3D Separation Pixel for Image Sensor Light Angle Margin
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional image sensors with multiple transistors suffer from reduced photodiode fill factor and sensitivity due to smaller pixel sizes, leading to light loss and image quality deterioration, especially when handling varying incident angles required for zoom and focus functions.
Innovation Solution
A separation type unit pixel with a 3D structure is developed, featuring a photodiode and transfer transistor connected in a separated portion, using a first wafer with a photodiode and floating diffusion area and a second wafer with peripheral circuits, allowing for improved light transmission and incident angle tolerance without relying on micro lenses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel size is decreased to increase resolution, then the number of pixels increases, but the photodiode fill factor and sensitivity decrease
Solution Approach 1:
The pixel structure is divided into distinct functional regions: a photodiode region for light detection and a transistor region for signal processing. This segmentation allows the photodiode to occupy maximum area for sensitivity while transistors are confined to specific zones, preventing them from encroaching on the light-sensitive area even as pixel size decreases.
Solution Approach 2:
The patent employs a planar layout optimization where the photodiode is positioned to extend across available space in a two-dimensional arrangement, maximizing the fill factor. The separation of the photodiode and transistor regions in the planar domain allows efficient space utilization without requiring vertical stacking, thus maintaining high sensitivity in small pixels.
2Reliability
If photodiode area is increased to improve sensitivity, then sensitivity increases, but pixel size must increase
Solution Approach 1:
The patent applies local quality by creating a photodiode region with optimized properties specifically for light detection, separated from the transistor region. The photodiode area is maximized locally within the pixel structure, allowing high sensitivity in that specific zone while the overall pixel size remains small due to efficient packing and separation from other components.
3Use of energy by moving object
If micro lens is used to condense light onto photodiode, then light condensation improves, but diffraction phenomenon increases when pixel size decreases
Solution Approach 1:
The patent extracts the light condensation function from the micro lens and transfers it to a lens array structure positioned at a different height above the photodiode. This separation allows the micro lens to be removed or minimized, eliminating the diffraction problem while maintaining effective light guidance through the lens array's collective focusing capability.
4Area of stationary object
If pixel size is decreased to reduce sensor size, then sensor miniaturization achieves, but dynamic range and image quality deteriorate
Solution Approach 1:
By segmenting the pixel into a large photodiode region and a compact transistor region, the patent maximizes the charge storage capacity of the photodiode even in small pixels. This segmentation ensures that the photodiode area is not compromised by transistor components, maintaining adequate dynamic range and image quality despite overall pixel miniaturization.
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 enhances sensitivity and maintains image quality by maximizing photodiode area and accommodating varying light angles, enabling mini camera modules with zoom and focus functions.
Implementation Method 1
a photodiode which contains impurities that are opposite type of a semiconductor material
Data Source
Figure 1~4
Figure 5~8
Figure 9~10
AI summary
A separation type unit pixel of an image sensor, which can handle light that incidents onto a photodiode at various angles, and provides a zoom function in a mini camera module by securing an incident angle margin, and a manufacturing method thereof are provided. The separation type unit pixel having a 3D structure for an image sensor, composed of a plurality of transistors, includes: a first wafer which includes a photodiode, a transfer transistor, a node of a floating diffusion area functioning as static electricity for converting electric charge into a voltage, and a pad connecting the floating diffusion area and the transfer transistor to an external circuit, respectively; a second wafer which includes the rest of the circuit elements constituting a pixel (i.e., a reset transistor, a source-follower transistor, and a blocking switch transistor), a read-out circuit, a vertical/horizontal decoder, a correlated double sampling (CDS) circuit which involves in a sensor operation and an image quality, an analog circuit, an analog-digital converter (ADC), a digital circuit, and a pad connecting each pixel; and a connecting means which connects the pad of the first wafer and the pad of the second wafer. Accordingly, by forming an area for a photodiode and an area for a pixel almost the same, an image sensor can be manufactured to have a good sensitivity, without having to use a micro lens. In addition, by disposing the photodiode at the top layer, an incident angle margin of incident light can be secured, which has to be basically provided by the sensor for its auto focusing function or zoom function.