Floating Body Biasing for SOI Transistor Threshold Control
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Solution Overview
Problem
Transistors on semiconductor-on-insulator substrates face challenges in adjusting voltage thresholds due to floating bodies, which complicates body-biasing and increases layout size and parasitics, making it impractical to achieve optimal tradeoff between transistor speed and leakage current.
Innovation Solution
A dual-semiconductor-on-insulator substrate is used, with a biasing layer that provides a first and second bias charge to respective bias regions at different levels, allowing for independent control of voltage thresholds of transistors by electrically isolating channel regions from bias regions, facilitating the formation of transistors with controlled voltage thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If body-biasing techniques are used to control transistor voltage thresholds, then voltage threshold control is achieved, but layout size increases and parasitics are introduced due to required body contacts
Solution Approach 1:
The substrate is segmented into multiple independent floating body regions, each capable of receiving different bias charges. This segmentation allows independent voltage threshold control for transistors formed over different regions without requiring interconnecting body contacts, thereby maintaining voltage threshold control while avoiding the layout complexity and parasitics associated with traditional body-biasing techniques
Solution Approach 2:
Floating body regions serve as intermediary structures between the substrate and transistor channels, enabling voltage threshold control through charge injection into these intermediate regions. This intermediary approach eliminates the need for direct body contacts while maintaining the ability to control transistor characteristics through electrical biasing of the floating bodies
2Speed
If transistors with lower threshold voltages are used, then transistor switching speed improves, but leakage current increases
Solution Approach 1:
The voltage threshold of transistors is made dynamically adjustable through the injection and removal of bias charges from floating body regions. This dynamic control enables the system to switch between different operating states: high-speed mode with lower threshold voltages when performance is critical, and low-leakage mode with higher threshold voltages when power consumption is the primary concern, thereby resolving the static tradeoff between speed and leakage
Solution Approach 2:
The invention changes the electrical parameters of the transistor by injecting different amounts and polarities of bias charges into the floating body regions. By controlling the magnitude and sign of the bias charge, the voltage threshold can be precisely adjusted across a wide range, enabling optimization of the speed-leakage tradeoff for different operating conditions without changing the physical transistor structure
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 enables the control of voltage thresholds for transistors, allowing for a balance between speed and leakage current, without the need for body contacts, thus overcoming the limitations of traditional semiconductor-on-insulator substrates.
Implementation Method 1
The voltage threshold of a transistor is the voltage at which a field effect transistor begins to conduct
Implementation Method 2
While in bulk semiconductor technology body-biasing techniques can be used to affect transistor threshold voltages
Data Source
AI summary
A first bias charge is provided to first bias region at a first level of an electronic device, the first bias region directly underlying a first transistor having a channel region at a second level that is electrically isolated from the first bias region. A voltage threshold of the first transistor is based upon the first bias charge. A second bias charge is provided to second bias region at the first level of an electronic device, the second bias region directly underlying a second transistor having a channel region at a second level that is electrically isolated from the first bias region. A voltage threshold of the second transistor is based upon the second bias charge.