Solid State Image Sensor Gate Electrode Depth Configuration
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Solution Overview
Problem
CMOS solid state image sensors face challenges with misalignment during manufacturing, leading to reduced photoelectric conversion efficiency and increased noise due to the proximity of the photo diode and gate electrode, which affects the transfer of electric charges.
Innovation Solution
A solid state image sensor design where the gate electrode of the transfer transistor is formed in a depth direction toward the photoelectric conversion unit, surrounding the channel portion in multiple directions, and a discharge transistor is used in parallel with the transfer transistor, with adjacent gate electrodes, to improve charge transfer and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the gate electrode is formed close to the photo diode to improve charge transfer efficiency, then photoelectric conversion efficiency is improved, but misalignment during manufacturing increases noise and reduces reliability
Solution Approach 1:
The gate electrode is extended in the depth direction (vertical dimension) to surround the channel portion from multiple directions. This three-dimensional configuration increases the electric field interaction area between the gate electrode and channel, improving charge transfer efficiency without requiring lateral proximity that would be sensitive to misalignment.
Solution Approach 2:
The gate electrode is positioned to surround the channel portion in a nested configuration, with the gate electrode wrapping around the channel region. This nested arrangement maximizes the electric field interaction while maintaining spatial separation, thereby improving charge transfer without increasing sensitivity to lateral misalignment.
2Object-affected harmful factors
If the photo diode area is reduced to accommodate shaded regions for noise prevention, then noise is reduced, but light reception capability decreases
Solution Approach 1:
The shading function is achieved by extending the gate electrode vertically to surround the channel portion, creating a three-dimensional shading structure. This vertical extension blocks light from reaching the channel region without requiring lateral shading structures that would reduce the photo diode area.
Solution Approach 2:
The gate electrode performs dual functions: it controls the channel for charge transfer and simultaneously acts as a shading structure to prevent light from reaching the channel region. This multi-functionality eliminates the need for separate lateral shading structures, preserving photo diode area while preventing noise.
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 enhances the robustness against misalignment and increases the photoelectric conversion efficiency by efficiently transferring electric charges and reducing noise, resulting in a more reliable and high-performance image sensor.
Implementation Method 1
a photoelectric conversion unit formed and embedded in a semiconductor substrate
Data Source
AI summary
There is provided a solid state image sensor including a photoelectric conversion unit formed and embedded in a semiconductor substrate, an impurity region that retains an electric charge generated by the photoelectric conversion unit, and a transfer transistor that transfers the electric charge to the impurity region. A gate electrode of the transfer transistor is formed in a depth direction toward the photoelectric conversion unit in the semiconductor substrate, from a surface of the semiconductor substrate on which the impurity region is formed. A channel portion of the transfer transistor is surrounded by the gate electrode in two or more directions other than a direction of the impurity region, as seen from the depth direction.