CMOS Image Sensor FD Switching With Shared Microlens Layout
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Solution Overview
Problem
Existing solid-state image sensors face challenges in optimizing microlens curvature for both normal and ZAF pixels, leading to increased costs and compromised sensitivity or phase difference detection characteristics, as well as inability to switch FD conversion efficiency in all pixels due to differing parasitic capacitances.
Innovation Solution
A front-surface illuminated solid-state image sensor with a metallic light blocking film forming an additional capacitor, allowing switching of FD conversion efficiency by connecting or disconnecting charge-to-voltage converter and charge storage, and using a common layout for both normal and ZAF pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If microlenses with different curvatures are produced for normal pixels and ZAF pixels to optimize both sensitivity and phase difference detection characteristics, then the sensitivity and phase difference detection characteristics are improved, but the number of processes increases and manufacturing cost increases
Solution Approach 1:
The patent applies universality by using identical microlenses for both normal pixels and ZAF pixels. The microlens common to both pixel types focuses light onto different targets: for normal pixels, light is focused onto the photodiode surface to maximize sensitivity, while for ZAF pixels, light is focused onto the light blocking film surface to enable phase difference detection. This universal microlens design eliminates the need for different curvature microlenses, reducing manufacturing complexity while maintaining optimal performance for both pixel types.
2Manufacturing precision
If the light blocking wiring layer for ZAF is positioned away from the photodiode surface to enable phase difference detection, then the phase difference detection characteristic is improved, but the optimum curvature of the microlens differs between normal and ZAF pixels requiring different microlenses
Solution Approach 1:
The patent applies local quality by having the single microlens perform different focusing functions for different pixel types. The microlens is positioned and designed to focus light onto the photodiode surface for normal pixels (local quality A) while simultaneously focusing light onto the light blocking film surface for ZAF pixels (local quality B). This allows the light blocking wiring layer to be positioned away from the photodiode surface for ZAF pixels, enabling phase difference detection without requiring different microlens curvatures.
3Ease of manufacture
If priority is given to reducing the number of processes and using identical microlenses for all pixels, then the manufacturing cost is reduced, but at least either the sensitivity characteristic of normal pixels or the phase difference detection characteristic of ZAF pixels will be sacrificed
Solution Approach 1:
The patent applies dynamics by making the microlens positioning and light focusing path adaptable to different pixel types. The microlens is designed with specific optical characteristics that allow it to dynamically adjust its effective focal point based on the pixel type. For normal pixels, the optical path is configured to focus on the photodiode surface, while for ZAF pixels, the light blocking film structure causes the light to focus on its surface instead. This dynamic adaptability allows a single microlens design to optimize both sensitivity and phase difference detection characteristics without sacrificing either.
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
Enables uniform FD conversion efficiency switching in all pixels, reducing process complexity and cost by using identical microlenses and maintaining sensitivity and phase difference detection characteristics without sacrificing either.
Implementation Method 1
an additional capacitor configured to add a capacity to the charge storage
Implementation Method 2
a photoelectric converter configured to perform photoelectric conversion of incident light
Data Source
AI summary
The present technology relates to a solid-state image sensor, an imaging device, and an electronic device capable of switching FD conversion efficiency in all pixels of a solid-state image sensor. A photodiode performs photoelectric conversion on incident light. A floating diffusion (FD) stores charge obtained by the photodiode. FD2, which is a second FD to which the capacity of an additional capacitor MIM is added, adds the capacity to the FD. The additional capacitor MIM is constituted by a first electrode formed by a wiring and a second electrode formed by a metallic light blocking film provided on a surface of a substrate on which the photodiode is formed. Switching between the FD and FD+FD2 allows switching of the FD conversion efficiency. The present technology is applicable to a CMOS image sensor.