Grain boundary Josephson junctions (GBJJs) with high-quality NdBa2Cu3O7−y (NBCO) thin films were fabricated on SrTiO3/BaTiO3 buffered MgO (100) bicrystal substrates by using a novel process of tri-phase epitaxy (TPE). This film growth method is based on an application of pulsed laser deposition (PLD) under compositions and conditions predetermined from the relevant thermodynamic phase diagram. The film grain boundary was sharp and along with the bicrystal substrate boundary. A sub-micron size microbridge was patterned on the NBCO/SrTiO3/BaTiO3 films across the tilted grain boundary by electron beam lithography and focused ion beam etching. The junctions exhibited resistively shunted junction (RSJ) like current–voltage (I–V) characteristics at temperatures up to 90 K. The critical current (Ic) of 3.3 mA at 4.2 K was completely depressed by 20 GHz microwave radiation. Microwave induced steps were clearly observed over 2 mV at 10 K with voltages corresponding to the Josephson frequency–voltage relationship.
