Isolated Floating Well Biasing for FDSOI Leakage Control
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Solution Overview
Problem
Fully depleted semiconductor on insulator (FDSOI) transistors face leakage issues due to parasitic well diodes, which are corrected by connecting a deep N-well to a fixed bias, but this requires additional masks and increases fabrication costs.
Innovation Solution
A semiconductor structure with a floating well of a first dopant type and a second well of an opposite dopant type, featuring a reverse bias diode at the junction between the floating well and the substrate, and a forward bias diode at the junction between the floating well and the second well, allowing for independent biasing of the deep N-well without additional tap connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a contact and metal are added to connect the deep N-well to provide fixed bias, then the leakage issue is corrected, but additional masks are required and fabrication costs increase
Solution Approach 1:
The deep N-well is configured to be self-biased through its inherent parasitic diode structure. The body of the transistor connected to the deep N-well serves as the anode, and the N-well itself serves as the cathode, creating a parasitic diode that automatically provides the necessary reverse bias without requiring external contacts or additional fabrication masks.
Solution Approach 2:
The parasitic diode structure serves multiple functions: it provides the fixed reverse bias for the deep N-well to prevent leakage, while simultaneously utilizing existing transistor components (the body region) rather than requiring separate biasing circuitry. This multi-functional approach eliminates the need for dedicated bias contacts and reduces overall device complexity.
2Reliability
If a contact and metal are added to connect the deep N-well to provide fixed bias, then the leakage issue is corrected, but fabrication costs increase
Solution Approach 1:
The deep N-well is configured to be self-biased through its inherent parasitic diode structure. The body of the transistor connected to the deep N-well serves as the anode, and the N-well itself serves as the cathode, creating a parasitic diode that automatically provides the necessary reverse bias without requiring external contacts or additional fabrication masks.
Solution Approach 2:
The solution utilizes existing parasitic diode structures that are inherently present in the transistor fabrication process, rather than requiring additional expensive metal contacts and mask layers. By leveraging these already-present structures, the method avoids incremental fabrication costs while achieving the desired leakage correction.
3Reliability
If additional tap connections are made to bias the deep N-well, then fixed bias is achieved, but area requirements increase
Solution Approach 1:
The parasitic diode structure serves multiple functions: it provides the fixed reverse bias for the deep N-well to prevent leakage, while simultaneously utilizing existing transistor components (the body region) rather than requiring separate biasing circuitry. This multi-functional approach eliminates the need for dedicated bias contacts and reduces overall device complexity.
Solution Approach 2:
The biasing function is merged with the existing transistor body structure. The body region serves dual purposes: as the active transistor component and as the anode for the parasitic diode that provides reverse bias to the deep N-well. This consolidation eliminates the need for separate tap connections and reduces the overall area required.
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
This solution reduces manufacturing costs by minimizing the mask count and enables efficient biasing of deep N-wells with existing parasitic diodes, improving design flexibility and reducing area requirements.
Implementation Method 1
a reverse bias diode at a junction between the floating well and the semiconductor substrate
Implementation Method 2
a forward bias diode at a junction between the floating well and the second well
Data Source
AI summary
The present disclosure relates to semiconductor structures and, more particularly, to a structure with an isolated well and methods of manufacture. The structure includes: a floating well of a first dopant type within a semiconductor substrate; a second well of a second dopant type within the floating well of the first dopant type; a reverse bias diode at a junction between the floating well and the semiconductor substrate; and a forward bias diode at a junction between the floating well and the second well.