Simulation of Self-Heating and Temperature Effect in GaN-based Metal-Semiconductor Field-Effect Transistor
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0892-FF13-05.1
Simulation of Self-Heating and Temperature Effect in GaN-based Metal-Semiconductor Field-Effect Transistor Valentin O. Turin1 and Alexander A. Balandin Nano-Device Laboratory, Department of Electrical Engineering University of California at Riverside Riverside, CA 92521, U.S.A.
ABSTRACT Two-dimensional electro-thermal simulations of GaN-based metal-semiconductor fieldeffect transistor are performed in the framework of the drift-diffusion model. The dependence of the hot spot temperature in transistors with many gates on the gate-to-gate pitch is studied. The case of SiC substrate is compared to the case of sapphire substrate. The ambient temperature effect on transistor performance is simulated. The specific of a thermal breakdown in GaN-based devices is discussed. The results obtained can be useful for the optimization of the thermal design for field-effect transistors.
INTRODUCTION Understanding the self-heating and the temperature effect in GaN-based field-effect transistors (FETs) [1] is an important problem because these devices are promising candidates for ultra-high-power microwave systems, power electronics and high temperature applications [2-4]. In this paper, two-dimensional (2D) electro-thermal simulations for the GaN metalsemiconductor field-effect transistor (MESFET) are performed in the framework of the driftdiffusion model (DDM). These simulations are executed with the DESSIS software. As is usual, the devices under consideration have a top passivation coating with good thermal insulation properties. Therefore, we will ignore the heat sink from the top of the device as well as heat loss by radiation and convection.
HEAT TRANSFER IN SUBSTRATE Let us consider heat diffusion from the point and linear heat sources under thermoinsulating passivation coating in simplified transistor structure with lateral boundaries extended to infinity. The heat source is deposited on the top of a thick substrate with thickness L and with thermal conductivity k1 placed on a half-space heat sink material with thermal conductivity k2. The approach based on a method of images [5] can be employed to write explicit form expressions for temperature distribution from the point (q) and linear (σ) heat sources in the substrate. Due to the symmetry of a schematic two-layer transistor structure, we can consider the doubled heat source (x=L) centered in the layer with thermal conductivity k1 surrounded by the
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Corresponding author: [email protected]
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Figure 1. The dependence of the size of a heat flow through the substrate bottom (measured in the substrate thickness units) on parameter K = k2/k1 from the point heat source (a) and from the linear heat source (b). Figure on each curve shows respective fraction of the whole heat flow.
ambient with thermal conductivity k2. For this case, following the method of images, we have temperature distribution in the central layer from the set of heat sources: qN = α
N
2q , x N = L(1 + 2 N ), N = 0,±1,±2...
(1)
Now we can find a temperature distributio
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