Thin Films

Abstract

Thin films are often encountered in micro systems. They are important in semiconductor devices, in microelectromechanical devices such as sensors and actuators, and in masks. Heat transport through thin films is of vital importance in microtechnology applications. In some electronic applications, the reduction of the device size to microscale has the advantage of enhancing the switching speed of the device. On the other hand, size reduction increases the rate of heat generation which can lead to higher thermal load on the device. Heat transfer at the microscale is also important in the processing of materials with pulsed lasers. The high power of the laser on the surface of a metal film can result in a build-up of temperature on the film surface causing thermal damage. When a significant temperature rise occurs in a solid, deformation or highly elevated stress occurs caused by thermal expansion. Deformation and stress waves are major causes of thermal damage in laser processing of materials. Hence, studying the thermal behavior of thin films (in one or in multilayers) is useful for predicting the performance of a microelectronic device or for the manufacturing of microstructures. Heat transfer at the microscale cannot be properly described by the conventional heat transfer equation. In the classical theory of diffusion, the heat flux vector (q) and the temperature gradient (ΔT) across a volume of material are assumed to occur at the same instant of time. However, if the scale in one direction is at the microscale, the flux and temperature gradient in this direction will occur at different times. This time lag requires a new approach in the study of heat transfer at the microscale. In this chapter we discuss heat transfer models in single or multilayer thin films with time lags.