Defective P-N Junction for FDSOI Backbias Stability
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Solution Overview
Problem
In backgated fully depleted silicon on insulator (FDSOI) MOSFETs, the p-n junction's leakage resistance is inadequate during AC operation due to capacitive voltage dividers, causing fluctuations in the applied backbias voltage.
Innovation Solution
Creating defects at the p-n junction interface between the well and the pocket, either as part of the same implantation used to form the pocket or through a separate blanket implantation, to intentionally reduce the leakage resistance and ensure most of the applied voltage drops at the buried oxide interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a p-n junction is formed between the well and pocket to apply backbias, then the backbias can be applied to the BOX, but during AC operation a capacitive voltage divider is formed causing the actual backbias to fluctuate
Solution Approach 1:
The patent intentionally creates defects at the p-n junction to increase leakage current, converting the harmful effect of leakage into a beneficial effect. The increased leakage provides a low-impedance path that stabilizes the backbias voltage during AC operation by preventing the capacitive voltage divider from causing fluctuations, thus converting the previously harmful leakage into a stabilizing mechanism.
Solution Approach 2:
The patent changes the electrical parameters of the p-n junction by introducing defects that increase leakage current. This parameter change transforms the p-n junction from a high-impedance capacitive element into a low-impedance conductive path, fundamentally altering its behavior in the AC regime and eliminating the voltage divider effect.
2Stability of the object's composition
If the p-n junction has high leakage resistance, then DC operation is maintained, but during AC operation the capacitive voltage divider causes voltage fluctuations
Solution Approach 1:
The patent makes the p-n junction's electrical characteristics dynamic by frequency-dependent behavior. The introduced defects create a leakage path that is particularly effective at AC frequencies, allowing the junction to maintain its capacitive characteristics at DC while providing a low-impedance path during AC operation, thus adapting its behavior to different operating conditions.
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 approach makes the p-n junction leaky, allowing most of the AC signal to drop across the buried oxide, effectively addressing the voltage divider issue and stabilizing the backbias voltage during AC operation.
Implementation Method 1
during AC operation, there is a capacitive voltage divider formed by the MOS (metal-oxide-semiconductor) capacitor associated with the BOX and the depletion capacitor associated with the p-n junction between the well and pocket
Implementation Method 2
Defects are created at the p-n junction such that a leakage resistance of the p-n junction is decreased
Data Source
AI summary
Methods for semiconductor fabrication include forming a well in a semiconductor substrate. A pocket is formed within the well, the pocket having an opposite doping polarity as the well to provide a p-n junction between the well and the pocket. Defects are created at the p-n junction such that a leakage resistance of the p-n junction is decreased.