RTL-to-GDS Tool Flow and Design-for-Test Solutions for Monolithic 3D ICs

Monolithic inter-layer vias (MIVs) used in 3D integration technology are much smaller than through-silicon vias (TSVs) used in TSV-based 3D integration. Thus, monolithic 3D integration provides shorter wire length, better performance, and lower power consumption than TSV-based 3D integration. Multi-tier monolithic 3D integration stacks more than two silicon layers, thereby increasing the device density, which reduces the wire length and power consumption and improves performance further than two-tier monolithic 3D integration. Since the size of an MIV is comparable to that of a local via, the wire lengths of multi-tier gate-level monolithic 3D IC layouts are expected to be close to the ideal wire length reduction ratio, for example, 29, 42, and 50 percent for two-, three-, and four-tier designs, respectively. However, it is still unknown whether it would be possible to achieve the ideal wire length reduction ratios by multi-tier gate-level monolithic 3D integration. In this paper, we propose an efficient routing methodology to design multi-tier monolithic 3D ICs. Using the design methodology, we design two- to eight-tier gate-level monolithic 3D IC layouts and thoroughly investigate the wire length characteristics of the layouts. The simulation results show that the proposed routing methodology reduces the wire length by 12 to 53 percent compared to the 2D designs. In addition, the proposed routing methodology builds multi-tier monolithic 3D IC layouts more efficiently than a state-of-the-art methodology with comparable routed wire length.

Monolithic 3D IC is an emerging technology to continuously satisfy demands for power reduction under challenges posed by traditional device scaling. In this paper, for the first time, we study power benefits of 4-tier monolithic 3D ICs compared with 2-tier monolithic 3D and 2D ICs. We present a tier partitioning methodology that significantly extends the capability of a state-of-the-art flow built for 2-tier monolithic 3D ICs. We develop two complete RTL-to-GDSII design flows to achieve this goal and offer quantitative comparisons. In addition, we study impacts of inter-tier via usage on 2-tier and 4-tier monolithic 3D ICs. Our experiments show that poorly controlled inter-tier via usage results in up to 6.05% degradation in total power savings. Thus, we develop an effective strategy to achieve inter-tier via configurations to optimize power metrics. Experiments show that 4-tier monolithic 3D ICs outperform 2-tier and 2D IC by 15% and 50% in terms of power and 25% and 75% in area under the same performance.

Monolithic three-dimensional (3D) integration enables revolutionary digital system architectures of computation immersed in memory. Vertically-stacked layers of logic circuits and memories, with nano-scale inter-layer vias (with the same pitch and dimensions as tight-pitched metal layer vias), provide massive connectivity between the layers. The nano-scale inter-layer vias are orders of magnitude denser than conventional through silicon vias (TSVs). Such digital system architectures can achieve significant performance and energy efficiency benefits compared to today's designs. The massive vertical connectivity makes such architectures particularly attractive for abundant-data applications that impose stringent requirements with respect to low-latency data processing, high-bandwidth data transfer, and energy-efficient storage of massive amounts of data. We present an overview of our progress toward realizing monolithic 3D ICs, enabled by recent advances in emerging nanotechnologies such as carbon nanotube field-effect transistors and emerging memory technologies such as Resistive RAMs and Spin-Transfer Torque RAMs.

In this paper, we present an optimization flow for monolithic 3D ICs called Pin-3D Optimizer. Compared with the state-of-the-art RTL-to-GDS flows that rely on ad-hoc technology file tweaks and RC scaling, Pin-3D offers a streamlined method to run commercial 2D IC tools to obtain high-quality monolithic 3D IC designs. Specifically, Pin-3D supports effective legalization, routing, timing closure, and ECO optimization for monolithic 3D IC designs. We propose a novel optimization methodology where the cells in each tier of a 3D IC are optimized using cell data and constraints of the full 3D design. The optimizations in a tier also directly influence the timing, power in the other tiers, leading to better overall PPA of the 3D IC. With the help of two industry processors designed with a 28 nm technology node, we show that Pin-3D provides up-to 9.0% smaller wirelength and 88% smaller total negative slack than die-by-die M3D flows. We also observe up-to 8.7% lower power and 26% smaller wirelength than 2D ICs. In addition, Pin-3D is the first flow that supports routing and timing optimization in heterogeneous logic-on-logic monolithic 3D ICs. We demonstrate this capability by performing area-balanced tier partitioning, routing, and timing closure of a 3D design with different technologies on each die.

