The Josephson junction (JJ) is basically an insulator sandwitched between the two semiconductor layers. Hence the device is also called as a SIS (Superconductor-Insulator-superconductor). A tunneling phenomenon called Josephson tunneling takes place through the insulator when the thickness of the insulator is very thin (less than 1.5 nm) and the insulator turns into a superconductor due to the tunneling of charge carriers from the 1st to the 2nd super conductor; through the insulator.
The basic block diagram is as follows. http://seminars4u.thextremehosting.com/e...age001.gif To explain the working of the device we need to analyze the principles of superconductivity & the principles of tunneling. The superconductivity is explained in terms of BCS theory & tunneling in terms of the uncertainity principle.