5 - Measuring parameters

Other temperature sensitive resistors made of crystalline materials, mainly of silicon, have also been developed. Devices based on the closely linear PTC behavior characteristic for slightly doped silicon found application in integrated microelectronic circuits. The structure of the so-called spreading resistance thermometer is shown in this animation. The resistance is practically measured between two strongly doped diffusion islands as two resistor elements between the latter ones and the highly doped film on the bottom, as shown in the figure. Because of applying silicon processing, the elements may show very good reproducibility.

The pn-junction has a temperature dependent voltage-current characteristic: where U is the diode voltage; I its current; k the Boltzmann-constant; e is the electron charge, and is the reverse current. Multi-emitter transistors can easily be prepared with exact basis-emitter junction area ratio. Connecting them as diodes that are driven by the same current (using an analog current mirror, for example), their voltage difference will be independent of the reverse currents, only the area ratio appears in the result.