Abstract: Current controlled superconductor switches formed by reactive patterning or other fabrication techniques may be used to form logic circuits including OR, AND, NOR, NAND, and NOT gates, a circuit breaker or an analog-to-digital converter. Each switch contains a superconductor resistor electrically connected in parallel with a non-superconductor resistor. The superconductor resistor has a critical current I.sub.c, such that it exhibits no electrical resistance to current flow less than I.sub.c, and exhibits positive electrical resistance to current flow greater than or equal to I.sub.c. The switch can accordingly be toggled between two states (i.e. superconducting and non-superconducting) by suitably controlling the current flowing through the switch. This switching behaviour provides the basis for constructing logic gates and other digital circuit devices.

Abstract: The temperature of a substrate on which a thin film structure is to be fabricated in a low pressure environment is controlled by supporting the substrate on a heater block having a rim which defines first and second regions between the substrate and the heater block. The first region is inside the rim. The second region is outside the rim, surrounding the first region. Heat is applied to the heater block and an inert gas having good thermal conductivity is pumped through the block into the first region at a first controlled pressure. Gas is pumped away from the second region at a second pressure substantially less than the first pressure. A pressure differential is thus maintained between the two regions. This prevents the inert gas from contaminating the thin film fabrication environment by escaping past the substrate into the fabrication environment.