MCP Barrier Coatings for Stable Secondary Electron Yield
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Solution Overview
Problem
Conventional microchannel plates (MCPs) face challenges with unstable secondary electron emission due to environmental exposure, particularly from water and carbon dioxide, leading to reduced gain and undesirable properties from contaminant interactions and thermal annealing, which affects their performance in applications like night vision and medical imaging.
Innovation Solution
A method involving atomic layer deposition (ALD) using CaF2 as a secondary electron emissive coating, deposited with specific precursor pulsing and purging cycles, forms a stable barrier layer to prevent fluorine migration and environmental reactivity, enhancing the secondary electron yield and maintaining high gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If MgO SEY coatings are used to achieve high secondary electron yield, then the MCP gain is improved, but the coatings become highly susceptible to ambient exposure and form hydroxides and carbonates that reduce SEY
Solution Approach 1:
The patent uses a composite coating structure consisting of an inner MgO layer for high secondary electron yield and an outer Al2O3 barrier layer for environmental protection. This composite structure combines the advantageous properties of both materials: MgO provides high SEY while Al2O3 provides resistance to hydroxide and carbonate formation, thereby maintaining stable MCP gain in ambient conditions.
Solution Approach 2:
The Al2O3 layer acts as an intermediary barrier between the MgO SEY coating and the ambient environment. It prevents direct contact between water and carbon dioxide from the environment and the MgO surface, thereby preventing the formation of hydroxides and carbonates that would reduce secondary electron yield.
2Stability of the object's composition
If thermal annealing is performed to achieve stable MCP operation, then operational stability is improved, but solid state diffusion occurs that impacts SEY
Solution Approach 1:
The Al2O3 barrier layer serves as a protective intermediary that prevents solid state diffusion during thermal annealing processes. It acts as a diffusion barrier that stops element migration from the MCP substrate to the MgO SEY layer, thereby maintaining the integrity and secondary electron yield properties of the MgO coating even after thermal processing.
Solution Approach 2:
The Al2O3 barrier layer is deposited beforehand on the MCP substrate before the MgO SEY coating is applied. This preliminary protective layer is in place before any thermal annealing occurs, preventing solid state diffusion during subsequent thermal processing steps and ensuring the MgO layer maintains its SEY properties.
3Ease of manufacture
If conventional hydrogen firing is used to impart electrical conductivity and secondary electron emissivity, then the process is simple, but contaminants are introduced that affect MCP properties
Solution Approach 1:
The patent replaces the conventional chemical hydrogen firing process with a physical vapor deposition process (atomic layer deposition). Instead of using chemical reactions that introduce hydrogen and potential contaminants, the ALD process uses controlled deposition of precise thin film layers (MgO and Al2O3) to achieve both electrical conductivity and secondary electron emissivity without introducing harmful contaminants.
Solution Approach 2:
The invention changes the fabrication parameters from conventional hydrogen firing (chemical process at high temperature) to atomic layer deposition (controlled chemical vapor deposition at lower temperatures). This parameter change allows for precise control of film composition and thickness, achieving the desired electrical and emissive properties while avoiding contaminant introduction associated with traditional hydrogen firing.
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 ALD process with CaF2 coating significantly reduces fluorine migration and environmental reactivity, resulting in a stable and high secondary electron yield, maintaining the microchannel plates' performance even after thermal annealing, thus addressing the issues of contamination and environmental exposure.
Implementation Method 1
A coating of CaF2 is deposited by atomic layer deposition process including at least one cycle of: pulsing a first metal precursor comprising an alkaline metal amidinate into the reactor for a first metal precursor pulse time; purging the reactor of the first metal precursor; pulsing a second precursor comprising a fluorinated compound into the reactor for a second precursor pulse time; and purging the reactor of the co-reactant precursor
Implementation Method 2
The SEY itself is greatly impacted by factors such as the adsorption of molecules from the ambient environment, such as water or carbon dioxide
Implementation Method 3
Such thermal annealing can result in solid state diffusion of elements
Data Source
AI summary
A secondary electron emissive layer resistant to infiltration and fouling. A barrier layer is formed by atomic layer deposition. The barrier layer may be an emissive layer and/or an interlayer. The barrier layer may form an interlayer that is a part of an electron amplifier positioned between an emissive layer and a resistive layer. The barrier layer is resistive to fluorine migration from either the emissive layer or the resistive layer.