Imaging Device Pixel Electrode Segmentation for Leakage Current Reduction
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Solution Overview
Problem
Solid-state imaging devices face reliability issues due to leakage current and variations in threshold voltage caused by incident light, affecting the operating characteristics and temporal stability of pixels.
Innovation Solution
The imaging device incorporates a semiconductor substrate with a unit pixel cell featuring a photoelectric converter, a charge detection transistor, and a reset transistor, where the pixel electrode covers the reset transistor, preventing light entry into its channel region, and using a semiconductor with a larger band gap for the reset transistor to minimize leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the reset transistor is exposed to incident light, then the photoelectric converter can function, but the threshold voltage of the reset transistor varies due to light entry into its channel region
Solution Approach 1:
The pixel electrode is divided into a light-receiving region and a light-blocking region. The light-blocking region specifically covers the channel region of the reset transistor, segmenting the electrode function to protect the transistor from light while maintaining photoelectric conversion capability in other areas.
Solution Approach 2:
The pixel electrode acts as an intermediary element that simultaneously serves as a light-receiving component for photoelectric conversion and a light-blocking component for protecting the reset transistor. This dual-function intermediary structure resolves the contradiction by allowing the same component to fulfill both roles.
2Reliability
If conventional materials are used for the reset transistor, then manufacturing is easier, but leakage current increases
Solution Approach 1:
The semiconductor material of the reset transistor is changed to have a larger band gap than conventional materials. This parameter change in material properties reduces leakage current while the patent provides guidance on suitable material selections to balance manufacturing considerations.
3Reliability
If the pixel electrode does not cover the reset transistor, then manufacturing is simpler, but operating characteristics vary due to light-induced threshold voltage changes
Solution Approach 1:
The pixel electrode is segmented into functional regions: a light-receiving region for photoelectric conversion and a light-blocking region for protecting the reset transistor. This segmentation adds structural complexity but resolves the operating characteristic stability issue.
Solution Approach 2:
The pixel electrode is designed to perform multiple functions: it serves as the light-receiving element for photoelectric conversion, the charge collection electrode, and simultaneously as a light-blocking shield for the reset transistor. This multi-functionality justifies the increased structural complexity.
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 suppresses variation in threshold voltage and operating characteristics, enhancing the reliability and longevity of the imaging device by reducing light-induced effects and leakage current.
Implementation Method 1
a photoelectric converter that includes a pixel electrode and a photoelectric conversion layer located on the pixel electrode, the photoelectric converter converting incident light into electric charges
Data Source
AI summary
An imaging device includes a semiconductor substrate; and a unit pixel cell provided to a surface of the semiconductor substrate. The unit pixel cell includes: a photoelectric converter that includes a pixel electrode and a photoelectric conversion layer located on the pixel electrode, the photoelectric converter converting incident light into electric charges; a charge detection transistor that includes a part of the semiconductor substrate and detects the electric charges; and a reset transistor that includes a first gate electrode and initializes a voltage of the photoelectric converter. The pixel electrode is located above the charge detection transistor. The reset transistor is located between the charge detection transistor and the pixel electrode. When viewed from a direction normal to the surface of the semiconductor substrate, the pixel electrode covers an entire portion of the first gate electrode.