3D Integrated Water Cooling of a Composite Multilayer Stack of Chips

Abstract

New generation supercomputers with three dimensional stacked chip architectures pose a major challenge with respect to removal of dissipated heat which can reach currently as high as 250 W/cm2 in multilayer chip stacks of less than 0.3 cm3 volume. Interlayer integrated water cooling [1] is a very promising approach for such high heat flux removal due to much larger thermal capacity and conductivity of water compared to air, the traditional cooling fluid. In the current work, a multiscale conjugate heat transfer model is developed for integrated water cooling of chip layers and validated with experimental measurements on a specially designed thermal test vehicle that simulates a four tier chip stack with a footprint of 1 cm2. The cooling heat transfer structure, which consists of microchannels with cylindrical pin fins, is conceived in such a way that it can be directly integrated with the device layout in multilayer chips. Every composite layer is cooled by water flow in microchannels (height: 100 μm), which are arranged in 2 port water inlet-outlet configuration. The total power removed in the stack is 390 W at a temperature gradient budget of 60 K from liquid inlet to maximal junction temperature, corresponding to about 1.3 kW/cm3 volumetric heat flow. The computational cost and complexity of detailed CFD modeling of heat transfer in stacked chips with integrated cooling can be prohibitive. Therefore, the heat transfer structure is modeled using a porous medium approach, where the model parameters of heat transfer and hydrodynamic resistance are derived from averaging the results of the detailed 3D-CFD simulations of a single stream-wise row of fins. The modeling results indicate that an isotropic porous medium model does not accurately predict the measured temperature fields. The variation of material properties due to temperature gradients are found to be large, therefore variable properties are used in the model. It is also shown that the modeling of the heat transfer in the cooling sublayers requires the implementation of a porous medium approach with a local thermal non-equilibrium as well as orthotropic heat conduction and hydrodynamic resistance. The improved model reproduces the temperatures measured in the stack within 10%. The model is used to predict the behavior of multilayer stacks mimicking the change of heat fluxes resulting from variations in the computational load of the chips during their operation.

GreenCool: An Energy-Efficient Liquid Cooling Design Technique for 3-D MPSoCs Via Channel Width Modulation

“…Prototypes of 3-D chips with interlayer microchannel heat sinks have been shown to handle up to 250 W/cm 2 of hot spot heat fluxes, demonstrating the scalability of interlayer liquid cooling [8], [9]. Enhanced heat transfer geometries, such as pin fins, have also been built as an alternative to microchannels, improving the heat transfer characteristics at the cost of higher unpredictability in coolant flow patterns [7], [21].…”

“…7, the energy spent on pumping the coolant for both the GreenCool without modulation and with modulation cases is shown in Table II. We limit the maximum pumping pressure applied to 10 bars, as indicated by our industry partners [8]. In Table II, we mark the operating points that exceed the maximum possible pressure drop with XX.…”

“…In our experiments, we use TSVs with a diameter of 50 μm and a center-to-center pitch of 100 μm. We select these TSV parameters as they are verified to be compatible with interlayer liquid cooling in manufactured prototypes [6], [8], [18].…”

Temperature-Aware Design and Management for 3D Multi-Core Architectures

“…This methodology is being extended to incorporate two-phase cooling [88], where the fluid phase change absorbs significant thermal energy values, hence cooling down the target 3D MPSoC. Additional research efforts have investigated micro pin-fin structures [89,90] for enhanced single-phase fluid cooling potential. While these active cooling mechanisms are shown to be effective in heat removal, these techniques can be over utilized, hence resulting in resources (e.g.…”

A Semi-Analytical Thermal Modeling Framework for Liquid-Cooled ICs

“…Hence, it is touted as a long-term green energy solution for next-generation datacenters [6]. Prototypes of 2-D and 3-D stacked ICs with microchannel liquid cooling have been built by various research groups around the world with promising results [3], [7], [8]. An example from IBM is shown in Fig.…”