• Energy Research

Thermal management in integrated chips is one of the major challenges on micro- and nanoelectronics. The rise of power density raised the need for microchannel liquid cooling solutions. This technology has poor temperature uniformity and requires high pumping powers. In this work, a cooling scheme aiming for high temperature uniformity and low pumping power is numerically studied. The cooling scheme consists in a matrix of microfluidic cells with thermally activated microvalves, which tailor the local coolant flow rates to avoid overcooling and improve the temperature uniformity. This system is assessed with steady state CFD studies combined with temporal integration in a time dependent and non-uniform heat load scenario. The studied cooling scheme improves, with respect to existing devices for similar applications, the chip temperature uniformity while reducing the pumping power by 50%. The research leading to these results has been performed within the STREAMS project and received funding from the European Community's Horizon 2020 program under Grant Agreement No. 688564.

Thermal dissipation is a major concern in microelectronics, especially for compact packages and 3D circuits where the dense stacking of thin silicon layers leads to a significant increase of heat densities. Direct hybrid bonding is considered as one of the most promising technologies for future 3D-ICs. Its face-to-face structure allows significant inter-connexion capabilities but it also implies increased thermal densities that will be reflected in both tiers due to the lack of insulating barriers. A specific test vehicle for 3D hybrid bonding including heaters and temperature sensors on each tiers has been fabricated and characterized. Several packaging configurations including different silicon thicknesses, substrate thermal design or the integration of a patterned graphite heat spreader have been tested. The best results were obtained with the integration of the graphite heat spreader which led to a reduction in thermal resistance by 11%. These experimental results have been retro-simulated to establish a thermal model. This model was then used to analyse the heat path and explore the thermal impact of the different packaging parameters.

Poor temperature uniformities and high pumping powers due to large pressure drops are the major drawbacks of the conventional microchannel cooling solutions. In this work, a liquid cooling device based on a matrix of microfluidic cells is presented. The coolant flow rate in each microfluidic cell is individually tailored, through thermally activated microvalves, to the local heat extraction needs in order to improve the temperature uniformity and avoid overcooling. A numerical study is implemented to assess the thermo-hydraulic performance of the cooling device. The analysis is performed in a steady state CFD study and integrated along a time dependent and non-uniform heat load scenario. The results show an enhancement of the temperature uniformity along the whole system while reducing the energy needed for the pumping power by 89.2% compared to the conventional microchannel technology.

We have developed high power integrated thermoelectric generators (µTEGs). These µTEGs are CMOS compatible, i.e. based on polycristalline SiGe materials. These µTEGs have been processed directly on a silicon interposer. Even if poly-SiGe exhibits low thermoelectric performances at room temperature, the specific design and proposed architecture enable µTEGs to deliver up to 680 µW for a temperature difference at 15.5 K. To reach such high power, an original 2.5D structure has been developed and µchannels technology has been associated, below the µTEG, to dissipate heat coming from the hot side. µTEGs have been tested in real environment, located below a hot test chip. Such µTEG performances overtake those from similar state-of-the-art CMOS compatible devices, and pave the way for a potential use in different applications such as sensors power supply or battery charger. International audience