P21 978-1-4799-5288-5/14/$31.00 c ⃝ 2014 IEEE 233 Modeling Self-Heating Effects in AlGaN/GaN Electronic Devices during Static and Dynamic Operation Mode Andrea Natale Tallarico*, Paolo Magnone, Enrico Sangiorgi, and Claudio Fiegna ARCES, DEI-“Guglielmo Marconi”, University of Bologna, Cesena, Italy *a.tallarico@unibo.it Abstract—In this paper, we present a study of the self-heating effects in GaN-based power devices during static and dynamic operation mode by means of Sentaurus TCAD. A physical model interface (PMI), accounting for the temperature dependence of the thermal boundary resistance (TBR), has been implemented in the simulator in order to realistically model self-heating effects. In particular, we take into account for the TBR associated to the nucleation layer between GaN and SiC substrate. Moreover, the thermal contribution of the mutual heating among adjacent devices has been considered. Finally, we have investigated the influence of the temperature on the surface charges trapping and de-trapping phenomena showing two different traps occupancy transients. While one of the two occurs also in the isothermal condition, the second one is temperature activated. Keywords — GaN HEMT, self-heating, mutual-heating, thermal boundary resistance (TBR), surface trapping/de-trapping charges, drain-lag measurement. I. INTRODUCTION GaN-based transistors, thanks to the intrinsic properties of the adopted materials, represent today a potential technology for switching power applications [1-3]. However, high performance is not enough, as a high level of reliability must be guaranteed under heavy-duty operation. For this reason, different works about hetero-structures reliability have been focused on the charges trapping/de-trapping mechanisms. Del Alamo et al. [4] have shown how the crystallographic defects generation in the AlGaN barrier, under high voltage conditions, is responsible for the formation of a path for gate leakage current and electron trapping, leading to the degradation of many figures of merit, whereas in [5-7] the current dispersion effects due to surface and/or AlGaN barrier traps have been investigated. Since a power transistor is subject to high temperatures during its normal operation, in this paper a simulation study of self-heating effects has been performed in order to understand the performance limitations, under both static and dynamic operation modes. Several studies reported in the literature [8- 10] have pointed out as the contribution of the thermal boundary resistance (TBR), introduced by oxide nucleation layer between GaN-buffer and Si- or SiC-substrate in order to reduce the lattice constants mismatch, is fundamental for modeling the self-heating effects in the devices. Indeed, Sarua et al. [9] have experimentally proposed a model able to describe the temperature dependence of the TBR emphasizing how its contribution becomes more and more important with the temperature increase. To this purpose, the implementation of a physical model able to account for the realistic temperature dependence of the equivalent thermal boundary resistance ascribed to oxide nucleation layer, turned out to be necessary in our study. II. DEVICE STRUCTURE AND PHYSICAL MODELS Fig. 1 shows the simulated AlGaN/GaN structure. It was defined considering typical geometric characteristics and material parameters proposed in experimental works reported in the literature (e.g. [5]). The structure features a stack of SiN/AlGaN/GaN/Oxide/SiC layers with thickness of 50 nm / 29 nm / 1.5 µm / 10 nm / 100 µm, respectively. The aluminum concentration in AlGaN barrier, which plays an important role in device operation through the piezoelectric charge induced by mechanical stress, is set to 35%, representing a typical value for state-of-art devices [5]. Drain and source electrodes are modeled as ohmic contacts with length L S = L D = 0.5 µm, whereas the 0.7 µm long gate electrode is modeled as a Schottky contact, with 1.1 eV barrier height, representing a typical measured value for realistic devices [11, 12]. The drain- and source-to channel access regions feature lengths of L SG = 0.7 µm and L GD = 2 µm, respectively. Finally, a device pitch (L DEV_PITCH ) of 4.4 µm was assumed. Fig. 1. Simulated AlGaN/GaN HEMT structure. To allow a self-heating study, a thermode contact, fixed at the temperature of 300 K, is introduced at the bottom of the SiC substrate. Figure not in scale.