Tapered Insulating Layer for Leakage Current Suppression in X-ray Photodiodes
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Solution Overview
Problem
The existing X-ray imaging devices with indirect conversion systems have insufficient measures to suppress leakage current in photodiodes, affecting imaging performance.
Innovation Solution
The proposed imaging device incorporates a photoelectric conversion part with photodiodes and thin film transistors, featuring a tapered insulating layer between the lower electrode and semiconductor layer, and a two-layer structure with silicon nitride and silicon oxide layers, along with In-Ga-Zn-O-based oxide semiconductor transistors to reduce leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional insulating layer configuration is used in the photodiode, then the device structure is simple, but the leakage current of the photodiode is insufficiently suppressed
Solution Approach 1:
The insulating layer is divided into multiple distinct layers (first insulating layer and second insulating layer) with different functions. The first insulating layer provides electrical insulation between the lower electrode and semiconductor layer, while the second insulating layer provides additional insulation and structural support. This segmentation allows each layer to be optimized for its specific function, effectively suppressing leakage current while maintaining reasonable device complexity.
Solution Approach 2:
The insulating layers are strategically positioned only in specific regions where leakage current occurs. The first insulating layer is located between the lower electrode and semiconductor layer in the region where leakage current flows, providing localized suppression. This approach focuses insulation resources where most needed rather than uniformly insulating the entire photodiode structure.
2Reliability
If the insulating layer end has a non-tapered shape, then the manufacturing process is simpler, but the leakage current suppression is insufficient
Solution Approach 1:
The end of the insulating layer is designed with a tapered shape rather than a sharp or flat end. This tapered configuration smoothly transitions the insulating layer into the surrounding structure, eliminating sharp edges that could concentrate electric fields and generate leakage current. The curved/tapered geometry distributes electric field lines more evenly, effectively suppressing leakage current while the taper angle constraints maintain manufacturing feasibility.
3Reliability
If a single-layer insulating structure is used, then the device complexity is low, but the imaging performance is degraded due to insufficient leakage current suppression
Solution Approach 1:
The insulating system is segmented into multiple functional layers, each contributing to different aspects of leakage current suppression and overall device performance. This multi-layer segmentation enables optimized performance for imaging applications while keeping each individual layer relatively simple in structure.
Solution Approach 2:
The insulating layers are formed from different materials with complementary properties. The first insulating layer and second insulating layer use different material compositions optimized for their specific functions, creating a composite insulating system that provides superior leakage current suppression compared to a single-material approach, thereby enhancing imaging performance.
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 decreases leakage current, enhancing imaging performance and sensitivity, leading to improved contrast and efficiency in X-ray imaging.
Implementation Method 1
a photoelectric conversion part which converts incident light into electric charge
Implementation Method 2
an X-ray conversion part which when irradiated with X-rays, generates light corresponding to the intensity of the X-rays
Data Source
AI summary
An imaging device according to an embodiment of the present invention includes a photoelectric conversion part that converts incident light into electric charge, and a detection part that detects the electric charge generated in the photoelectric conversion part. The photoelectric conversion part includes a plurality of photodiodes arranged in a matrix, and the detection part includes a plurality of thin film transistors provided corresponding to the plurality of photodiodes and arranged in a matrix. Each of the photodiodes includes a lower electrode, a semiconductor layer, and an upper electrode, and an insulating layer is provided between at least a portion of the lower electrode in the thickness direction and the semiconductor layer in the peripheral portion of the semiconductor layer. An end of the insulating layer has a tapered shape having an acute angle between the lower surface and the side surface of the insulating layer.