CMOS Inverter Layout Using Segmented Gates for Delay
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Solution Overview
Problem
Conventional CMOS inverters face difficulties in aligning gate electrodes at regular intervals when integrating circuits with different poly lengths, leading to non-uniform poly pitch and increased process variations, costs, and layout areas.
Innovation Solution
The CMOS inverter layout increases the effective channel length by forming multiple active regions and conductive MOS transistors, with gate electrodes set to the minimum feature size, allowing for uniform poly intervals and pitch, reducing process variations, and achieving a longer delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the poly length is reduced to the minimum feature size to increase circuit density, then the channel length is reduced and delay is decreased, but the effective channel length cannot be increased to achieve longer delay
Solution Approach 1:
The gate electrode is divided into multiple segments (first gate, second gate, third gate) arranged in series along the channel direction. Each gate segment controls a corresponding active region segment, allowing the effective channel length to be extended by combining multiple minimum-feature-size gates rather than using a single long gate, thus maintaining manufacturing precision while achieving longer delay
Solution Approach 2:
Multiple gate electrodes are arranged in the channel length direction (series arrangement) rather than extending a single gate in that direction. This dimensional reorganization allows the effective channel length to be increased through the cumulative effect of multiple gates while each individual gate maintains the minimum feature size for uniform poly pitch
2Duration of action of moving object
If different poly lengths are used for different circuit types (hold buffer vs. other circuits), then specific delay requirements can be met, but uniform poly intervals and pitch cannot be maintained, increasing process variations
Solution Approach 1:
The number of gate segments is used as a variable parameter to achieve different effective channel lengths. By changing the number of gates in series (e.g., three gates for hold buffer, fewer for other circuits), different delay characteristics are obtained while all gates maintain the same minimum feature size and uniform poly intervals, thus achieving circuit differentiation without sacrificing manufacturing precision
Solution Approach 2:
The gate electrode is divided into multiple segments that can be selectively arranged. For circuits requiring longer delay (hold buffer), more gate segments are used in series; for other circuits, fewer segments are used. This segmentation approach allows delay differentiation while maintaining uniform poly pitch and intervals across all circuits
3Duration of action of moving object
If the poly length is increased to achieve longer delay, then the effective channel length increases, but the poly length exceeds the minimum feature size, making it difficult to align with other circuits at regular intervals
Solution Approach 1:
Instead of using a single long gate electrode that exceeds the minimum feature size, the gate is segmented into multiple shorter gates arranged in series. Each segment maintains the minimum feature size, allowing uniform alignment with other circuits, while the cumulative effective channel length provides the required delay
Solution Approach 2:
The gate structure is reorganized from a single extended element to multiple discrete elements arranged in series along the channel direction. This allows the effective channel length to be increased through the series arrangement of multiple minimum-size gates, simplifying layout alignment while achieving longer delay
Data Source
AI summary
Provided is a complementary metal oxide semiconductor (CMOS) inverter layout for increasing an effective channel length. The CMOS inverter layout may include first and second conductive MOS transistors respectively formed in first and second active regions, metal lines electrically connecting the first and second conductive MOS transistors, and one or more gate electrodes electrically connecting the gates of the first and second conductive MOS transistors. The widths of one or more gate electrodes may be set to a reduced and/or minimum feature size to reduce and/or minimize a process variation and a layout area of the CMOS inverter. Also, the first and second conductive MOS transistors may be connected in series via the metal lines to increase an effective channel length, thereby realizing a layout of the CMOS inverter having a longer delay than a conventional CMOS inverter.