Leakage current is an important qualitative metric of LSI (Large Scale Integrated circuit). In this paper, we focus on reduction of leakage current variation under the process variation. Firstly, we derive a set of quadratic equations to evaluate delay and leakage current under the process variation. Using these equations, we discuss the cases of varying leakage current without degrading delay distribution and propose a procedure to reduce the leakage current variations. From the experiments, we show the proposed method effectively reduces the leakage current variation up to 50% at 90 percentile point of the distribution compared with the conventional design approach.

This paper proposes a new efficient method of characterizing a memory compiler in order to reduce the computation time and remove human error. The new features that make our method greatly efficient are the following three points: (1) high-speed circuit simulation of the whole memory module using a hierarchical LPE (Layout Parasitic Extractor) and a hierarchical circuit simulator, (2) automatic generation of circuit simulation input data from corresponding parameterized description termed the template file, and (3) carefully selected environmental conditions of circuit level simulator and minimizing the number of runs of it. We demonstrate the effectiveness of the proposed method by application to the single-port SRAM generators using 90 nm CMOS technology.

We have developed a macro model, which allows us to describe precise LDMOS DC/AC characteristics. Characterization of anomalous gate input capacitance is the key issue in the LDMOS model development. We have newly employed a T-type distributed RC scheme for gate overlapped LDMOS drift region. The bias dependent resistance and capacitance are modeled independently in Verilog-A as R-model and PMOS-capacitance. The dividing factor of the distributed R is introduced to reflect the shield effect of the gate overlap capacitance. Comparison between the new model and measurement results has proven that the developed macro model reproduces accurately not only the gate input capacitance, but also DC characteristics.

This paper proposes a new non-destructive methodology to estimate physical parameters for LSIs. In order to resolve the estimation accuracy degradation issue for low-k dielectric films, we employ a parallel-plate capacitance measurement and a wire resistance measurement in our non-destructive method. Due to (1) the response surface functions corresponding to the parallel-plate capacitance measurement and the wire resistance measurement and (2) the searching of the physical parameter values using our cost function and simulated annealing, the proposed method attains higher precision than that of the existing method. We demonstrate the effectiveness of our method by application to our 90 nm SoC process using low-k materials.

In this letter, we discuss the impact of intrinsic error in parasitic capacitance extraction programs which are commonly used in today's SoC design flows. Most of the extraction programs use pattern-matching methods which introduces an improvable error factor due to the pattern interpolation, and an intrinsically inescapable error factor from the difference of boundary conditions in the electro-magnetic field solver. Here, we study impact of the intrinsic error on timing and crosstalk noise estimation. We experimentally show that the resulting delay and noise estimation errors show a scatter which is normally distributed. Values of the standard deviations will help designers consider the intrinsic error compared with other variation factors.

Layout-aware compact models proposed so far have been generally verified only for simple test patterns. However, real designs use much more complicated layout patterns. Therefore, models must be verified for such patterns to establish their practicality. This paper proposes a methodology and test patterns for exhaustively and systematically validating layout-aware compact models for general layout patterns for the first time. The methodology and test patterns are concretely shown through validation of a shallow trench isolation (STI) stress compact model proposed in [1]. First, the model parameters for a 55-nm CMOS technology are extracted, and then the model is verified and established to be accurate for the basic patterns used for parameter extraction. Next, fundamental ideas of model operation for general layout patterns are verified using various verification patterns. These tests revealed that the model is relatively weak in some cases not included in the basic patterns. Finally, the errors for these cases are eliminated by enhancing the algorithm. Consequently, the model is confirmed to have high generality. This methodology will be effective for validating other layout-aware compact models for general layout patterns.

This paper studies impact of well edge proximity effect on circuit delay, based on model parameters extracted from test structures in an industrial 65 nm wafer process. Experimental results show that up to 10% of delay increase arises by the well edge proximity effect in the 65 nm technology, and it depends on interconnect length. Furthermore, due to asymmetric increase in pMOS and nMOS threshold voltages, delay may decrease in spite of the threshold voltage increase. From these results, we conclude that considering WPE is indispensable to cell characterization in the 65 nm technology.

