This paper describes the architecture, design, analysis, and simulation and measurement results of the 3D-MAPS (3D massively parallel processor with stacked memory) chip built with a 1.5 V, 130 nm process technology and a two-tier 3D stacking technology using 1.2$\micro\hbox{m}$-diameter, 6$\micro \hbox{m}$-height through-silicon vias (TSVs) and$3.4\nbsp\micro\hbox{m}$-diameter face-to-face bond pads. 3D-MAPS consists of a core tier containing 64 cores and a memory tier containing 64 memory blocks. Each core communicates with its dedicated 4KB SRAM block using face-to-face bond pads, which provide negligible data transfer delay between the core and the memory tiers. The maximum operating frequency is 277 MHz and the maximum memory bandwidth is 70.9 GB/s at 277 MHz. The peak measured memory bandwidth usage is 63.8 GB/s and the peak measured power is approximately 4 W based on eight parallel benchmarks.

The complex buses consume significant power in graphics processing units (GPUs). In this paper, we demonstrate how the power consumption of buses in GPUs can be reduced with 3D IC technologies. Based on layout simulations, we found that partitioning and floorplanning of 3D ICs affect the power benefit amount, as well as the technology setup, target clock frequency, and circuit switching activity. For 3D IC technologies using two dies, we achieved the total power reductions of up to 21.5% over a baseline 2D design.

The nano-scale 3D interconnects available in monolithic 3D IC technology enable ultra-high density device integration at the individual transistor-level. In this paper we demonstrate the power benefits of transistor-level monolithic 3D designs. We first build a cell library that consists of 3D gates and model their timing/power characteristics. Next, we build timing-closed, full-chip GDSII layouts and perform sign-off iso-performance power comparisons with 2D IC designs. We also study the characteristics of benchmark circuits that maximize the power benefits in monolithic 3D designs. Lastly, our study is extended to predict the power benefits of monolithic 3D designs built with future devices.

The nano-scale 3-D interconnects available in monolithic 3-D integrated circuit (IC) technology enable ultrahigh density device integration at the individual transistor level. In this paper, we investigate the benefits and challenges of monolithic 3-D integration technology for ultrahigh density logic designs. We first build a 3-D standard cell library for transistor-level monolithic 3-D ICs and model their timing and power characteristics. Then, we explore various interconnect options for monolithic 3-D ICs that improve design quality. Next, we build timing-closed, full-chip GDSII layouts and perform sign-off iso-performance power comparisons with 2-D IC designs. Based on layout simulations, we compare important design metrics such as area, wirelength, timing, and power consumption of transistor-level monolithic 3-D designs with traditional 2-D, gate-level monolithic 3-D, and TSV-based 3-D designs.

Recent innovations in monolithic 3D technology enable much higher-density vertical connections than today's through-silicon-via (TSV)-based technology. In this paper, we investigate the benefits and challenges of monolithic 3D integration technology for ultra high-density logic designs. Based on our layout experiments, we compare important design metrics such as area, wirelength, timing, and power consumption of monolithic 3D designs with the traditional 2D designs. We also explore various interconnect options for monolithic 3D ICs that improve design density and quality. Depending on the interconnect settings of monolithic 3D ICs and the benchmark circuit characteristics, we observe that our two-tier monolithic 3D design provides up to 40% reduced footprint, 27.7% shorter wirelength, 39.7% faster operation, and 9.7% lower power consumption over the 2D counterpart.

Heat removal and power delivery have become two major reliability concerns in 3-D integrated circuit (IC) technology. To alleviate thermal problem, two possible solutions have been proposed: thermal-through-silicon-vias (T-TSVs) and micro-fluidic channel (MFC)-based cooling. In case of power delivery, a complex power distribution network is required to deliver currents reliably to all parts of the 3-D IC while suppressing the power supply noise to an acceptable level. However, these thermal and power networks pose major challenges in signal routability and congestion. This is because signal, power, and thermal interconnects are all competing for routing space, and the related TSVs interfere with gates and wires in each die. We present a co-optimization methodology for signal, power, and thermal interconnects in 3-D ICs based on design of experiments (DOE) and response surface methodology (RSM). The goal of our holistic approach is to improve signal, thermal, and power noise metrics and to provide fast and accurate design space exploration for early design stage. We also provide an in-depth comparison between T-TSV versus MFC-based cooling method and discuss how to employ DOE and RSM techniques to co-optimize the interconnects. Our DOE-based optimization found the optimal design point with less effort than a gradient search-based optimization.

