Oxide Semiconductor TFT Image Sensor with Gas Barrier Film
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Solution Overview
Problem
Current X-ray image sensors face challenges in achieving high-speed operation due to variations in oxide semiconductor TFT characteristics caused by hydrogen diffusion from the raw gas used in forming a-Si PDs, leading to insufficient spatial resolution and frame rate limitations in medical and industrial applications.
Innovation Solution
Incorporating a gas barrier film, such as an organic insulating film like p-xylene polymer or m-xylene polymer, between the oxide semiconductor TFT and the a-Si PD to suppress hydrogen diffusion, ensuring stable TFT characteristics and enabling high-frame-rate X-ray fluoroscopy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If oxide semiconductor TFT is used as switching element to enable high-speed operation, then frame rate increases, but TFT characteristic varies significantly due to hydrogen diffusion from a-Si PD formation process
Solution Approach 1:
A hydrogen barrier dielectric layer is introduced as an intermediary component between the oxide semiconductor TFT and the a-Si PD. This layer acts as a mediator that blocks hydrogen diffusion from the a-Si PD formation process to the oxide semiconductor TFT, thereby maintaining TFT characteristic stability while enabling high-speed operation.
Solution Approach 2:
The harmful factor (hydrogen) is extracted or blocked from reaching the oxide semiconductor TFT by introducing a hydrogen barrier dielectric layer. This layer specifically targets and prevents hydrogen diffusion, separating the harmful effect from the functional components.
2Measurement precision
If a-Si PD is formed using raw gas containing large amount of hydrogen, then photoelectric conversion efficiency improves, but hydrogen diffuses to oxide semiconductor TFT causing characteristic variation
Solution Approach 1:
The hydrogen barrier dielectric layer serves as a protective intermediary between the a-Si PD formation process and the oxide semiconductor TFT. It allows the a-Si PD to be formed with high photoelectric conversion efficiency using hydrogen-containing raw gas, while simultaneously blocking hydrogen diffusion to the TFT.
Solution Approach 2:
The hydrogen that would normally be harmful by diffusing into the oxide semiconductor TFT is instead utilized beneficially in the a-Si PD formation process. The hydrogen barrier dielectric layer enables this arrangement by directing hydrogen to where it is needed (a-Si PD formation) while preventing it from reaching where it is harmful (oxide semiconductor TFT).
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 gas barrier film effectively prevents hydrogen diffusion, stabilizing the oxide semiconductor TFT characteristics, allowing for precise and high-speed X-ray imaging, enhancing the image sensor's operational reliability and yield.
Implementation Method 1
a gas barrier film, such as an organic insulating film like p-xylene polymer or m-xylene polymer, between the oxide semiconductor TFT and the a-Si PD to suppress hydrogen diffusion
Data Source
AI summary
In manufacturing an image sensor for FPD having an oxide semiconductor TFT as a switching element, a large amount of hydrogen contained in raw gas is diffused in the oxide semiconductor at the time of forming a-Si photo diode (PD) which is a photoelectric conversion element, causing significant variation in the characteristic of TFT which may thereby not operate. In an image sensor in which an oxide semiconductor TFT and a-Si PD are formed on a substrate in this order, a gas barrier film is disposed between the oxide semiconductor TFT and the PD, and the drain terminal (drain metal) of the oxide semiconductor TFT is connected to one terminal (lower electrode) of the PD via connection wiring (bridge wiring) formed on a protective film arranged over the PD.