Development of a Heat Sink With Periodic Asymmetric Structures Using Grayscale Lithography and Deep Reactive Ion Etching

This letter describes the fabrication and development of a novel heat sink for two-phase liquid cooling of electronics. The surface of the heat sink is asymmetric in the form of sawtooth ratchets with the long slope at an angle of 24° and is enhanced with reentrant cavities, which act as vapor trapping sites. The sawtooth ratchets were fabricated using grayscale lithography and deep reactive ion etching and the reentrant cavities using anisotropic etching. In pool boiling experiments with deionized water, surface asymmetry results in a net force imbalance acting on the vapor bubbles departing from the reentrant cavities, thereby resulting in bubbles departing at an angle with instantaneous velocities in excess of 600 mm/s. This novel surface developed demonstrates the ability to effect lateral motion of bubbles and the liquid in vicinity.