As the geometry shrinking faces severe limitations, 3D wafer stacking with through silicon via (TSV) has gained interest for future SOC integration. Since TSV fill material and silicon have different coefficients of thermal expansion (CTE), TSV causes silicon deformation due to different temperatures at chip manufacturing and operating. The widely used TSV fill material is copper which causes tensile stress on silicon near TSV. In this paper, we propose systematic TSV stress aware timing analysis and show how to optimize layout for better performance. First, we generate a stress contour map with an analytical radial stress model. Then, the tensile stress is converted to hole and electron mobility variations depending on geometric relation between TSVs and transistors. Mobility variation aware cell library and netlist are generated and incorporated in an industrial timing engine for 3D-IC timing analysis. It is interesting to observe that rise and fall time react differently to stress and relative locations with respect to TSVs. Overall, TSV stress induced timing variations can be as much as ± 10% for an individual cell. Thus as an application for layout optimization, we can exploit the stress-induced mobility enhancement to improve timing on critical cells. We show that stress-aware perturbation could reduce cell delay by up to 14.0% and critical path delay by 6.5% in our test case.

In 3D integrated circuits through silicon vias (TSVs) are used to connect different dies stacked on top of each other. These TSV occupy silicon area and have significantly larger area than regular gates. In this paper, we address two critical aspects of TSV management in 3D designs. First, we address the problem of how many TSVs to add in a design. Since TSVs occupy significant silicon area, a general tendency has been to use a minimum number of TSVs in 3D circuits. We show that such an approach does not give us the best possible result. Second, we address the problem of TSV insertion. Because TSVs occupy silicon area, their location is decided during the placement stage of 3D design. However, we show that this is not the best possible stage for TSV insertion. We propose a change in the physical design flow for 3D integrated circuits to address the limitations of existing TSV placement methodology. All our algorithms are integrated with commercial tools, and our results are validated based on actual GDSII layouts. Our experimental results show the effectiveness of our methods.

Heat removal and power delivery are two major reliability concerns in the 3D stacked IC technology. Liquid cooling based on micro-fluidic channels is proposed as a viable solution to dramatically reduce the operating temperature of 3D ICs. In addition, designers use a highly complex hierarchical power distribution network in conjunction with decoupling capacitors to deliver currents to all parts of the 3D IC while suppressing the power supply noise to an acceptable level. These so called silicon ancillary technologies, however, pose major challenges to routing completion and congestion. These thermal and power/ground interconnects together with those used for signal delivery compete with one another for routing resources including various types of Through-Silicon-Vias (TSVs). This paper presents the work on routing with these interconnects in 3D: signal, power, and thermal networks. We demonstrate how to consider various physical, electrical, and thermo-mechnical requirements of these interconnects to successfully complete routing while addressing various reliability concerns.

Heat removal and power delivery have become two major reliability concerns in 3D stacked IC technology. For thermal problem, two possible solutions exist: thermal-through-silicon-vias (T-TSVs) and micro-fluidic channel (MFC) based liquid cooling. In case of power delivery, a highly complex power distribution network is required to deliver currents reliably to all parts of the 3D stacked IC while suppressing the power supply noise to an acceptable level. However, these thermal and power networks pose major challenges in signal routability and congestion. This is because the signal, power, and thermal interconnects are all competing for routing space. In this paper, we present a co-optimization methodology for the signal, power, and thermal interconnects for 3D stacked ICs based on design of experiments (DOE) and response surface method (RSM). The goal is to improve performance, thermal, noise, and congestion metrics with our holistic approach. We also provide in-depth comparison between T-TSV and MFC based cooling method and discuss how to employ DOE and RSM to best co-optimize the multi-functional interconnects simultaneously.