1. Introduction

Because of advanced developments in circuit and component technologies, the electric circuit becomes more efficient and thus, heat dissipation from an individual device such as transistor is also less as given in Figure 1.1.[1]. Miniaturization of the circuits greatly decreases the size of individual devices, however, and increases the number of circuits integrated on a single chip. The net result is that the chip heat flux (per unit surface area) has significantly increased in the past decades.