Aluminum Oxide Microchannel Plates

 

 

K.Delendik, I.Emeliantchik*, A.Litomin, V.Rumyantsev, O.Voitik

 

Introduction

At present microchannel electron multipliers (or microchannel plates – MCP) are widely used in different fields of science and technology. MCP have good operational parameters: gain up to 106, response time 1 ns and less, spatial resolution of the order of channel diameter, sensitivity up to single electron mode, high radiation hardness, ability to work in strong magnetic fields.. MCP are used in brightness amplifiers, navigation equipment, electron-optic converters, scientific measuring devices, medical diagnostic equipment, night vision devices, detectors of charged particles and gamma-quanta etc.

Existing MCP and technology of their production

MCP is a matrix of parallel microchannels. Each microchannel can be considered as a continuous dynode structure having necessary resistive and secondary-emissive properties.

Concept of continuous dynode of channel type was formulated by Farnswort (1930) [1], the first operating prototype of MCP was created by I.Pesyatsky (1943) [2].. In 1960s technology of MCP was actively developed [3-6]. The basic elements of modern MCP technology were created at that time.

Modern MCPs are plates with thichness of 0.4 – 4 mm, having channels with diameters of 10 – 100 mcm with package density up to 106 см-2. Due to small dimensions of channels MCP has good time resolution (hundreds of picoseconds) and spatial resolution (comparable with channel diameter), the gain is up to 105. MCP channels are usually slightly tilted (5°-15°) in relation to the perpendicular to the plate surface, which is diminishing parasitic ion feedback.

Currently the main material for MCP production is lead-silicate glass. Modern technology of lead glass MCP production is based on methods of optic fibers production and consists of multiple processes of dragging and agglomeration of fibers having soluble metal or glass core resulting in production of primary multivein fibers. Then the block is cut under certain angle into separate plates, their surfaces are being polished. Thermohydrogen reduction provides necessary electrophysical parameters of MCP and consists of reduction of lead oxide in the surface area of channels by heating of MCP in the hydrogen flow. It’s necessary to maintain precise time-temperature profile of hydrogen reduction, which complecates lead glass MCP technology.

Shortcomings of existing MCP technology

Lead glass MCP have good parameters, but there are also serious disadvantages:

· very complex, labour consuming and expensive technology;

· large parameter deviation and low repeatability of MCP due to possible glass irregularities;

· large deviation of channel diameters within MCP;

· spottiness of the image due to difference of thermal histories of elements of MCP block;

· during MCP production the glass undergoes different influences: thermochemical, mechanical, chemical, which causes defects due to plate deformations caused by changes of glass composition and its temperature expansion coefficient;

· limit of spatial resolution is already reached – channels with diameters less than 10 mcm are impossible to produce with conventional methods;

· it’s difficult to produce llarge area MCP.

Attempts to create alternative technology

So, development of the alternative MCP technology, less expensive and able to produce MCP with larger area and smaller channel diameters, is quite urgent.

There were many attempts to create new MCP technology during the last 20 years. In [7] multilayer structure made of etched glass plates is proposed. In [8] and [9] microshere plates made of agglomerated glass balls are described. In patents [10 - 18] different versions of microchannel structures made of glass,

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