With continued and aggressive scaling, using ultralow thickness SiO2 for the transistor gates, tunneling current has emerged as the major component of leakage in CMOS circuits. In this paper, we propose a new approach called dual dielectrics of dual thicknesses (DKDT) for the reduction of both ON and OFF state gate tunneling currents. We claim that the simultaneous utilization of SiON and SiO2 each with multiple thicknesses is a better approach for gate leakage reduction than the conventional one that uses a single gate dielectric, SiO2 , of multiple thicknesses. We develop an algorithm for the corresponding assignment of dual dielectric and dual thickness cells that minimizes the overall tunneling current for a circuit without compromising its performance. We performed extensive experiments on ISCAS'85 benchmarks using 45 nm technology which demonstrate that our approach can reduce the tunneling current by as much as 98.7% (on average 94.8%), without performance degradation.

Gate oxide direct tunneling current is the major component of static power dissipation of a CMOS circuit for low-end technology, where the gate dielectric (SiO 2 ) thickness is very low. This paper presents a novel direct tunneling current reduction method during behavioral synthesis of nanometer CMOS circuits. We provide analytical models to calculate the direct tunneling current and the propagation delay of behavioral level components. We then characterize those components for various gate oxide thicknesses. We also provide an algorithm for behavioral scheduling for minimizing the overall tunneling current dissipation of datapath circuits. The algorithm explores dual oxide thickness option for reducing direct tunneling current. We have carried out extensive experiments for various behavioral level benchmarks under various resource constraints and observed significant reductions in tunneling current.

Abstract — For a nanoCMOS of sub-65nm technology, where the gate oxide (SiO2) thickness is very low, the gate leakage is one of the major components of power dissipation. In this paper, we provide analytical models to describe the tunneling current and propagation delay of behavioral level components considering various physical effects in the absence of foundry data. Subsequently, we explore the use of multiple oxide thickness resources as a technique for the reduction of gate leakage. In particular, we introduce a behavioral datapath scheduler that maximizes the utilization of higher gate oxide thickness resources. We characterize behavioral components for both 65nm and 45nm technologies in order to study the trend of tunneling current as technology scales, and provide them as inputs to the scheduler. We carried out extensive experiments for several benchmarks and observed significant reduction in gate leakage. I.

As a result of aggressive technology scaling, gate leakage (gate oxide direct tunneling) has become a major component of total power dissipation. Use of dielectrics of higher permittivity (Dual-K) or use of silicon dioxide of higher thicknesses (Dual-T) are being considered as methods for its reduction. This paper presents a comparative view of dual dielectric and dual thickness low leakage design techniques from a behavioral synthesis perspective. An algorithm is presented for the gate leakage current reduction that does simultaneous scheduling, allocation and binding during behavioral synthesis while accounting for process variations. The algorithm minimizes the gate leakage for given time constraints. We performed experiments for a number of benchmark circuits using a 45nm CMOS technology datapath library. We obtained gate leakage reduction as high as 95 % for the dual-K (SiO2 and Si3N4) and 91 % for the dual-T (1.4nm and 1.7nm) approaches. It is observed that the dual-K approach outperformed the dual-T approach for all benchmark circuits. 1

Aggressive CMOS scaling results in low threshold voltage and thin oxide thickness for transistors manufactured in very deep submicron regime. As a result, reducing the subthreshold and gate-tunneling leakage currents has become one of the most important criteria in the design of VLSI circuits. This paper presents a method based on dual-V and dual-T ox assignment to reduce the total leakage power dissipation of SRAMs while maintaining their performance. The proposed method is based on the observation that the read and write delays of a memory cell in an SRAM block depend on the physical distance of the cell from the sense amplifier and the decoder. Thus, the idea is to deploy different types of sixtransistor SRAM cells corresponding to different threshold voltage and oxide thickness assignments for the transistors. Unlike other techniques for low-leakage SRAM design, the proposed technique incurs neither area nor delay overhead. In addition, it results in a minor change in the SRAM design flow. Simulation results with a 65nm process demonstrate that this technique can reduce the total leakage power dissipation of a 64Kb SRAM by more than 50%.

For CMOS technologies below 65nm, gate oxide direct tunneling current is a major component of the total power dissipation. This paper presents a simulated annealing based algorithm for the gate leakage current reduction by simultaneous scheduling, allocation and binding during behavioral synthesis. Gate leakage current reduction is based on the use of functional units of different oxide thickness while simultaneously accounting for process variations. We present a cost function that minimizes leakage and area overhead. The algorithm minimizes the cost function for a given delay trade-off factor. It uses a pre-characterized cell library for tunneling current, delay and area, expressed as analytical functions of the gate oxide thickness Tox. We tested our approach using a number of behavioral level benchmark circuits characterized for a 45nm library by integrating our algorithm into a high-level synthesis system. We obtained an average gate leakage reduction of 76.88% with an average area overhead of 17.38 % for different delay trade-off factors ranging from 1.0 to 1.4. 1

Abstract — With aggressive technology scaling, gate oxide tunneling current is emerging as a prominent component of power dissipation in nanoCMOS circuits. This paper presents a novel approach for reduction of tunneling current (gate leakage) during behavioral synthesis using simultaneous scheduling and binding of resources made of transistors of different gate oxide thicknesses. We provide a heuristic algorithm for optimizing allocation and utilization of resources while scheduling operations with the objective of reducing gate leakage. We selectively bind the off-critical operations to instances of functional units that have transistors of higher oxide thickness, and critical operations to the functional units of lower oxide thickness. We performed extensive experiments for several behavioral synthesis benchmarks using a 45nm technology library. For a time constrained approach we achieved a maximum reduction of 84.8%, while for a resourcetime constrained approach the reduction is 75.8%. I.

Conventional CAD methodologies optimize a processor module for correct operation, and prohibit timing violations during nominal operation. In this paper, we propose recovery-driven design, a design approach that optimizes a processor module for a target timing error rate instead of correct operation. We show that significant power benefits are possible from a recovery-driven design flow that deliberately allows errors caused by voltage overscaling ([10],[3]) to occur during nominal operation, while relying on an error recovery technique to tolerate these errors. We present a detailed evaluation and analysis of such a CAD methodology that minimizes the power of a processor module for a target error rate. We demonstrate power benefits of up to 25%, 19%, 22%, 24%, 20%, 28%, and 20% versus traditional P&R at error rates of 0.125%, 0.25%, 0.5%, 1%, 2%, 4%, and 8%, respectively. Coupling recovery-driven design with an error recovery technique enables increased efficiency and additional power savings.