Image Sensor Doping Profile for Uniform Transfer Characteristics
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current image sensors face challenges in achieving uniform transfer characteristics and stable optical performance due to variations in the alignment and doping concentrations of the floating diffusion (FD) isolation region and photodiode (PD) regions, which affect the channel lengths and doping concentrations of the transfer gates.
Innovation Solution
The method involves forming an image sensor with a specific doping concentration profile, where the P-type ion doping concentration of the PD isolation region is higher than the N-type ion doping concentration, and the P-type ion doping concentration of the FD isolation region is higher than the PD isolation region, with the N-type ion doping concentration of the floating diffusion being higher than the FD isolation region, to ensure uniform channel lengths and maximize photodiode volumes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the floating diffusion (FD) isolation region and photodiode (PD) regions are formed with conventional doping concentrations, then the manufacturing process is simple, but the transfer characteristics become non-uniform and optical performance becomes unstable
Solution Approach 1:
The patent applies local quality by implementing a multi-layer doping concentration profile where different regions (PD isolation region, FD isolation region, floating diffusion) have specifically optimized doping concentrations. The PD isolation region has a first doping concentration, the FD isolation region has a second doping concentration higher than the first, and the floating diffusion has a third doping concentration higher than the second, creating locally optimized electrical characteristics for uniform transfer performance.
Solution Approach 2:
The patent changes the doping concentration parameter across different regions to resolve the contradiction. By systematically varying the doping concentration from the PD isolation region to the FD isolation region to the floating diffusion, the patent achieves uniform transfer characteristics and stable optical performance while managing the complexity through a structured parameter progression.
2Manufacturing precision
If the channel lengths of transfer gates are not uniformly controlled, then the device structure is simpler to fabricate, but the transfer characteristics become non-uniform
Solution Approach 1:
The patent applies preliminary action by pre-forming the FD isolation region with a specific doping concentration before forming the transfer gates. This preliminary doping creates a well-defined reference structure that guides subsequent gate formation, ensuring uniform channel lengths are achieved more easily during the fabrication process rather than requiring complex post-processing adjustments.
Solution Approach 2:
The patent uses local quality by creating a specifically doped FD isolation region that serves as a localized reference structure. This region with its higher doping concentration provides a stable electrical and physical reference that helps define uniform channel lengths for all transfer gates, making the fabrication process more manageable while achieving precision.
3Reliability
If the photodiode volumes are not maximized, then the device structure is simpler, but the optical performance becomes unstable
Solution Approach 1:
The patent applies segmentation by dividing the isolation structure into distinct functional regions: PD isolation regions that separate individual photodiodes and an FD isolation region that isolates the floating diffusion. This segmented approach allows each region to be optimized independently for its specific function, maximizing photodiode volumes while maintaining stable optical performance through proper electrical isolation.
Solution Approach 2:
The patent uses local quality by assigning different doping concentrations to different isolation regions. The PD isolation regions have a first doping concentration optimized for photodiode separation, while the FD isolation region has a higher second doping concentration optimized for floating diffusion isolation. This localized optimization enables maximum photodiode volumes with stable optical performance.
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 approach results in uniform transfer characteristics and stable optical performance by maximizing photodiode volumes and reducing lag phenomena, ensuring consistent channel lengths across the image sensor.
Implementation Method 1
forming an N-type doped region in a substrate, forming a PD isolation region to separate the N-type doped region into a plurality of PD regions in the substrate, forming an FD isolation region to be partially overlapped with the PD isolation region and the plurality of PD regions in the substrate
Data Source
AI summary
Disclosed is an image sensor, which includes a first PD isolation region for determining first to fourth PD regions, an FD isolation region formed between the first to fourth PD regions, and a floating diffusion formed in the FD isolation region. Horizontal distances from a perimeter of the floating diffusion to interfaces between the FD isolation region and the first to fourth PD regions are equal to each other.