Enhanced high-resistivity silicon-based substrates for RF and mmWave FD-SOI circuits
(2025)
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- Authors
- Supervisors
- Raskin, Jean-Pierre
- Abstract
- This thesis delves into the intricate advancements in mobile phone technology, where the integration of cutting-edge components such as front-end modules(FEM), RF transceivers, and systems on chips (SoCs) is critical for handling the complex demands of modern communication. These technologies ensure that mobile devices can efficiently manage and transmit signals across multiple frequency bands, while also optimizing power consumption and supporting a wide range of advanced applications. A key focus is the role of CMOS technology, particularly the silicon substrate that not only provides mechanical support for integrated circuits but also plays a pivotal role in the electromagnetic environment surrounding RF components. The substrate’s electrical properties, including permittivity and conductivity, significantly affect RF circuit performance, influencing factors like signal propagation and crosstalk. Therefore, understanding and optimizing the substrate is crucial for achieving high-performance outcomes in RF systems. Over the past two decades, silicon-on-insulator (SOI) technology has seen remarkable progress, especially in developing substrates aimed at minimizing losses and enhancing linearity. Among these, the polysilicon trap-rich eSI™ substrate has become a cornerstone in mobile technology, used in all RF switches found in today’s mobile phones. This substrate has proven successful in partially depleted SOI (PDSOI) technology, with several circuits built on it showing excellent RF performance. However, the emergence of fully depleted SOI (FDSOI) technology, which offers reduced gate lengths, higher transition frequencies, and improved power capabilities suitable for millimeter-wave applications, has introduced new challenges. Integrating the trap-rich substrate into FDSOI has proven difficult due to compatibility issues with the defect-rich polysilicon layer, leading to concerns about increased reverse current and the potential degradation of the substrate’s performance under high thermal budgets. Additionally, the high cost of the trap-rich substrate poses further challenges to its widespread adoption. This thesis explores alternative substrates that are compatible with FDSOI technology, comparing them against the trap-rich and high-resistivity substrates to assess their effectiveness. Proposed solutions include the field effect (FE) passivation technique and smart buried PN junctions, both validated through proof-of-concept experiments at UCLouvain and successfully implemented using industrial FDSOI processes. Another promising approach developed at UCLouvain is the double-buried oxide (double-BOX) substrate, which builds on the trap-rich concept to enhance RF performance. Additionally, gold-doped silicon substrates and porous silicon are investigated for their excellent RF performance, offering viable alternatives starting from highly doped silicon substrates. To validate these novel solutions, this thesis includes the design and evaluation of three RF circuits—switches, power amplifier, and mixers—using 22FDX® and 28FDSOI technologies. These circuits are analyzed to determine the impact of different substrates on their performance, providing a comprehensive understanding of how substrate technology influences RF circuit behavior in the context of FDSOI advancements. This work offers valuable insights into the future of mobile technology and the critical role of substrates in pushing the boundaries of RF performance.
- Affiliations
Citations
Nabet, M. (2025). Enhanced high-resistivity silicon-based substrates for RF and mmWave FD-SOI circuits. https://hdl.handle.net/2078.5/244199