The state-of-the-art Monolithic 3D (M3D) IC design methodologies~\citem3d:Ku-tcad-Compact2D, m3d:Panth-tcad-Shrunk2D use commercial electronic design automation tools built for 2D ICs to implement a pseudo-3D design and split it into two dies that are routed independently to create an M3D design. Therefore, an accurate estimation of 3D wire parasitics at the pseudo-3D stage is important to achieve a well optimized M3D design. In this paper, we present a regression model based on boosted decision tree learning to better predict the 3D wire parasitics (RCs) at the pseudo-3D stage. Our model is trained using individual net features as well as the full-chip design metrics using multiple instantiations of 8 different netlists and is tested on 3 unseen netlists. Compared to the Compact-2D~\citem3d:Ku-tcad-Compact2D flow on its own as the reference pseudo-3D, the addition of our predictive model achieves up to $2.9 \times$ and $1.7 \times$ smaller root mean square error in the resistance and capacitance predictions respectively. On an unseen netlist design, we observe that our model provides 98.6% and 94.6% RC prediction accuracy in 3D and up to $6.4 \times$ smaller total negative slack of the design compared to the result of Compact-2D flow resulting in a more timing-robust M3D IC. This model is not limited to Compact-2D, and can be extended to other pseudo-3D flows.

Network-on-chips (NoCs) with traditional regular topologies generally have an average-hop-count increased, polynomially, with the network size. This brief proposes to generate brain-network-inspired (BNI) topologies on monolithic 3D (M3D) ICs, where the average hop count scales up logarithmically, for large-scale systems with tens of thousands of cores. We propose a routability-driven method to generate BNI topologies on M3D ICs with scale-free and small-world properties. Moreover, we present an iterative method to reduce the network diameter using as few tier-crossing routers as possible. The resulting BNI topologies not only have over 50% lower average hop count and lower diameter than traditional regular topologies, but also have shorter total link length than other irregular topologies. The performance is further validated by the cycle-accurate simulation.

Monolithic three-dimensional (3D) integration enables the most fine-grained integration of transistors by stacking very thin layers and fabricating monolithic inter-layer vias as small as local vias. Thus, monolithic 3D integration is expected to provide a higher degree of wirelength reduction, performance improvement, and power saving. Due to the prospective properties of the monolithic 3D integration technology, research on multilayer monolithic 3D integration that stacks more than two device layers is also ongoing. In this paper, we propose an algorithm that optimizes dynamic power consumption of gate-level monolithic 3D ICs. Under the same timing constraints, our algorithm reduces dynamic power consumption more effectively than a uniform-scaling-based placement algorithm. We also design multi-tier monolithic 3D ICs and show that our algorithm outperforms the uniform-scaling-based placement algorithm by 11.4% on average.

Monolithic 3D (M3D) is an emerging technology that enables integration density which is orders of magnitude higher than that offered by through-silicon-vias. In this paper, we demonstrate that a modified 2D placement technique coupled with a post-placement partitioning step is sufficient to produce high-quality M3D placement solutions. We also present a commercial router-based monolithic intertier via insertion methodology that improves the routability of M3D ICs. We demonstrate that, unlike in 2D ICs, the routing supply and demand in M3D ICs are not completely independent of each other. We develop a routing demand model for M3D ICs, and use it to develop an O(N) min-overflow partitioner that enhances routability by off-loading demand from one tier to another. This technique reduces the routed wirelength and the power delay product by up to 7.44% and 4.31%, respectively. This allows a two-tier M3D IC to achieve, on average, 19.9% and 11.8% improvement in routed wirelength and power delay product over 2D, even with reduced metal layer usage.

