Via Wave Guide Curved Light Concentrator CMOS Image Sensor
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Solution Overview
Problem
Conventional CMOS image sensors (CISs) suffer from reduced light capture and image quality due to the obstruction of metal address and signal lines, which limits the amount of light reaching the photodiodes, and introduces blurring and color inaccuracies from light reflection and refraction through semi-opaque insulation material.
Innovation Solution
The introduction of via wave guides with a curved light concentrator and a high refractive index light-guiding material, which redirects light beams from the metal lines to the photodiodes, minimizing light loss and reducing cross-talk between pixels, and optionally incorporating a mirror coating and color filter within the via wave guide to enhance light concentration and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal address and signal lines are used to connect control circuits to pixels, then electrical connectivity is achieved, but light transmission is blocked and image quality deteriorates
Solution Approach 1:
The pixel array is divided into light-receiving regions and non-light-receiving regions (containing metal lines and insulating films). The via waveguide structure segments the light path, allowing light to pass through dedicated channels (via holes) while metal lines remain in non-light-receiving regions, thus resolving the conflict between electrical connectivity and light transmission.
Solution Approach 2:
Transparent insulating films and via waveguide structures act as intermediaries between the metal lines and the light path. These intermediary layers allow electrical signals to be transmitted through metal lines while simultaneously allowing light to pass through the transparent insulating films and via waveguides to reach photodiodes, thus mediating the conflict between electrical and optical functions.
2Ease of manufacture
If conventional planar structure is used, then manufacturing is simple, but light capture efficiency is low
Solution Approach 1:
The via waveguide structure employs curved sidewalls instead of straight vertical walls. This curvature is designed to reflect and guide incident light toward the photodiode, improving light capture efficiency. The curved structure can be formed using standard semiconductor manufacturing techniques such as anisotropic etching, thus maintaining ease of manufacture while significantly improving optical performance.
Solution Approach 2:
The invention transitions from a conventional planar structure to a three-dimensional via waveguide structure with curved sidewalls. This dimensional change allows light to be captured and guided through the vertical dimension, enabling more efficient light collection while maintaining compatibility with standard planar manufacturing processes for the overall device structure.
3Measurement precision
If color filters are placed over photodiodes, then color image sensing is achieved, but light transmission is reduced
Solution Approach 1:
The via waveguide structure with curved sidewalls is formed beforehand to optimize light guidance before color filters are applied. This preliminary structural preparation ensures that maximum light is directed toward photodiodes through the curved waveguide paths, and then color filters are added to achieve color separation. The preliminary optimization of light paths minimizes the impact of subsequent color filter placement on overall light transmission.
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 solution significantly increases the amount of light captured by the photodiodes, improving image detection and reducing color inaccuracies, allowing for more complex metal line structures and potentially eliminating the need for microlenses.
Implementation Method 1
the light concentrator includes a curved (e.g., parabolic) surface shaped such that light beams directed into the light concentrator are redirected by a suitable light-guiding material layer formed on the curved surface into the lower section and toward the photodiode
Implementation Method 2
each via wave guide includes a relatively large light concentrator formed over the metal lines of the metallization layer, and a relatively narrow lower section extending between the light concentrator and the pixel's photodiode through the space separating the metal lines
Data Source
AI summary
A CMOS image sensor (CIS) device includes an array of pixels, each pixel including a sensing element (e.g., a photodiode) and access circuitry. To facilitate the passage of light to the photodiode, each pixel includes a via wave guide (VWG) defined in the metallization layer formed over the pixel's photodiode. The VWG includes an upper light concentrator having a curved (e.g., parabolic) surface extending from a relatively wide upper opening to a relatively small lower opening. The VWG also includes a lower section extending between the lower opening of the light concentrator and the associated photodiode. A mirror coating is optionally formed on the surface of the VWG. An optional light-guiding material and/or color filter materials are disposed inside the VWG. An optional microlens is formed over the VWG.