Self-heating and thermal effects

Within semiconductor devices under external bias, the carriers experience successive scatterings while traveling under the influence of an electric field. In most scattering events, they give up kinetic or potential energy they retained, which is converted into various other forms of energy as a result of generating phonons, photons, or electron-hole pairs. Among these energy-conversion modes, the generation of phonons, or the increase of lattice vibration level, is the most frequently encountered mode and results in the generation of heat in the devices. The consequent junction temperature rise, or self-heating, significantly influences device behaviors. It modulates the device operation condition since the characteristics of semiconductors are inherently given as a function of temperature. Device reliability is also affected since the raised temperature promotes most of the long-term degradation mechanisms as well as the catastrophic failures of the devices. Therefore, an accurate characterization of self-heating is critical for the precise prediction of device operation and degradation as well as the prevention of device failures. Historically, self-heating has been a concern mainly for high-power devices in which extensive power consumption results in a great heat generation. However, recent aggressive scalings intended for speed enhancement, which usually accompany a considerable increase in operation current level, have made the self-heating in high-speed devices a major concern. Hence, self-heating has become a generic issue for semiconductor systems in general, and their thermal properties need to be properly analyzed along with the electrical properties.