTS film etching. The SFFT shows promise as a microwave amplifier, oscillator, and active impedance converter and may also have many other applications. The advantages of the device include high speed, potentially low noise, and, for some applications, useful impedance levels.