SPAD Pixel Layout for Phase-Detection Focus and Natural Bokeh
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Solution Overview
Problem
Imaging devices using SPADs that divide photoelectric conversion units for focus detection with phase difference methods struggle to achieve bokeh similar to those without pupil division, due to reduced detection efficiency and altered light incidence angle properties.
Innovation Solution
The imaging device incorporates a configuration with multiple pixels, each featuring a microlens, first and second semiconductor regions of specific conductivity types, and quenching circuits, allowing for focused light incidence and efficient avalanche multiplication, enabling bokeh similar to non-divided pupil systems through precise light management and electrical field control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photoelectric conversion units are divided for focus detection using phase difference method, then focus detection capability is improved, but bokeh characteristics and photon detection efficiency deteriorate
Solution Approach 1:
The photoelectric conversion unit is divided into multiple first semiconductor regions (first region, second region, third region) with different conductivity types arranged in an alternating pattern. This segmentation enables phase difference detection while maintaining overall detection efficiency by creating multiple detection paths within a single pixel structure.
Solution Approach 2:
Different regions within the photoelectric conversion unit are assigned different conductivity types (first conductivity type and second conductivity type) to create localized functional differences. This allows each region to contribute differently to photon detection while collectively maintaining the bokeh characteristics similar to non-divided systems.
2Adaptability or versatility
If photoelectric conversion units are divided into multiple regions, then phase difference detection is enabled, but avalanche multiplication efficiency decreases
Solution Approach 1:
Multiple first semiconductor regions with the same conductivity type are electrically connected through a common second semiconductor region, merging their avalanche multiplication functions. This combining approach maintains high gain properties by ensuring all regions contribute to the same signal output while still enabling phase difference detection through their spatial separation.
Solution Approach 2:
The photoelectric conversion unit is designed to serve multiple functions simultaneously: it performs phase difference detection through divided regions while also maintaining high photon detection efficiency through avalanche multiplication. The alternating conductivity type structure enables both functions to coexist within a single integrated pixel.
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 allows for effective focus detection using phase difference methods while maintaining image quality by enhancing photon detection efficiency and maintaining bokeh characteristics, thus addressing the limitations of divided pupil systems.
Implementation Method 1
The SPAD uses an avalanche multiplication phenomenon, produced by a strong electrical field induced at a pn junction of a semiconductor, to amplify a signal charge excited by a photon
Implementation Method 2
The SPAD uses an avalanche multiplication phenomenon, produced by a strong electrical field induced at a pn junction of a semiconductor, to amplify a signal charge excited by a photon by approximately several times to several millions of times
Data Source
AI summary
An imaging device comprises pixels. The pixel includes first semiconductor regions of a first conductivity type provided in a surface part of a semiconductor substrate and a second semiconductor region of a second conductivity type provided in the surface part of the semiconductor substrate between the first semiconductor regions. The pixel includes: a light-receiving unit in which photodiodes each configured between the second semiconductor region and one of the first semiconductor regions; quenching circuits, each connected to a corresponding one of the first semiconductor regions; and a counter unit connected to each of connection nodes between the first semiconductor regions and the quenching circuits and counts a pulse generated in response to a photon being incident on the light-receiving unit. The second semiconductor region is provided across a deeper part of the semiconductor substrate than the first semiconductor regions.