Source-Side VRM Structure for Floating-Body N-Type MOSFETs
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The floating body effect (FBE) in N-type MOSFETs, particularly those using silicon-on-insulator (SOI) technology, leads to adverse effects such as parasitic transistor activation and increased hot carrier injection, affecting reliability and switching characteristics.
Innovation Solution
Incorporating a source-side structure with a Vbi Reduction Material (VRM) layer having a lower bandgap than silicon, allowing freer movement of holes from the body to the source region, thereby reducing the built-in voltage (Vbi) and mitigating the FBE.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional N-type MOSFET structure is used, then the device can handle high drain voltages, but the floating body effect causes parasitic transistor activation and increased hot carrier injection
Solution Approach 1:
The patent applies local quality by introducing a specialized source region with distinct material composition (silicon-germanium alloy) only at the source side of the device. This localized modification creates a lower built-in potential at the source-body junction, enhancing hole collection efficiency specifically where needed to mitigate the floating body effect, while preserving the overall high-voltage capability of the device structure.
2Reliability
If the built-in voltage is reduced by adding a Vbi Reduction Material layer, then body hole collection efficiency increases and floating body effect is reduced, but the device structure becomes more complex
Solution Approach 1:
The patent employs composite materials by integrating a silicon-germanium alloy layer within the source region structure. This composite approach combines the properties of silicon and germanium to achieve a lower bandgap material that reduces the built-in potential at the source-body junction, thereby enhancing hole collection efficiency and mitigating the floating body effect through material composition rather than structural complexity.
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
Significantly reduces the floating body effect by enhancing body hole collection efficiency, minimizing off-state leakages and maintaining reliable switching characteristics under high drain voltages.
Implementation Method 1
VRM has a bandgap less than the bandgap of Si and, for an N-type device, a valence band that is higher than the valence band of the body material
Implementation Method 2
The low Vbi of the VRM layer on the source-side of an N-type MOSFET device that would otherwise exhibit an FBE allows significantly freer movement of holes from the body of the device towards the source region
Data Source
AI summary
Novel NEDMOS and/or LDMOS FET integrated circuit structures that reduce or eliminate the floating body effect by reducing the built-in voltage Vbi of the device. Reduction of Vbi includes adding a source-side structure that includes a “Vbi Reduction Material” (VRM) layer. VRM has a bandgap less than the bandgap of Si and, for an N-type device, a valence band that is higher than the valence band of the body material. The low Vbi of the VRM layer on the source-side of a MOSFET device that would otherwise exhibit a floating body effect allows significantly freer movement of holes from the body of the device towards the source region, thus increasing body hole collection efficiency, and significantly reduces the floating body effect.