Bubble nucleation and behavior on micro square heaters

Abstract

In this study, micro square polysilicon heaters having dimensions of 65 x 65 mu m(2) and 100 x 100 mu m(2) were fabricated on a silicon dioxide layer, and bubble nucleation experiments on the heaters were performed. Bubble nucleation temperature was measured using a bridge circuit, and the photographs of bubble nucleation and subsequent growth were taken by a 35-mm camera with a mu s flash unit. Measured bubble nucleation temperatures were found to be closer to the superheat limit of the working fluid of FC-72. A quasi-1-D solution obtained from the 2-D heat diffusion equation yielded proper temperature distribution of the square heaters at steady state; however, it failed to predict the temperature rise up to the steady state. The time-dependent temperatures similar to the observed values can be obtained with much lower value of thermal diffusivity than the bulk property of the polysilicon heater used. For the 100 x 100 mu m(2) square heater, nucleation of several bubbles was observed, but for the 65 x 65 mu m(2) heater, only that of one bubble was observed.