Electro-thermal Behavior Of The Third Generation Semiconductor GaN Microwave Power Devices

The RF power amplifier based on AlGaN/GaN HEMT process is widely used in advanced equipment because of its good performance.As a power device,high temperature has a particularly significant impact on the performance of the device.In order to have better heat dissipation and reduce ground impedance,through substrate via(TSV)is introduced.Although the heat is effectively removed and the electrical characteristics are greatly improved,the introduction of through substrate vias,especially when it is placed inside the active area,the area utilization of the die will be greatly reduced.Therefore,this work will force on how to increase die area utilization when through substrate vias are introduced.The thesis used Silvaco TCAD tool to study electro-thermal properties of a widely used AlGaN/GaN HEMT device of 0.25?m gate length,and introduced the insideactive-area substrate via(ISV)and the outside-active-area substrate via(OSV).The IV characteristics,maximum temperature and main heating location of the two were compared.As a result,the heating body inside the device is mainly on the surface of the GaN channel between the gate and drain,and it can be simplified as a rectangular body for three-dimensional steady-state thermal simulation.By using ANSYS simulation tool,three-dimensional full layout thermal simulations of the RF power dies with OSV and ISV were carried out.The steady-state thermal simulation was done for the two devices of the same total gate width and single gate finger width.The results show that the ISV die has a better heat dissipation,but the area is nearly as twice as that of the OSV die.The OSV die was optimized to keep maximum temperature close to that of the ISV die so that the performance of the two is basically the same,meanwhile maintaining its high die area utilization.By reducing the width per gate finger and increasing the number of gates,the heat dissipation in the OSV device similar to that of the ISV device was achieved,but the die area was saved by 45%.Then,fallowing the design rule of the 0.25?m GaN HEMT process,the number of ISV's between two gates was changed to 2.The steady-state thermal simulation was performed again,and the same optimization method was used to optimize the OSV die.Similarly,reducing the width per gate finger and increasing the number of gates for OSV die can not only improve heat dissipation,but also increase the die area utilization.