Stacked Image Sensor Reflective Gate Structure for Small-Pixel Sensitivity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The reduction in pixel area of image sensors to minimize device size and enhance camera performance leads to decreased sensitivity, as smaller pixels capture less light.
Innovation Solution
The image sensor design involves stacking three structures vertically, with the third structure featuring a photoelectric conversion region, a transfer gate, and a reflective structure comprising refractive index layers that enhance light reflection and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the pixel area is reduced to minimize device size, then the device size is reduced, but the sensitivity of the image sensor decreases
Solution Approach 1:
The patent transitions from a planar pixel structure to a three-dimensional stacked structure with multiple layers (first structure, second structure, third structure) vertically arranged. This vertical stacking allows the photoelectric conversion region to extend in the depth direction, increasing the effective light capture volume without expanding the horizontal pixel area, thus maintaining small device size while improving sensitivity.
Solution Approach 2:
The patent employs a reflective structure comprising multiple layers with different refractive indices (first refractive index layer, second refractive index layer, third refractive index layer) stacked on the photoelectric conversion region. This composite layered structure enhances light reflection and trapping within the pixel, improving light capture efficiency and sensitivity without requiring larger pixel area.
2Productivity
If the pixel area is reduced to enhance camera performance, then the camera performance is improved, but the light capture ability decreases
Solution Approach 1:
The stacked three-layer structure extends the photoelectric conversion region vertically, increasing the volume available for light capture within the constrained horizontal pixel area. This dimensional transition enables enhanced light capture capability while maintaining small pixel size for high-resolution cameras.
Solution Approach 2:
The multi-layer reflective structure with varying refractive indices creates optical pathways that trap and redirect light within the photoelectric conversion region, increasing the effective light capture quantity within the limited pixel area, thereby improving camera performance.
3Reliability
If a reflective structure with multiple refractive index layers is added, then the sensitivity is improved, but the device complexity increases
Solution Approach 1:
The reflective structure is segmented into multiple distinct layers (first, second, and third refractive index layers) with different refractive indices, where each layer serves a specific optical function. This segmentation allows for optimized light reflection and trapping at different interfaces, improving sensitivity while maintaining a systematic and manufacturable structure.
Solution Approach 2:
The stacked structure integrates multiple functions: the first structure contains transfer gates and floating diffusion regions, the second structure contains photoelectric conversion regions, and the third structure provides reflective enhancement. This multi-functional integration achieves sensitivity improvement without requiring separate dedicated components, thereby limiting the increase in overall 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 design effectively increases the sensitivity of the image sensor by improving light reflection and capture, thereby mitigating the sensitivity loss associated with smaller pixel sizes.
Implementation Method 1
a reflective structure disposed on the lower surface of the third substrate and on a lower surface and side surface of the transfer gate. The reflective structure includes a first refractive index layer disposed on the lower surface of the third substrate and on the lower surface and the side surface of the transfer gate
Implementation Method 2
The reflective structure includes a first refractive index layer disposed on the lower surface of the third substrate and on the lower surface and the side surface of the transfer gate, and a second refractive index layer disposed on a lower surface of a portion of the first refractive index layer
Data Source
AI summary
An image sensor includes a first structure, a second structure, and a third structure that are sequentially stacked in a vertical direction. The first structure includes a first substrate and at least one first transistor disposed on the first substrate. The second structure includes a second substrate and at least one second transistor disposed on the second substrate. The third structure includes a third substrate that includes an upper surface on which light is incident and a lower surface that is opposite to the upper surface, a photoelectric conversion region disposed in the third substrate, a transfer gate disposed on the lower surface of the third substrate, and a reflective structure disposed on the lower surface of the third substrate and on a lower surface and side surface of the transfer gate.