Deep Trench Transfer Gates for Image Sensor Light Reception
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Solution Overview
Problem
Current image sensors face challenges in achieving high integration and performance, particularly in applications requiring advanced auto-focusing technologies, such as digital cameras and medical micro cameras, due to limitations in light reception area and dark current reduction.
Innovation Solution
The design incorporates transfer gates in deep trenches with a conformally formed insulating layer and gate electrode, along with shallow trench isolation regions and floating diffusion regions, allowing for vertical overlap and improved channel width, which enhances light sensing capability and reduces dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If transfer gates are formed in deep trenches with vertical channels, then the light reception area is increased and dark current is reduced, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent transitions from conventional planar transfer gate structures to vertical transfer gates extending deep into trenches (e.g., 500nm to 2μm depth). This vertical dimensionality change allows the transfer gate to control charge carriers in a three-dimensional space, enabling larger photodiode areas without proportionally increasing the transfer gate footprint, thus resolving the contradiction between light reception area and device complexity
Solution Approach 2:
The transfer gate structure is nested within deep trenches that are formed within the substrate. The trench isolation structures and transfer gate electrodes are nested concentrically, with the transfer gate electrode surrounded by insulating layers and enclosed within the trench walls. This nesting approach allows compact integration of complex structures while maintaining large photodiode areas for light reception
2Productivity
If transfer gates are formed in deep trenches, then the channel width is improved and driving capability is enhanced, but the manufacturing precision requirements increase
Solution Approach 1:
The patent applies different materials and structures to different regions of the transfer gate. The trench is filled with conductive material for the gate electrode, while the walls are lined with insulating materials. The bottom of the trench may have different properties than the walls. This local differentiation allows optimization of each region's function while maintaining manufacturability through standardized processing steps
Solution Approach 2:
The deep trenches are formed and lined with insulating materials before the transfer gate electrodes are deposited. This preliminary preparation ensures that when the electrodes are later formed, they automatically achieve the correct positioning and dimensions. The trench depth and insulation layer thickness are predetermined, so subsequent electrode formation becomes a simpler, more precise operation rather than requiring complex real-time adjustments
3Area of stationary object
If shallow trench isolation regions with elbow shapes are used, then the integration density is improved, but the manufacturing complexity increases
Solution Approach 1:
The patent employs elbow-shaped (curved) STI regions instead of sharp rectangular corners. These curved transitions allow photodiodes to be positioned closer together while maintaining adequate isolation, thereby increasing integration density. The curved geometry also reduces stress concentrations and facilitates more uniform material deposition during manufacturing, partially offsetting the increased pattern 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 configuration increases the light reception area, improves the driving capability of transfer gates, and reduces dark current, resulting in enhanced image sensor performance and efficiency.
Implementation Method 1
An image sensor is a device that converts an optical image into electrical signals
Data Source
AI summary
An image sensor is described. The image sensor includes a photodiode that is formed in a substrate, a floating diffusion region that vertically overlaps with a first portion of the photodiode, a shallow trench isolation (STI) region that vertically overlaps with a second portion of the photodiode and has an elbow shape, and a transfer gate that is adjacent to at least two sides of the photodiode and has an elbow shape.