Particle-in-Binder X-ray Coating with Polyimide
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Solution Overview
Problem
Existing X-ray sensitive coatings for direct conversion X-ray imaging face issues such as low X-ray stopping power, high reactivity, chemical instability, and high leakage currents, particularly with amorphous selenium, HgI2, and organic semiconductor binders, which are not compatible with PbO and incur significant costs and radiation damage.
Innovation Solution
A particle-in-binder (PIB) material using PbO particles in a polyimide binder, where the PbO particles are dispersed in a sparse fibrous polyimide matrix, reducing leakage currents and enhancing X-ray sensitivity by applying a bias voltage and using standard screen printing processes, which are more cost-effective than vacuum deposition methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If amorphous selenium is used as photoconductor material, then direct conversion X-ray imaging is achieved, but stopping power for X-rays above 30 kVp is low and vacuum vapor deposition incurs incremental costs
Solution Approach 1:
The patent uses a composite material system consisting of HgI2 particles dispersed in an epoxy binder matrix. This composite structure combines the high X-ray stopping power of HgI2 particles with the structural support and cost-effectiveness of epoxy binder, achieving both improved reliability and ease of manufacture compared to pure amorphous selenium
Solution Approach 2:
The patent changes the material parameters by transitioning from amorphous selenium to HgI2 particles with specific size ranges (0.5-50 micrometers) and controlled concentration (40-80 weight percent), optimizing both X-ray stopping power and manufacturing characteristics
2Reliability
If HgI2 particle-in-binder materials are used, then X-ray sensitivity is improved, but chemical stability and reactivity become problematic
Solution Approach 1:
The epoxy binder acts as an intermediary material that stabilizes the highly reactive HgI2 particles. The binder matrix isolates and protects the chemically unstable HgI2 particles while maintaining their X-ray sensitivity, resolving the contradiction between sensitivity and chemical stability
Solution Approach 2:
The composite structure of HgI2 particles in epoxy binder provides both the desired X-ray sensitivity from HgI2 and chemical stability from the epoxy matrix, achieving a balance between reactivity and stability
3Adaptability or versatility
If epoxy binders are used with PbO particles, then compatibility issues arise due to polar hydroxyl groups, but if other binders are used, then radiation damage stability and leakage current control are insufficient
Solution Approach 1:
The patent changes the binder material parameters by selecting polyimide instead of epoxy, fundamentally altering the chemical properties to achieve both PbO compatibility and radiation stability. This parameter change resolves the compatibility issue while maintaining reliability
Solution Approach 2:
The patent applies local quality optimization by using polyimide binder specifically tailored for PbO particle compatibility, creating a localized chemical environment that is compatible with PbO surface properties while maintaining overall system radiation stability
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 PIB material achieves higher X-ray sensitivity and reduced leakage currents, making it suitable for medical imaging applications while being more cost-effective and stable against radiation, with a porous structure that passivates surface states and improves uniformity.
Implementation Method 1
amorphous selenium (a-Se) has relatively low stopping power for X-rays having energy levels approximately above 30 kVp
Implementation Method 2
a porous structure that passivates surface states and improves uniformity
Data Source
AI summary
An X-ray sensitive coating (22) for a flat panel direct conversion X-ray detector for medical or industrial imaging. A composite particle-in-binder (PIB) material (22) may contain X-ray photoconductive particles (23) such as PbO (lead monoxide) in a binder of polyimide (23). This PIB material may be prepared in precursor paste form, and applied as a coating (22) onto a thin film transistor array (26) having a storage capacitor (31) at each pixel (30). The coating (22) is cured, and an electrically conducting layer (34) is applied to the exposed surface of the coating (22), to provide a bias voltage. X-ray photons striking the photoconductive particles (23) cause localized electrical conduction proportional to the number of photons. This charges respective capacitors (31) that provide image data input to a computer.