Frank Liu

Bio: Frank Liu is an academic researcher from Oak Ridge National Laboratory. The author has contributed to research in topics: Threshold voltage & Transistor. The author has an hindex of 30, co-authored 109 publications receiving 2734 citations. Previous affiliations of Frank Liu include Loughborough University & University of Aberdeen.

The Impact of NBTI Effect on Combinational Circuit: Modeling, Simulation, and Analysis

Abstract: Negative-bias-temperature instability (NBTI) has become the primary limiting factor of circuit life time. In this paper, we develop a hierarchical framework for analyzing the impact of NBTI on the performance of logic circuits under various operation conditions, such as the supply voltage, temperature, and node switching activity. Given a circuit topology and input switching activity, we propose an efficient method to predict the degradation of circuit speed over a long period of time. The effectiveness of our method is comprehensively demonstrated with the International Symposium on Circuits and Systems (ISCAS) benchmarks and a 65-nm industrial design. Furthermore, we extract the following key design insights for reliable circuit design under NBTI effect, including: 1) During dynamic operation, NBTI-induced degradation is relatively insensitive to supply voltage, but strongly dependent on temperature; 2) There is an optimum supply voltage that leads to the minimum of circuit performance degradation; circuit degradation rate actually goes up if supply voltage is lower than the optimum value; 3) Circuit performance degradation due to NBTI is highly sensitive to input vectors. The difference in delay degradation is up to 5× for various static and dynamic operations. Finally, we examine the interaction between NBTI effect, and process and design uncertainty in realistic conditions.

Full chip leakage-estimation considering power supply and temperature variations

Abstract: Leakage power is emerging as a key design challenge in current and future CMOS designs. Since leakage is critically dependent on operating temperature and power supply, we present a full chip leakage estimation technique which accurately accounts for power supply and temperature variations. State of the art techniques are used to compute the thermal and power supply profile of the entire chip. Closed-form models are presented which relate leakage to temperature and VDD variations. These models coupled with the thermal and VDD profile are used to generate an accurate full chip leakage estimation technique considering environmental variations. The results of this approach are demonstrated on large-scale industrial designs.

The impact of NBTI on the performance of combinational and sequential circuits

Abstract: Negative-bias-temperature-instability (NBTI) has become the primary limiting factor of circuit lifetime. In this work, we develop a general framework for analyzing the impact of NBTI on the performance of a circuit, based on various circuit parameters such as the supply voltage, temperature, and node switching activity of the signals etc. We propose an efficient method to predict the degradation of circuit performance based on circuit topology and the switching activity of the signals over long periods of time. We demonstrate our results on ISCAS benchmarks and a 65 nm industrial design. The framework is used to provide key design insights for designing reliable circuits. The key design insights that we obtain are: (1) degradation due to NBTI is most sensitive on the input patterns and the duty cycle; the difference in the delay degradation can be up to 5X for various static and dynamic conditions, (2) during dynamic operation, NBTI-induced degradation is relatively insensitive to supply voltage, but strongly dependent on temperature; (3) NBTI has marginal impact on the clock signal.

A test structure for characterizing local device mismatches

Abstract: We present a test structure for statistical characterization of local device mismatches. The structure contains densely populated SRAM devices arranged in an addressable manner. Measurements on a test chip fabricated in an advanced 65 nm process show little spatial correlation. We vary the nominal threshold voltage of the devices by changing the threshold-adjust implantations and observe that the ratio of standard deviation to mean gets worse with threshold scaling. The large variations observed in the extracted threshold voltage statistics indicate that the random doping fluctuation is the likely reason behind mismatch in the adjacent devices

A general framework for spatial correlation modeling in VLSI design

Abstract: Many characteristics of VLSI designs, such as process variations, demonstrate strong spatial correlations. Accurately modeling of these correlated behaviors is crucial for many timing and power analyses to be valid. This paper proposes a new spatial model with a long-range trend component, a smooth correlation component, as well as a truly random component. The efficient method to construct such a spatial model is based on the Generalized Least Square fitting and the structured correlation functions, which are actually the generalization of the popular Pelgrom mismatch models. Experimental results on industrial benchmarks show that the method is not only highly effective for variability modeling, but can also be used for other spatially distributed characteristics such as IR drops and on-chip temperature distributions.

Economics of Information

Abstract: The author systematically examines one of the important issues of information — establishing the market price. He introduces the concept of «search» — where a buyer wanting to get a better price, is forced to question sellers. The article deals with various aspects of finding the necessary information.

Linear and nonlinear waves, by G. B. Whitham. Pp.636. £50. 1999. ISBN 0 471 35942 4 (Wiley).

Abstract: to be done in this area. Face recognition is a problem that scarcely clamoured for attention before the computer age but, having surfaced, has involved a wide range of techniques and has attracted the attention of some fine minds (David Mumford was a Fields Medallist in 1974). This singular application of mathematical modelling to a messy applied problem of obvious utility and importance but with no unique solution is a pretty one to share with students: perhaps, returning to the source of our opening quotation, we may invert Duncan's earlier observation, 'There is an art to find the mind's construction in the face!'.