THERMAL BUBBLE FORMATION ON POLYSILICON MICRO RESISTORS

Thermal bubble formation in the microscale is of importance for both s cientific research and practical applications. A bubble generation sys tem that creates individual, spherical vapor bubbles from 2 to 500 mu m in diameter is presented. Line shape, polysilicon resistors with a t ypical size of 50 x 2 x 0.53 mu m(3) are fabricated by means of microm achining. They function as resistive heaters and generate thermal micr obubbles in working liquids such as Fluorinert fluids (inert, dielectr ic fluids available from the 3M company), water, and methanol. Importa nt experimental phenomena are reported, including Marangoni effects in the microscale; controllability of the size of microbubbles; and bubb le nucleation hysteresis. A one-dimensional electrothermal model has b een developed and simulated in order to investigate the bubble nucleat ion phenomena. It is concluded that homogeneous nucleation occurs on t he microresistors according to the electrothermal model and experiment al measurements.