TEMPERATURE DISTRIBUTION IN CYLINDER SYMMETRICAL MM-WAVE DEVICES

A general solution of the nonlinear heat equation for temperature depe ndent thermal conductivity has been developed in cylinder coordinates. The solution is helpful in the design and analysis of high frequency power devices and circuits. The application to diamond heatsinks leads to a design rule height of diamond almost-equal-to 0.5 x radius of di amond. Coplanar circuits with an active device modeled as a focal plan e can be analyzed. Due to the temperature dependent thermal conductivi ty the thermal resistance becomes dependent on the input power. Especi ally for small radii of the focal plane and large input powers signifi cant deviations from the approximation ''constant thermal conductivity '' result The results are used to calculate the maximum current densit y of monolithically integrated transit time devices. The comparison wi th experimental results yields a rather good agreement.