Semiconductor diode thermometer

Electrical effects. Electrical methods are convenient because an electrical signal can be easily processed. Resistance thermometers (including thermistors) and thermocouples are the most widely used. Other electrical methods include noise thermometers using the Johnson noise as a temperature indicator resonant-frequency thermometers, which rely on the temperature dependence of the resonant frequency of a medium, including nuclear quadrupole resonance thermometers, ultrasonic thermometers, and quartz thermometers and semiconductor-diode thermometers, where the relation between temperature and junction voltage at constant current is used. 

Other Thermometers. Among the many other types of thermometers, we will briefly discuss the following bimetallic thermometers, noise thermometers, resonant-frequency thermometers, and semiconductor diode thermometers... 

The most promising semiconductors seem to be germanium, silicon, and carbon. The latter, though not strictly a semiconductor, is included in this group because of its similarity in behavior to semiconductors. Diode thermometers will be included here for the same reason. 

If the temperature range of interest is large, say 1 to 400 K, then diode thermometers are recommended. Diodes have other advantages compared to resistance thermometers. By contrast, diode thermometers are veiy much smaller and faster. Bv selection of diodes all from the same melt, they may be made interchangeable. That is, one diode has the same cahbration cui ve as another, which is not always the case with either semiconductor or metallic-resistance thermometers. It is well known, however, that diode thermometers may rectify an ac field, and thus may impose a dc noise on the diode output. Adequate shielding is required. 

Semiconductor p-n junction diode thermometers (Swartz and Gaines, 1972 Verster, 1972 Ohteetal., 1982) are becoming widely used throughout the range from liquid helium temperatures (1 K) to about 200°C. The diodes are currently made of germanium, silicon, or gallium arsenide. These thermometers are based on the principle that for forward-biased... 

For most purposes, the platinum resistance thermometer is still the first choice among metallic resistance thermometers. For measurements extending either over a broad temperature range from 1 to 300 K or for a narrower temperature range below 30 K, semiconductor and diode thermometers are the principal competitors to PRTs and are often to be preferred. 

Instruments based on the contact principle can further be divided into two classes mechanical thermometers and electrical thermometers. Mechanical thermometers are based on the thermal expansion of a gas, a liquid, or a solid material. They are simple, robust, and do not normally require power to operate. Electrical resistance thermometers utilize the connection between the electrical resistance and the sensor temperature. Thermocouples are based on the phenomenon, where a temperature-dependent voltage is created in a circuit of two different metals. Semiconductor thermometers have a diode or transistor probe, or a more advanced integrated circuit, where the voltage of the semiconductor junctions is temperature dependent. All electrical meters are easy to incorporate with modern data acquisition systems. A summary of contact thermometer properties is shown in Table 12.3. 

Soft, silver white metal that melts in the hand (29.8 °C) and remains liquid up to 2204 °C (difference 2174 °C, suitable for special thermometers). Gallium is quite widespread, but always in small amounts in admixtures. Its "career" took off with the advent of semiconductors. Ga arsenide and Ga phosphide, which are preferential to silicon in some applications, have extensive uses in microchips, diodes, lasers, and microwaves. The element is found in every mobile phone and computer. Ga nitride (GaN) is used in UV LEDs (ultraviolet light-emitting diodes). In this manner, a curiosity was transformed into a high-tech speciality. 

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