Process variation is becoming a primal concern in timing closure of LSI (Large Scale Integrated Circuit) with the progress of process technology scaling. To overcome this problem, SSTA (Statistical Static Timing Analysis) has been intensively studied since it is expected to be one of the most efficient ways for performance estimation. In this paper, we study variation of output transition-time. We firstly clarify that the transition-time variation can not be expressed accurately by a conventional first-order sensitivity-based approach in the case that the input transition-time is slow and the output load is small. We secondly reveal quadratic dependence of the output transition-time to operating margin in voltage. We finally propose a procedure through which the estimation of output transition-time becomes continuously accurate in wide range of input transition-time and output load combinations.

This paper evaluates impact of self-heating in wire interconnection on signal propagation delay in an upcoming 32 nm process technology, using practical physical parameters. This paper examines a 64-bit data transmission model as one of the most heating cases. Experimental results show that the maximum wire temperature increase due to the self-heating appears in the case where the ratio of interconnect delay becomes largest compared to the driver delay. However, even in the most significant case which induces the maximum temperature rise of 11.0, the corresponding increase in the wire resistance is 1.99% and the resulting delay increase is only 1.15%, as for the assumed 32 nm process. A part of the impact reduction of wire self-heating on timing comes from the size-effect of nano-scale wires.

This paper proposes a simple yet sufficient Si-substrate modeling for interconnect resistance and inductance extraction. The proposed modeling expresses Si-substrate as four filaments in a filament-based extractor. Although the number of filaments is small, extracted loop inductances and resistances show accurate frequency dependence resulting from the proximity effect. We experimentally prove the accuracy using FEM (Finite Element Method) based simulations of electromagnetic fields. We also show a method to determine optimal size of the four filaments. The proposed model realizes substrate-aware extraction in SoC design flow.

This paper proposes a new parallel method of producing the adjacent net pair list from the LSI layouts, which is run on workstations connected with the network. The pair list contains pairs of adjacent nets and the probability of a bridging fault between them, and is used in fault diagnosis of LSIs. The proposed method partitions into regions each mask layer of the LSI layout, produces a pair list corresponding to each region in parallel and merges them into the entire pair list. It yields the accurate results, because it considers the faults between two wires containing different adjacent regions. The experimental results show that the proposed method has greatly reduced the processing time from more than 60 hrs. to 3 hrs. in case of 42M-gate LSIs.

In advanced ASIC/SoC physical designs, interconnect parasitic extraction is one of the important factors to determine the accuracy of timing analysis. We present a formula-based method to efficiently extract interconnect capacitances of interconnects with dummy fills for VLSI designs. The whole flow is as follows: 1) in each process, obtain capacitances per unit length using a 3-D field solver and then create formulas, and 2) in the actual design phase, execute a well-known 2.5-D capacitance extraction. Our results indicated that accuracies of the proposed formulas were almost within 3% error. The proposed formula-based method can extract interconnect capacitances with high accuracy for VLSI circuits. Moreover, we present formulas to evaluate the effect of dummy fills on interconnect capacitances. These can be useful for determining design guidelines, such as metal density before the actual design, and for analyzing the effect of each structural parameter during the design phase.

Floating dummy metal fills inserted for planarization of multi-dielectric layers have created serious problems because of increased interconnect capacitance and the enormous number of fills. We present new dummy filling methods to reduce the interconnect capacitance and the number of dummy metal fills needed. These techniques include three ways of filling: 1) improved floating square fills, 2) floating parallel lines, and 3) floating perpendicular lines (with spacing between dummy metal fills above and below signal lines). We also present efficient formulas for estimating the appropriate spacing and number of fills. In our experiments, the capacitance increase using the conventional regular square method was 13.1%, while that using the methods of improved square fills, extended parallel lines, and perpendicular lines were 2.7%, 2.4%, and 1.0%, respectively. Moreover, the number of necessary dummy metal fills can be reduced by two orders of magnitude through use of the parallel line method.

We present a practical method of dealing with the influences of floating dummy metal fills, which are inserted to assist planarization by chemical-mechanical polishing (CMP) process, in extracting interconnect capacitances for system-on-chip (SoC) designs. The method is based on reducing the thicknesses of dummy metal layers according to electrical field theory. We also clarify the influences of dummy metal fills on the parasitic capacitance, signal delay, and crosstalk noise. Moreover, we address that interlayer dummy metal fills have more significant influences than intralayer ones in terms of the impact on coupling capacitances. When dummy metal fills are ignored, the error of capacitance extraction can be more than 30%, whereas the error of the proposed method is less than about 10% for many practical geometries. We also demonstrate, by comparison with capacitance results measured for a 90-nm test chip, that the error of the proposed method is less than 8%.