Nested Microlens Pedestal for Image Sensor Sensitivity
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Solution Overview
Problem
In image sensors with CMOS technology, the decrease in pixel size to accommodate more pixels on a substrate leads to a reduction in photosensitive area, causing light to be misdirected and resulting in decreased sensitivity, as the photosensitive area is often offset from the microlens's optical axis, and adjusting microlenses to align with varying photosensitive positions is impractical.
Innovation Solution
The implementation of a second microlens partially or completely covering a pedestal on adjacent pixels, which extends over the first microlens, allowing for more efficient light redirection to the photosensitive area, maintaining sensitivity while accommodating offset photosensitive areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel size is decreased to accommodate more pixels on substrate, then pixel density increases, but photosensitive area decreases causing sensitivity loss
Solution Approach 1:
The patent implements nested microlenses where a second microlens is positioned on a pedestal that extends over the first microlens. This nested configuration allows multiple focusing functions within a compact vertical space, enabling efficient light redirection to offset photosensitive areas without increasing pixel footprint, thus maintaining high pixel density while improving sensitivity
Solution Approach 2:
The patent introduces a vertical dimension by placing the second microlens on a pedestal that extends over the first microlens in the vertical direction. This three-dimensional microlens arrangement allows light focusing in multiple planes, effectively addressing offset photosensitive areas without consuming additional horizontal pixel area, thereby resolving the contradiction between pixel density and sensitivity
2Device complexity
If photosensitive area is offset from microlens optical axis to accommodate addressing devices, then device integration improves, but light redirection efficiency decreases
Solution Approach 1:
The patent employs a dynamic microlens configuration where the second microlens on the extending pedestal can adaptively focus light to the offset photosensitive area. This dynamic arrangement allows the optical system to compensate for the offset position, maintaining efficient light redirection while accommodating addressing devices in the pixel center region
Solution Approach 2:
The second microlens on the extending pedestal acts as an intermediary optical element that bridges the gap between the first microlens and the offset photosensitive area. It receives light from the first microlens and redirects it to the photosensitive area, maintaining focusing efficiency despite the offset configuration
3Productivity
If microlens dimensions are decreased to match smaller pixels, then pixel density increases, but light collection area decreases
Solution Approach 1:
The patent compensates for reduced microlens area by utilizing the vertical dimension through the pedestal structure. The second microlens on the extending pedestal creates an additional light collection path, effectively increasing the functional light collection area without increasing horizontal footprint, thus maintaining high pixel density while preserving light collection capability
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 enhances light redirection to the photosensitive area, minimizing sensitivity loss and ensuring consistent light reception across pixels, even when photosensitive areas are offset, thereby improving image sensor performance.
Implementation Method 1
a microlens 21, of optical axis Δ, is arranged on equalization layer 18, opposite to photosensitive area PH to focus the light rays towards photosensitive area PH
Implementation Method 2
Substrate 7 is covered with a stack of transparent insulating layers 9, 11, 12, 13
Data Source
AI summary
An image sensor having a surface intended to be illuminated and pixels, each pixel including a photosensitive area formed in an active area of the substrate, at least one first pixel including a first microlens located on the surface, the sensor including at least one second pixel including a transparent portion forming a pedestal located at least partly on the surface and a second microlens at least partially covering the pedestal.