Imaging Device Vertical Stacking Reduces Leakage Current
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Solution Overview
Problem
Existing solid-state imaging devices face challenges in reducing device area while maintaining image quality, as they suffer from leakage current and characteristic deterioration due to the integration of transistors and photoelectric conversion layers.
Innovation Solution
The design incorporates a semiconductor substrate with a photoelectric converter, a charge detection transistor, and a reset transistor, where the reset transistor, composed of a semiconductor with a larger band gap, is positioned between the charge detection transistor and the pixel electrode, minimizing area and suppressing leakage current through vertical alignment and optimal layer placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the area of the imaging device is reduced by integrating components vertically, then the device area is reduced, but leakage current increases and characteristic deterioration occurs
Solution Approach 1:
The patent transitions from a planar layout to a three-dimensional vertical stacking architecture, where the photoelectric converter, charge detection transistor, and reset transistor are arranged in vertical layers. This dimensional change allows compact integration while maintaining functional separation, reducing device area without compromising performance
Solution Approach 2:
The patent applies different semiconductor materials with optimized properties to different functional regions: the photoelectric converter uses one semiconductor material while the transistors use another, allowing each component to operate in its optimal material environment. This local optimization minimizes leakage current while maintaining small area
2Adaptability or versatility
If transistors are integrated with photoelectric conversion layers, then device functionality is enhanced, but leakage current increases
Solution Approach 1:
The patent introduces a charge storage node as an intermediary between the photoelectric converter and charge detection transistor, and uses a reset transistor with specific material properties as a mediator to control and minimize leakage current pathways, enabling functional integration while suppressing harmful leakage
Solution Approach 2:
The patent changes the material parameter (band gap) of the semiconductor used in the reset transistor, selecting a material with larger band gap than the photoelectric converter material. This parameter change optimizes the reset transistor for low leakage operation while maintaining its charge initialization function
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 effectively reduces the device area while maintaining circuit operation characteristics and minimizing leakage current, thereby enhancing image capture performance.
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 comprising a first semiconductor; and a unit pixel cell provided to the semiconductor substrate. The unit pixel cell includes: a photoelectric converter that includes a pixel electrode and a photoelectric conversion layer, 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 at least a part of a first semiconductor layer comprising a second semiconductor 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. A band gap of the second semiconductor is larger than a band gap of the first semiconductor.