Experimental study about JFET behaviour at low temperatures

Data acquisition and control of cryogenic plants requires the use of adequate transducers, which work under special conditions (low temperatures, high pressures, vacuum, industrial vibrations, a.s.o.) their behaviour under cryogenic conditions being different of those encountered at positive temperatures. Generally, the output signal level of that transducers is very low. Therefore, we imagine a way to increase the accuracy and reduce the noise of measurements by designing and introducing multiplexers, input amplifiers and other circuits in cold boxes and making them work under cryogenic conditions. In order to do that devices' characteristics at low temperature mass be determined. Field effect transistors being widely used in electronic circuits for measurements and data acquisition, we begin by studying their behaviour at low temperature. We choose a junction field effect transistor, BFW10, manufactured by ROMES SA Bucharest. Its characteristics were investigated in the temperature range of 20 K to 300 K in order to determine his behaviour at low temperatures and the possibility of using it in cryogenic electronic circuits. The BFW10 JFET behaviour under d.c. conditions at low temperature shows an increase in drain current and transconductance down to 100 K. Under that temperature the devices exhibits radical changes due to the carrier freeze out. The experiments must be continued over a large number of devices in order to determine by statistical calculations a temperature coefficient of the drain current which would allow the prediction of their low temperature characteristics with an acceptable accuracy. (authors)