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A Brief History of NTC Thermistors

Michael Faraday. Image Credit: AIP Emilio Segre Visual Archives, W. Casidy Collection The great British chemist and physicist, Michael Faraday [1791-1867], is famous for his work and discoveries in electromagnetic induction and electrochemistry during the early 1800's. One of his lesser known contributions to science was the first recorded discovery of an NTC thermistor in 1833, when Faraday reported on the semiconducting behavior of Ag2S (Silver sulfide). Because the early thermistors were difficult to produce and applications for the technology were limited, commercial production and utilization of thermistors did not begin until 100 years later. During the early 1940's, Bell Telephone Laboratories developed techniques to improve the consistency and repeatability of the manufacturing process for NTC thermistors. Some of the first commercial thermistors were the disc type, formed by a “pill press” technology, and, by today’s standards, their tolerances were quite broad. These devices were used primarily for regulation, protection, and temperature compensation of electronic circuits and for temperature measurement. As more sophisticated requirements for thermistors began to arise from the expanding aerospace industry during the 1950's, the need for more accurate and stable devices increased as well. As a result of this market demand, several improvements in materials occurred. During the 1960's and 1970's increasing needs for greater accuracy, interchangeability, and stability of thermistors created significant challenges for thermistor manufacturers who faced the corresponding requirement for large-volume production capabilities. This market demand for a tighter tolerance product available in high-volume at a lower cost gave birth to the “chip” style thermistor. The chip thermistor is so-called because it is diced from a ceramic wafer. During the early 1980's, the use of NTC thermistors for single-use, disposable medical temperature applications accelerated as the utilization of electronic thermometers became more prevalent throughout the healthcare industry. As a result of significant improvements in ceramics processing technology and manufacturing process control, the chip type NTC thermistor became better suited for a variety of high-volume applications requiring small size, accuracy, interchangeability, and stability at lower cost than other types of configurations previously used. Interchangeable NTC thermistors are now available in packages as small as 0.020 in.

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