Technology-Aware 3D Placement with ILP-Based Region Planning for Soft Modules

Three-dimensional (3D) ICs promise to overcome barriers in interconnect scaling by leveraging fast, dense inter-die vias, thereby offering benefits of improved performance, higher memory bandwidth, smaller form factors, and heterogeneous integration. However, when deciding to adopt this emerging technology as a mainstream design approach, designers must consider the cost of 3D integration. IC testing is a key factor that affects the final product cost, and it could be a major portion of the total IC cost. In 3D IC design, various testing strategies and different integration methods could affect the final product cost dramatically, and the interaction with other cost factors could result in various trade-offs. This paper develops a comprehensive and parameterized testing cost model for 3D IC integration, and analyzes the trade-offs associated with testing strategies and testing circuit overheads. With the proposed testing cost model, designers can explore the most cost-effective integration and testing strategies for 3D IC chips.

Machine learning based effective linear regression model for TSV layer assignment in 3DIC

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.

3D IC integration is very important to overcome the technology scaling barriers and to satisfy mobile devices' demand. In this paper, we describe the challenges we are facing in developing 3D IC design methodology, especially in the case of TSV-SiP (Logic-Memory die stacking). Also, appropriate development approaches are proposed. The EDA tools for TSV-SiP, which are initially provided by extending current conventional tools, will be gradually enhanced to better support 3D IC designs.

Three-dimensional integrated circuits (3D ICs) attract much interest due to several advantages over traditional microelectronics design, such as electrical performance improvement and reducing interconnect delay. While the power density of 3D ICs increases because of vertical integration, the available substrate area for heat removal does not change. Thermal modeling of 3D ICs is important for improving thermal and electrical performance. Experimental investigation on the thermal measurement of 3D ICs and determination of key physical parameters in 3D ICs thermal design are curtail. One such important parameter in thermal analysis is the interdie thermal resistance between adjacent die bonded together. This paper describes an experimental method to measure the value of interdie thermal resistance between two adjacent dies in a 3D IC. The effect of heating one die on the temperature of the other die in a two-die stack is measured over a short time period using high-speed data acquisition to negate the effect of boundary conditions. Numerical simulation is performed and based on a comparison between experimental data and the numerical model, the interdie thermal resistance between the two dies is determined. A theoretical model is also developed to estimate the value of the interdie thermal resistance. Results from this paper are expected to assist in thermal design and management of 3D ICs.

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

A Survey of Lagrangean Techniques for Discrete Optimization

Traditional multilevel SRAM-based cache hierarchies, especially in the context of chip multiprocessors (CMPs), present many challenges in area requirements, core--to--cache balance, power consumption, and design complexity. New advancements in technology enable caches to be built from other technologies, such as Embedded DRAM (EDRAM), Magnetic RAM (MRAM), and Phase-change RAM (PRAM), in both 2D chips or 3D stacked chips. Caches fabricated in these technologies offer dramatically different power-performance characteristics when compared with SRAM-based caches, particularly in the areas of access latency, cell density, and overall power consumption. In this article, we propose to take advantage of the best characteristics that each technology has to offer through the use of Hybrid Cache Architecture (HCA) designs. We discuss and evaluate two types of hybrid cache architectures: intercache-Level HCA (LHCA), in which the levels in a cache hierarchy can be made of disparate memory technologies; and intracache-level or cache-Region-based HCA (RHCA), where a single level of cache can be partitioned into multiple regions, each of a different memory technology. We have studied a number of different HCA architectures and explored the potential of hardware support for intracache data movement and power consumption management within HCA caches. Utilizing a full-system simulator that has been validated against real hardware, we demonstrate that an LHCA design can provide a geometric mean 6% IPC improvement over a baseline 3-level SRAM cache design under the same area constraint across a collection of 30 workloads. A more aggressive RHCA-based design provides 10% IPC improvement over the baseline. A 2-layer 3D cache stack (3DHCA) of high density memory technology within the same chip footprint gives 16% IPC improvement over the baseline. We also achieve up to a 72% reduction in power consumption over a baseline SRAM-only design. Energy-delay and thermal evaluation for 3DHCA are also presented. In addition to the fast-slow region based RHCA, we further evaluate read-write region based RHCA designs.

With the rapid advance of enabling technologies, the era of 3D ICs is near. Yet, there are several practical problems to be solved for 3D ICs. Especially, heat removal and power delivery have become two major reliability concerns in 3D stacked IC technology. Recently, liquid cooling based on micro-fluidic channels is proposed as a viable solution to dramatically reduce the temperature of 3D ICs. In addition, a highly complex power distribution network is required to deliver currents to all parts of the 3D IC stack while suppressing power noise to an acceptable level. These technologies pose major challenges to signal routing. With a given amount of silicon area, signal, power, and thermal interconnects compete against one another for routing space. This paper presents an optimization study on signal, power, and thermal networks in 3D ICs. We demonstrate how to optimize various design parameters by adopting design of experiments and response surface method.

