# Lattice Heating Modeled in S-Pisces 2B Thermal Effects Module Completed Ahead of Schedule

Lattice Heating Modeled in S-Pisces 2B
Thermal Effects Module Completed Ahead of Schedule

Dr. E.Lyumkis, Dr. Y.Apanovich, Dr. B.Polsky, and Dr. B. Freydin

Most device simulators assume that the lattice temperature is constant within the simulated structure. This is often a reasonable approximation, but lattice temperature variations within a structure must be taken into account for some applications. One example is in large power devices and another is in electrostatic discharge (ESD) protection circuits. Nonuniform lattice temperatures may also be significant in some submicron SOI devices, due to the low thermal conductivity of the oxide layers.

A self-consistent model for lattice heating has been implemented into the general purpose device simulator S-Pisces 2B. It is based on the model of Wachutka [1] and includes all thermal sources and sinks (Joule heat, Thomson term, etc.). Successful thermal modeling requires appropriate boundary conditions to be specified. S-Pisces 2B now gives the user the opportunity to specify arbitrary thermal boundary conditions at any point on the exterior boundary of the simulated structure.

Two examples illustrate the capabilities of the new model. Figure 1 shows the calculated snap-back drain current behavior of an channel MOS transistor with a 6µm channel length. Note that this is a linear scale so that the pre-breakdown current is scarcely distinguishable from the x-axis. Figure 2 shows the calculated internal temperature distribution at the point where Vd = 19.5 V and Id = 1.3 x 10-3A/µm. The maximum value of the temperature is 828 K in the region of the drain junction. Such plots can be used in detailed investigations of failure mechanisms. Figure 3 shows the temperature distribution in a submicron SOI device biased in the breakdown region. The nonuniformity of the temperature is illustrated clearly.

Figure 1.Snapback with lattice heating.

Figure 2.

Figure 3.

SILVACO pioneered commercial power device simulation by offering the Giga simulator. Giga offers 1 and 2D simulation capabilities optimized for modeling bipolar power devices, including the effect of thermal packages (heatsinking). The new capabilities in S-Pisces 2B complement those in Giga very well. SILVACO now caters to all needs in the area of power device simulation.

SILVACO has experienced power specialists on its staff. These specialists provide customers with expert advice on thermal modeling. The contact person at SILVACO is Dr. Boris Freydin, manager of the power device modeling group.

Reference

[1]. G. K. Wachutka,
Rigorous Thermodynamic Treatment of Heat Generation and Conduction in Semiconductor Device Modeling,
IEEE Trans., CAD-9, pp. 1141-1149, 1990.