A novel and efficient timing-driven global router for standard cell layout design based on critical network concept

Prior to 90nm the main contributor to yield loss was particle contamination. Random particle defects were directly proportional to particle density and chip size. To maximize yield, manufacturing was done in clean rooms where particles were reduced to a minimum. Yield was then directly proportional to the chip size. At 90nm and below, systematic defects play major roles in yield. Two designs of the same size can result in very different yield. This paradigm shift is caused by the printability problems that are inherent to process technologies operating in the sub-wavelength regime. The technology for printing patterns on silicon has not kept up with Moore's law. The wavelength of lithography equipment is as much as 6 times larger than the silicon features. This results in greater variation on silicon, which directly affects yield. How the design is implemented is becoming as important as how small you make it. Even at the standard cell level different solutions can demonstrate increased sensitivity to particles, short, opens, gate leakage and other yield issue. We present in this paper a methodology for grading how well standard cells will print on silicon. Using standard cell layouts, we predict a silicon image under different process conditions and take CD measurements on these images. These measurements are converted into a printability factor for each cell. This printability factor is used to grade cells and identify which cells have the largest impact on printability and which should be optimized. To help with this optimization the measurements are also used to mark printability hot spots in the cell layouts.

Standard cells are the most critical and reusable elements to build up the whole chip, therefore foundry has to fully qualify the standard cell libraries to ensure their high quality when releasing to the customers for the chip design. To prevent pattern dependent lithographic difficulty in manufacturing is one target of standard cell qualification and becomes mandatory especially in advanced nodes due to tighter design rules and smaller design size. To identify a lithographic problematic standard cell, we have to take its surroundings within the optical diameter range into consideration because lithographic effects are intrinsically context-dependent. One critical step is to imitate standard cells placements in real designs and consider some important factors like VIA location as it impacts the mask shape directly. When the placement is completed, lithographic simulation is performed by LFD (Litho Friendly Design) to highlight risky locations. Every standard cell has to occur enough number of times to make sure the statistics of possibility of being a problem is reliable. The final statistics will instruct engineers on how to handle the problematic standard cells, either standard cell layouts have to be optimized or building a pattern database to prevent the abutments of particular standard cell combinations.

Intelligent design technology co-optimization (iDTCO) methodology for next generation logic architecture pathfinding and its application results are presented in this paper. There are 2 major steps in our iDTCO framework; standard cell (STC)-level iDTCO and block-level iDTCO. STC-level iDTCO, the main focus of this paper, consists of 4 major components; (1) full 3D process emulation with litho contour of standard cell (STC) layout, (2) auto-extraction of transistor compact model & parasitic RC extraction (PEX) in 3D, (3) performance-power-yield (PPY) analyzer, (4) multi-objective optimization of layout & process assumption (PA) to get best PPY. Applying our STC-level iDTCO flow to logic arch pathfinding, we could speed up our PPY analysis TAT by 5$\sim$10 times with good accuracy of >95%.

Process-induced mechanical stress is used to enhance carrier transport and achieve higher drive currents in current complementary metal-oxide-semiconductor technologies. This paper explores how to fully exploit the layout dependence of stress enhancement and proposes a circuit-level, block-based, stress-enhanced optimization algorithm that uses stress-optimized layouts in conjunction with dual- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> assignment to achieve optimal power-performance tradeoffs. We begin by studying how channel stress and drive current depend on layout parameters such as active area length and contact placement, while considering all layout-dependent sources of mechanical stress in a 65 nm industrial process. We then investigate the three main layout properties that impact mechanical stress in this process and discuss how to improve stress-based performance enhancement in standard cell libraries. While varying the stress-altering layout properties of a number of standard cells in a 65 nm industrial library, we show that ?dual-stress? standard cell layouts (analogous to ?dual- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ?) can be designed to achieve drive current differences up to ~ 14% while incurring less than half the leakage penalty of dual- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> . Therefore, when the flexibility of ?dual-stress? assignment is combined with dual- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> assignment (within the proposed joint optimization framework), simulation results for a set of benchmark circuits show that leakage is reduced by ~ 24% on average, for iso-delay, when compared to dual- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> assignment. Since mobility enhancement does not incur the exponential leakage penalty associated with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> assignment, our optimization technique is ideal for leakage power reduction. However, our framework can also be used to achieve higher performance circuits for iso-leakage and our joint optimization framework can be used to reduce delay on average by ~ 5%. In both cases, the proposed method only incurs a small area penalty (<0.5%).

