High leakage current in deep-submicrometer regimes is becoming a significant contributor to power dissipation of CMOS circuits as threshold voltage, channel length, and gate oxide thickness are reduced. Consequently, the identification and modeling of different leakage components is very important for estimation and reduction of leakage power, especially for low-power applications. This paper reviews various transistor intrinsic leakage mechanisms, including weak inversion, drain-induced barrier lowering, gate-induced drain leakage, and gate oxide tunneling. Channel engineering techniques including retrograde well and halo doping are explained as means to manage short-channel effects for continuous scaling of CMOS devices. Finally, the paper explores different circuit techniques to reduce the leakage power consumption.

Leakage current mechanisms and leakage reduction techniques in deep-submicrometer CMOS circuits

Steep subthreshold swing transistors based on interband tunneling are examined toward extending the performance of electronics systems. In particular, this review introduces and summarizes progress in the development of the tunnel field-effect transistors (TFETs) including its origin, current experimental and theoretical performance relative to the metal-oxide-semiconductor field-effect transistor (MOSFET), basic current-transport theory, design tradeoffs, and fundamental challenges. The promise of the TFET is in its ability to provide higher drive current than the MOSFET as supply voltages approach 0.1 V.

/pdf/low-voltage-tunnel-transistors-for-beyond-cmos-logic-3w5c8knrc5.pdf

Low-Voltage Tunnel Transistors for Beyond CMOS Logic

International Technology Roadmap for Semiconductors 2003の要求清浄度について － シリコンウエハ表面と雰囲気環境に要求される清浄度, 分析方法の現状について －

Deep-submicron CMOS designs have resulted in large leakage energy dissipation in microprocessors. While SRAM cells in on-chip cache memories always contribute to this leakage, there is a large variability in active cell usage both within and across applications. This paper explores an integrated architectural and circuit-level approach to reducing leakage energy dissipation in instruction caches. We propose, gated-V/sub dd/, a circuit-level technique to gate the supply voltage and reduce leakage in unused SRAM cells. Our results indicate that gated-V/sub dd/ together with a novel resizable cache architecture reduces energy-delay by 62% with minimal impact on performance.

/pdf/gated-v-sub-dd-a-circuit-technique-to-reduce-leakage-in-deep-4yt3m1ejmg.pdf

Gated-V/sub dd/: a circuit technique to reduce leakage in deep-submicron cache memories

Power dissipation is increasingly important in CPUs ranging from those intended for mobile use, all the way up to high-performance processors for high-end servers. While the bulk of the power dissipated is dynamic switching power, leakage power is also beginning to be a concern. Chipmakers expect that in future chip generations, leakage's proportion of total chip power will increase significantly.This paper examines methods for reducing leakage power within the cache memories of the CPU. Because caches comprise much of a CPU chip's area and transistor counts, they are reasonable targets for attacking leakage. We discuss policies and implementations for reducing cache leakage by invalidating and “turning off” cache lines when they hold data not likely to be reused. In particular, our approach is targeted at the generational nature of cache line usage. That is, cache lines typically have a flurry of frequent use when first brought into the cache, and then have a period of “dead time” before they are evicted. By devising effective, low-power ways of deducing dead time, our results show that in many cases we can reduce LI cache leakage energy by 4x in SPEC2000 applications without impacting performance. Because our decay-based techniques have notions of competitive on-line algorithms at their roots, their energy usage can be theoretically bounded at within a factor of two of the optimal oracle-based policy. We also examine adaptive decay-based policies that make energy-minimizing policy choices on a per-application basis by choosing appropriate decay intervals individually for each cache line. Our proposed adaptive policies effectively reduce LI cache leakage energy by 5x for the SPEC2000 with only negligible degradations in performance.

