MCP: Fabrication with Leadsilicate Glass

The traditional process of MCP manufacturing starts with filling lead glass tubes with glass rods. The tube and rod assemblies undergo a thermal co-drawing process. This process causes the tube to collapse around the rod, resulting in the creation of long, thin fibres that have a lead glass cladding and an inner core glass. These fibres are then stacked in parallel and stretched together. Subsequently, multiple fibre assemblies are fused together in a parallel arrangement. Wafers are cut across these fibre assemblies, with the wafer plane positioned almost perpendicular to the fibre axis. The core glass is then etched away, leaving behind an array of pores, each typically around 6–20μm in diameter. This structure, known as a lead glass capillary array, is heated in a hydrogen environment. This process chemically reduces the glass surface, creating a resistive and emissive surface suitable for electron amplification.

Resistive and SEE Layers in Conventional MCP Fabrication

In the conventional fabrication of microchannel plates (MCPs), the resistive layer and the secondary electron emissive (SEE) layer are not separate, distinct layers. Instead, they are created together as a single entity during the manufacturing process. This process involves several steps:

• Lead Glass Structure: Initially, lead glass tubes filled with glass rods are drawn and fused to form a structure with a lead glass cladding and an inner core glass.
• Etching and Reduction: The core glass is etched away, leaving an array of pores. The lead glass capillary array is then heated in a hydrogen environment, chemically reducing the glass surface.
• Combined Resistive and Emissive Surface: This chemical reduction process forms a surface layer that provides both resistive and emissive properties, enabling the electron amplification function of the MCP.

Therefore, unlike the ALD MCP fabrication where resistive and SEE layers are applied separately, conventional MCPs create these properties simultaneously on a single surface layer through chemical reduction.

 

Resistive Layer: Traditional MCPs are treated with hydrogen during the manufacturing process. The hydrogen chemically reduces the surface of the lead glass, creating a layer that is both resistive and electron emissive. This alkali-rich surface layer, approximately 20-50 nm thick, contains elements like potassium, cesium, and rubidium.

SEE Layer: This alkali-rich layer, formed by the hydrogen treatment, also serves as the secondary electron emissive (SEE) layer in conventional MCPs. Notably, the alkali constituents, especially potassium, are believed to be crucial for secondary electron emission. However, electron stimulated desorption and alkali migration within the glass can lead to a reduction in these alkali elements, contributing to a decline in MCP gain over time.