Thermal design in sub-100nm technologies has become one of the major challenges to the CAD community. Thermal effects on design aspects such as performance, power and reliability have to be thoroughly and seriously considered during the entire design flow in order to achieve faster design convergence and optimal design. This paper expands the discussion in our conference paper [8]. We first introduce the idea of temperature-aware design. We then propose a compact thermal model which can be integrated with modern CAD tools to achieve a temperature-aware design methodology. Finally, we use the compact thermal model in a case study of microprocessor design to show the importance of using temperature as a guideline for the design. The results from our thermal model show that a temperatureaware design approach can provide more accurate estimations, and therefore better decisions and faster design convergence. 1.

As the technology node progresses, thermal problems are becoming more prominent especially in the developing technology of three-dimensional (3D) integrated circuits. The thermal placement method presented in this paper uses an iterative force-directed approach in which thermal forces direct cells away from areas of high temperature. Finite element analysis (FEA) is used to calculate temperatures efficiently during each iteration. Benchmark circuits produce thermal placements with both lower temperatures and thermal gradients while wirelength is minimally affected. 1.

Abstract—This paper presents HotSpot—a modeling methodology for developing compact thermal models based on the popular stacked-layer packaging scheme in modern very large-scale integration systems. In addition to modeling silicon and packaging layers, HotSpot includes a high-level on-chip interconnect self-heating power and thermal model such that the thermal impacts on interconnects can also be considered during early design stages. The HotSpot compact thermal modeling approach is especially well suited for preregister transfer level (RTL) and presynthesis thermal analysis and is able to provide detailed static and transient temperature information across the die and the package, as it is also computationally efficient. Index Terms—Compact thermal model, early design stages, interconnect self-heating, temperature, VLSI. I.

3-D IC has a great potential for improving circuit performance and degree of integration. It is also an attractive platform for system-on-chip or system-in-package solutions. A critical issue in 3-D circuit design is heat dissipation. In this paper we propose an efficient 3-D multilevel routing approach that includes a novel through-the-silicon via (TS-via) planning algorithm. The proposed approach features an adaptive lumped resistive thermal model and a two-step multilevel TSvia planning scheme. Experimental results show that with multilevel TS-via planning, the thermal-driven approach can reduce the maximum temperature to the required temperature with reasonable wirelength increase. Compared to a post processing approach for dummy TS-via insertion, to achieve the same required temperature, our approach uses 80 % fewer TS-vias. To our knowledge, this proposed approach is the first thermal-driven 3-D routing algorithm. I.

In this paper, we show how 3D stacking technology can be used to implement a simple, low-power, high-performance chip multiprocessor suitable for throughput processing. Our proposed architecture, PicoServer, employs 3D technology to bond one die containing several simple slow processing cores to multiple DRAM dies sufficient for a primary memory. The 3D technology also enables wide low-latency buses between processors and memory. These remove the need for an L2 cache allowing its area to be re-allocated to additional simple cores. The additional cores allow the clock frequency to be lowered without impairing throughput. Lower clock frequency in turn reduces power and means that thermal constraints, a concern with 3D stacking, are easily satisfied. The PicoServer architecture specifically targets Tier 1 server applications, which exhibit a high degree of thread level parallelism. An architecture targeted to efficient throughput is ideal for this application domain. We find for a similar logic die area, a 12 CPU system with 3D stacking and no L2 cache outperforms an 8 CPU system with a large on-chip L2 cache by about 14 % while consuming 55 % less power. In addition, we show that a PicoServer performs comparably to a Pentium 4-like class machine while consuming only about 1/10 of the power, even when conservative assumptions are made about the power consumption of the PicoServer.

