###### Abstract  
New technological and packaging solutions are more and more being employed for power semiconductor switches in an automotive environment, especially the SiC- and GaN-based ones. In this framework, new front-end and back-end solutions have been developed, and many more are in the design stage. New and more integrated power devices are useful to guarantee the performances in electric vehicles, in terms of thermal management, size reduction, and low power losses. In this paper, a GaN-based system in package solution is simulated to assess the structure temperature submitted to a Joule heating power loss. The monolithic package solution involves a half-bridge topology, as well as a driver logic. A novel integrated electromagnetic and thermal method, based on finite element simulations, is proposed in this work. More specifically, dynamic electric power losses of the copper interconnections are computed in the first simulation stage, by an electromagnetic model. In the second stage, the obtained losses' geometrical map is imported in the finite element thermal simulation, and it is considered as the input. Hence, the temperature distribution of the package's copper traces is computed. The simulation model verifies the proper design of copper traces. The obtained temperature swing avoids any thermal-related reliability bottleneck. automotive; gallium nitride; power devices; integrated package; finite element simulation; electromagnetic simulation; thermal simulation; half-bridge  
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GaN-based power devices are intrinsically normally-on: they have a 2 DEG channel as the conduction zone [12; 17]. However, this can be a problem, especially for safety reasons in real-world applications. Therefore, in most cases, a normally-off device is constructed by means of various techniques. In the GaN framework, there exist both radio-frequency and power devices: the latter will be the object of this work. High electron mobility transistors (HEMTs) are currently being employed on the market. From a physics point of view, GaN-on-Si technology, that is, with GaN on a silicon substrate, is today industrially mature [18]. Another important feature of GaN HEMT devices is the absence of the body diode; however, they can conduct in both directions, and reverse recovery losses are not present [20]. The physical characteristics of GaN-based switches are far from the topics discussed in this paper; however, the structure of a typical lateral GaN device is showed in Figure 1[21]. With reference to the voltage classes, in the context of power devices, both high voltage (HV, until 650 V) and low-voltage (LV, under 100 V) switches do exist today. Miniaturization can be possible because there is a low contribution in parasitic elements, such as intrinsic device capacitances, that results in lower heating, and, as a consequence, a smaller die and occupied area by the package. This also results in low power losses. In the GaN framework, new LV and HV power devices are important, among the others, for the following applications: DC-DC converters, onboard chargers, adapters, wireless charging, class D amplifiers, flyback SMPS, boost converters, and LiDAR [22]. In Figure 2, the possible applications of Si, SiC, and GaN devices, in terms of output power and operating frequency, are depicted [23]. For LV applications, GaN devices are commonly employed in monolithic packages, because they dissipate lower switching and conduction losses. Figure 1: GaN-on-Si power device lateral structure. Image from [21]. Figure 2: Application framework, based on output power and operating frequency, for Si-based IGBTs and MOSFETs, and SiC- and GaN-based power devices. Image from [23]. The principal challenges currently present in the design and application of GaN-based power devices mainly rely on thermal management [24], parasitic contributions with high switching frequency (high dv/dt and di/dt slew rates coupled with parasitic elements) [25], reliability [26], and dynamic on-state resistance.