EXPERIMENTAL-DETERMINATION OF SELF-HEATING IN SUBMICROMETER MOS-TRANSISTORS OPERATED IN A LIQUID-HELIUM AMBIENT

Self-heating (SH) in submicrometer CMOS transistors operated in a liquid-helium temperature (T(A)) and under different bias conditions is experimentally verified by measuring the temperature T(Si) in the proximity of the device. The temperature T(Si) is measured by using a silicon resistor, placed in the same bulk nearby the device under test, as a temperature sensor. It is found that the heat generated by the NMOS transistor of a CMOS inverter structure penetrates deep into the substrate reducing very strongly the n-well impedance, giving rise to large variations in the kink of the I(drain)-V(drain) characteristics of the neighbor PMOS transistor. Experimental observation of SH in a submicrometer CMOS inverter is for the first time reported in this work. Experimental results shown here confirm that SH must not be underestimated when characterizing and modeling low-temperature device operation.