Thermal challenges in MEMS applications: phase change phenomena and thermal bonding processes

Two thermal challenges for current and next generation microelectromechanical systems (MEMS) applications are discussed. The first topic is the fundamental investigations of phase change phenomena in the microscale. It has been demonstrated that microresistive heaters can generate single, spherical and controllable thermal bubbles with diameters between 2 and 500 mm. Both simplified steady state and transient analyses that provide the scientific foundation of bubble nucleation in the microscale have been established but require further investigations. Several device demonstrations are briefed including microbubble-powered actuators, microbubble-powered nozzle-diffuser pumps and microbubble-powered micromixers for applications in microfluidic systems. The second topic addresses key heat transfer issues during the thermal bonding processes for MEMS fabrication and packaging applications. Basic thermal analyses on the microscale bonding processes have been developed while in-depth study is required to advance the understandings of the thermal bonding processes in the microscale. Successful new thermal bonding processes are introduced, including localized eutectic bonding, localized fusion bonding, localized chemical vapor deposition (CVD) bonding, localized solder bonding and nanosecond laser bonding for encapsulation of MEMS devices. q 2003 Elsevier Science Ltd. All rights reserved.