Microminiature refrigeration

We present a review of the recently developed microminiature, Joule–Thomson cryogenic refrigerators. These extremely small devices are finding wide scale use in instrumentation and as coolers for the study of materials. They have recently become available through the development of a novel, low-cost photolithographic fabrication process. We present the essentials of heat exchanger design, upon which the refrigerators are critically dependent, discuss the fabrication process, and review some of the present applications and limitations of the refrigerators, together with possible future application for cooling SQUID devices.