I. VLSI Systems: A Glance Into The Last Decades Since their inception in 1970s, VLSI systems have enabled several new technological capabilities and made them accessible to an unceasingly wider range of users, reaching a scale that has been exponentially increasing over the decades[1](seeFig. 1). Relentless integration of more complex systems has driven such remarkable evolution, as made possible by the inexorable miniaturization. As shown inFig. 1, more functionality has been crammed in a consistently smaller form factor, as exemplified by the physical volume shrinking of computers by 100 X/decade[2],[3]. At the same time, the energy per task has been decreasing at 10–100 X/decade, as shown inFig. 2, for several systems and system-on-chip subsystems[4]. This allowed packing more capabilities into the same power envelope, as generally observed in the electronic systems, even before the advent of the integrated circuit[5].

No abstract available.

We present a ROM based logic design technique using reduced ROM size by eliminating identical rows and columns along with fast and low power single transistor cells. It substantially reduces the critical path length and thereby, improves the performance yet achieves low-power dissipation due to reduced number of switching. We present the ROM based design of a carry select adder (CSA) and two parallel prefix adders, which achieve more than 30% (in 32bit adder) delay reduction over their conventional designs at 90nm technology with as low as 9% (CSA) active power increase.

Circuit failure prediction is used to predict occurrences of circuit failures, during system operation, before errors appear in system data and states. This technique is applicable for overcoming major scaled-CMOS reliability challenges posed by aging mechanisms such as Negative-Bias-Temperature-Instability (NBTI). This is possible because of the gradual nature of degradation associated with such aging mechanisms. Circuit failure prediction uses special on-chip circuits called aging sensors. In this paper, we experimentally demonstrate correct functionality and practicality of two flavors of flip-flop designs with built-in aging sensors using 90 nm test chips. We also present an aging-aware timing analysis technique to strategically place such flip-flops with built-in aging sensors at selective locations inside a chip for effective circuit failure prediction. This aging-aware timing analysis approach also minimizes the chip-level area impact of such aging sensors. Results from two 90 nm designs demonstrate the practicality and effectiveness of optimized circuit failure prediction with overall chip-level area impact of 2.5% and 0.6%.

Circuit failure prediction predicts the occurrence of a circuit failure before errors actually appear in system data and states. This is in contrast to classical error detection where a failure is detected after errors appear in system data and states. Circuit failure prediction is performed during system operation by analyzing the data collected by sensors inserted at various locations inside a chip. We demonstrate this concept of circuit failure prediction for a dominant PMOS aging mechanism induced by negative bias temperature instability (NBTI). NBTI-induced PMOS aging slows down PMOS transistors over time. As a result, the speed of a chip can significantly degrade over time and can result in delay faults. The traditional practice is to incorporate worst-case speed margins to prevent delay faults during system operation due to NBTI aging. A new sensor design integrated inside a flip-flop enables efficient circuit failure prediction at a low cost. Simulation results using 90nm and 65nm technologies demonstrate that this technique can significantly improve system performance by enabling close to best-case design instead of traditional worst-case design.

With the advent of carbon nanotube technology, evaluating circuit and system performance using these devices is becoming extremely important. In this article, we present a quasi-analytical device model for intrinsic ballistic CNFET, which can be used in any conventional circuit simulator like SPICE. This simple quasi-analytical model is effective in a wide variety of CNFET structures as well as for a wide range of operating conditions in the digital circuit application domain. We also provide insight into how the parasitic fringe capacitance in state-of-the-art CNFET geometries impacts the overall performance of CNFET circuits. We show that unless the device width can be significantly reduced, the effective gate capacitance of CNFET will be strongly dominated by the parasitic fringe capacitances, and the superior performance of intrinsic CNFET over silicon MOSFET cannot be achieved in circuit. We further show that unlike conventional MOSFET, nanotube FETs are significantly less sensitive to many process parameter variations due to their inherent device structures and cylindrical gate geometry.

Negative bias temperature instability (NBTI) has become one of the major causes for temporal reliability degradation of nanoscale circuits. In this paper, we analyze the temporal delay degradation of logic circuits due to NBTI. We show that knowing the threshold-voltage degradation of a single transistor due to NBTI, one can predict the performance degradation of a circuit with a reasonable degree of accuracy. We also propose a sizing algorithm, taking the NBTI-affected performance degradation into account to ensure the reliability of nanoscale circuits for a given period of time. Experimental results on several benchmark circuits show that with an average of 8.7% increase in area, one can ensure a reliable performance of circuits for ten years

With the advent of carbon nanotube technology, evaluating circuit and system performance using these devices is becoming extremely important. In this paper, we propose a quasi-analytical device model for intrinsic ballistic CNFET, which can be used in any conventional circuit simulator like SPICE. This simple quasi-analytical model is seen to be effective in a wide variety of CNFET structures as well as for a wide range of operating conditions in the digital circuit application domain. We also provide an insight how the parasitic fringe capacitance in state-of-the-art CNFET geometries impacts the overall performance of CNFET circuits. We show that unless the device width can be significantly reduced, the effective gate capacitance of CNFET will be strongly dominated by the parasitic fringe capacitances and the superior performance of intrinsic CNFET over silicon MOSFET cannot be achieved in circuit.

