C-axis junction-arrays, with a-b plane sizes of sub-microns to 10 microns, were patterned on Bi2Sr2CaCu2O8+x single crystals with either a mesa or an overlap structure. We measured the current-voltage (I-V) characteristics with microwave irradiation at a few to 100 gigahertz. At a few gigahertz, often observed were chaotic properties. Under irradiation at 100 GHz, we successfully performed harmonic mixings between the 100 GHz signal and up to the 100th harmonic of a local oscillator at about 1 GHz. Given in this paper are discussions on the observation of individual Shapiro steps, and descriptions of the relevant results. Our experimental results show that intrinsic Josephson junctions in layered superconductors can be good candidates for high frequency applications.

In this paper, we review the progress in BiSrCaCuO-2212 Intrinsic Josephson junctions (IJJs) by summarizing our recent results in fabrication and high frequency experiments. Using a double-side fabrication process, a well defined number of intrinsic Josephson junctions in a well defined geometry can be fabricated. The junctions in the stack are quite homogeneous, and the power distribution of external irradiation among the junctions is even. Shapiro steps are clearly observed up to 2.5 THz, and the general condition for the occurrence of Shapiro steps at frequency frf is that it should be much greater than the plasma frequency fpl. Under certain conditions the Shapiro steps are zero-crossing, making some applications possible, such as quantum voltage standard etc.

The utilization of a high-Tc superconductor for implementing a superconducting qubit is to be expected. Recent researches on the quantum property of Josephson junctions in high-Tc superconductors indicate that the low energy quasiparticle excitation is weak enough to observe the macroscopic quantum tunneling. Therefore, a detailed study on the quantum property of high-Tc Josephson junctions becomes more important for applications. We show our experimental results of the macroscopic tunneling of current biased intrinsic Josephson junctions in Bi-2212 and its resonant activation in the presence of microwave radiation.