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Physical Design Methodologies for the More-than-Moore Era

  • Author(s): Chan, Wei-Ting
  • Advisor(s): Kahng, Andrew B.
  • et al.

In the past decades, device scaling along the Moore's Law

trajectory has been the major focus of technology innovation in

the semiconductor industry. However, this scaling has in recent

years slowed down due to power limits, lithography complexity,

and other physics limitations. The semiconductor industry has

identified several looming technology challenges and expected

new design paradigms that demand new "design-based equivalent

scaling" approaches to enable continuation of Moore's Law. This

thesis addresses several aspects of these challenges, for both

the "More-Moore" and "More-than-Moore" domains.

Interconnect reliability increases the design uncertainty in

advanced node technologies. Electromigration is a growing

concern in sub-22nm technology. To close a costly "chicken-egg"

loop that spans library characterization and signoff in the

presence of design adaptivity, we study the interlock among

front-end (device) aging, voltage scaling, and

electromigration; we furthermore quantify timing and power

costs of meeting lifetime requirements. Based on this, we

provide new signoff guidelines and demonstrate that suboptimal

choice of voltage step size and scheduling strategy can result

in decreased product lifetime.

As semiconductor technology advances, leading-edge product

companies must rapidly improve yield for designs that seek to

reach mass production while still early in the adoption of a

new technology node. We study the possible mitigation of yield

loss by opportunistic, last-stage redundant logic insertion in

early advanced-node production. We describe a yield estimation

methodology, and propose an integer linear programming-based

optimization of redundant logic insertion for opportunistic

yield optimization.

In sub-14nm processes, routability challenges arise from

multiple patterning and pin access constraints that drastically

weaken the correlation between global-route congestion and

detailed-routing design rule violations. We present a method

that applies machine learning techniques to effectively predict

detailed-routing design rule violations after global routing,

as well as detailed placement techniques to effectively reduce

detailed-routing design rule violations.

Beyond conventional design paradigms, three-dimensional

integrated circuits (3DICs) with multiple tiers are expected to

achieve large benefits (e.g., in terms of power and area) as

compared to conventional two-dimensional designs. However,

upper bounds on the potential power and area benefits from 3DIC

integration with multiple tiers are not well-explored. We use

the concept of implementation with infinite dimension to

estimate upper bounds on power and area benefits achievable by

3DICs versus 2DICs. We observe that design power sensitivity to

implementation with different dimensions correlates well with

placement-based Rent parameter of the netlist. We show that the

quality of netlist synthesis and optimization benefits from

awareness of the target implementation dimension (e.g., 2D

versus 3D).

Last, aggressive requirements for low power and high

performance in VLSI designs have led to increased interest in

non-conventional computation paradigms. Approximate and

stochastic hardware can achieve improved energy efficiency

compared to accurate, traditional hardware modules. To exploit

any benefits of approximate and stochastic hardware modules,

design tools should be able to quickly and accurately estimate

the output quality of composed approximate designs. We propose

new accuracy estimation methodologies for approximate hardware

and stochastic hardware, respectively. For stochastic circuits,

we further investigate opportunities to optimize circuits under

aggressive voltage scaling. We find that logical and physical

design techniques can be combined to significantly expand the

already powerful accuracy-energy tradeoff possibilities of

stochastic circuits.

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