Pixel Isolation Biasing for Low-Dark-Current Imaging Elements
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Solution Overview
Problem
In imaging elements used for autofocus and phase difference detection, the photoelectric conversion units within pixels cannot be effectively isolated from each other, leading to issues with dark current generation and image signal error due to interface states at the semiconductor substrate.
Innovation Solution
The imaging element incorporates a pixel with multiple photoelectric conversion units, an overflow path, a pixel isolation unit, an in-pixel isolation unit, and specific bias voltage applied electrodes to isolate and manage charge transfer, reducing dark current and improving image signal accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an isolation region is formed on the semiconductor substrate to suppress charge transfer between pixels, then dark current is reduced, but photoelectric conversion units within a pixel cannot be isolated from each other
Solution Approach 1:
The patent divides the isolation structure into two segments: a first isolation region formed on the semiconductor substrate between pixels, and a second isolation region formed on the isolation region between photoelectric conversion units within a pixel. This segmentation allows each isolation region to perform its specific isolation function effectively, solving the contradiction by providing both pixel-level and unit-level isolation.
Solution Approach 2:
The patent introduces a light-blocking layer as an intermediary structure between the first isolation region and the second isolation region. This light-blocking layer prevents incident light from reaching the second isolation region, ensuring that the second isolation region can effectively suppress charge transfer between photoelectric conversion units without being affected by light, thus maintaining isolation effectiveness.
2Object-affected harmful factors
If a conductive member with negative bias voltage is applied to the isolation region to accumulate holes and prevent charge transfer, then dark current is reduced, but photoelectric conversion units within the pixel still cannot be isolated
Solution Approach 1:
The patent segments the isolation structure into multiple functional regions: the first isolation region with negative bias voltage for pixel-level isolation and dark current suppression, and the second isolation region for unit-level isolation within pixels. This segmentation allows each region to address specific isolation needs simultaneously.
Solution Approach 2:
The patent applies different properties to different parts of the isolation structure: the first isolation region is made conductive with negative bias voltage applied to suppress dark current at the pixel level, while the second isolation region is configured to isolate photoelectric conversion units within a pixel. Each region has optimized local properties suited to its specific isolation 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
Effective isolation of photoelectric conversion units within the pixel reduces dark current and enhances image signal quality by managing charge transfer and accumulation, thereby improving the accuracy and linearity of image signals.
Implementation Method 1
a pixel that includes a plurality of photoelectric conversion units that is formed in a semiconductor substrate and performs photoelectric conversion of incident light from a subject to generate charges
Implementation Method 2
By applying the negative bias voltage, holes are accumulated in the vicinity of the interface of the semiconductor substrate in contact with the isolation region. The accumulated holes prevent the charge transfer from the interface state, and the dark current can be reduced.
Data Source
AI summary
An imaging element according to the present disclosure includes a pixel, an overflow path, a pixel isolation unit, a pixel isolation electrode, an in-pixel isolation unit, and an in-pixel isolation electrode. The pixel includes a plurality of photoelectric conversion units formed in a semiconductor substrate having an interconnect region arranged on a front surface side and performs photoelectric conversion of incident light. The overflow path mutually transfers charges between the plurality of photoelectric conversion units. The pixel isolation unit is at a boundary of the pixel. The pixel isolation electrode is in the pixel isolation unit, and a first bias voltage is applied to the pixel isolation electrode. The in-pixel isolation unit isolates the plurality of photoelectric conversion units from each other. The in-pixel isolation electrode is arranged in the in-pixel isolation unit, and a second bias voltage is applied to the in-pixel isolation electrode.