Transient Bubble Formation on a Polysilicon Micro Resister

Transient bubble formation has been investigated on a polysilicon micro resister of 95μm long, 10μm wide, and 0.5μm thick. The polysilicon micro resister functions as both a heating source and a temperature transducer of thermal bubble nucleation process. At input current of 22 to 30 milliamps, a single spherical bubble is nucleated with a waiting period, when the heating wall temperature drops up to 8°C before a bubble nucleated, of about 1 to 2 seconds depending on the input current. Analytical models are developed to characterize the wall temperature behavior in this micro scale. Substrate warming is found effective to the wall temperature after 0.4 second of heating. Furthermore, evaporation is identified as the major contribution mechanism of the temperature drop before the bubble nucleation. An equivalent heat transfer coefficient is found in the order of 105 W/m2°C with the time constant of 1.25 to 2.5 seconds varying with input current.