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Definition
The 20th century saw many developments in the field of electronics because
of basically two reasons 1. The development
of transistors, which forms the basics of everything that is electronics.
2. The development of IC, which helped in the fabrication of fast, compact &
sophisticated electronic circuits. In the
21st century we are going to see some radical changes in the approach towards
electronics. These are :
1. The replacement of semiconducting devices with
superconducting devices.
2. The use of new classical theories in physics like
the relative physics & quantum mechanics to explain various phenomenon, application
& working of electronic devices. The first
step to integrate the previously separate branches, electronics &super conductivity
was done by the scientist called Brian Josephson by the invention of the JJ in
the year 1962 for which he received the Nobel prize in the year 1973.The
analysis of the device is impossible using classical theories of physics. The
device has immense potential & numerous applications in almost all fields
of applied electronics.
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.
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.
Superconductivity
It is a remarkable property in which there is a complete
loss of resistivity in a metal or alloy, usually at temperature close to the absolute
zero & this property was discovered by Kammerlingh Onnes. As perfect conductors,
superconductors will carry current without resistance loss, i.e, the current applied
will persist forever without any loss of power. These materials are also perfect
diamagnetic & magnet placed above the super conductor will levitate under
its own magnetic field. Low temperature superconductors
exhibit property at temperature near-250?C. LBCO &certain alloys of La &
Ba shows this property near 35k, RBa2Cu3O7, Bi2Sr2ca2Cu3O10 can show the property
near 90k. Thallium based & mercury based cuprates can show superconductivity
at 134k.
Progress in the development of high temperature superconductivity &
particular cuprate based superconductors has made significant advances. Some organic
compounds have lately been developed as Superconductors.
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