This study investigates the thermal design of 2-D vertical-cavity surface-emitting laser (VCSEL) arrays for optical output power improvement. Considering the temperature dependencies of bias current, internal quantum efficiency, internal optical loss, and thermal resistance of each array cell, a compact electro-opto-thermal model of 2-D VCSEL arrays with linear power dissipation and quadratic power dissipation in each array cell is established to study the effects of array cell spacing and layout on the device performance. At the same time, the power dissipation mechanisms contributing to thermal rollover are also studied. It is found that the array cell spacing has a strong influence on the linear power dissipation, and the layout (such as hexagonal design) influences quadratic power dissipation obviously. With the careful design of array cell spacing and layout, both the temperature profile and the thermal resistance matrix of VCSEL arrays are improved, which is helpful to delay the onset of thermal rollover and hence enhance the optical output power. The simulation results are consistent with experimental results.

In this paper, we propose an optimal pin assignment algorithm with improvement of cell placement in standard cell layout. The objective of the algorithm is to minimize the channel density by assigning nets to terminals of cells. If the number of possible terminal assignments for each cell is bounded by some constant r, then the proposed algorithm runs in linear time. In most practical cases, the value of r is relatively small, and thus the proposed algorithm is effective and efficient to reduce the chip area.

This paper proposes a yield optimization method for standard cells under timing constraints. Yield-aware logic synthesis and physical optimization require yield enhanced standard cells and the proposed method automatically creates yield enhanced cell layouts by decompacting the original cell layout using linear programming. We develop a novel accurate linear delay model which approximates the difference from the original delay and use this model to formulate the timing constraints into linear programming. Experimental results show that the proposed method can pick up the yield variants of a cell layout from the tradeoff curve of cell delay versus critical area and is used to create the yield enhanced cell library which is essential to realize yield-aware VLSI design flows.

Cell formation (CF) and machine cell layout are two critical issues in the design of a cellular manufacturing system (CMS). The complexity of the problem has an exponential impact on the time required to compute a solution, making it an NP-hard (complex and non-deterministic polynomial-time hard) problem. Therefore, it has been widely solved using effective meta-heuristics. The paper introduces a novel meta-heuristic strategy that utilizes the Genetic Algorithm (GA) and the Technique of Order Preference Similarity to the Ideal Solution (TOPSIS) to identify the most favorable solution for both flexible CF and machine layout within each cell. GA is employed to identify machine cells and part families based on Grouping Efficiency (GE) as a fitness function. In contrast to previous research, which considered grouping efficiency with a weight factor (q = 0.5), this study utilizes various weight factor values (0.1, 0.3, 0.7, 0.5, and 0.9). The proposed solution suggests using the TOPSIS technique to determine the most suitable value for the weighting factor. This factor is critical in enabling CMS to design the necessary flexibility to control the cell size. The proposed approach aims to arrange machines to enhance GE, System Utilization (SU), and System Flexibility (SF) while minimizing the cost of material handling between machines as well as inter- and intracellular movements (TC). The results of the proposed approach presented here show either better or comparable performance to the benchmark instances collected from existing literature.

Reliable power delivery is regarded as one of primary challenging problems in nano-meter VLSI design diagram. For dynamic voltage fluctuations on a power/ground(P/G) network, adding on-chip decoupling capacitors(decaps) is regarded as the most efficient way to reduce such noises. In this paper, we present an efficient heuristic method to allocate decaps based on transient analysis of p/g network. Our algorithm utilizes adjoint network method to efficiently calculate the sensitivity of objective function with respect to each decap value. Experimental results demonstrate that the algorithm is capable of optimizing p/g networks with hundreds of thousand nodes in 3.30 hours.

