High-performance Microchannel Plates Based On Functional Nano Films Design And Performance Modulation

Microchannel plate（MCP）is a typical channel electron multiplier device.Compared to other types of electron multipliers with discrete dynode structure,MCP with some additional advantages such as fast time response,high spatial resolution,low operating voltage and low power consumption.In addition,MCP can realize two-dimensional imaging detection of photons,electrons,ions and high-energy particles,which is widely used in electron multiplier device,night vision instrument,mass spectrometer,spectrometer,laser radar,gated imaging,medical diagnosis and other high-end instruments or equipment.At present,commercial MCP products in China still use the traditional high lead silicate glass materials developed in the 1970s,accompanied with the process technologies such as single fiber and hexagonal multi-fiber redrawing techniques,melt pressing,acid dissolution,and thermal hydrogen reduction.This leads to MCP’s main specifications such as gain,noise,and lifetime etc,are far behind the foreign developed countries,and becomes a development bottleneck such as space ultraviolet single photon counting imaging detection,analytical instruments,medical imaging equipment and low-light night vision.While the western developed countries impose an embargo on China for high performance microchannel electron multiplier with high gain,low noise,long life,and environmental reliability.The study of MCP’s conductive and secondary electron emission layers by atomic layer deposition（ALD）technology is a newly arisen research area in recent years.Commercialized ALD-MCP products have already emerged in Europe and the United States,while Chinese ALD-MCP products that are in the laboratory research phase of development.Such ALD-MCP cutting-edge technology can perform work gain increase,noise reduction and good environmental reliability.Therefore,the research in this dissertation focuses on the urgent demand for high-performance ALD-MCP devices in high-end High-end analytical instruments or equipment fields such as low light level night vision devices and time-of-flight mass spectrometers in China.We investigated the secondary electron emission layer and conductive thin films layer’s design and preparation technologies,and the corresponding experimental and theoretical analysis methods were surveyed.The purpose of this thesis is to get ALD-MCP devices technologies with both high gain and high reliability.The details are as follows:（1）Mg O and Al₂O₃ nanofilms with various thicknesses were prepared by ALD process,and the dependence of secondary electron emission coefficient（SEY）of thin films on the thickness of nanofilms was investigated.A semi-physical theory of secondary electrons that is suitable for the bilayer structure of nanofilms was derived by applying classical secondary electron emission theory,and quantitative explanation with calculation of double layer structure SEY was realized.The intrinsic relationship between the surface SEY of nanofilms and their thickness was quantitatively explained.Combining experimental results and theoretical analysis,the SEY values suitable for typical electron energy ranges in MCP were obtained.（2）Carrying out research on the environmental stability of SEY.During this research some phenomenens was discovered,such as Al₂O₃ nanofilms SEY have good stability,and SEY in Mg O thinfilms presented the serious attenuation due to surface deliquescence.The environmental stability of Mg O thinfilms was effectively improved by plating a protective layer on the surface and sputtering doped gold particles with a slight loss of SEY.The charge accumulation behavior on the surfaces of Al₂O₃ and Mg O nanofilms were analyzed by theoretical calculation under the continuous bombardment of the electron beam,by which the physical mechanism of charge accumulation affecting the electron multiplication process in MCP was revealed,and the charge level of Al₂O₃ nanofilms under typical energy electron bombardment is weaker than of Mg O nanofilms at the same time.（3）Research on the conductivity characteristics of Ti N thinfilms,the influence of film element composition on electrical conductivity was obtained,and a process method for preparing high conductivity Ti N thinfilms was acquired through process adjustment and theoretical guidance.The applicability of Ti N thinfilms in MCP conductive layer was confirmed.Ti N/Al₂O₃and Ru/Al₂O₃ conductive composite films were prepared by ALD process,and deposition process parameters of composite thinfilms that is suitable for the body resistance requirements of MCP were obtained.（4）Research on modeling and parameter simulation using CST software for MCP,the effects of operating voltage bias,electrode penetration depth,and functional layer thickness on MCP gain were quantitatively calculated.The results showed that the simulation and experimental results have good consistency within the range of operating voltage less than 1000 V.MCP with high gain,low dark current,and high reliability was achieved through optimizing the ALD process for functional layer deposition.The effective photon counting imaging detection was presented by applying ALD-MCP devices to microchannel plate single photon counting imaging detector.0.12counts/s.cm² dark count rate was obtained through dark count imaging detection.Compared to the domestic traditional microchannel plate,the noise was reduced by an order of magnitude;when application in third generation Ga As image intensifier,excellent noise and gain characteristics of ALD-MCP devices were acquired,which can compensate the low integrated sensitivity of some cathodes in the image intensifier,and brightness gain and other indicators have reached the international level.