Monzurul Alam

A Comparative Study of Different Physics-Based NBTI Models

Different physics-based negative bias temperature instability (NBTI) models as proposed in the literature are reviewed, and the predictive capability of these models is benchmarked against experimental data. Models that focus exclusively on hole trapping in gate-insulator-process-related preexisting traps are found to be inconsistent with direct experimental evidence of interface trap generation. Models that focus exclusively on interface trap generation are incapable of predicting ultrafast measurement data. Models that assume strong correlation between interface trap generation and hole trapping in switching hole traps cannot simultaneously predict long-time dc stress, recovery, and ac stress and cannot estimate gate insulator process impact. Uncorrelated contributions from generation and recovery of interface traps, together with hole trapping and detrapping in preexisting and newly generated bulk insulator traps, are invoked to comprehensively predict dc stress and recovery, ac duty cycle and frequency, and gate insulator process impact of NBTI. The reaction-diffusion model can accurately predict generation and recovery of interface traps for different devices and experimental conditions. Hole trapping/detrapping is modeled using a two-level energy well model.

On the dispersive versus arrhenius temperature activation of nbti time evolution in plasma nitrided gate oxides: measurements, theory, and implications

Negative bias temperature instability (NBTI) is studied in p-MOSFETs having decoupled plasma nitrided (DPN) gate oxides (EOT range of 12 Aring through 22Aring). Threshold voltage shift (DeltaVT) is shown to be primarily due to interface trap generation (DeltaNIT) and significant hole trapping (DeltaNOT) has not been observed. DeltaVT follows power-law time (t) dependence and Arrhenius temperature (T) activation

Mechanism of negative bias temperature instability in CMOS devices: degradation, recovery and impact of nitrogen

NBTI mechanism is discussed for a wide range of stress conditions. Conditions for interface and bulk-trap generation are shown. The bias, time and temperature dependence of interface-trap buildup and recovery are discussed using the framework of the R-D model. The AC frequency dependence and impact of gate oxide nitridation are also discussed.

A predictive reliability model for PMOS bias temperature degradation

Bias temperature degradation is studied in p-MOSFETs. The physical mechanisms responsible for degradation over a wide range of stress bias and temperature have been identified. A novel scaling methodology is proposed that helps in obtaining a simple, analytical model useful for reliability projection.

A new observation of enhanced bias temperature instability in thin gate oxide p-MOSFETs

Bias temperature instability (BTI) and its underlying physical mechanism are studied for thin gate oxide MOSFETs. For p-MOSFETs stressed in inversion for a long-time, BTI increase is observed at high stress temperature. This is shown to be due to higher interface trap generation because of faster hydrogen diffusion in the gate poly. Enhanced BTI affects device lifetime and is strongly influenced by gate oxide scaling, as discussed.

Impact of substrate bias on p-MOSFET negative bias temperature instability

The negative bias temperature instability (NBTI) of p-MOSFETs is an important reliability issue for digital as well as analog CMOS circuits. To date, characterization and modeling efforts to analyze the NBTI mechanism involve devices stressed with zero substrate bias (VB). However, many circuits utilize nonzero V/sub B/ to vary the device threshold voltage (V/sub T/), (e.g., for dual V/sub T/ CMOS, standby leakage reduction, etc.). This paper aims to systematically study NBTI for V/sub B/>0 V stress, which, to the best of our knowledge, has not been done so far. It is shown that NBTI increases for V/sub B/>0 V stress. This is attributed to enhanced interface (N/sub IT/) and bulk (N/sub OT/) trap generation due to impact ionization and hot-hole (HH) generation. The role of gate bias (V/sub G/), V/sub B/, temperature (T) and oxide thickness (T/sub PHY/) is studied. This work would help all efforts in determining: (i) reliability budget for any operating V/sub B/; (ii) proper choice of stress V/sub B/ during accelerated aging tests; and (iii) suitable TCAD and SPICE models.

Robust transmit beamforming against steering vector uncertainty in cognitive radio networks

A robust transmit beamforming scheme is proposed for green cognitive radio networks in presence of incorrect steering vector estimations. The beamformer is designed using a stochastic optimization approach. The proposed beamforming scheme achieves three objectives: a) Probability for large-than-a-threshold for secondary users received power in the steering direction is maximized; b) Probabilities for less-than-a-threshold interferences to the primary users in different locations are bounded; and c) Transmitted power along the directions of the moving secondary receiver is maintained as a constant. In addition, we present an algorithm to calculate the inverse Marcum Q function, and use it to solve the optimization problem for proposed beamforming scheme. Simulation results demonstrate that the proposed robust beamformer can achieve significant BER reductions for primary users while ensuring secondary users BER is not sacrificed.

Robust cooperative beamforming against steering vector uncertainty in cognitive radio networks

Transmit beamforming is one of the promising ways of accessing spectrum in an underlay cognitive radio network (CRN). In this paper, a robust cooperative transmit beamforming scheme is proposed for a mobile (or stationary) secondary receiver in a CRN where steering vector available at the distributed transmitters is error prone. The solution to the beamforming problem is based on stochastic optimization theory. Specifically, the proposed beamforming scheme achieves the following three objectives: i) probability of large-than-a-threshold for received power in the direction of the secondary receiver is maximized; ii) probabilities of less-than-a-threshold for received interference power in the direction of primary receivers are bounded; and iii) transmit power along the directions of the moving secondary receiver is forced to be uniform so as to ensure the same quality of service. Our simulation results demonstrate that the proposed robust cooperative beamformer can achieve noticeable bit-error-rate reductions for primary users as compared to the non-robust approach, where inaccuracy in the estimation of the steering vector is not considered, while ensuring almost the same quality of communication for the secondary user.

Online prognostics of aircraft turbine engine component's remaining useful life (RUL)

Prognostics refers to the estimation of remaining useful life (RUL) of components of a system after a fault has been identified. Online prognostics indicates the estimation of RUL every time a new health data is provided to the user. In this paper, an artificial neural network (ANN) based approach is proposed for designing a prognostic system for aircraft turbine engine. A trained ANN is developed to estimate the health parameters such as component efficiency (η) and flow capacity (γ). The ANN was trained for a very small value of mean squared error (MSE). Then a forecasting (prediction) method is used to model the trend of estimated health parameters. The model is developed by autoregressive technique (AR) and all the data processing is done online. The proposed prognostic system also compute the distribution of the end of life (EoL) estimation of the failed component. The EoL and RUL estimation are implemented by modeling the health data using moving window and progressive window. The standard deviation (σ) of the distribution of estimated EoL indicates that progressive window performs better than the moving window with a σ reduction factor of 0.6 and 0.5 for η and γ respectively.

Practical Design of 4H-SiC Superjunction Devices in the Presence of Charge Imbalance

In the ideal case, superjunction (SJ) drift regions theoretically exhibit a linear relationship between specific-on resistance Ron,sp and blocking voltage VBR, but this requires perfect charge balance between the alternating n and p pillars. If any degree of imbalance exists, the relationship becomes quadratic, similar to a conventional drift region, although with somewhat improved performance. In this work, we analyze superjunction drift regions in 4H-SiC under realistic degrees of charge imbalance and show that, with proper design, a reduction in specific on-resistance of 2~10x is possible as long as the imbalance remains less than ±20%.