Chalcopyrite Solid State Imaging Device Dark Current Reduction
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Solution Overview
Problem
Conventional solid state imaging devices with chalcopyrite structure semiconductor thin films face challenges in achieving high sensitivity across a wide wavelength region from visible light to near infrared light due to dark current issues and limitations in film formation temperatures, which affect the quality and leakage current of the films.
Innovation Solution
A solid state imaging device is designed with a photoelectric conversion unit incorporating a compound semiconductor film of Cu(In, Ga)Se2 in a chalcopyrite structure, integrated with a circuit unit and an optical transparent electrode layer, utilizing a non-doped ZnO film to reduce dark current and voids, and a fabrication method that includes low-temperature processing to maintain film quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If film formation temperature is increased to 550°C to improve film quality, then film quality improves, but leakage current increases and dark current characteristics deteriorate
Solution Approach 1:
The patent changes the substrate temperature parameter during film formation from the conventional 550°C to a lower temperature range (200-400°C). This parameter change allows the formation of high-quality compound semiconductor films with reduced leakage current and improved dark current characteristics, resolving the contradiction between film quality and harmful current effects.
2Object-generated harmful factors
If film formation temperature is decreased below 550°C to reduce leakage current, then leakage current decreases, but film quality deteriorates
Solution Approach 1:
The patent optimizes multiple parameters simultaneously: substrate temperature (200-400°C), film thickness (2-5 μm), and composition ratios (Cu/(In+Ga) = 0.8-1.2). These coordinated parameter changes enable high-quality film formation at lower temperatures, achieving both reduced leakage current and maintained film quality.
Solution Approach 2:
The patent uses compound semiconductor materials with chalcopyrite structure (Cu(In, Ga)Se2) that inherently provide both good film quality and low leakage current properties. The composite material approach allows achieving performance benefits that cannot be obtained with single-element semiconductors.
3Device complexity
If amorphous semiconductor layer is used for photo sensor area, then device structure is simplified, but photoelectric conversion wavelength range is limited to visible light region
Solution Approach 1:
The patent employs compound semiconductor films with chalcopyrite structure (Cu(In, Ga)Se2) that possess unique optical properties enabling photoelectric conversion across a broad wavelength range from visible light to near-infrared region. This composite material provides extended adaptability while maintaining the simple layered device structure.
Solution Approach 2:
The patent adjusts the composition parameters of the compound semiconductor film, specifically the Ga content in Cu(In, Ga)Se2, to control the bandgap and optimize photoelectric conversion characteristics across different wavelength regions. This parameter optimization enables versatile wavelength response while keeping the device structure simple.
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
The device achieves high sensitivity across a wide wavelength range, reducing dark current and improving optical absorption, making it suitable for applications like security cameras and personal authentication cameras, while simplifying the fabrication process by allowing the optical transparent electrode layer to be formed in one piece on the substrate.
Implementation Method 1
a compound semiconductor thin film of chalcopyrite structure which is placed on the lower electrode layer and functions as an optical absorption layer
Data Source
AI summary
A solid state imaging device includes a circuit unit formed on a substrate and a photoelectric conversion unit. The photoelectric conversion circuit includes a lower electrode layer placed on the circuit unit, a compound semiconductor thin film of chalcopyrite structure which is placed on the lower electrode layer and functions as an optical absorption layer, and an optical transparent electrode layer placed on the compound semiconductor thin film. The lower electrode layer, the compound semiconductor thin film, and the optical transparent electrode layer are laminated one after another on the circuit unit.