Abstract- Although the emerging three-dimensional integration technology can significantly reduce interconnect delay, chip area, and power dissipation in nanometer technologies, its impact on overall system performance is still poorly understood due to the lack of tools and systematic flows to evaluate 3D microarchitectural designs. The contribution of this paper is the development of MEVA-3D, an automated physical design and architecture performance estimation flow for 3D architectural evaluation which includes 3D floorplanning, routing, interconnect pipelining and automated thermal via insertion, and associated die size, performance, and thermal modeling capabilities. We apply this flow to a simple, out-of-order superscalar microprocessor to evaluate the performance and thermal behavior in 2D and 3D designs, and demonstrate the value of MEVA-3D in providing quantitative evaluation results to guide 3D architecture designs. In particular, we show that it is feasible to manage thermal challenges with a combination of thermal vias and double-sided heat sinks, and report modest system performance gains in 3D designs for these simple test examples. 1.

As thermal problems become more evident, new physical design paradigms and tools are needed to alleviate them. Incorporating thermal vias into integrated circuits (ICs) is a promising way of mitigating thermal issues by lowering the thermal resistance of the chip itself. However, thermal vias take up valuable routing space, and therefore, algorithms are needed to minimize their usage while placing them in areas where they would make the greatest impact. With the developing technology of three-dimensional integrated circuits (3D ICs), thermal problems are expected to be more prominent, and thermal vias can have a larger impact on them than in traditional 2D ICs. In this paper, thermal vias are assigned to specific areas of a 3D IC and used to adjust their effective thermal conductivities. The thermal via placement method makes iterative adjustments to these thermal conductivities in order to achieve a desired maximum temperature objective. Finite element analysis (FEA) is used in formulating the method and in calculating temperatures quickly during each iteration. As a result, the method efficiently achieves its thermal objective while minimizing the thermal via utilization.

Heat dissipation is one of the most serious challenges in 3D IC designs. One e#ective way of reducing circuit temperature is to introduce thermal through-the-silicon (TTS) vias. In this paper, we extended the TTS-via planning in a multilevel routing framework as in [7], but use a much enhanced TTS-via planning algorithm. We formulate the TTSvia minimization problem with temperature constraints as a constrained nonlinear programming problem (NLP) based on the thermal resistive model and develop an e#cient heuristic algorithm, named m-ADVP, which solves a sequence of simplified via planning subproblems in alternating direction in a multilevel framework. The vertical via distribution is formulated as a convex programming problem, and the horizontal via planning is based on two e#cient techniques: path counting and heat propagation. Experimental results show that the m-ADVP algorithm is more than 200 faster than the direct solution to the NPL formulation for via planning with very similar solution quality (within 1% of TS-vias count). However, compared to a recent work of multilevel TS-via planning algorithm based on temperature profiling [7], our algorithm can reduce the total TS-via number by over 68% for the same required temperature with similar runtime.

Modeling and analyzing detailed die temperature with a full-chip thermal model at early design stages is important to discover and avoid potential thermal hazards. However, omitting important aspects of package details in a thermal model can result in significant temperature estimation errors. In this paper, we discuss the applications of an existing compact thermal model that models both die and package temperature details. As an example, a thermally selfconsistent leakage power calculation of a POWER4-like microprocessor design is presented. We then demonstrate the importance of including detailed package information in the thermal model by several examples considering the impact of thermal interface material (TIM), which glues the die to the heat spreader. The fact that detailed package information is needed to build an accurate compact thermal model implies a design flow, in which the chip- and package-level compact thermal model acts as a convenient medium for more productive collaborations among circuit designers, computer architects and package designers, leading to early and efficient evaluations of different design tradeoffs for an optimal design from a thermal point of view. Categories and Subject Descriptors:

Abstract – We present timing-driven partitioning and simulated annealing based placement algorithms together with a detailed routing tool for 3D FPGA integration. The circuit is first divided into layers with limited number of inter-layer vias, and then placed on individual layers, while minimizing the delay of critical paths. We use our tool as a platform to explore the potential benefits in terms of delay and wire-length that 3D technologies can offer for FPGA fabrics. Experimental results show on average a total decrease of 21 % in wire-length and 24 % in delay, can be achieved over traditional 2D chips, when five layers are used in 3D integration. I.