In recent years, there was some progress in developing HTS three-terminal devices based on quasi-particles injection with a current gain of up to 10. This is still one order less than already demonstrated for low-T_c junctions. The main obstacle for further progress is the unsolved problem of a suitable THS barrier which allows for quasi-particle tunneling. If the preparation conditions for barrier materials such as natural YBa_2Cu_3O_(7-#delta#) and SrTiO_3 can be better controlled, as well as the quality of the YBa_2Cu_3O_(7-#delta#) surface improved, this kind of device could be developed into a useful fast current switch or even implemented in superconducting digital electronics. We investigated the properties of planar injection devices with (001) YBa_2Cu_3O_(7-#delta#) as HTS superconductor, a natural oxide, PrBa_2Cu_3O_(7-#delta#) and PrBa_2Cu_(3-x)Ga_xO_(7-#delta#) barriers with a normal conducting counter electrode. YBa_2Cu_3O_(7-#delta#) films used showed an average surface roughness between 1 and 6 nm. The observed current gain for devices with a natural barrier was 6.2 at 40 K and for PBCO and PBCGO barrier less than one between T_c and 10K.
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