General Introduction

Abstract

There are numerous reasons for operating electronic devices and circuits below room temperature:

• 1) improved performance such as:

  • — Higher speed due to improved transport properties, ideal subthreshold operation and reduced interconnect resistance

  • — Lower thermal electrical noise

  • — Reduction or suppression of parasitic effects leading to an improvement of device reliability, for instance latch-up and leakage currents for CMOS circuits or electromigration for the interconnects

  • — Increased thermal conductivity for silicon and many other materials allowing higher integration density;

• 2) refined characterization methods, for instance dealing with the determination of interface or bulk defects, the study of scattering mechanisms or the investigation of quantum effects;

• 3) physical and technological limitations for the ultimate integration of silicon circuits down to nanometric dimensions which could be overcome using low temperature electronics;

• 4) need to couple electronics to other devices which are in a cold environment, such as read-out circuits with cooled detectors;

• 5) study and use of physical phenomena that occur only or are magnified at low temperature such as single electron effects or superconductivity;

• 6) a conventional electronic circuit has to operate in a wide temperature range, from 125°C down to −55°C, and therefore needs also to be evaluated at low temperature. Note also that the lowest temperature observed on earth is about −90°C. Other very interesting temperature ranges are liquid nitrogen (77K = −196°C=−320°F) and liquid helium temperatures (4K=−269°C=−452°F).