This paper presents HotSpot-a modeling methodology for developing compact thermal models based on the popular stacked-layer packaging scheme in modern very large-scale integration systems. In addition to modeling silicon and packaging layers, HotSpot includes a high-level on-chip interconnect self-heating power and thermal model such that the thermal impacts on interconnects can also be considered during early design stages. The HotSpot compact thermal modeling approach is especially well suited for preregister transfer level (RTL) and presynthesis thermal analysis and is able to provide detailed static and transient temperature information across the die and the package, as it is also computationally efficient.

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HotSpot: a compact thermal modeling methodology for early-stage VLSI design

In this paper, novel n- and p-type tunnel field-effect transistors (T-FETs) based on heterostructure Si/intrinsic-SiGe channel layer are proposed, which exhibit very small subthreshold swings, as well as low threshold voltages. The design parameters for improvement of the characteristics of the devices are studied and optimized based on the theoretical principles and simulation results. The proposed devices are designed to have extremely low off currents on the order of 1 fA/mum and engineered to exhibit substantially higher on currents compared with previously reported T-FET devices. Subthreshold swings as low as 15 mV/dec and threshold voltages as low as 0.13 V are achieved in these devices. Moreover, the T-FETs are designed to exhibit input and output characteristics compatible with CMOS-type digital-circuit applications. Using the proposed n- and p-type devices, the implementation of an inverter circuit based on T-FETs is reported. The performance of the T-FET-based inverter is compared with the 65-nm low-power CMOS-based inverter, and a gain of ~104 is achieved in static power consumption for the T-FET-based inverter with smaller gate delay.

Steep Subthreshold Slope n- and p-Type Tunnel-FET Devices for Low-Power and Energy-Efficient Digital Circuits

Nonuniform thermal profiles on the substrate in high-performance ICs can significantly impact the performance of global on-chip interconnects. This paper presents a detailed modeling and analysis of the interconnect performance degradation due to the nonuniform temperature profiles that are encountered along long metal interconnects as a result of existing thermal gradients in the underlying Silicon substrate. A nonuniform temperature-dependent distributed RC interconnect delay model is proposed. The model is applied to a wide variety of interconnect layouts and substrate temperature distributions to quantify the impact of such thermal nonuniformities on signal integrity issues including speed degradation in global interconnect lines and skew fluctuations in clock signal distribution networks. Subsequently, a new thermally dependent zero-skew clock-routing methodology is presented. This study suggests that thermally aware analysis should become an integrated part of the various optimization steps in physical-synthesis flow to improve the performance and integrity of signals in global ultra large scale integration interconnects.

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Modeling and analysis of nonuniform substrate temperature effects on global ULSI interconnects

Three-dimensional (3-D) integrated circuits have emerged as promising candidates to overcome the interconnect bottlenecks of nanometer scale designs. While they offer several other advantages, it is expected that the benefits from this technology can potentially be off-set by thermal considerations which impact chip performance and reliability. The work presented in this paper is the first attempt to study the performance benefits of 3-D technology under the influence of such thermal constraints. Using a processor-cache-memory system and carefully chosen applications encompassing different memory behaviors, the performance of 3-D architecture is compared with a conventional planar (2-D) design. It is found that the substantial increase in memory bus frequency and bus width contribute to a significant reduction in execution time with a 3-D design. It is also found that increasing the clock frequency translates into larger gains in system performance with 3-D designs than for planar 2-D designs in memory intensive applications. The thermal profile of the vertically stacked chip is generated taking into account the highly temperature sensitive leakage power dissipation. The maximum allowed operating frequency imposed by temperature constraint is shown to be lower for 3-D than for 2-D designs. In spite of these constraints, it is shown that the 3-D system registers large performance improvement for memory intensive applications.

/pdf/a-thermally-aware-performance-analysis-of-vertically-1b09oowexp.pdf

A thermally-aware performance analysis of vertically integrated (3-D) processor-memory hierarchy

Power-related issues have become important considerations in current generation microprocessor design. One of these issues is that of elevated on-chip temperatures. This has an adverse effect on cooling cost and, if not addressed suitably, on chip reliability. In this paper we investigate the general trade-offs between temporal and spatial hot spot mitigation schemes and thermal time constants, workload variations and microprocessor power distributions. By leveraging spatial and temporal heat slacks, our schemes enable lowering of on-chip unit temperatures by changing the workload in a timely manner with Operating System(OS) and existing hardware support.

Thermal-aware task scheduling at the system software level

Accurate estimation of the silicon junction (or die) temperature in high-end microprocessors is crucial for various performance analyses and also for chip-level thermal management This work introduces for the first time, the notion of self-consistency in estimating the die temperature for sub-100 nm CMOS technologies by taking into account various electrothermal couplings between supply voltage, operating frequency, power dissipation and die temperature It also comprehends chip-level reliability constraints and the impact of employing various packaging and cooling solutions in an integrated manner The self-consistent solutions of die temperature are shown to have significant implications for evaluating various power-performance-reliability-cooling cost tradeoffs and can be used to optimize the performance of nanoscale ICs

A self-consistent junction temperature estimation methodology for nanometer scale ICs with implications for performance and thermal management

This paper introduces the idea of electrothermally coupled evaluation of junction temperature to accurately estimate the lifetime of interconnects under electromigration (EM) constraints in leakage dominant technologies. The junction temperature thus evaluated with our proposed methodology is incorporated into the interconnect temperature-rise equation (which includes Joule-heating) and is solved self-consistently with both unipolar and bipolar EM lifetime equations to estimate accurate interconnect metal temperature and to provide comprehensive design guidelines for maximum allowable current density in power/ground and signal lines.

A. Keshavarzi

Papers

A self-consistent junction temperature estimation methodology for nanometer scale ICs with implications for performance and thermal management

Impact of off-state leakage current on electromigration design rules for nanometer scale CMOS technologies