Context

With the continued miniaturization and increase in power density in modern electronics, efficient thermal management is essential to prevent overheating and ensure optimal device performance [1]. In power electronics today, new, faster and more compact devices are being used based on higher-performance semiconductors such as silicon carbide and galium nitride, particularly in electric vehicles, energy, defense, transportation, and aerospace. They generate significant localized heat, reaching several hundred degrees [2]. This requires advanced solutions to dissipate heat, including thermal interface materials (TIMs), which reduce thermal resistance at the interfaces while ensuring efficient heat transfer and mechanical compatibility between materials.

At the ESYCOM laboratory, research is underway on various materials, such as polymers, superlattices, and semiconductors such as Si and silicon carbide (SiC), as well as on innovative metamaterials based on diamond and microstructured silicon. The main objective of the micro-energy team is to optimize thermal transport in microelectronic devices and to develop metamaterials with innovative and modular thermal properties. However, some current experimental limitations hinder the full characterization of these materials. For example, although the 3-omega technique that is used at ESYCOM [3] Has made it possible to measure the thermal conductivities of multilayer materials and to perform a 3D thermal mapping of an RF SOI component [4], it remains impossible to measure the thermal resistances at the interfaces (TBR) experimentally, which increases the uncertainty of the measurements. In addition, the brittle nanostructures of microstructured silicon samples are not compatible with surface heating techniques, leading to their deterioration. Despite possible solutions, such as the deposition of insulating layers, the increased complexity of the systems remains a challenge.

This project therefore aims to develop TIMs based on diamond and SiC-based composites to reduce TBR and improve the thermal management of high-power electronic systems. These advances will help improve the reliability and performance of modern microelectronic devices, especially those incorporating SiC and GaN components.

 

Subject of the thesis

Typically, TIMs play a key role in reducing thermal resistance at interfaces, improving heat transfer and managing mechanical stresses due to differences in the thermal expansion coefficients of materials. In microprocessor packaging, heat passes through several layers, each adding thermal resistance that can degrade performance [2]. These constraints require TIMs with high thermal conductivity, low thermal resistance at interfaces, and compatibility with material expansion properties.

Current TIMs include metal thermal greases [5], carbon-based materials [6] and polymer composites [7], each offering specific benefits. Polymer TIMs are flexible and inexpensive but less conductive, metal TIMs excel in conductivity but pose problems with stiffness and contact resistance, while carbon-based TIMs combine high conductivity and flexibility, but still need improvements to optimize their mechanical and thermal performance.

The properties of SiC, a wide-bandgap semiconductor, make it an ideal material for high-power, high-frequency applications, offering significant advantages over silicon, including tolerance to high temperatures (up to 400 °C or more) and reduced thermal stress due to its favorable coefficient of thermal expansion [8]. In addition, diamond (which is also a wide-bandgap semiconductor), especially when deposited by chemical vapor deposition (CVD), complements the properties of SiC with its even more exceptional thermal conductivity. Hybrid chillers combining CVD diamond and SiC can improve performance by 30% compared to SiC alone [9], and the use of thin diamond heat sinks (HS) can reduce the overall thermal resistance by 50-70% compared to traditional aluminum heatsinks [10]. 

These solutions, even if they may seem expensive due to the complexity and high energy demand of the processes, it should be noted that thanks to today's industrial investments, these processes are already integrated into standard installations, in production lines. This thesis focuses on integrating the exceptional thermal properties of SiC and diamond to develop lower cost and high efficiency thermal management solutions for modern electronic devices. In addition, the study of plasmon surface polaritons (SPPs) in SiC, as a polar material, will provide valuable information on energy transport at the nanoscale, thus optimizing interface design and reducing TBR for better thermal management. Also, although diamond is not inherently polar, it can withstand SPPs when mixed with materials like metals.

The expected improvements in thermal resistance ((m²· K/W)) compared to the current values of the literature ((m²· K/W)) illustrate the potential of these advanced materials to reduce thermal resistance.

 

Scientific objectives

This thesis project aims to go beyond the current state of the art through the following advances:

• One of the main objectives of this thesis is the improvement of the 3-omega measurement system currently used at ESYCOM, to allow the study of smaller and more complex samples. 
• Study of the influence of thermal resistance at interfaces (TBR), a critical parameter for the thermal management of microsystems, at different stages and dimensions of microelectronic packaging. 
• Plasmonic investigation of surface plasmons (SPPs) at the interfaces between massive SiC (bulk) and other materials. This innovative approach aims to explore plasmonic interactions on massive materials, a field that has been little studied to date, and to reveal new possibilities to improve the thermal management of devices.
• Testing innovative packaging solutions using carbon-based materials, with development of prototypes for efficient thermal management in high-power electronic chips.

 

The overall goal is to improve the thermal efficiency and reliability of heat sinks, addressing the growing heat dissipation challenges in the microelectronics industry. This project could pave the way for innovative and commercially viable solutions to overcome the current limitations of thermal management technologies.

 

 

Work required

1. Update of the 3-omega measuring bench

• Reconfigure the current system from a two-tip configuration to a four-point configuration.
• This update will allow for the measurement of weaker electrical signals with a significant reduction in noise. It will also make it possible to carry out simultaneous measurements on two resistors: one dedicated to heating by the Joule effect and the other used as a thermometer.
• This advanced configuration will allow a better characterization of thermal conductivities in the plane and in the volume, especially for anisotropic materials.

2. Study of surface polariton plasmons (SPPs)

• To study SPPs in SiC, as a polar material, to explore energy transport at the nanoscale.
• Optimize interface design by studying the impact of SPPs on TBR reduction.
• Analyze plasmonic interactions when diamond is combined with materials such as metals, in order to understand and exploit plasmonic properties in advanced composite systems.