We propose a flow for routing nets within a standard cell that 1) generates candidate routes for point-to-point segments; 2) finds conflicts (electrical shorts and geometric design rule violations) between candidate routes; and 3) solves a SAT instance producing a legal and complete routing for all nets in the standard cell. This approach enables routing automation for cutting-edge process technology nodes. We present how to make this technique more effective by introducing pruning techniques to reduce the work required in all three steps. We also show how we can further optimize routing quality within the SAT formulation through the use of successively more stringent constraints. Recent improvements in the speed of SAT solvers make such a formulation practical for even complex standard cells. A routing tool based on our SAT formulation is currently being used to route real industrial standard cell layouts. It demonstrates acceptable runtime and 89% coverage of our industrial standard cell library, including scan flip-flops, adders, and multiplexers. We also observe a significant reduction in amount of metal2 routing in comparison with industrial hand-crafted standard cells.

Carbon nanotube field-effect transistors (CNFETs) are promising candidates for building energy-efficient digital systems at highly-scaled technology nodes. However, carbon nanotubes (CNTs) are inherently subject to variations that reduce circuit yield, increase susceptibility to noise, and severely degrade their anticipated energy and speed benefits. Joint exploration and optimization of CNT processing options and CNFET circuit design are required to overcome this outstanding challenge. Unfortunately, existing approaches for such exploration and optimization are computationally expensive, and mostly rely on trial-and-error-based ad hoc techniques. In this paper, we present a framework that quickly evaluates the impact of CNT variations on circuit delay and noise margin, and systematically explores the large space of CNT processing options to derive optimized CNT processing and CNFET circuit design guidelines. We demonstrate that our framework: 1) runs over 100x faster than existing approaches, and 2) accurately identifies the most important CNT processing parameters, together with CNFET circuit design parameters (e.g., for CNFET sizing and standard cell layouts), to minimize the impact of CNT variations on CNFET circuit speed with less than 5% energy cost, while simultaneously meeting circuit-level noise margin and yield constraints.

In this paper, we describe a way to build and explore auxiliary boundary constraints used to layout standard cells. It is required to build an electronic component of VLSI chip, a standard cell, given a set of constraints: geometrical design rules and additional electrical requirements. During layout of standard cells, additional constraints are formulated to avoid possible violations at cell boundaries when cells are abutted in a horizontal row. Current work proposes a flow to compute such auxiliary rules.

Standard cell libraries are an important part of many of today's integrated circuit (IC) designs. The design of all digital ASICs (Application Specific Integrated Circuit) essentially involves the use of an ASIC standard cell library comprising logic functional primitives such as basic gate functions, complex combinational functions, sequential elements, arithmetic elements and 1I0s. In this paper the work involves, designing standard cell layouts with different cells using fixed height of standard cell template and characterizing standard cells using liberate and generating. lib file for standard cell. This Standard cell library was designed an industry academia chip collaborative project. By using Cadence virtuoso, liberate tools high performance with low power consumption standard cell library was developed.

In recent years, researchers have devoted continuous efforts to study different facet of cellular manufacturing system (CMS). However, very few of them have tried to investigate both cell formation and the cell layout simultaneously. Different order/sequence of machine cells allocation may result in different total intercellular movement distance unit. Solving this problem is indeed very important in reducing the total intracellular and intercellular part movements which is especially significant with large production volume. In this paper, a mathematical model has been proposed to tackle the cell formation and cell layout simultaneously with consideration of both alternative routing and production volume. Due to the combinatorial nature of this model, a hybrid tabu search algorithm was applied to solve it. Unlike the existing method, the proposed algorithm does not demand a priori specification of the number of cells. Moreover, it can determine linear single-row layout or linear double-row layout. The results of the proposed method are compared with well-known approaches that are introduced in literature. These comparisons show that the proposed method offers good solutions for the CMS problem.

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