Negative Bias Temperature Instability (NBTI) has become one of the major causes for temporal reliability degradation of nanoscale circuits. In this paper, we analyze the temporal delay degradation of logic circuits due to NBTI. We show that knowing the threshold voltage degradation of a single transistor due to NBTI, one can predict the performance degradation of a circuit with a reasonable degree of accuracy. We also propose a sizing algorithm taking NBTI-affected performance degradation into account to ensure the reliability of nanoscale circuits for a given period of time. Experimental results on several benchmark circuits show that with an average of 8.7% increase in area one can ensure reliable performance of circuits for 10 years.

This paper presents a novel design methodology for ultralow power design (in bulk and double-gate SOI technology) using sub-threshold leakage as the operating current (suitable for medium frequency of operation: tens to hundreds of MHz). It has been shown that a complete co-design at all levels of hierarchy (device, circuit and architecture) is necessary to reduce the overall power consumption. Simulation results of co-design on a five-tap FIR filter shows ~2.5times (for bulk) and ~3.8times (for SOI) improvement in throughput at iso-power compared to a conventional design. It has been further demonstrated that the double-gate SOI technology is better suited for sub-threshold operation

An analytical model is proposed to compute the fringe capacitance between two nonoverlapping interconnects in different layers using a conformal mapping technique. With this technique, electric field lines are geometrically approximated to separately model the different capacitive components. These components are finally combined to obtain the equivalent fringe capacitance. Using the aforementioned technique, a model was developed to compute the capacitances of typical interconnect geometries using technology-dependent parameters. The proposed model closely matches with FASTCAP results and significantly reduces the computational complexity and time in calculating the interconnect capacitances

Variability in process parameters is making accurate timing analysis of nano-scale integrated circuits an extremely challenging task. In this article, we propose a new algorithm for statistical static timing analysis (SSTA) using levelized covariance propagation (LCP). The algorithm simultaneously considers the effect of die-to-die variations in process parameters as well as within-die variation, including systematic and random variations. In order to efficiently handle complicated process variation models while contending with the arbitrary correlation among timing signals, we employ a compact form of the levelized statistical data structure. Furthermore, we propose two enhancements to the LCP algorithms to the make it practical for the analysis of large sized circuits. Results on several ISCAS'85 benchmark circuits in predictive 70nm technology show an average of 0.19% and 0.57% errors in the mean and standard deviation, respectively, of timing analysis using the proposed technique, as compared to the Monte Carlo-based approach.

Variability in process parameters is making accurate timing analysis of nanoscale integrated circuits an extremely challenging task. In this paper, we propose a new algorithm for statistical timing analysis using levelized covariance propagation (LCP). The algorithm simultaneously considers the impact of random placement of dopants (which makes every transistor in a die independent in terms of threshold voltage) and the spatial correlation of the process parameters such as channel length, transistor width and oxide thickness due to the intra-die variations. It also considers the signal correlation due to reconvergent paths in the circuit. Results on several benchmark circuits in 70 nm technology show an average of 0.21 % and 1.07 % errors in mean and the standard deviation, respectively, in timing analysis using the proposed technique compared to the Monte-Carlo analysis.

Process parameter variations are expected to be significantly high in a sub-50-nm technology regime, which can severely affect the yield, unless very conservative design techniques are employed. The parameter variations are random in nature and are expected to be more pronounced in minimum geometry transistors commonly used in memories such as SRAM. Consequently, a large number of cells in a memory are expected to be faulty due to variations in different process parameters. We analyze the impact of process variation on the different failure mechanisms in SRAM cells. We also propose a process-tolerant cache architecture suitable for high-performance memory. This technique dynamically detects and replaces faulty cells by dynamically resizing the cache. It surpasses all the contemporary fault tolerant schemes such as row/column redundancy and error-correcting code (ECC) in handling failures due to process variation. Experimental results on a 64-K direct map L1 cache show that the proposed technique can achieve 94% yield compared to its original 33% yield (standard cache) in a 45-nm predictive technology under /spl sigma//sub Vt-inter/=/spl sigma//sub Vt-intra/=30 mV.

