PDAF Pixel Microlens Array Layout for Large-Pixel Focus Accuracy
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Solution Overview
Problem
Phase detection autofocus (PDAF) pixels in CMOS image sensors face limitations due to the limited focusing capabilities of microlenses, particularly for large pixels, leading to reduced contrast and accuracy in autofocusing.
Innovation Solution
The use of multiple smaller microlenses with associated light shields, offset from the optical axis, organized in a regular array pattern, to improve light focusing and selectivity, enhancing the phase detection autofocus functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single microlens is used in each PDAF pixel, then the device complexity is reduced, but the focusing capability and measurement precision deteriorate
Solution Approach 1:
The patent divides a single microlens into multiple smaller microlenses (e.g., four microlenses arranged in a 2x2 array) within each PDAF pixel. This segmentation allows each microlens to be optimized for specific light beam directions, improving the ability to distinguish between different focus states while maintaining manageable device complexity through systematic arrangement.
Solution Approach 2:
Each microlens in the array is positioned and sized to optimize detection of light beams from specific directions. The microlenses have different local optical properties and orientations, allowing tailored optimization for detecting light beams at different angles, thereby improving overall focusing accuracy without requiring complete redesign of the entire pixel structure.
2Area of stationary object
If microlenses are made larger to cover large pixels, then the area of detection is improved, but the manufacturing precision and focusing capability worsen
Solution Approach 1:
Instead of forming one large microlens that is difficult to manufacture with precision, the patent segments the large pixel area into multiple smaller microlenses. Each small microlens can be manufactured with high precision using standard processes, while collectively they cover the entire large pixel area, maintaining both manufacturing feasibility and detection coverage.
Solution Approach 2:
The patent introduces adjustable light shields that can dynamically block or transmit light to different microlenses based on the desired measurement direction. This dynamic control allows the system to adapt its effective detection area and optimize performance for different focusing scenarios, compensating for the distributed nature of multiple microlenses.
3Measurement precision
If light shields are used to block unwanted light, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
Light shields are positioned locally adjacent to specific microlenses rather than implementing a complex global blocking structure. Each light shield is tailored to block light for its associated microlens in a specific direction, providing simple local optimization that collectively improves overall measurement precision without requiring complex system-level coordination.
Solution Approach 2:
The light shields act as intermediary elements between the microlenses and the photodiode, selectively controlling which light beams reach which microlenses. This intermediary structure simplifies the optical path management by providing clear separation of light beam paths, improving image contrast while maintaining relatively simple device architecture.
4Reliability
If multiple microlenses are used per pixel, then the focusing capability and sensitivity are improved, but the device complexity increases
Solution Approach 1:
The pixel structure is segmented into multiple functional units (microlenses with associated light shields) that can be systematically arranged in regular patterns. This segmentation improves autofocus reliability by providing redundant detection paths and better directional discrimination, while the regular arrangement keeps the increased complexity manageable through predictable structural repetition.
Solution Approach 2:
Each microlens unit serves multiple functions: it detects light from specific directions, contributes to phase difference measurement, and works with its light shield to reject unwanted light. This multi-functionality of each segmented unit improves overall autofocus reliability without requiring proportionally more complex individual components, as each unit is a self-contained functional module.
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 achieves better sensitivity and angular response, resulting in improved focusing accuracy and contrast between images detected by PDAF pixels, even for large pixels, where traditional manufacturing techniques struggle to form well-formed microlenses.
Implementation Method 1
a plurality of microlenses for concentrating light, incident on each of the microlenses, onto the photodiode
Implementation Method 2
for each microlens, a light shield associated therewith, for blocking part of the light transmitted by the microlens towards the photodiode
Implementation Method 3
a photodiode, and a plurality of microlenses for concentrating light, incident on each of the microlenses, onto the photodiode
Data Source
Figure 1A~1B
Figure 2~3
Figure 4A~4B
AI summary
A phase detection autofocus pixel (1) comprising, a photodiode (2), a plurality of microlenses (3) for concentrating light, incident on each of the microlenses (3), onto the photodiode (2), and for each microlens (3), a light shield (4) associated therewith, for blocking part of the light transmitted by the microlens (3) towards the photodiode (2), wherein the light shields (4) are offset from an optical axis (31) of their associated microlenses (3) in a same offset direction (X).