| Cooling of portable electronic modules becomes more challenging as the ever increasing integration of active electronic components is required to meet the demand for high functionality with their small weight and volume. Highly localized temperature rise and temperature gradients raise serious concerns for the thermal reliability of a micro chip incorporating high power transistor circuits. In the past decades, several new approaches taking advantage of the advancement of microfabrication techniques have been proposed to effectively remove heat from compact electronic systems. However, the implementation of these techniques still needs external power, expensive manufacturing cost, or inefficient cooling operation. An electronic cooling technology employing highly sophisticated device structures often sacrifices reliability for its performance.; This research proposes the use of a miniature thermosyphon with sub-millimeter- or millimeter-scale dimensions as a new approach to on-chip cooling in modern electronic systems. The thermosyphon operation principle is simply based on liquid-vapor two-phase coolant flow, hence requiring no external power input. However, the device miniaturization causes the surface-to-volume ratio of the working fluid to be large, making surface tension effects significant. Existing design knowledge on macro scale thermosyphons no longer serves for the development of the proposed on-chip cooling technology.; This research performs fundamental studies to provide design guidelines that indicate the lower bound for thermosyphon miniaturization for a given power-handling requirement. To achieve this goal, the bubble formation process in the thermosyphon cavity during the heat removal operation is carefully studied and modeled using the first principles of thermodynamics. The presented experimental work shows that entrapment of the generated bubble caused by significant surface tension, which is a phenomenon unique to the small device dimensions, limits the device performance. The developed model allows us to relate the bubble size to the amount of the input heat flux and to quantitatively predict the maximum heat power that can be handled by a thermosyphon of a given cavity size.; The design rules and methodology presented in this thesis can be also applied to other on-chip cooling methods which involve a coolant boiling process in a micro scale cavity or a channel. |
