Image Sensor Gate Feature Substrate Extension Fill Factor
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Solution Overview
Problem
Conventional image sensor devices have a reduced fill factor due to laterally extending pixel transistors, which limits the area available for photodiodes, thereby decreasing quantum efficiency and overall performance.
Innovation Solution
The image sensor device incorporates pixel transistors with gate features that partially extend into the semiconductor substrate, reducing the lateral distance and allowing more photodiodes to be disposed over a given chip area, thereby increasing the fill factor and improving quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If pixel transistors are formed with laterally extending gate features along the major surface, then the device complexity is reduced and fabrication is simplified, but the fill factor is significantly reduced and quantum efficiency deteriorates
Solution Approach 1:
The gate feature is configured to extend partially into the substrate vertically rather than only laterally along the major surface. This dimensional change from purely lateral to partially vertical extension allows the gate to control the photodiode region without occupying excessive lateral area, thereby maintaining high fill factor while enabling transistor formation.
Solution Approach 2:
The gate feature is nested within the pixel structure by extending into the substrate and surrounding a portion of the photodiode region. This nesting arrangement allows the transistor gate to be integrated within the pixel area rather than occupying separate lateral space, increasing the fill factor while maintaining device functionality.
2Device complexity
If pixel transistors are formed with laterally extending gate features, then the device structure is simplified, but the chip area available for photodiodes is reduced
Solution Approach 1:
The gate feature extends vertically into the substrate rather than only laterally, utilizing the vertical dimension to achieve transistor control function. This reduces the lateral footprint of the transistor, thereby increasing the chip area available for photodiodes while maintaining simplified device structure.
3Ease of manufacture
If the gate feature extends laterally along the major surface, then the transistor can be formed with standard planar processing, but the quantum efficiency is reduced
Solution Approach 1:
The gate feature extends partially into the substrate vertically, changing from standard planar configuration to a three-dimensional structure. This vertical extension allows the gate to effectively control the photodiode region without requiring large lateral dimensions, thereby maintaining quantum efficiency while still being manufacturable with adapted processing techniques.
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 design significantly enhances the performance of the image sensor device by increasing the fill factor and quantum efficiency while maintaining the same chip area, improving the detection and conversion of incident light into electrical signals.
Implementation Method 1
Each pixel includes at least one photosensitive diode (hereinafter 'photodiode') configured to detect the incident light and convert the detected incident light into an electrical signal (e.g., a photocurrent/current signal)
Data Source
AI summary
A semiconductor device includes: a photodiode formed in a substrate; and at least one transistor having a gate feature that comprises a first portion and a second portion coupled to an end of the first portion, the first portion disposed above and extending along a major surface of the substrate and the second portion extending from the major surface of the substrate into the substrate, wherein the photodiode and the at least one transistor at least partially form a pixel.