How do temperature capabilities differ between the two main types of devices: field-effect transistors and bipolar transistors?
Low temperature Field-effect transistors (FETs): Characteristics of FETs generally improve with cooling, such astransconductance, leakages, and white (high-frequency) noise (although Si JFETs degrade below about 100 K); low-frequency noise is less predictable. The low-temperature limit of field-effect devices depends on the particular type and material: Si JFETs, are limited by their freeze-out temperature (about 40 K), but their performance actually degrades at a higher temperature. Ge JFETs have a similar behavior, although the relevant temperatures are lower, and under proper biasing can operate to the lowest cryogenic temperatures. Properly designed n-channel GaAs JFETs can also operate to the lowest temperatures, although they are uncommon. Si MOSFETs, enhancement type, can also operate to the lowest temperatures because the carriers needed for conduction in the channel can be ionized by an electric field from the gate. Si MOSFETs and CMOS circuits are often used at deep cryogenic
