Divided Pixel Separation Walls for Charge Isolation in CMOS Sensors
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Solution Overview
Problem
In solid-state image pickup devices, intense light can cause charge saturation and leakage between adjacent pixels, leading to degradation of imaging characteristics due to color mixture and overflow.
Innovation Solution
A solid-state image pickup device with a pixel separation wall system, including front-side and backside trenches, is implemented to prevent charge leakage between adjacent pixels by electrically isolating them and providing a path for overflowed charges to be discharged to a power supply electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-layer pixel separation wall is used, then the structure is simple and manufacturing is easier, but charge leakage between adjacent pixels occurs under intense light conditions
Solution Approach 1:
The pixel separation wall is divided into two separate layers: a first pixel separation wall extending from the front surface to a first depth, and a second pixel separation wall extending from the front surface to a second depth greater than the first depth. This segmentation allows each layer to perform charge isolation functions at different depths, effectively preventing charge leakage between adjacent pixels while maintaining manufacturing feasibility through sequential formation processes.
Solution Approach 2:
The invention introduces a depth dimension differentiation by creating pixel separation walls at two distinct depth levels within the substrate. The first pixel separation wall operates at a shallower depth while the second pixel separation wall extends deeper, creating a multi-level isolation architecture that enhances charge containment in the vertical dimension without complicating the horizontal manufacturing process.
2Reliability
If deeper trenches are formed to improve charge isolation, then charge leakage prevention is enhanced, but manufacturing complexity and difficulty increase
Solution Approach 1:
The complex deep isolation requirement is segmented into two manageable components: a first pixel separation wall at a moderate depth and a second pixel separation wall extending deeper. This segmentation transforms a single complex deep structure into two simpler structures that can be formed using standard manufacturing processes, reducing overall device complexity while achieving the required isolation depth.
Solution Approach 2:
The first pixel separation wall is formed in advance before the second pixel separation wall. This preliminary action allows the shallower isolation structure to be established first, providing initial charge containment, and then the deeper second pixel separation wall is added to enhance isolation. This sequential approach simplifies manufacturing by breaking down the complex deep isolation task into preparatory and enhancement stages.
3Reliability
If the pixel separation wall extends deeper into the substrate, then charge leakage is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The deep pixel separation requirement is segmented into two depth levels, with the first pixel separation wall formed to a first depth and the second pixel separation wall formed to a greater second depth. Each segmented structure can be manufactured with standard precision tolerances, avoiding the need for a single ultra-precise deep trench formation process.
Solution Approach 2:
The first pixel separation wall is formed as a preliminary structure before forming the second pixel separation wall. This preliminary formation establishes a reference structure that guides subsequent processing, allowing the second deeper wall to be aligned relative to the existing first wall, thereby reducing the cumulative precision requirements compared to forming a single deep structure in one step.
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 solution effectively prevents charge leakage and maintains imaging quality by ensuring that overflowed charges are properly managed, reducing the impact on adjacent pixels and enhancing the overall imaging characteristics.
Implementation Method 1
a photodiode (photoelectric conversion device) that performs photoelectric conversion
Data Source
AI summary
The present disclosure relates to a solid-state image pickup device and an electronic apparatus that are capable of preventing leakage of charges between adjacent pixels. A plurality of pixels perform photoelectric conversion on light incident from a back surface via different on-chip lenses for each pixel. A pixel separation wall is formed between pixels adjacent to each other, and includes a front-side trench formed from a front surface and a backside trench formed from the back surface. A wiring layer is provided on the front surface. The present disclosure is applicable to, for example, a backside illuminated CMOS image sensor.