Superconducting tunnel junction
![Image of a Josephson voltage standard chip containing approximately 300,000 microfabricated Josephson junctions. Image credit: NIST.](/Images/godic/202502/14/NIST_Josephson_voltage_standard4044.jpg")
![Illustration of a thin-film superconducting tunnel junction (STJ). The superconducting material is light blue, the insulating tunnel barrier is black, and the substrate is green.](/Images/godic/202502/14/STJ_Device_Sketch4044.jpg")
![Energy diagram of a superconducting tunnel junction. The vertical axis is energy, and the horizontal axis shows the density of states. Cooper pairs exist at the Fermi energy, indicated by the dashed lines. A bias voltage V is applied across the junction, shifting the Fermi energies of the two superconductors relative to each other by an energy eV, where e is the electron charge. Quasiparticle states exist for energies greater than Δ from the Fermi energy, where Δ is the superconducting energy gap. Green and blue indicate empty and filled quasiparticle states, respectively, at zero temperature.](/Images/godic/202502/14/STJ_Energy_Diagram4044.jpg")
![Sketch of the current-voltage (I-V) curve of a superconducting tunnel junction. The Cooper pair tunneling current is seen at V = 0, while the quasiparticle tunneling current is seen for V > 2Δ/e and V < -2Δ/e.](/Images/godic/202502/14/STJ_IV_Curve4044.jpg")
The superconducting tunnel junction (STJ) — also known as a superconductor–insulator–superconductor tunnel junction (SIS) — is an electronic device consisting of two superconductors separated by a very thin layer of insulating material. Current passes through the junction via the process of quantum tunneling. The STJ is a type of Josephson junction, though not all the properties of the STJ are described by the Josephson effect.