INVESTIGATIONS OF FIELD EFFECT TRANSISTORS AT CRYOGENIC TEMPERATURES.
TEXAS UNIV AUSTIN ELECTRONICS RESEARCH CENTER
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Various JFET and MOSFET devices have been studied at LN and L He temperatures. A strong increase in transconductance and decrease in equivalent input noise is registered when the ambient temperature changed from 300K to 77K. A very small change in electrical parameters of the device was noticed when the environment temperature was further lowered to 4.2K. Transient and steady state heating of the devices at 4.7K is investigated and it is found that the active part of the device heats up typically to a steady state value of 40 - 60K. In most of the devices this agrees with the thermal noise observed. A transient and steady state device heating model is constructed and the results are found to be in good agreement with the measured temperatures and measured heating transients. The equivalent input noise studies for a germanium FET device have shown a strong 1F-noise for frequencies up to approximately 100 kHz and thermal noise for higher frequencies. At cryogenic temperatures JFET devices show a slight decrease in noise spectrum. The noise spectrum of the MOSFET devices in most cases is by an order of magnitude larger than that of the JFET device. Some of the MOSFET devices show a substantial increase in noise at lower frequencies when the environment temperature is lowered to a cryogenic level. Author
- Electrical and Electronic Equipment