CMOS Image Sensor Superlattice Channel for Mobility and Thermal Management
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Solution Overview
Problem
Current semiconductor devices, such as CMOS image sensors, face limitations in achieving enhanced performance due to constraints in charge carrier mobility and thermal management, despite advancements in strained materials and superlattice technologies.
Innovation Solution
The implementation of a superlattice structure with energy band-modifying layers, comprising semiconductor and non-semiconductor monolayers, which reduces the effective mass of charge carriers and enhances mobility, while also providing thermal management and barrier properties, is used in CMOS image sensors to improve device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If strained material layers (silicon, silicon-germanium) are used to enhance charge carrier mobility, then device speed and performance are improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent employs a composite superlattice structure comprising alternating layers of silicon and silicon-germanium materials. This composite approach enables enhanced charge carrier mobility through strain engineering while maintaining compatibility with standard CMOS manufacturing processes, thus improving device speed without proportionally increasing complexity
Solution Approach 2:
The superlattice structure introduces localized strain fields specifically in the channel region where charge carriers flow. By confining the strained material layers to the critical transport region rather than the entire device, the patent achieves mobility enhancement with minimal impact on overall device complexity
2Speed
If superlattice structures with multiple alternating layers are implemented to reduce effective mass and enhance mobility, then charge carrier mobility increases, but manufacturing precision requirements increase
Solution Approach 1:
The patent systematically varies the thickness and composition parameters of alternating silicon and silicon-germanium layers to optimize the superlattice periodicity. By carefully controlling these parameters, the structure achieves reduced effective mass and enhanced mobility while remaining compatible with existing epitaxial growth techniques and manufacturing capabilities
Solution Approach 2:
The channel region is segmented into multiple thin alternating layers rather than using a single homogeneous material. This segmentation creates the superlattice structure that produces beneficial quantum mechanical effects and strain fields, achieving high mobility through distributed microstructural features rather than requiring extreme precision in a single layer
3Reliability
If impurity-free zones are introduced to prevent performance degradation, then device reliability improves, but device complexity increases
Solution Approach 1:
The patent extracts and eliminates impurity regions from the superlattice channel structure by using molecular beam epitaxy to grow highly pure alternating layers. This extraction of harmful impurities maintains reliability while the regular superlattice pattern actually simplifies the overall device architecture compared to conventional approaches requiring separate impurity-free zones
4Speed
If advanced strained material technologies are used to enhance performance, then device speed improves, but thermal management challenges increase
Solution Approach 1:
The superlattice structure introduces localized strain fields specifically in the channel region where charge carriers flow. By confining the strained material layers to the critical transport region rather than the entire device, the patent achieves mobility enhancement with minimal impact on overall device 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
This approach leads to increased charge carrier mobility, reduced thermal noise, and improved device speed, along with enhanced thermal management, thereby addressing the limitations of existing technologies and improving overall performance in CMOS image sensors.
Implementation Method 1
a superlattice structure with energy band-modifying layers, comprising semiconductor and non-semiconductor monolayers, which reduces the effective mass of charge carriers and enhances mobility
Implementation Method 2
The resulting biaxial strain in the upper silicon layer alters the carrier mobilities enabling higher speed and/or lower power devices
Implementation Method 3
Electrons having a smaller effective mass, and which have been induced by an electric field applied to the gate electrode, are confined in the second silicon layer
Data Source
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AI summary
A CMOS image sensor may include a first semiconductor chip including an array of image sensor pixels and readout circuitry electrically connected thereto, and a second semiconductor chip coupled to the first semiconductor chip in a stack and including image processing circuitry electrically connected to the readout circuitry. The readout circuitry may include a plurality of transistors each including spaced apart source and drain regions, a superlattice channel extending between the source and drain regions, and a gate including a gate insulating layer on the superlattice channel and a gate electrode on the gate insulating layer.