Allowable Repetition Frequency of Pulse Heating in Microactuators Using Rapid Boiling : (Effect of Electrical Insulation Layer beneath Heater)

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High-frequency pulse heating of heaters in microactuators utilizing the rapid expansion of boiling bubbles causes a gradual increase in the temperature of the heater and the substrate material in the immediate vicinity of the heater, resulting in a loss of reproducibility of the boiling phenomena. In the present report, the maximum frequency at which the steady increase in heater temperature can be maintained within the allowable limit for the succession of pulse heating is obtained by numerical simulations based on the heat conduction from the heater to the adjacent materials in the system having an electrical insulation layer between the heater element and the silicon substrate. Calculations are carried out using a model in an axisymmetrical system for two different heating conditions, that is, transient heating by a single pulse and steady heating by the time-averaged power during repetition of pulses, instead of the direct calculation of the entire repetition process. The effects of heater size and pulse width on the allowable repetition frequency are examined over wide ranges of these parameters. The influence of the insulation layer on allowable repetition frequency is investigated by comparing the calculation results with those of the case of without the insulation layer. Approximate correlations for the allowable repetition frequency are also derived based on an analytical examination.