Integer Linear Programming (ILP) is commonly used in high level and system level synthesis. It is an NP-Complete problem (in general cases). There exists some tools that give an optimal solution for small ILP formulations. Nevertheless, these tools may not give solutions for complex formulations. In this paper, we present a solution to overcome the problem of complexity in ILP formulations. We propose a partitioning methodology based on a constraint graph representing all the constraints included in any ILP formulation. To direct the partitioning, the constraint graph nodes are grouped to represent Data Flow Graph (DFG) nodes. This reduced constraint graph can be used to partition any ILP formulation based on DFG. We illustrate this method on ILP formulation for scheduling. Results on ILP scheduling formulations are promising.

Theoretical studies in the 1980s [1, 2] suggested that significant reductions in signal delay and power consumption could be achieved with 3D integrated circuits (3D ICs). A 3D IC is a chip that consists of multiple tiers of thinned-active 2D integrated circuits (2D ICs) that are stacked, bonded, and electrically connected with vertical vias formed through silicon or oxide layers and whose placement within the tiers is discretionary. The term “tier” is used to distinguish the transferred layers of a 3D IC from design and physical layers and is the functional section of a chip or wafer that consists of the active silicon, the interconnect, and, for a silicon-on-oxide (SOI) wafer, the buried oxide (BOX). The basic features of a 3D IC are illustrated in Fig. 2.1 in a symbolic drawing along with a cross-section of an actual 3D IC. The TSV (through silicon via) is an essential feature of the 3D IC technology and is the vertical-electrical connection formed between tiers and through silicon or oxide. A TSV is formed by aligning, defining, and etching a cavity between two tiers to expose an electrode in the lower tier; lining the sidewalls of the cavity with an insulator; and filling the cavity with metal or doped polysilicon to complete the connection. A TSV drawing and a cross-section of a TSV are shown in Fig. 2.2.

Fault Modeling, Testing, and Repair for Chiplet Interconnects

Three-dimensional integrated circuits gain more and more attention due to their benefits in wirelength reduction and their potential for heterogeneous integration of systems on a chip. Besides the advantages they also lead to new challenges and increasing complexity in designing such systems. This paper focuses on floorplanning such systems. It describes a new data structure called T∗-tree which enables the design of three-dimensional integrated circuits considering vertically aligned rectilinear 2D modules. The problem formulation of the new T∗-tree differs from the T-tree proposed in [1]. Furthermore, an optimization algorithm is presented which is aware of fixed-outline constraints using a longest path based method. Experimental results show that the T∗-tree is competitive to other approaches. It is also able to consider more appropriate modules for three-dimensional integration.

Technological advances and rapid development of handheld wireless terminals have facilitated the rapid growth of wireless communications and mobile computing. Essentially we have a limited resource transmission spectrum, which must be shared by several users. Since the available frequency spectrum is limited the channels must be reused as much as possible in order to increase the system capacity. This requires a proper channel allocation scheme. The role of a channel allocation scheme is to allocate channels to cells or mobiles in such a way as to minimize call blocking or call dropping probabilities. The process of channel allocation must satisfy the electromagnetic compatibility constraints known as hard constraints and the demand of channels in a cell for new calls as well as existing calls. The proposed scheme presents new Hybrid Channel Allocation (HCA) scheme that allocate a channel to an incoming call from pool of available channel such as basic constraints are satisfied. The proposed scheme presents an efficient Integer Linear Program (ILP) formulation that helps to allocate channel to a new call. This formulation does not allow channel reassignment of existing calls. We have simulated the formulation on a standard ideal network model of 70 channels and 49 cells. We have done our experiments using MATLAB 7.9.0 R2009b.

The 3D IC is an emerging technology. The primary emphasis on 3D-IC routing is the interface issues across dies. To handle the interface issue of connections, the inter-die routing, which uses micro bumps and two single-layer RDLs (Re-Distribution Layers) to achieve the connection between adjacent dies, is adopted. In this paper, we present an inter-die routing algorithm for 3D ICs with a pre-defined netlist. Our algorithm is based on integer linear programming (ILP) and adopts a two-stage technique of micro-bump assignment followed by non-regular RDL routing. First, the micro-bump assignment selects suitable micro-bumps for the pre-defined netlist such that no crossing problem exists inside the bounding boxes of each net. After the micro-bump assignment, the netlist is divided into two sub-netlists, one is for the upper RDL and the other is for the lower RDL. Second, the non-regular RDL routing determines minimum and non-crossing global paths for sub-netlists in the upper and lower RDLs individually. Experimental results show that our approach can obtain optimal wirelength and achieve 100% routability under reasonable CPU times.