3. Study of the thermophysical properties of new composites

• Analyze metal matrix composites with diamond inclusions or thin films of diamond on SiC substrate using the 3-omega technique.
• Extract their thermophysical properties, such as thermal conductivity () and thermal diffusivity (), as a function of temperature.

4. Simulation of effective thermal conductivity and TBR

• Simulate the effective thermal conductivity (TC) of a composite matrix incorporating diamond flakes using a model based on the effective media approach.
• Integrate the Kapitza Thermal Resistance (TBR) concept to predict the thermal behavior of the composite.
• Explore, through numerical simulations, the influence of particle size, particle shape, and TBR in order to optimize the design of materials.

5. Integration of advanced TIMs into functional devices 

• Incorporate advanced TIMs on commercial functional devices (e.g., Wolfspeed's CPM4-0120-0104JS0A SiC chip).
• Realize the direct bonding of test SiC chip, diamond/SiC heat splitter, and metal microchannel heat sink.

 

These tasks will allow the PhD student to contribute to both the experimental development and the modeling of advanced materials for thermal management.

 

References

[1]        G. Jiang, L. Diao, K. Kuang, G. Jiang, L. Diao, and K. Kuang, “Introduction to Thermal Management in Microelectronics Packaging,” Advanced Thermal Management Materials, vol. 9781461419, pp. 1–154, 2013, doi: 10.1007/978-1-4614-1963-1.

[2]        F. Sarvar, D. Whalley, and P. Conway, “Thermal Interface Materials - A Review of the State of the Art,” in 2006 1st Electronic Systemintegration Technology Conference, Dresden, Germany: IEEE, 2006, pp. 1292–1302. doi: 10.1109/ESTC.2006.280178.

[3]        R. G. Bhardwaj and N. Khare, “Review: 3omega Technique for Thermal Conductivity Measurement—Contemporary and Advancement in Its Methodology,” Int J Thermophys, vol. 43, no. 9, p. 139, Sep. 2022, doi: 10.1007/s10765-022-03056-3.

[4]        T. Nguyen et al., “Measurement and simulation of the three-dimensional temperature field in an RF SOI,” in 27th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC), IEEE, 2021, pp. 1–5. doi: 10.1109/THERMINIC52472.2021.9626402.

[5]        H. Wang, W. Xing, S. Chen, C. Song, M. D. Dickey, and T. Deng, “Liquid Metal Composites with Enhanced Thermal Conductivity and Stability Using Molecular Thermal Linker,” Advanced Materials, vol. 33, no. 43, p. 2103104, Oct. 2021, doi: 10.1002/adma.202103104.

[6]        W. Dai et al., “Metal-Level Thermally Conductive yet Soft Graphene Thermal Interface Materials,” ACS Nano, vol. 13, no. 10, pp. 11561–11571, Oct. 2019, doi: 10.1021/acsnano.9b05163.

[7]        T.-C. Chang, Y.-K. Kwan, and Y.-K. Fuh, “A reduced percolation threshold of hybrid fillers of ball-milled exfoliated graphite nanoplatelets and AgNWs for enhanced thermal interface materials in high power electronics,” Composites Part B: Engineering, vol. 191, p. 107954, Jun. 2020, doi: 10.1016/j.compositesb.2020.107954.

[8]        S. A. Mohammed, “A Review of the State-of-the-Art of Power Electronics for Power System Applications”.

[9]        J. P. Calame, R. E. Myers, S. C. Binari, F. N. Wood, and M. Garven, “Experimental investigation of microchannel coolers for the high heat flux thermal management of GaN-on-SiC semiconductor devices,” International Journal of Heat and Mass Transfer, vol. 50, no. 23–24, pp. 4767–4779, Nov. 2007, doi: 10.1016/j.ijheatmasstransfer.2007.03.013.

[10]      M. Malakoutian et al., “Cooling future system-on-chips with diamond inter-tiers,” Cell Reports Physical Science, vol. 4, no. 12, p. 101686, Dec. 2023, doi: 10.1016/j.xcrp.2023.101686.

 

www.esiee.fr • www.univ-gustave-eiffel.fr • http://esycom.cnrs.fr/

Contrat doctoral

Funding for this thesis has not yet been secured. The candidate will apply for a ministerial scholarship through the MSTIC doctoral school. This type of scholarship will fully finance the thesis for its entire duration, with a monthly salary of about 1800 euros per month of net salary. This salary can be increased by approximately 200 euros per month if the doctoral student is also recruited for a teaching assistant position (64 hours per year of teaching). It should be noted, however, that the availability of vacancies varies each year, and that they generally remain limited for non-French-speaking doctoral students.

Experimental thesis in the field of thermophysical characterization of metamaterials which will take place at the ESYCOM laboratory (Marne-la-Vallée, France) within the Gustave Eiffel University.

 

 

 

The ESYCOM laboratory is part of the fields of communication systems engineering, sensors and microsystems for the city, the environment and the person.

The topics covered are more specifically:

• antennas and propagation in complex media, photonicmicrowave components;
• microsystems for environmental analysis and remediation, for health and interface with living things;
• microdevices for mechanical, thermal or electromagnetic ambient energy recovery.

Université Gustave Eiffel

MSTIC

The candidate should have a physicist profile and knowledge of materials science, thermodynamics and heat/energy transfer. Knowledge of signal processing, Matlab/Python language, LabVIEW software, as well as experience in numerical simulation with the COMSOL multiphysics finite element method will be a plus. He/she must be motivated to carry out both theoretical and experimental work. A good command of written/spoken English is essential, as well as a good aptitude for teamwork in an international environment.