Germanium thermistors

E. E. Haller, K. M. Itoh, J. W. Beeman, W. L. Hansen, V. I. Ozhogin, Neutron transmutation doped natural and isotopically engineered germanium thermistors, SPIE Proc., 2198,630 (1994). 

Impurity substitution that is effectively neutral, that is, neither donor nor acceptor, can also lead to significant changes in properties that are utilized in NTC thermistors. For example, the replacement of Ga3+ in the spinel MgGa204 by Mn3+ involves no apparent donor or acceptor action. The conductivity in the system MgGa2 Jt.MnJt.04 evolves from insulating (conductivity about 10-9 0 1m 1) for the parent phase with x = 0, to a conductivity approximately equal to that of germanium (10 10-1 m-1) in the compound MgGaMn04, in which x = 1. The resistivity decreases markedly with temperature and the compounds display typical NCT behavior. 

In this section, the design and operation of familiar liquid thermometers, thermocouples, platinum resistance thermometers, thermistors, and optical pyrometers are discussed in detail. Briefer descriptions are also given of a variety of special thermometric devices such as quartz thermometers, germanium resistance thermometers, and sihcon-diode thermometers. 

The bolometer is another type of thermal detector that can offer extreme sensitivity for specialized applications, t This is essentially a resistance thermometer, usually with a platinum, nickel, carbon, or germanium element, although a semiconductor thermistor can also be used. Typically, two elements are used in a bridge circuit with one exposed to radiation and the other kept dark as a reference. The germanium bolometer provides exceptional... 

Another type of resistance thermometer uses metal oxides, instead of metals it is frequently referred to as a thermistor. Electrical resistance of these metal oxides changes rapidly with even rather small temperature changes. Hence, thermistors are often emplyed to measure small temperature changes such as 1°C to 5 °C. The thermistor proper tends to have low purchase prices. Metal oxides, which are semiconductors, include mixtures of the following oxides nickel, manganese, copper, cobalt, tin, germanium, etc. [1]. 

A bolometer is a type of resistance thermometer constructed of strips of metals, such as platinum or nickel, or of a semiconductor. Semiconductor bolometers are often called thermistors. These materials exhibit a relatively large change in resistance as a function of temperature, The responsive element is kept small and blackened to absorb radiant heat. Bolometers are not so extensively used as other infrared transducers for the mid-infrared region, Flowever, a germanium bolometer. operated at 1..3 K, is nearly an ideal transducer for radiation in the. 5 to 400 cm (2000 to 2.3 pm) range. 

There are three main families of temperature sensors thermocouples, resistance thermometers and thermistors. Some old reactors still have bimetalic thermometers (binary or with local readings), but it is suggested that they be replaced in order to allow the operator to follow closer any temperature transient from the control room. Other temperature sensors, like semi-conductor thermometers, consisting of doped germanium sensors, have a complex resistance temperature relationship and are useful only for very low temperature measurements. 

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