Dynamic NBTI Modeling for PMOS Reliability
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Solution Overview
Problem
Conventional methods for determining Negative Bias Temperature Instability (NBTI) effects in integrated circuits rely on static analysis, which may be overly pessimistic due to the annealing of interface states during the off-state of transistors in dynamic operations, necessitating a more accurate model that accounts for both degradation and recovery during voltage cycles.
Innovation Solution
A method that specifies parameters for degradation and recovery models based on measurements across various voltage, temperature, and geometric ranges, calculates degradation and recovery values, and combines them to determine the NBTI effect, incorporating these values into IC simulations to accurately model dynamic NBTI impacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If static or DC analysis is used for NBTI modeling, then the modeling approach is simple, but the prediction is too pessimistic and inaccurate for dynamic operation
Solution Approach 1:
The patent transitions from static DC analysis to dynamic AC analysis by introducing time-dependent degradation and recovery models that capture the transient behavior of PMOS devices during voltage cycling. The model incorporates stress time, recovery time, and duty cycle parameters to dynamically predict NBTI effects under alternating current conditions, resolving the contradiction between simplicity and accuracy.
Solution Approach 2:
The patent introduces new parameters specific to dynamic operation including stress time (ton), recovery time (toff), duty cycle (D), and activation energy (Ea). These parameters enable the model to adapt to varying operational conditions and accurately predict NBTI degradation and recovery, improving measurement precision while maintaining manageable complexity through systematic parameterization.
2Adaptability or versatility
If static NBTI tests are used where transistor is always on, then the testing methodology is simple, but the results do not reflect dynamic operation conditions
Solution Approach 1:
The patent implements periodic stress and recovery cycles that mirror actual dynamic operation conditions. The model alternates between stress phases (transistor on-state) and recovery phases (transistor off-state), with each cycle characterized by stress time ton and recovery time toff. This periodic approach enables the model to adapt to dynamic operation while maintaining systematic testing procedures.
Solution Approach 2:
The patent performs preliminary extraction of degradation and recovery parameters from separate stress and recovery measurements before combining them to predict overall NBTI effects. This preliminary action allows the model to capture dynamic operation characteristics without requiring complex simultaneous measurements, balancing adaptability with testing feasibility.
3Reliability
If recovery effect is not considered in NBTI modeling, then the modeling is simpler, but the assessment is overly pessimistic
Solution Approach 1:
The patent incorporates feedback mechanisms by modeling the recovery process where interface states generated during stress are partially annealed during recovery. The recovery model uses parameters such as recovery time toff and activation energy Ea to quantify the reduction in degradation, providing feedback that improves reliability assessment accuracy while maintaining manageable modeling complexity through systematic formulation.
Data Source
AI summary
A method of determining a Negative Bias Temperature Instability (NBTI) effect that combines degradation and recovery for dynamic operation of an integrated circuit (IC) includes: specifying one or more parameters for a degradation model for the IC during a stressed portion of a voltage cycle; specifying one or more parameters for a recovery model for the IC during an unstressed portion of the voltage cycle; determining a degradation value for the voltage cycle from the degradation model; determining a recovery value for the voltage cycle from the recovery model; determining an NBTI value that combines the degradation value and the recovery value for the voltage cycle; and saving at least one value for the NBTI value.