Abstract
A three-dimensional thermal and stress analysis of bonded GaN on diamond substrate is investigated using finite element method. The transition layer thickness, thermal conductivity of transition layer, diamond substrate thickness and the area ratio of diamond and GaN are considered and treated appropriately in the numerical simulation. The maximum channel temperature of GaN is set as a constant value and its corresponding heat power densities under different conditions are calculated to evaluate the influences that the diamond substrate and transition layer have on GaN. The results indicate the existence of transition layer will result in a decrease in the heat power density and the thickness and area of diamond substrate have certain impact on the magnitude of channel temperature and stress distribution. Channel temperature reduces with increasing diamond thickness but with a decreasing trend. The stress is reduced by increasing diamond thickness and the area ratio of diamond and GaN. The study of mechanical and thermal properties of bonded GaN on diamond substrate is useful for optimal designs of efficient heat spreader for GaN HEMT.
Highlights
Wide-bandgap semiconductors can operate under a high supply voltage and withstand a high temperature
A theoretical thermal and stress model based on finite element analysis is presented for the heat spreading capability and stress distribution of GaN with polycrystalline diamond substrates
The diamond substrate structure and thermal conductivity and thickness of transition layer have a clear influence on the heat power density and the heat spreading capability
Summary
Wide-bandgap semiconductors can operate under a high supply voltage and withstand a high temperature. Self-heating leads to increased channel temperature which causes the deterioration of the output power density and efficiency of GaN devices. The heat dissipation has become the biggest bottleneck to the further development and application of GaN power device technology.[7]. Using diamond as the thermal spreader of GaN HEMTs can greatly reduce the channel temperature and avoid self-heating. The bonding technology of GaN-on-diamond has been developed to reduce the thermal resistance of near junction area of GaN HEMT which include GaN buffer layer, transition layer and diamond substrate. A theoretical model based on finite element method (FEM) is applied to characterize the impacts diamond substrates and transition layer have on thermal power density under different conditions. The difference in coefficient of thermal expansion of diamond substrate, transition layer and GaN buffer will introduce mechanical stress.
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