FET Threshold Voltage Restoration via OFF-State Stress Compensation
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Solution Overview
Problem
OFF-state stress degradation in high-κ metal gate field-effect transistors leads to significant threshold voltage shifts, causing reliability issues in advanced semiconductor devices like DRAM modules and system-on-chip devices, which has not been adequately addressed in previous technologies.
Innovation Solution
A method and device that determine a signal indicative of threshold voltage changes due to OFF-state stress and apply a restoration signal to shift the threshold voltage in the opposite direction, using voltage pulses with specific bias conditions to compensate for the degradation, ensuring the threshold voltage remains within a predetermined tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the gate oxide dielectric thickness is reduced to scale down transistor size, then the transistor can be miniaturized for advanced technology nodes, but the OFF-state current increases due to Drain Induced Barrier Lowering and Gate Induced Barrier Leakage
Solution Approach 1:
The patent applies parameter changes by modifying the gate voltage parameter dynamically. A restoration signal with specific voltage parameters (amplitude and duration) is applied to the gate terminal to counteract the threshold voltage shift caused by OFF-state stress, thereby compensating for the increased OFF-state current without changing the physical structure
2Length of moving object
If the gate length is reduced to miniaturize transistors, then device density increases, but the lateral electric field strengthens causing higher impact ionization and reliability problems
Solution Approach 1:
The patent changes the electrical parameter (gate voltage) to compensate for the structural parameter (gate length) reduction. By applying a restoration voltage signal, the threshold voltage shift caused by strengthened lateral electric field and impact ionization is counteracted, maintaining device reliability despite miniaturization
3Use of energy by moving object
If OFF-state stress occurs with high drain voltage and zero gate voltage, then power consumption is reduced, but threshold voltage degradation occurs
Solution Approach 1:
The patent applies preliminary action by proactively applying a restoration signal after OFF-state stress detection. The restoration signal is applied in advance of potential circuit failure to counteract the threshold voltage degradation, preventing reliability issues before they occur
Solution Approach 2:
The patent implements feedback by detecting the threshold voltage shift caused by OFF-state stress and applying a compensating restoration signal. The restoration signal parameters are determined based on the detected degradation level, creating a closed-loop system that maintains threshold voltage stability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively stabilizes the threshold voltage, enhancing the reliability and lifespan of transistors by remedying the detrimental effects of OFF-state stress, thereby improving the performance and longevity of high-κ/metal gate field-effect transistors in high-volume manufacturing.
Implementation Method 1
applying at least one voltage pulse to the field-effect transistor such that a gate terminal of the field-effect transistor is connected to a higher voltage level than a drain terminal of the field-effect transistor and higher than a source terminal of the field-effect transistor
Data Source
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AI summary
The present invention relates to a method (10) for at least partially compensating for a change in threshold voltage level of a FET transistor induced by OFF-state stress degradation. The method comprises determining (12) a signal indicative of a change in threshold voltage level of the FET with respect to a reference threshold voltage level, and applying (15) a restoration signal to the FET. This restoration signal is adapted for shifting the threshold voltage level of the FET in a direction having opposite sign with respect to the change in threshold voltage level. The step of applying the restoration signal is furthermore taking into account the signal indicative of the change in threshold voltage level.