CMOS Pixel Light Shielding Layout for Global Shutter Noise Control
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Solution Overview
Problem
Conventional CMOS image sensors face challenges such as decreased aperture ratio, sensitivity, and increased optical noise due to the limited pixel layout and the need for charge holding parts, which can lead to distortion and image quality issues.
Innovation Solution
The proposed imaging device incorporates a photoelectric conversion part, a holding part, and a light shielding part formed in a semiconductor substrate. The light shielding part is designed as a non-penetrating part in the transfer region and a penetrating part elsewhere, effectively shielding light and reducing optical noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a charge holding part is provided in each pixel to enable global shutter scheme, then exposure timing becomes the same for all pixels and distortion is avoided, but pixel layout is limited, aperture ratio decreases, and sensitivity of the photodiode may decrease
Solution Approach 1:
The invention moves the charge holding part from a two-dimensional planar layout to a three-dimensional structure by forming it in a deeper region of the semiconductor substrate. This vertical positioning allows the photodiode and charge holding part to overlap in the planar view, enabling global shutter functionality without reducing the aperture ratio of the photodiode.
Solution Approach 2:
The charge holding part is formed within the vertical space beneath or adjacent to the photodiode, effectively nesting the holding function within the same pixel footprint. This nested arrangement allows both the photodiode and charge holding part to coexist without increasing the planar area, thus maintaining aperture ratio while enabling simultaneous charge storage from all pixels.
2Stability of the object's composition
If a charge holding part is provided in each pixel to enable global shutter scheme, then exposure timing becomes the same for all pixels and distortion is avoided, but capacity of the photodiode and charge holding part may decrease
Solution Approach 1:
By forming the charge holding part in a deeper region of the semiconductor substrate beneath the photodiode, the invention increases the available volume for charge storage without increasing the planar footprint. This three-dimensional charge storage region provides sufficient capacity for both photodiode and charge holding part to maintain high charge capacity while enabling global shutter operation.
3Stability of the object's composition
If a charge holding part is provided in each pixel to enable global shutter scheme, then exposure timing becomes the same for all pixels, but optical noise may be generated by light incident into the charge holding part while holding a charge
Solution Approach 1:
The invention extracts the charge holding part from the light-exposed region by positioning it in a deeper region of the semiconductor substrate beneath the photodiode. This spatial separation ensures that light incident on the pixel primarily reaches the photodiode during exposure, while the charge holding part remains in a shaded region, preventing optical noise generation during charge storage.
Solution Approach 2:
The vertical positioning of the charge holding part in a deeper region creates a natural light shielding effect, as the photodiode and overlying structures block light from reaching the charge holding part during exposure. This three-dimensional arrangement eliminates optical noise without requiring additional light shielding layers.
4Object-affected harmful factors
If light shielding part is formed as penetrating structure, then light shielding is effective, but charge transfer path may be blocked in the transfer region
Solution Approach 1:
The invention applies different light shielding configurations to different regions: in the charge transfer region, the light shielding part is formed as a non-penetrating structure that does not extend through the entire substrate thickness, preserving the charge transfer path; in other regions, penetrating light shielding structures are used to effectively block light. This localized differentiation resolves the contradiction between light shielding effectiveness and charge transfer 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 enables better pixel signals by reducing optical noise and maintaining sensitivity, thus improving image quality and avoiding distortion caused by exposure timing differences.
Implementation Method 1
light incident on a CMOS image sensor is subjected to photoelectric conversion in a photodiode (PD) included in a pixel
Implementation Method 2
a light shielding part configured to shield light between the photoelectric conversion part and the holding part
Data Source
AI summary
The present disclosure relates to an imaging device and an electronic device that make it possible to obtain a better pixel signal. A photoelectric conversion part that converts received light into a charge; a holding part that holds a charge transferred from the photoelectric conversion part; and a light shielding part that shields light between the photoelectric conversion part and the holding part are provided. The photoelectric conversion part, the holding part, and the light shielding part are formed in a semiconductor substrate. The light shielding part of a transfer region that transfers the charge from the photoelectric conversion part to the holding part is formed as a non-penetrating light shielding part that does not penetrate the semiconductor substrate. The light shielding part other than the transfer region is formed as a penetrating light shielding part that penetrates the semiconductor substrate. The present technology is applicable to an imaging device.