PDSOI Transistor Structure for Floating Body Charge Extraction
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Solution Overview
Problem
PDSOI transistors suffer from the floating body effect (FBE) due to a partially depleted active body region, leading to issues like threshold voltage shifting, parasitic bipolar transistor effects, reduced output resistance, and increased power consumption.
Innovation Solution
A PDSOI transistor design with specific spacings and contact structures that allow electric charge to be picked up from the body region, avoiding the FBE by incorporating a source contact structure that extends into the source and a third space between the buried oxide layer, facilitating improved charge migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a partially depleted active body region is used in PDSOI transistors, then the transistor structure is simpler and manufacturing is easier, but the floating body effect causes threshold voltage shifting, parasitic bipolar transistor effects, reduced output resistance, and increased power consumption
Solution Approach 1:
The active body region is segmented into multiple depleted regions through selective doping, creating isolated depleted zones that prevent charge carrier accumulation. This segmentation approach maintains the partially depleted structure's manufacturing simplicity while eliminating the floating body effect that causes reliability issues.
Solution Approach 2:
Different regions of the active body are given different doping characteristics - some regions are depleted while others remain partially depleted. This local quality differentiation allows the transistor to maintain overall simplicity while specific localized depleted regions prevent charge carrier accumulation and eliminate the floating body effect.
2Reliability
If the active body region is fully depleted to eliminate the floating body effect, then reliability improves, but manufacturing complexity and difficulty increase
Solution Approach 1:
Instead of fully depleting the entire active body region, the invention applies partial depletion through selective doping in specific areas. This partial action is sufficient to eliminate charge carrier accumulation and the floating body effect, while avoiding the excessive complexity of complete depletion structures.
Solution Approach 2:
The invention creates localized depleted regions within the active body rather than uniform full depletion. This local quality approach achieves the necessary charge carrier removal to eliminate FBE while maintaining a simpler overall device structure compared to fully depleted designs.
3Device complexity
If charge carriers are allowed to accumulate in the floating body region, then the transistor structure remains simple, but parasitic bipolar transistor effects and threshold voltage shifting occur
Solution Approach 1:
The invention extracts or removes the harmful charge carrier accumulation from the active body region by introducing selective depleted zones. These depleted regions act as barriers that prevent charge carrier buildup, thereby eliminating parasitic bipolar transistor effects while maintaining overall structural simplicity.
Solution Approach 2:
The invention converts the potentially harmful floating body effect into a beneficial structure by strategically placing depleted regions. These same regions that prevent charge carrier accumulation also serve to stabilize threshold voltage and eliminate parasitic effects, turning the FBE challenge into a solution.
Data Source
AI summary
A partially depleted silicon-on-insulator (PDSOI) transistor and a method for fabricating the PDSOI transistor are disclosed. In PDSOI transistor, a first space is provided between a bottom surface of a source and a top surface of a buried oxide layer, and a second space is provided between a bottom surface of a drain and the top surface of the buried oxide layer. Moreover, a source contact structure extends into the source and a third space is provided between the source contact structure and the top surface of the buried oxide layer. With this configuration, electric charge can be picked up from the body region through the third space and the source contact structure, thereby avoiding the problem of the floating body effect (FBE) and enabling the PDSOI transistor to have improved quality and reliability.