Image Sensor Transfer Transistor Vertical Channel Integration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge is to enhance the integration density of image sensors while maintaining the quality of unit pixels, as reducing the physical size of unit pixels leads to decreased photon incidence and degraded characteristics due to increased integration density.
Innovation Solution
The image sensor design incorporates a transfer transistor with a vertical channel and multiple transfer gates, along with a photoelectric conversion element, where the channel layer is formed between the first and second transfer gates, and the floating diffusion layer has a smaller area than the first transfer gate, allowing for efficient photon collection and reduced dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the physical size of unit pixels is reduced to increase integration density, then the number of pixels per unit area increases, but the photon incidence decreases and image sensor characteristics degrade
Solution Approach 1:
The transfer transistor is configured with a vertical channel extending in the depth direction rather than a horizontal channel in the planar direction. This vertical configuration allows the transistor to occupy less lateral space while maintaining effective channel length, enabling higher integration density without compromising pixel characteristics. The vertical channel structure transforms the problem from a 2D plane constraint to a 3D spatial solution.
Solution Approach 2:
The transfer gate is formed with a hole penetrating through it, and the vertical channel is positioned within this hole structure. The channel layer extends vertically through the transfer gate thickness, effectively nesting the channel within the gate structure. This nested configuration reduces the overall device footprint while maintaining functional integrity, allowing more pixels to be packed into the same area without degrading performance.
2Productivity
If the physical size of unit pixels is reduced, then integration density increases, but the fill factor and quantum efficiency decrease
Solution Approach 1:
By transitioning from a planar horizontal channel to a vertical channel extending in the depth direction, the invention maximizes the use of the third dimension (z-axis) for transistor conduction path. This allows the photoelectric conversion element to maintain a larger lateral area for photon collection, improving fill factor and quantum efficiency while the vertical channel provides the necessary transistor function in a compact footprint.
Solution Approach 2:
The transfer gate is designed with a hole structure that is selectively formed, creating different functional zones: the regions around the hole maintain gate control function while the hole region allows vertical channel formation. This local differentiation optimizes both the gate's control capability and the channel's conduction path, enabling efficient charge transfer without sacrificing photon collection area.
3Productivity
If the physical size of unit pixels is reduced, then integration density increases, but dark current increases
Solution Approach 1:
The vertical channel configuration reduces the lateral diffusion path length for minority carriers, confining them more effectively to the photoelectric conversion element. By extending the channel in the vertical direction rather than laterally, the structure minimizes the surface area exposed to thermal generation sites, thereby reducing dark current while enabling higher integration density.
Solution Approach 2:
The channel layer is nested within the hole of the transfer gate, creating a confined vertical conduction path. This nested structure effectively shields the channel from lateral thermal generation and reduces the exposure to surfaces where dark current typically originates, thereby suppressing dark current generation while maintaining compact pixel dimensions for high integration density.
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 enables higher integration density without degrading the image sensor's characteristics, improving quantum efficiency and fill factor, while preventing dark current occurrence through controlled bias application.
Implementation Method 1
a photoelectric conversion element provided in a semiconductor substrate and suitable for generating a photo charge in response to incident light
Data Source
AI summary
An image sensor may include: a photoelectric conversion element suitable for generating a photo charge in response to incident light; and a transfer transistor suitable for transferring the photo charge generated by the photoelectric conversion element to a floating diffusion in response to a transfer signal, the transfer transistor comprising a first transfer gate formed over the photoelectric conversion element; an opening formed in the first transfer gate and exposing the photoelectric conversion element; a second transfer gate formed in the opening; and a channel layer interposed between the first and second transfer gates and between the photoelectric conversion element and the second transfer gate.