Elliptical Filament Electron Source Vibration Resistance
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Solution Overview
Problem
Electron sources with needle cathodes are susceptible to vibrations, leading to noise and resonance issues, which affect the stability of the electron beam and require increased heating current, making it challenging to maintain rigidity without increasing the filament cross section.
Innovation Solution
An electron source design featuring a filament with a cross-sectional shape having a long direction at least 1.5 to 5 times the short direction and an angle of ±10° with respect to the normal plane formed by the cathode and conductive terminals, enhancing rigidity without increasing the filament cross section, thus reducing noise and heating current requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the filament cross section is made small to enable heating to high operating temperature (at least 1700 K), then the filament becomes less rigid and more susceptible to vibrations, but making it thicker to increase rigidity increases the heating current requirement beyond apparatus capacity
Solution Approach 1:
The patent applies asymmetry by changing the filament cross-section from a conventional circular shape to an elliptical shape with a specific aspect ratio (1.5 to 5 times longer in one direction). This asymmetric geometry increases the moment of inertia and rigidity in the critical vibration direction without increasing the cross-sectional area, thereby maintaining the ability to heat the filament to high operating temperatures (at least 1700 K) while suppressing vibrations and resonance noise.
2Use of energy by moving object
If the filament is made thinner to reduce heating current, then it becomes more susceptible to vibrations and resonance, but making it thicker to reduce vibration susceptibility increases heating current beyond apparatus capacity
Solution Approach 1:
The elliptical cross-section with aspect ratio of 1.5 to 5 provides asymmetric distribution of material that maximizes rigidity in the direction perpendicular to the plane formed by the cathode and conductive terminals. This allows the filament to be sufficiently rigid to suppress vibrations and resonance without requiring increased cross-sectional area, thereby keeping the heating current within apparatus capacity.
Solution Approach 2:
The patent addresses the rigidity issue by transitioning from considering only the cross-sectional area (two-dimensional measure) to optimizing the moment of inertia through asymmetric shape geometry. By elongating the cross-section in one direction while maintaining or reducing the overall area, the filament achieves higher bending stiffness in the critical direction without proportionally increasing the heating current requirement.
3Ease of manufacture
If conventional circular filament is used, then the structure is simple and easy to manufacture, but it cannot effectively suppress vibrations and resonance noise
Solution Approach 1:
The patent replaces the symmetric circular cross-section with an asymmetric elliptical cross-section having a specific aspect ratio (1.5 to 5 times longer in one direction). This asymmetric geometry is designed to maximize the moment of inertia in the direction perpendicular to the plane formed by the cathode and conductive terminals, thereby effectively suppressing vibrations and resonance noise while remaining manufacturable through conventional filament drawing and shaping processes.
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 design effectively suppresses noise and resonance due to vibrations, maintaining stable electron beams while keeping the heating current within the apparatus' capacity, without the need for complex anti-vibration structures.
Implementation Method 1
The cathode is electrically heated to about 1800 K by means of the filament 3
Implementation Method 2
ZrO/W electron sources are widely used in critical dimension SEM and wafer inspection equipment
Data Source
Figure 1(a)~1(b)
Figure 2~3
Figure 4~5
AI summary
Provided is an electron source which outputs a stable electron beam even when vibration is applied from the external to an apparatus which uses the electron source. The electron source is provided with an insulator (5); two conductive terminals (4) arranged at an interval on the insulator (5); a long filament (3) stretched between the conductive terminals (4); and a needle-like cathode (1) having an electron emitting section attached to the filament (3). The vertical cross-section shape of the filament (3) in the axis direction has a long direction and a short direction, and the maximum length in the long direction is 1.5 times or more but not more than 5 times the maximum length in the short direction.