Jack M. Higman

Understanding SRAM High-Temperature-Operating-Life NBTI: Statistics and Permanent vs Recoverable Damage

The paper shows using deconvolution, SRAM Vmin shift statistics yield a spread that follows Poisson area scaling and a time- and voltage-dependence of t1/6 and V3, respectively. This is demonstrated to be consistent with permanent NBTI shift (Si-H bond breaking) relevant for end-of-life extrapolation. In contrast recoverable NBTI shift (hole trapping/detrapping) is shown to be only a function of stress duty and can be very small for realistic product duties.

Realistic Projections of Product Fails from NBTI and TDDB

Statistical models for deconvolving the effects of competing mechanisms on product failures are presented. Realistic projections of product fails are demonstrated on high performance microprocessors by quantifying the contribution of NBTI, TDDB and extrinsic fail mechanisms. In particular, it is shown that transistor shifts due to NBTI manifest as population tails in the products minimum operating voltage (Vmin) distribution, while TDDB manifests as single-bit or logic failures that constitute a separate sub-population. NBTI failures are characterized by lognormal statistics combined with a slower degradation rate (Deltat ~ t0.15 -t0.25), in contrast to TDDB failures that follow extreme-value statistics and exhibit a faster degradation rate (DeltaVt ~ t0.5)

Product NBTI Distribution and Voltage Dependence - impact of relaxation and droops

The impact of relaxation and droops in determining the voltage dependence of NBTI during product stressing is discussed. This has implications on the Fmax and Vmin guardbands extrapolated from product stress to use conditions. Voltage dependence for the shift of the 3sigma tail bits in both new and old technology nodes are compared to illustrate the importance of relaxation and droops.