Nanoribbon Transistor Threshold Tuning by Layer-Selective Doping
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Solution Overview
Problem
Conventional methods for threshold voltage tuning of nanoribbon-based transistors lack versatility in tuning threshold voltages across different nanoribbons within a stack and between adjacent stacks, limiting the performance and flexibility of semiconductor devices.
Innovation Solution
A fabrication method involving selective doping of semiconductor layers on a layer-by-layer basis, combined with the use of different work function materials, gate dielectric materials, nanoribbon widths, and spacing between nanoribbons within a stack, to achieve varying threshold voltages in a single nanoribbon stack.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional methods for threshold voltage tuning are used, then the manufacturing process is simple, but the versatility in tuning threshold voltages across different nanoribbons is limited
Solution Approach 1:
The fabrication process is segmented into discrete stages: forming sacrificial material layers, depositing semiconductor material layers, selectively doping specific layers, and removing sacrificial material. This segmentation enables independent control of each nanoribbon's threshold voltage through selective doping at specific fabrication stages, resolving the contradiction between versatility and complexity by making the complex process manageable and controllable
Solution Approach 2:
Doping is performed preliminarily during the layer-by-layer fabrication process rather than as a post-processing step. By doping semiconductor layers selectively before final nanoribbon formation, the method establishes different threshold voltages early in the fabrication process, enabling versatile tuning while maintaining a systematic workflow that doesn't excessively complicate manufacturing
2Adaptability or versatility
If selective doping of semiconductor layers is performed, then diverse threshold voltages are achieved, but the manufacturing precision requirements increase
Solution Approach 1:
Different semiconductor layers are doped with different dopant concentrations or types to create local quality variations. This enables each nanoribbon to have customized threshold voltage characteristics while using standard doping equipment and processes, thereby achieving diverse threshold voltages without excessively increasing manufacturing precision requirements
Solution Approach 2:
The method varies doping parameters (dopant type, concentration, diffusion time, temperature) across different semiconductor layers to achieve different threshold voltages. By changing these parameters systematically during fabrication, the patent achieves threshold voltage diversity using conventional doping equipment, avoiding the need for ultra-precise specialized manufacturing
3Adaptability or versatility
If different work function materials and gate dielectric materials are used, then additional degrees of freedom in transistor choices are provided, but the device complexity increases
Solution Approach 1:
The fabrication method is designed to accommodate multiple material types (different work function materials, gate dielectric materials, dopant types) within a single unified process framework. This universality allows manufacturers to choose from various material options to achieve different transistor characteristics without requiring separate fabrication processes for each material combination, thereby providing flexibility without proportionally increasing 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
Enhances the ability to form transistors with diverse threshold voltages, providing additional degrees of freedom in transistor choices for high-voltage handling and speed, thereby improving the performance and versatility of nanoribbon-based transistors.
Implementation Method 1
a gate field to wrap around at least a portion of the channel material... to form a nanoribbon-based field-effect transistor
Implementation Method 2
implanting dopants into the individual semiconductor layers on an as-needed basis
Data Source
AI summary
Fabrication methods that may provide greater versatility in tuning threshold voltage of transistors implemented in different nanoribbons within a given stack and in tuning threshold voltage of transistors implemented in adjacent nanoribbon stacks, as well as corresponding devices, are disclosed. An example fabrication method includes selectively doping portions of semiconductor layers from which individual nanoribbons will be formed later. The selective doping is performed on a layer-by-layer basis, i.e., after a given semiconductor layer is deposited and before the next layer is deposited. In this manner, some nanoribbons of a given nanoribbon stack may be doped, while other nanoribbons of the same stack may be substantially undoped, or, more generally, different nanoribbons of a given nanoribbon stack may have different dopant concentrations. The differences in the dopant concentration of different nanoribbons within the stack advantageously allows forming transistors with different threshold voltages in a single nanoribbon stack.