Global Shutter CMOS Image Sensor Light Pipe Refraction
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Solution Overview
Problem
Conventional CMOS image sensors with global shutters face issues of parasitic light sensitivity and reduced efficiency due to the shrinking size of pixels, leading to light leakage between the photosensitive and storage elements, which affects image quality when capturing high-speed moving objects.
Innovation Solution
A global shutter CMOS image sensor design featuring a photodiode, floating diffusion region, and storage diode with a light pipe and light-shielding layer, where the light pipe has a higher refractive index than the surrounding dielectric layer, confining incident light and reducing leakage to the storage diode through self-aligned formation and light-shielding mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel size is reduced to increase resolution, then the image sensor can capture finer details, but the distance between the photosensitive element and storage element decreases causing light leakage and worsening parasitic light sensitivity
Solution Approach 1:
A light pipe structure is introduced as an intermediary component between the photodiode and the storage diode. The light pipe has a higher refractive index than the surrounding dielectric layer, creating optical confinement that prevents light from leaking directly to the storage diode. This mediator structure enables the pixel to maintain small dimensions while preventing parasitic light sensitivity.
Solution Approach 2:
The patent applies local quality by creating a specific optical environment around the photodiode through the light pipe structure. The light pipe provides localized optical confinement with different refractive index properties compared to the surrounding dielectric layer, ensuring that light is confined to the intended photosensitive region while allowing the overall pixel structure to remain compact.
2Reliability
If a global shutter structure is implemented to reduce image distortion of moving objects, then image quality improves, but the complexity of the pixel structure increases with additional storage elements and transfer gates
Solution Approach 1:
The patent extracts the light management function from the overall pixel structure by implementing a dedicated light pipe structure. This separates the optical confinement function from the electrical signal processing components, allowing the global shutter mechanism to function with reduced complexity while maintaining image quality through the specialized light pipe design.
3Object-affected harmful factors
If light-shielding layers are added to prevent light leakage, then parasitic light sensitivity is reduced, but the manufacturing process complexity increases
Solution Approach 1:
Instead of adding complex light-shielding layers, the patent changes the optical parameters of the existing structures by implementing a light pipe with a higher refractive index than the surrounding dielectric layer. This parameter change creates optical confinement through refraction principles, preventing light leakage without requiring additional light-shielding manufacturing steps.
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 design enhances the absorption and confinement of incident light on the photodiode, significantly reducing parasitic light sensitivity and improving global shutter efficiency, thereby minimizing image distortion when capturing high-speed objects.
Implementation Method 1
The light pipe has a refractive index higher than that of the first dielectric layer
Data Source
AI summary
A global shutter CMOS image sensor includes a photodiode, a floating diffusion region, and a storage diode disposed in the upper portion of the substrate. The storage diode is disposed between the photodiode and the floating diffusion region. A first transfer gate is disposed on the substrate between the photodiode and the storage node. A second transfer gate is disposed on the substrate between the storage diode and the floating diffusion region. A first dielectric layer is disposed on the substrate and covers the first transfer gate and the second transfer gate. A light-shielding layer is disposed on the first dielectric layer. A light pipe is disposed through the light-shielding layer and a portion of the first dielectric layer, and is correspondingly disposed above the photodiode. The light pipe has a higher refractive index than the first dielectric layer.