Impingement Cooled Embedded Diamond Multiphysics Co-Design

This paper describes engineering analysis and experimental evaluations used to design an innovative imbedded cooling concept for RF thermal management. The concept, called Impingement Cooled Embedded Diamond (ICED), uses liquid flowing through diamond-lined microchannels etched into the back of a GaN-on-SiC RF die to manage heat produced by the transistors. This approach combines the superior heat spreading of high-conductivity diamond with the outstanding convection capability of impinging jets to manage local heat fluxes as high as 30 kW/cm(2). The first part of this paper presents the CFD analysis used to design the microfluidics, select diamond thickness, and understand the sensitivity of performance to component assembly, coolant temperature and composition, and channel dimensions. It also describes the structural analysis used to evaluate ICED mechanical stress levels, including those imposed by diamond growth and hardware assembly. The second part of this paper presents experimental measurements performed to validate the computer models and demonstrate the thermal management capability of the proposed design. These experiments confirmed the effectiveness of the impinging jets at drawing heat produced by the transistors directly to the coolant, reducing transistor mutual heating and enabling a four-fold increase in expected RF output power. They also showed the proposed cooling concept mitigates self-heating thermal limitations and enables aggressive design compaction not possible with existing conduction GaN-on-SiC cooling solutions.