PDAF Pixel Electrical Shielding Replacement for Stable Autofocus
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Solution Overview
Problem
Manufacturing of differential shielding structures for phase detection auto focus (PDAF) in image sensors is prone to process variations, leading to defects and inconsistencies between center and edge pixels, necessitating improved autofocusing methods that minimize these issues.
Innovation Solution
The implementation of image sensors with photodiodes electrically connected to a known potential to emulate fully optically shielded pixels, using techniques such as connecting photodiodes to the pixel voltage supply or omitting doping steps, to generate digital outputs equivalent to fully shielded pixels, thereby enhancing autofocusing without relying on differential optical shielding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If differential shielding structures are used for phase detection auto focus, then autofocusing capability is improved, but manufacturing precision deteriorates due to process variations
Solution Approach 1:
The patent replaces the mechanical/optical shielding structure with an electrical field-based solution. Instead of using physical light-blocking structures to create phase detection signals, the invention uses electric fields generated by charged particles (electrons or ions) to modulate the optical path and create the necessary phase differences for autofocus. This substitution eliminates the manufacturing complexity and process variation issues associated with precise shielding structure fabrication.
Solution Approach 2:
The patent changes the fundamental parameter used for phase detection from optical path blocking (mechanical/shielding approach) to electrical field modulation. By controlling the charge state and position of particles within the photodiode, the system dynamically adjusts the refractive index or optical path length, achieving phase detection through electrical parameter control rather than fixed mechanical shielding structures.
2Reliability
If differential shielding structures are implemented, then phase detection is enabled, but device complexity increases
Solution Approach 1:
The patent replaces complex mechanical/optical shielding structures with a simpler electrical field modulation mechanism. The shielding structures that would normally require precise alignment and fabrication are replaced by controlling the electrical charge state of particles within the photodiode, which can be achieved through standard semiconductor doping and control circuitry already present in modern image sensors.
Solution Approach 2:
The patent makes the photodiode itself multi-functional by enabling it to perform both image sensing and phase detection for autofocus using the same pixel elements. By controlling the charge state of particles within the photodiode, the same pixel can switch between capturing image data and generating autofocus signals, eliminating the need for separate shielding structures or dedicated autofocus pixels.
3Reliability
If optical shielding structures are used, then light differential for focus detection is achieved, but ease of manufacture deteriorates
Solution Approach 1:
The patent replaces the fabrication of precise optical shielding structures with electrical control mechanisms. Instead of requiring additional lithography steps, etching processes, and alignment procedures to create shielding patterns, the invention uses electrical fields generated by charged particles to achieve the same optical modulation, leveraging existing semiconductor manufacturing capabilities.
Solution Approach 2:
The patent enables the photodiode to self-generate the phase detection signals through internal charge modulation. The charged particles within the photodiode naturally create electric fields that modulate the optical path, eliminating the need for external shielding structures. The system uses its own internal electrical characteristics to achieve the focus detection function.
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 improves autofocusing accuracy by reducing manufacturing variability and defects, allowing for more reliable and consistent image sensor performance across different pixel locations.
Implementation Method 1
a photodiode (PD) 210, which may include a P-type or N-type photodiode
Data Source
AI summary
Electrical Phase Detection Auto Focus. In one embodiment, an image sensor includes a plurality of pixels arranged in rows and columns of a pixel array disposed in a semiconductor material. Each pixel includes a plurality of photodiodes configured to receive incoming light through an illuminated surface of the semiconductor material. The plurality of pixels includes at least one autofocusing phase detection (PDAF) pixel having: a first subpixel without a light shielding, and a second subpixel without the light shielding. Autofocusing of the image sensor is at least in part determined based on different electrical outputs of the first subpixel and the second sub pixels.