Split-Gate FinFET Threshold Drift Correction via Control Gate Bias
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Solution Overview
Problem
Metal oxide semiconductor (MOS) transistors in integrated circuits undergo performance degradation due to mechanisms like negative bias temperature instability and hot carrier effects, leading to reduced on-state current and increased off-state leakage, which existing methods cannot effectively alleviate beyond initial adjustments.
Innovation Solution
The use of split-gate fin field effect transistors (finFETs) with adjustable voltage sources connected to their control gates allows for dynamic adjustment of threshold voltages to maintain desired signal thresholds, thereby compensating for performance shifts during the operational life of the IC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MOS transistors are used in integrated circuits, then initial performance can be achieved, but performance degradation occurs during operation due to NBTI and hot carrier mechanisms
Solution Approach 1:
The patent applies the Dynamics principle by making the transistor threshold voltage adjustable during operation through a control gate. The control gate voltage can be dynamically modified to compensate for threshold voltage shifts caused by degradation mechanisms like NBTI and hot carrier effects, allowing the transistor to maintain optimal performance throughout its operational lifetime rather than being fixed at initial design values.
Solution Approach 2:
The patent implements Parameter changes by modifying the electrical parameters of the transistor, specifically the threshold voltage, through application of different voltages to the control gate. This allows the transistor characteristics to be adjusted to counteract degradation effects, changing the operating parameters dynamically rather than relying on fixed initial parameters.
2Manufacturing precision
If initial adjustments are made to compensate for performance mismatch, then performance can be optimized at start-up, but subsequent performance shifts cannot be alleviated
Solution Approach 1:
The patent applies Continuity of useful action by enabling continuous performance compensation throughout the transistor's operational life. The control gate can be continuously adjusted to maintain optimal threshold voltage, rather than performing a one-time adjustment at manufacturing or initial operation. This continuous adaptability ensures performance is maintained despite ongoing degradation.
Solution Approach 2:
The patent implements Feedback mechanisms where the transistor performance is monitored and the control gate voltage is adjusted accordingly to compensate for threshold voltage shifts. This closed-loop approach allows the system to detect performance degradation and automatically correct for it, rather than relying solely on open-loop initial adjustments.
3Reliability
If split-gate finFETs with control gates are used, then threshold voltage can be adjusted to compensate for degradation, but device complexity increases
Solution Approach 1:
The patent applies Segmentation by dividing the gate structure into two separate gates: a signal gate that receives the input signal and a control gate that adjusts the threshold voltage. This segmentation allows independent control of signal processing and threshold adjustment functions, enabling performance compensation without requiring complete redesign of the entire transistor structure.
Solution Approach 2:
The patent implements Universality by designing the control gate to serve multiple functions: it can adjust threshold voltage to compensate for degradation, it can optimize transistor matching, and it can adapt to different operating conditions. This multi-functional control gate reduces the need for separate compensation circuits and structures.
Data Source
AI summary
A pair of split-gate fin field effect transistors (finFETs) in an IC, each containing a signal gate and a control gate, in which an adjustable voltage source, preferably in the form of a digital-to-analog-converter (DAC), is connected to the control gate of one of the finFETs, is disclosed. Threshold measurement circuits on the signal gates enable a threshold adjustment voltage from the adjustable voltage source to reduce the threshold mismatch between the finFETs. Adding a second DAC to the second finFET allows a simpler DAC design. Threshold correction may be performed during the operational life of the IC. Implementations in a differential input stage of an amplifier and in a current mirror circuit are described.