Electrical eFfects on InterfaCial thermAl resistanCE – EFICACE

Nowadays, integrated circuits consist of very dense assemblies of heterogeneous materials at lengths scales below the diffusive regime of heat conduction. These materials are the place of many interfaces that are limiting heat dissipation. In this context, metal semi-conductor junctions are targets for heat transfer optimization.
The project EFFICACE aims at improving the understanding of heat transfer at interfaces between a metal and a semiconductor (SC), i.e. at Schottky contacts, and providing solutions to enhance heat transport at contacts. Lower thermal boundary resistances (TBR) are effectively obtained for metal/metal interfaces. The main idea is to find solution to obtain such low TBR in metal/SC interfaces with doped SC substrates for increasing electron/electron and electron/phonon interactions at interfaces. However, in some cases, the Schottky barrier (SB) limits these electron interactions. The goal is then to better understand the thermoelectric phenomena that occur at SB to be able to propose in the future solutions to the optimization of heat transfer management within dense electronic devices.
One of the fundamental issues in thermal transport at these scales is that heat transfer laws basically differ compared with those at macroscale. Kapitza or thermal boundary resistance and ballistic transport play important roles. The couplings between heat transport by phonons and electrons and thermoelectric effects simultaneously occur in active devices. In parallel, from the electronic transport point of view, it has been shown that a 2 nm interfacial dielectric layer can enhance the electrical contact by suppressing the Fermi level pinning and coupling via Metal Induced Gap States while preserving substantial electron transport by tunneling. Is it possible to obtain such a counter-intuitive, interface enhancement, from the thermal point of view? A multitude of questions can then emerge. What magnitude of electrical current influences heat transfer in Schottky diode? How does electron density or Schottky Barrier Height (SBH) affect the interfacial thermal resistance? What is the influence of temperature on all these effects? Our goal is to answer these questions.
To analyze the distinct phenomena and explore different routes to enhance interfacial transport and decrease TBR, we propose to study materials with different electrical properties:
1) Electronic density: Influence of the silicon doping level on metal/Si thermal resistance,
2) SBH: Is there a systematic correlation between barrier height and metal/Si TBR?
3) Electrical bias (electronic assisted heat transfer): Influence of electrical polarization on TBR. Electron current could increase heat transfer at interface and so decrease TBR but not in all configurations. Indeed, different cases occur depending on the electrical contact (rectifying or ohmic) and on the direction of the current.
4) Interface engineering: influence of a few nm dielectric layer (Al2O3 and HfO2) intercalation on TBR;
EFFICACE targets breakthroughs in developing the theoretical, modeling and experimental tools to control the electron energy/heat flux channels in a solid-state device. The outputs of the project are the critical parameters expected to significantly decrease the TBR. Through a global and fundamental understanding of interfacial heat transport, we will be able to propose new routes for efficient heat management in electronic devices and for thermal diodes, rectification effect, or heat-assisted data storage applications.