MOSFET Back Gate Segmentation for Leakage Control
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Solution Overview
Problem
Conventional MOSFETs face challenges with short channel effects and power consumption due to fixed threshold voltage, and the back gate can cause damage and increased footprint, limiting flexibility in adjusting threshold voltage and reducing leakage current.
Innovation Solution
A MOSFET with a back gate formed as a PNP or NPN junction, where the buried insulating layer acts as a gate dielectric, allowing for adjustable threshold voltage through capacitive coupling and reducing leakage current by avoiding conductive paths between source/drain regions, with a common conductive via for electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional back gate is used to increase threshold voltage to suppress short channel effects, then short channel effects are suppressed, but the back gate cannot be used for adjusting threshold voltage flexibly and requires additional chip area for electrical contacts
Solution Approach 1:
The back gate is segmented into multiple independently controllable back gate electrodes (first back gate electrode, second back gate electrode, third back gate electrode) with different conductivity types. Each electrode can be controlled separately through independent electrical contacts, enabling flexible threshold voltage adjustment while maintaining short channel effects suppression. This segmentation allows the back gate to serve multiple functions that were previously conflicting.
2Reliability
If a conventional back gate is used to increase threshold voltage, then short channel effects are suppressed, but additional chip area is required for providing electrical contacts with the back gate
Solution Approach 1:
The back gate electrical contacts are merged with the source/drain region contacts. The first back gate electrode is electrically connected to the first source/drain region through a shared contact, and the second back gate electrode is connected to the second source/drain region through another shared contact. This merging eliminates the need for separate back gate contacts, reducing chip area while maintaining the ability to suppress short channel effects.
3Adaptability or versatility
If the back gate is used for adjusting threshold voltage, then threshold voltage can be adjusted, but the MOSFETs may be damaged due to short circuit between source/drain regions via the back gate
Solution Approach 1:
Different regions of the back gate have different conductivity types (first conductivity type in first region, second conductivity type in second region). This local quality variation creates potential barriers at the interfaces between regions of opposite conductivity types, preventing carrier flow and short circuiting between source/drain regions while allowing threshold voltage adjustment in each region independently.
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 solution effectively suppresses short channel effects, allows flexible adjustment of threshold voltage for both N-type and P-type MOSFETs, reduces leakage current, and maintains a compact footprint by using asymmetric back gate configurations.
Implementation Method 1
a back gate also has a reduced effective length and actually controls fewer charges in a depletion region when a gate voltage is applied
Implementation Method 2
allowing for adjustable threshold voltage through capacitive coupling
Data Source
AI summary
The present application discloses an MOSFET and a method for manufacturing the same. The MOSFET comprises: a semiconductor substrate; a first insulation buried layer disposed on the semiconductor substrate; a back gate formed in a first semiconductor layer which is disposed on the first insulation buried layer; a second insulation buried layer disposed on the first semiconductor layer; source/drain regions formed in a second semiconductor layer which is disposed on the second insulation buried layer; a gate disposed on the second semiconductor layer; and electric connections to the source/drain regions, the gate and the back gate, wherein the back gate comprises first back gate regions of a first conductivity type which are disposed under the source/drain regions and a second back gate region of a second conductivity type which is disposed under a channel region, the first back gate regions adjoins the second back gate region, the first conductivity type is opposite to the second conductivity type, and the electric connection to the back gate comprise a conductive via contacted with one of the first back gate regions. The MOSFET, of any conductivity type, can have adjustable threshold voltage and reduced leakage current via the back gate between the source/drain regions by using the back gate in the form of a PNP junction or an NPN junction.