Vertical Transfer Gate Image Sensor Noise Reduction
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Solution Overview
Problem
Image sensors with vertical transfer gates face challenges in maintaining signal-to-noise ratio (SNR) due to complex doping processes and reduced floating diffusion region area, which degrades performance and increases fabrication costs.
Innovation Solution
The design includes a photoelectric conversion element with active pillars fully depleted in equilibrium, surrounded by a transfer gate with a charge blocking layer, and parallel transfer transistors to improve gate controllability and SNR, along with a source follower transistor coupled to one group of active pillars for enhanced sensitivity and noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a vertical transfer gate is used to improve gate controllability, then the gate controllability is improved, but the floating diffusion region area is reduced
Solution Approach 1:
The transfer gate is configured in a vertical orientation rather than horizontal, extending along the vertical direction to surround the active pillar. This dimensional change allows the gate to effectively control charge transfer while preserving sufficient area for the floating diffusion region, as the gate structure utilizes the vertical space above the photoelectric conversion element rather than consuming lateral area.
2Object-generated harmful factors
If the channel region is fully depleted to reduce noise, then the noise is reduced, but the manufacturing complexity increases
Solution Approach 1:
The channel region is configured to be fully depleted through specific doping concentration control, creating a localized high-quality region with optimized electrical properties. This local quality enhancement ensures complete depletion of the channel to prevent noise while managing the doping complexity through focused material property optimization in the channel region.
Solution Approach 2:
The doping concentration in the channel region is precisely controlled and optimized to achieve full depletion state. By adjusting the doping concentration parameter, the channel region can be fully depleted to reduce noise while managing the manufacturing complexity through parameter optimization rather than process complexity.
3Productivity
If the transfer gate surrounds all active pillars to improve transfer efficiency, then the transfer efficiency is improved, but the device complexity increases
Solution Approach 1:
The vertical transfer gate structure serves multiple functions simultaneously: it surrounds and controls multiple active pillars, enables efficient charge transfer, and maintains a relatively simple overall structure. This universal design allows a single gate configuration to perform the function of controlling multiple pillars without proportionally increasing 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 configuration enhances the SNR and sensitivity of image sensors by preventing leakage current and optimizing the doping state of channel regions, thereby improving overall performance and reducing fabrication complexities.
Implementation Method 1
An image sensor is a device that converts air optical image into an electrical signal
Data Source
AI summary
An image sensor may include: a photoelectric conversion element; a transfer gate formed over the photoelectric conversion element; a plurality of active pillars electrically coupled to the photoelectric conversion element by penetrating the transfer gate; a reset transistor coupled to the plurality of active pillars; and a source follower transistor having a gate electrically coupled to one or more active pillars among the plurality of active pillars.