/pdf/cache-decay-exploiting-generational-behavior-to-reduce-cache-3wl24vywlv.pdf

Cache decay: exploiting generational behavior to reduce cache leakage power

Low supply voltage requires the device threshold to be reduced in order to maintain performance. Due to the exponential relationship between leakage current and threshold voltage in the weak inversion region, leakage power can no longer be ignored. In this paper we present a technique to accurately estimate leakage power by accurately modeling the leakage current in transistor stacks. The standby leakage current model has been verified by IISPICE. We demonstrate that the dependence of leakage power on primary input combinations can be accounted for by this model. Based on our analysis we can determine good bounds for leakage power in the standby mode. As a by-product of this analysis, we can also determine the set of input vectors which can put the circuits in the low-power standby mode. Results on a large number of benchmarks indicate that proper input selection can reduce the standby leakage power by more than 50% for some circuits.

Estimation of standby leakage power in CMOS circuits considering accurate modeling of transistor stacks

Column-based dynamic power supply has been integrated into a high-frequency 70-Mb SRAM design that is fabricated on a high-performance 65-nm CMOS technology. The fully synchronized design achieves a 3-GHz operating frequency at 1.1-V power supply. The power supply at SRAM cell array is dynamically switched between two different voltage levels during READ and WRITE operations. Silicon measurement has proven this method to be effective in achieving both good cell READ and WRITE margins, while lowering the overall SRAM leakage power consumption.

A 3-GHz 70-mb SRAM in 65-nm CMOS technology with integrated column-based dynamic power supply

Reduction in leakage power has become an important concern in low-voltage, low-power, and high-performance applications. In this paper, we use the dual-threshold technique to reduce leakage power by assigning a high-threshold voltage to some transistors in noncritical paths, and using low-threshold transistors in critical path(s). In order to achieve the best leakage power saving under target performance constraints, an algorithm is presented for selecting and assigning an optimal high-threshold voltage. A general leakage current model which has been verified by HSPICE simulations is used to estimate leakage power. Results show that the dual-threshold technique is good for leakage power reduction during both standby and active modes. For some ISCAS benchmark circuits, the leakage power can be reduced by more than 80%. The total active power saving can be around 50% and 20% at low- and high-switching activities, respectively.

Design and optimization of dual-threshold circuits for low-voltage low-power applications

Reduction in leakage power has become an important concern in low voltage, low power and high performance applications. In this paper, we use dual threshold technique to reduce leakage power by assigning high threshold voltage to some transistors in non-critical paths, and using low-threshold transistors in critical paths. In order to achieve the best leakage power saving under target performance constraints, an algorithm is presented for selecting and assigning an optimal high threshold voltage. A general standby leakage current model which has been verified by IISPICE is used to estimate standby leakage power. Results show that dual threshold technique is good for power reduction during both standby and active modes. The standby leakage power savings for some ISCAS benchmarks can be more than 50%.

Design and optimization of low voltage high performance dual threshold CMOS circuits

Flip-flops and latches are crucial elements of a design from both a delay and energy standpoint. We compare several styles of single edge-triggered flip-flops, including semidynamic and static with both implicit and explicit pulse generation. We present an implicit-pulsed, semidynamic flip-flop (ip-DCO) which has the fastest delay of any flip-flop considered, along with a large amount of negative setup time. However, an explicit-pulsed static flip-flop (ep-SFF) is the most energy-efficient and is ideal for the majority of critical paths in the design. In order to further reduce the power consumption, dual edge-triggered flip-flops are evaluated. It is shown that classic dual edge-triggered designs suffer from a large area penalty and reduced performance, prohibiting their use in critical paths. A new explicit-pulsed dual edge-triggered flip-flop is presented which provides the same performance as the single edge-triggered version with significantly less energy consumption in the flip-flop as well as in the clock distribution network.

/pdf/comparative-delay-and-energy-of-single-edge-triggered-and-14dh63i68p.pdf

Zhanping Chen

Papers

Estimation of standby leakage power in CMOS circuits considering accurate modeling of transistor stacks

A 3-GHz 70-mb SRAM in 65-nm CMOS technology with integrated column-based dynamic power supply

Design and optimization of dual-threshold circuits for low-voltage low-power applications

Design and optimization of low voltage high performance dual threshold CMOS circuits

Comparative delay and energy of single edge-triggered and dual edge-triggered pulsed flip-flops for high-performance microprocessors