As Moore's law approaches its physical limits, 3D integrated circuit (3D IC) technology has emerged as a crucial way to increase chip integration density. Due to their small size, high carrier mobility, and low power consumption, carbon nanotube field‐effect transistors (CNTFETs) offer a promising way to overcome the limitations imposed by Moore's law. The evolution of ICs and 3D integration technologies for the post‐Moore era, such as chiplets and multilayer stacking are reviewed, and the potential applications and value of CNTFETs in 3D optoelectronics, memory, and monolithic 3D ICs are explored. The prospects of novel device structures like FinFETs and gate‐all‐around FETs are also discussed. CNT 3D ICs have tremendous potential for these applications, but challenges remain in material fabrication, device performance, and 3D structure design. Researchers are actively exploring solutions such as optimizing fabrication processes, developing new materials, and innovative logic design methodologies. Notably, the integration of CNTFETs with chiplet technology promises more efficient and flexible chip design and manufacturing, catering to the future demand for high‐performance, low‐power, and high‐density ICs.

Monolithic 3D ICs (M3D) are an emerging technology that offers an ultra-high-density 3D integration due to the extremely small size of monolithic inter-tier vias. We explore various design styles available in M3D and present design techniques to obtain GDSII-level signoff quality results for each of these styles. We also discuss various challenges facing each style and provide solutions to them.

The rise of three-dimensional (3D) IC layouts necessitates the development of unique partitioning methods that will be suitable for the 3D component designs. Net lists partitioning is a key aspect of the physical design of a 3D IC. Reducing wire lengths between gates is possible with 3D-ICs since they have a small footprint as well as vertical connectivity among dies. As a result, they consume less power and have shorter connection delays. This paper presents an efficient genetic algorithm (GA) based layer partitioning technique for 3D ICs that focuses on proper layer assignment to reduce area deviation and minimization of Through Silicon Vias (TSVs) to reduce IC footprint. The method starts with random initial solutions and refines the solutions with efficient crossover and mutation operator till the optimized solution is achieved. Our methodology produces high-quality solutions on well-known benchmarks. The experimental findings are compared with state-of-the-art methodologies and the suggested strategy is found to be very effective in the case of decreasing the TSV count and space need of the 3-dimensional IC design. In addition, the performance of our strategy is also compared with two recent publications that use GA and Particle Swarm Optimization (PSO) and it is found that the proposed method achieves 20.18% and 38.66% average reduction in terms of TSV count respectively. Thus, the suggested technique is beneficial for multilayered 3D IC partitioning, as it can reduce TSV count while also satisfying balancing criteria and latency.

To reduce interconnect delay and power consumption while improving chip performance, a three-dimensional integrated circuit (3D IC) has been developed with die-stacking and through-silicon via (TSV) techniques. The power supply problem is one of the essential challenges in 3D IC design because IR-drop caused by insufficient supply voltage in a 3D chip reduces the chip performance. In particular, power bumps and TSVs are placed to minimize IR-drop in a 3D power delivery network. In this paper, we propose a design methodology for 3D power delivery networks to minimize the number of power bumps and TSVs with optimum mesh structure and distribute voltage variation more uniformly by shifting the locations of power bumps and TSVs while satisfying IR-drop constraint. Simulation results show that our method can reduce the voltage variation by 29.7% on average while reducing the number of power bumps and TSVs by 76.2% and 15.4%, respectively.