This paper presents a novel design methodology for ultralow-power design using subthreshold leakage as the operating current (suitable for medium frequency of operation: tens to hundreds of millihertz). Standard design techniques suitable for super-threshold design can be used in the subthreshold region. However, in this study, it has been shown that a complete co-design at all levels of hierarchy (device, circuit, and architecture) is necessary to reduce the overall power consumption while achieving acceptable performance (hundreds of millihertz) in the subthreshold regime of operation. Simulation results of co-design on a five-tap finite-impulse-response filter shows /spl sim/2.5/spl times/ improvement in throughput at iso-power compared to a conventional design.

Due to process parameter variations, a large variability in circuit delay occurs in scaled technologies affecting the yield. In this paper, we propose a sizing algorithm to ensure the speed of a circuit under process variation with a certain degree of confidence while maintaining the area and power budget within a limit. This algorithm estimates the variation in circuit delay using statistical timing analysis considering both inter- and intra-die process variation and resizes the circuit to achieve a desired yield. Experimental results on several benchmark circuits show that one can achieve up to 19% savings in area (power) using our algorithm compared to the worst-case design.

Digital circuits operated in the sub-threshold region (supply voltage less than the transistor threshold voltage) can have orders of magnitude power advantage over standard CMOS circuits for applications requiring ultra-low power and medium frequency of operation. It is possible to implement sub-threshold logic circuits using the standard transistors that are designed primarily for ultra high performance super-threshold logic design. However, a Si MOSFET so optimized for performance in the super-threshold regime is not the best device to use in the sub-threshold domain. In this paper, we propose device designs apt for sub-threshold operation. Results show that the optimized device improves the delay and power delay product (PDP) of an inverter chain by 44% and 51%, respectively, over the normal super-threshold device operated in the sub-threshold region.

A body biasing technique has recently been proposed for microprocessors in sub-100 nm technology generations. It is shown that forward body bias (FBB) reduces the leakage power and suppresses the effect of process variation while reducing the complexity of dual V/sub th/ technology. We study the effect of body bias on the delay fault testing of CMOS circuits. We analyze the impact of both fixed and adaptive body biasing techniques on test cost and the quality of test. Statistical analysis on several benchmark circuits shows that the adaptive body biasing design have the most effective impact on delay fault by maintaining the test cost at its minimum under process variation while ensuring the test quality at its highest level.

In deep submicron (DSM) circuits the critical path obtained from static timing analysis may often be incorrect due to the significant effect of crosstalk. In this paper we present a new algorithm based on timed automatic test pattern generation (ATPG) to generate a list of critical paths of a circuit and the corresponding input vectors to sensitize these paths under cross-talk. The algorithm based on modified PODEM handles multiple aggressors to a victim node and properly activates the aggressors to obtain maximum coupling to the victim. Several circuits were tested using this algorithm and results were verified by HSPICE simulation.

A recently proposed noise model to measure the dynamic noise immunity of high speed circuits is adopted to verify a design for cross-talk faults. We also define a qualitative measure of delay fault immunity of a circuit. Design of a precharge-evaluate circuit was verified using this model and a number of nodes, which are susceptible to cross-talk faults were identified. Finally, we propose a new array based layout architecture namely, O/sup 2/ABA (optimized overlaying array based architecture) to improve performance predictability of a circuit through cross talk reduction. A 4-bit full adder circuit was implemented using both standard cell design and O/sup 2/ABA. It is observed that the circuit implemented using O/sup 2/ABA is significantly less sensitive to delay faults than its standard cell design counterpart.

Digital subthreshold logic circuits can be used for applications in the ultra-low power end of the design spectrum, where performance is of secondary importance. In this paper, we propose two different subthreshold logic families: 1) variable threshold voltage subthreshold CMOS (VT-Sub-CMOS) and 2) subthreshold dynamic threshold voltage MOS (Sub-DTMOS) logic. Both logic families have comparable power consumption as regular subthreshold CMOS logic (which is up to six orders of magnitude lower than that of normal strong inversion circuit) with superior robustness and tolerance to process and temperature variations than that of regular subthreshold CMOS logic.

Digital sub-threshold logic circuits have recently been proposed for applications in the ultra-low power end of the design spectrum, where the performance is of secondary importance. To improve switching performance of the sub-threshold logic family with comparable energy/switching, we propose the use of sub-DTMOS (sub-threshold Dynamic Threshold MOS) transistors. The stability of sub-threshold DTMOS logic to temperature and process variations eliminates the need of additional stabilization scheme that may be required for regular sub-threshold MOS logic families to ensure proper operation in the sub-threshold region.