Christian Schlünder

Analysis of NBTI Degradation- and Recovery-Behavior Based on Ultra Fast VT-Measurements

We present a new direct VT measurement technique with arbitrary choice of drain voltage and a mus delay (factor of 1000 improvement) after stress. As shown this technique enables a meaningful comparison of data to theory (e.g. DeltaVT measurable as response to stress times from 100mus over 10 decades in time and an analysis of recovery over 11 decades in time) which may lead to a better understanding of NBTI. A fast precursor due to bulk trapping was found to significantly influence degradation slopes for all times. Based on a physical model - standard reaction/diffusion model plus fast bulk trapping -with just 3 fit parameters experimental degradation can be well modelled and degradation slopes <frac14 as well as > frac14 (both reported in literature) can be explained. A lifetime extrapolation based on this physical model is superior to the common straight line fit. There is no satisfying agreement of recovery data with reaction/diffusion theory. Further experimental and theoretical work is going to be needed

The statistical analysis of individual defects constituting NBTI and its implications for modeling DC- and AC-stress

The physical origin of the Negative Bias Temperature Instability (NBTI) is still under debate. In this work we analyze the single defects constituting NBTI. We introduce a new measurement technique stimulating a charging of these defects. By employing a statistical analysis of many stochastic stimulation processes of the same defect we are able to determine the electric field and the temperature dependence of these defects with great precision. Based on our experiments we present and verify a new, physics-based, quantitative model allowing a precise prediction of NBTI degradation and recovery. This model takes the stress history into account and also provides a prediction for degradation due to AC-NBTI and an understanding of the special features seen in conjunction with AC-NBTI.

Understanding and modeling AC BTI

We present a model for AC NBTI which is based on capture and emission of charges in and out of oxide border traps. Capture and emission time constants of these traps are widely distributed from &#60;µs to >105s and have been experimentally determined. The model gives a good quantitative understanding of experimental data from alternating stress / recovery sequences. It also provides a physical understanding of all the special features seen in AC NBTI independently of technology parameters.

A Comparison of Very Fast to Very Slow Components in Degradation and Recovery Due to NBTI and Bulk Hole Trapping to Existing Physical Models

A new measuring technique with a 1mus measuring delay and a direct VT determination has been employed. The response to stress times as short as 100 mus to 105 has been studied as well as recovery over 12 decades in time. These experimental data allow a meaningful comparison to theory. Degradation data cut be precisely fitted to a simple physical model with 3 parameters thus enabling a reliable lifetime prediction from stress times below 104s.

Effects of inhomogeneous negative bias temperature stress on p-channel MOSFETs of analog and RF circuits

The effect of inhomogeneous negative bias temperature stress (NBTS) applied to p-MOS transistors under analog and RF CMOS operating conditions is investigated. Experimental data of a 0.18 and 0.25 μm standard CMOS process are presented and an analytical model is derived to physically explain the effect of stress on the device characteristics. The impact of inhomogeneous NBTS on device lifetime is considered and compared to the homogeneous case.

On the degradation of p-MOSFETs in analog and RF circuits under inhomogeneous negative bias temperature stress

The effect of inhomogeneous Negative Bias Temperature Stress (NBTS) applied to p-MOS transistors under analog and RF CMOS operating conditions is investigated. Experimental data of a 0.18 /spl mu/m standard CMOS process are presented and an analytical model is derived to physically explain the effect of stress on the device characteristics. The impact of inhomogeneous NBTS on device lifetime is considered and compared to the homogeneous case.

A study of NBTI by the statistical analysis of the properties of individual defects in pMOSFETS

Capture and emission of positive charge in individual defects has been studied using small area pMOSFETs. Analysis techniques similar to the ones used in RTS studies of nMOSFETs have been employed, with the difference that the capture process has been stimulated by stress pulses. We found that the recoverable part of the NBTI effect can be fully explained by capture and emission of these defects. As a consequence, a couple of previously used approaches trying to explain NBTI have to be discarded. The individual capture and emission time constants are widely spread over many orders of magnitude and are thermally activated with activation energies between 0.5 and 1.0 eV.

MOS transistor reliability under analog operation

Abstract Reliability evaluation for MOS transistors under analog operation requires different or specifically adapted approaches compared to the ones known from the digital world. Focussing on the particular analog operating conditions and the related lifetime criteria, a comprehensive discussion is performed of MOSFET reliability taking into account channel hot-carrier stress, bias temperature instabilities, and oxide wear-out. The conditions for the occurrence of these mechanisms and criteria for stress induced malfunction of analog circuits are discussed and the physics behind the behavior of typical analog device parameters after stress are addressed. Furthermore, specific aspects concerning the definition of analog lifetime criteria and strategies to guarantee reliability by means of circuit design are considered.

On the impact of the NBTI recovery phenomenon on lifetime prediction of modern p-MOSFETs

The NBTI recovery phenomenon leads to a fast reduction of the stress induced electrical device parameter degradation after end of stress. Delay times between device-stress and -characterization within NBTI-experiments affect the measurement values of degradation. This work discusses the impact of these delays on lifetime prediction for technology qualifications. For this reason we investigate delay times from 1mus up to 60s and stress times from 100ms up to 250000s. A correlation between stress time, delay time induced recovery and error in predicted lifetime is elaborated for the first time. Furthermore we give simple guidelines for measurement requirements and essential stress times for accurate lifetime evaluations

A novel multi-point NBTI characterization methodology using Smart Intermediate Stress (SIS)

In recent literature several measurement methods were introduced to characterize the Vth-degradation due to NBTI considering the recovery phenomenon. To our knowledge each method has a severe problem or at least a significant disadvantage. Either there are long delay times, the accuracy is not satisfactory or it is not possible to implement the method with customary equipment. A compromise is to perform a one point measurement in the subthreshold region and calculate Vth based on the assumption that the subthreshold slope is not affected by NBTI. In this paper we disprove the universality of this assumption. Vth determination using a one point measurement can lead to imprecise values. This extraction method disregards changes of the subthreshold slope due to NBTI, however a change of the slope impacts the extracted Vth. We clearly demonstrate this effect with our measurements. We introduce a new smart Vth extraction methodology offering both shortest possible delay times with customary equipment and consideration of NBTI-impact on subthreshold slope.