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Réalisation et optimisation de transistors HEMT GaN forte puissance et haute fréquence par technologie de transfert de couches sur substrat hôte

Abstract : Wireless telecommunication market largely benefits from new nitride technologies, which reach outstanding performance compared with traditional technologies. Current research is opening up many new strategies and alternative solutions to address simultaneously antagonist considerations such as cost, performances and/or reliability. Most AlGaN / GaN HEMTs are fabricated on a low cost, highly resistive silicon substrate or on a much more expensive and supply sensitive SiC substrate. However, the electrical performance constraints required when these technologies are integrating into radar systems, satellites and in telecommunications systems make them dependent to the operating temperature parameter, mainly linked to the high power dissipation during static/dynamic energy transfer. Indeed, these components are capable of generating high power densities in the microwave range. However, the operating frequency increase leads an increase of the power dissipation, generating the self-heating phenomenon which influences the devices performance (ID,max,ft,fmax...). In this context, several solutions were already proposed in the literature (use of composite substrates, passivation of devices, etc.). Furthermore, the layer transfer technology to report HEMTs from growth substrate onto a host substrate with a good thermal conductivity (such as diamond substrate) is a promising solution, still poorly detailed to date. The objective of this thesis work is to improve the heat dissipation and thus the performance and reliability of high-frequency HEMT transistors by using a layer transfer technology. AlGaN / GaN heterostructures are grown on a silicon substrate by MOCVD at CHREA. After the fabrication of HEMTs on a silicon substrate, AlGaN / GaN devices (for which the silicon substrate has been removed) are transferred onto a CVD diamond substrate. This transfer is obtained by thermocompression bonding of sputtered AlN layers on each surface to be assembled (backside of the transistors and diamond substrate). This transfer process has not damaged the functionality of the transistors with short gate length (Lg = 80 nm). The AlGaN/GaN HEMTs with a 2x35 µm development transferred onto diamond of feature a current ID,max = 710 mA.mm-1, a cutoff frequency ft of 85GHz and an oscillation frequency fmax of 144GHz. However, this transfer technique requires optimization phases (especially to reduce thickness and improve the crystalline quality and thermal conductivity of AlN layers) in order to reduce the thermal resistance of this adhesion layer and to limit the self-heating phenomenon noted at the end of this thesis work.
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Mahmoud Abou Daher. Réalisation et optimisation de transistors HEMT GaN forte puissance et haute fréquence par technologie de transfert de couches sur substrat hôte. Electronique. Université Paul Sabatier - Toulouse III, 2020. Français. ⟨NNT : 2020TOU30046⟩. ⟨tel-03001284⟩

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