Mixed-Vt Scan Flip-Flop Layout for Hold-Slack Compliance
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Solution Overview
Problem
Existing scan-insertion D flip-flops (SDFQs) face challenges in avoiding hold-slack violations without increasing the area/footprint or eliminating critical components, which can lead to data-racing issues and inefficiencies in semiconductor devices.
Innovation Solution
The implementation of a mix of threshold-voltages among transistors in the SDFQ, specifically using a combination of standard (Vt_std), low (Vt_low), and high (Vt_high) threshold-voltage transistors, allows for the retention of essential components like the fourth NS inverter while avoiding hold-slack violations, thereby maintaining efficient operation without area increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional SDFQ design is used, then the structure is simple, but hold-slack violations occur leading to data-racing issues
Solution Approach 1:
The patent applies local quality by assigning different threshold voltage characteristics to different transistor groups within the flip-flop circuit. Specifically, first group transistors have a first threshold voltage while second group transistors have a second threshold voltage, allowing localized optimization of transistor performance in different circuit regions to prevent hold-slack violations without requiring complete redesign of the entire circuit architecture.
Solution Approach 2:
The patent changes the electrical parameter (threshold voltage) of transistors to resolve the hold-slack issue. By modifying the threshold voltage parameter of specific transistor groups, the circuit achieves proper timing margins and prevents data-racing conditions while maintaining the overall flip-flop structure and functionality.
2Reliability
If additional transistors are added to prevent hold-slack violations, then reliability improves, but area/footprint increases
Solution Approach 1:
Instead of uniformly increasing transistor size or adding transistors throughout the circuit, the patent applies local quality by targeting specific transistor groups with different threshold voltages. This localized approach achieves hold-slack compliance without requiring area increases, as the solution is implemented only where needed rather than across the entire flip-flop structure.
Solution Approach 2:
The patent changes the threshold voltage parameter of existing transistors rather than adding new transistors or increasing device area. This parameter modification approach achieves the same reliability improvement as adding transistors would, but without the area penalty, by optimizing the electrical characteristics of the existing transistor network.
3Area of stationary object
If critical components are eliminated to reduce area, then footprint decreases, but data-racing issues occur
Solution Approach 1:
The patent maintains all critical components in the flip-flop circuit but applies local quality by giving different threshold voltage characteristics to different transistor groups. This allows the full circuit architecture to be preserved for data-racing prevention, while still achieving area efficiency through optimized transistor characteristics rather than component elimination.
4Reliability
If transistor threshold voltages are optimized, then hold-slack violations are prevented, but manufacturing complexity increases
Solution Approach 1:
The patent achieves local quality differentiation through standard semiconductor manufacturing techniques such as selective doping or work function adjustment during gate formation. These are conventional fabrication methods that can be applied to specific transistor regions without requiring entirely new manufacturing processes, thus maintaining ease of manufacture while achieving the desired threshold voltage differentiation.
Solution Approach 2:
The patent changes transistor threshold voltage parameters using established semiconductor manufacturing techniques. These parameter changes are achieved through controlled doping concentrations, gate material selection, or gate oxide thickness variations, all of which are standard fabrication variables that can be adjusted during normal manufacturing processes without significantly increasing complexity.
Data Source
AI summary
A method (of manufacturing) includes forming transistor components connected as transistors resulting in: first to third transistor-component (TC) sets being a primary latch, a secondary latch and a clock buffer that comprise D flip-flop (DFF); the primary latch including a first sleepy inverter and a first non-sleepy (NS) inverter; the secondary latch including a second sleepy inverter and a second NS inverter; the clock buffer including third and fourth NS inverters; a first group of some but not all of the transistors having members with a standard threshold voltage (Vt_std members); a second group of some but not all of the transistors having members with a low threshold voltage; and transistors which comprise at least one of the first NS inverter or the second NS inverter being Vt_low members of the second group.