Asymmetric Light Shielding Trench for CMOS Image Sensor Noise Reduction
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Solution Overview
Problem
Existing photoelectric conversion apparatuses, such as CMOS image sensors, suffer from optical noise due to light leakage between the photoelectric converting unit and the charge holding unit, which degrades pixel signals.
Innovation Solution
A photoelectric conversion apparatus with a light shielding unit embedded in a trench of the semiconductor substrate between the photoelectric converting unit and the charge holding unit, where the light shielding unit is positioned closer to the photoelectric converting unit than to the charge holding unit, and a transfer gate on the second surface to control charge transfer, effectively reducing light incidence on the charge holding unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a light shielding unit is provided between the photoelectric converting unit and the charge holding unit, then optical noise is reduced, but light may still leak into the charge holding unit causing noise-causing charge generation
Solution Approach 1:
The light shielding unit is positioned asymmetrically closer to the photoelectric converting unit than to the charge holding unit, creating different shielding effectiveness in different regions. This local quality adjustment optimizes the balance between reducing optical noise and maintaining pixel signal quality by providing enhanced shielding where photoelectric conversion occurs while allowing controlled light access to the charge holding unit
Solution Approach 2:
The light shielding unit acts as an intermediary element between the photoelectric converting unit and the charge holding unit. It mediates the light path by selectively blocking harmful light that would cause optical noise while permitting necessary light to reach the charge holding unit for proper charge transfer and signal generation
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 significantly reduces optical noise and improves pixel signal quality by effectively shielding light from reaching the charge holding unit, enhancing image signal integrity.
Implementation Method 1
a light shielding unit provided in a trench of the semiconductor substrate, the trench being formed between the photoelectric converting unit and the charge holding unit
Implementation Method 2
a photoelectric converting unit provided in the semiconductor substrate to convert incident light into charge
Data Source
AI summary
A photoelectric conversion apparatus, including: a semiconductor substrate having a first surface on which light is incident and a second surface; a photoelectric converting unit configured to convert incident light into charge; a charge holding unit configured to hold charge; a light shielding unit provided in a trench of the semiconductor substrate, the trench being formed between the photoelectric converting unit and the charge holding unit; and a transfer gate formed on a second surface side of the semiconductor substrate so as to overlap with the light shielding unit when viewed in a plan view for the second surface of the semiconductor substrate and configured to transfer the charge at the photoelectric converting unit to the charge holding unit, wherein a distance between the light shielding unit and the photoelectric converting unit is shorter than a distance between the light shielding unit and the charge holding unit.