An analytical model for negative bias temperature instability

ABSTRACT

Negative Bias Temperature Instability (NBTI) in PMOS transistors has become a significant reliability concern in present day digital circuit design. With continued scaling, the effect of NBTI has rapidly grown in prominence, forcing designers to resort to a pessimistic design style using guard-banding. Since NBTI is strongly dependent on the time for which the PMOS device is stressed, different gates in a combinational circuit experience varying extents of delay degradation. This has necessitated a mechanism of quantizing the gate-delay degradation, to pave the way for improved design strategies. Our work addresses this issue by providing a procedure for determining the amount of delay degradation of a circuit due to NBTI. An analytical model for NBTI is derived using the framework of the Reaction-Diffusion model, and a mathematical proof for the widely observed phenomenon of frequency independence is provided. Simulations on ISCAS benchmarks under a 70nm technology show that NBTI causes a delay degradation of about 8% in combinational logic based circuits after 10 years (≈ 3 x 10⁸s).

REFERENCES

• 1: A. T. Krishnan, V. Reddy, S. Chakravarthi, J. Rodriguez, S. John, and S. Krishnan, "NBTI Impact on Transistor and Circuit: Models, Mechanisms and Scaling Effects," in IEEE International Electronic Devices Meeting, pp. 14.5.1--14.5.4, December 2003.
• 2: M. A. Alam, "On the Reliability of Micro-electronic Devices: An Introductory Lecture on Negative Bias Temperature Instability," in Nanotechnology 501 Lecture Series, September 2005. Available at http://www.nanohub.org/resources/?id=193.
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INDEX TERMS

Primary Classification:
  B. Hardware
  B.6 LOGIC DESIGN
      B.6.1 Design Styles
          Subjects: Combinational logic

Additional Classification:
  B. Hardware
  B.6 LOGIC DESIGN
      B.6.3 Design Aids
  B.8 Performance and Reliability
      B.8.2 Performance Analysis and Design Aids
  B.m MISCELLANEOUS
      Subjects: Design management

General Terms:
Design, Performance