Through silicon via (TSV) based 3D integrated circuits have inspired a novel design paradigm which explores the vertical dimension, in order to alleviate the performance and power limitations associated with long interconnects in 2D circuits. TSVs enable vertical interconnects across stacked and thinned dies in 3D-IC designs, resulting in reduced wirelength, footprint, faster speed, improved bandwidth, and lesser routing congestion. However, the usage of TSVs itself gives rise to many critical design challenges towards the minimization of chip delay and power consumption. Therefore, realization of the benefits of 3D ICs necessitates an early and realistic prediction of circuit performance during the early layout design stage. The goal of this thesis is to meet the design challenges of 3D ICs by providing new capabilities to the existing floorplanning framework [87]. The additional capabilities included in the existing floorplanning tool is the co-placement of TSV islands with circuit blocks and performing non-deterministic assignment of signals to TSVs. We also replace the wirelength and number of TSVs in the floorplanning cost function with the total delay in the nets. The delay-aware cost function accounts for RC delay impact of TSVs on the delay of individual signal connection, and obviates the efforts required to balance the weight contributions of wirelength and TSVs in the wirelength-aware floorplanning. Our floorplanning tool results in 5% shorter wirelength and 21% lesser TSVs compared to recent approaches. The delay in the cost function improves total delay in the interconnects by 10% - 12% compared to wirelength-aware cost function. The influence of large coupling capacitance between TSVs on the delay, power and coupling noise in 3D interconnects also offers serious challenges to the performance of 3D-IC. Due to the degree of design complexity introduced by TSVs in 3D ICs, the importance of early stage evaluation and optimization of delay, power and signal integrity of 3D circuits cannot be ignored. The unique contribution of this work is to develop methods for accurate analysis of timing, power and coupling noise across multiple stacked device layers during the floorplanning stage. Incorporating the impact of TSV and the stacking of multiple device layers within floorplanning framework will help to achieve 3D layouts with superior performance. Therefore, we proposed an efficient TSV coupling noise model to evaluate the coupling noise in the 3D interconnects during floorplanning. The total coupling noise in 3D interconnects is included in the cost function to optimize positions of TSVs and

Cooling of a planar 2D IC chip utilizes heat transfer from a face of the chip though a heat sink. In case of a 3D IC chip stack, the individual chip faces are not available for mounting conventional heat sinks. Mounting the heat sinks on the ends is feasible, but the heat flow paths for the interior chips from the junction to the heat sink become longer. Further, multiple heat sources present along the heat flow paths in stacked chips may create localized hot spots which exceed the allowable junction temperatures. While 2.5D integration in complex ICs where individual layers are mounted on another base die called an interposer can alleviate the heat dissipation issues, it cannot deliver the benefits of monolithic 3D ICs due to the planar distance between the chips or chiplets over the interposer. Introducing interlayer cooling with microchannels and introducing fins in the coolant flow paths extend the thermal dissipation capability of a 3D stack; however this is often accompanied with taller microchannels that lead to longer lengths of through-silicon-vias (TSVs). Placement of TSVs, microchannels walls and fins present conflicting design requirements. Therefore co-design and innovative approaches are seen as critical before widespread commercialization of 3D ICs becomes a reality. An overview of the available cooling options for 3D ICs and their performance evaluation are presented in this chapter.

<p>Information technology-to-internet of things may have succeeded because of fast silicon chip capability expansion. Moore's law, which reduces device size, boosted integrated circuit (IC) performance. Delay rises with highdensity connection parasitic capacitance. Interconnect delays have surpassed transistor delays and slowed progress. An alternative is required now to reduce connection latency. The third dimension is used in popular 3D IC technology IC technology requires through silicon via (TSV) for signal integrity and heat mitigation. Noise coupling hinders electrical communication between signal-carrying TSVs (aggressive TSVs) and ground TSVs (victim TSVs), a 3D IC bottleneck. TSVs must be dielectrically insulated from Si substrates to avoid electrical signal interference. Additionally, first-order modelling will confirm the suggestions. This article proposes using the nanosheet field effect transistor (NSFET) to overcome 3D IC noise coupling and complementary metal oxide semiconductor (CMOS) technology nodes. After discussing the electronic industry and sub nm, several basic metrics and criteria for developing electronic components are presented. The first technique uses Perylene-N's exceptional noise-cancelling characteristics. Second technique uses electrical TSV (ETSV), thermal TSV (TTSV), and heat source models to measure noise coupling on numerous ICs. The third proposes many noise-reducing materials. The suggested structures outperform traditional approaches.</p>