MOS Device Compensation Doped Region Mitigates Threshold Voltage Roll-Off
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Solution Overview
Problem
Conventional MOS devices with small channel widths experience threshold voltage roll-off due to the formation of a recessed isolation region, which leads to undesirable inversion layers and unstable performance, as the recessed isolation region turns on the device at a voltage lower than the designed threshold voltage.
Innovation Solution
A compensation doped region is formed beneath the substrate, in contact with the recessed isolation region along the channel length direction, to mitigate the electric field and prevent premature inversion layer formation, comprising a well region and lightly doped diffusions, with specific width and depth constraints to ensure effective contact and reduced inversion layer formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a recessed isolation region is formed at the boundary of the operation region, then the device can be manufactured with standard isolation processes, but the recessed isolation region creates a higher electric field that causes premature inversion layer formation and threshold voltage roll-off
Solution Approach 1:
The patent applies local quality by creating a compensation doped region with specific doping concentration and depth only at the boundary area where the recessed isolation region is located. This localized doping compensation addresses the high electric field issue specifically at the problematic boundary region without affecting other areas of the device, thereby maintaining threshold voltage stability locally while preserving the overall device structure and manufacturing process.
2Productivity
If the channel width is reduced to achieve smaller device size, then device density increases, but the recessed isolation region effect becomes more pronounced causing greater threshold voltage roll-off
Solution Approach 1:
The patent employs parameter changes by adjusting the doping concentration and depth of the compensation doped region to compensate for the enhanced electric field effect in narrow channel devices. By modifying these doping parameters specifically at the isolation boundary, the invention counteracts the threshold voltage roll-off that becomes more severe with reduced channel width, enabling high device density while maintaining reliable threshold voltage control.
3Reliability
If the compensation doped region depth is increased to better compensate for the recessed isolation region effect, then threshold voltage stability improves, but the device complexity and manufacturing precision requirements increase
Solution Approach 1:
The patent applies preliminary action by forming the compensation doped region at a predetermined depth and concentration during the device fabrication process, before final device operation. This pre-established compensation structure proactively counteracts the electric field effect of the recessed isolation region, ensuring threshold voltage stability from the outset without requiring complex real-time adjustments or extremely tight manufacturing tolerances during operation.
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
The compensation doped region significantly reduces threshold voltage roll-off, allowing the MOS device to operate reliably at designed voltages, enabling smaller device sizes and faster operation speeds with reduced current leakage.
Implementation Method 1
the recessed isolation region, as compared to other parts of the operation region, will have a relatively higher electric field during conduction operation
Data Source
AI summary
The present invention provides a MOS (Metal-Oxide-Silicon) device having mitigated threshold voltage roll-off and a threshold voltage roll-off mitigation method therefor. The MOS device includes: a substrate, a well region, an isolation region, a gate, two LDDs (Lightly-Doped-Drains), a source, a drain and a compensation doped region. The compensation doped region is substantially in contact with at least a part of a recessed portion along the channel length direction. Viewing from a cross-section view, at a boundary where the compensation doped region is in contact with the isolation region along the channel length direction, the compensation doped region has two doped region widths along the channel width direction, wherein, the two doped region widths of the compensation doped region are both not greater than 10% of the width of the operation region. Two doped region widths are defined as distances within an interior part and an exterior part of the operation region, respectively.