Ion barrier film (IBF) on the input side surface of Micro-channel Plate (MCP ) has a dual role in the high electron transmittance and high ionic blocking rate, and the quality of the film is very strict, so to choose a good coating way to meet the application of IBF-MCP in the third image intensifier is very important. Ion beam sputtering deposition (IBSD) technology is a relatively mature coating technology which can obtain a dense strong adhesion and smooth, high-quality film. This paper is carried out from the quality analysis on surface morphology, crystal structure and coating quality and comparison with qualified film to determine a better way to prepare IBF on the input side surface of MCP.
The noise factor, which is the main factor affecting the noise performance of image intensifier and can accurately reflect the noise characteristics of the micro-channel plate(MCP), is the ratio of the input signal to noise ratio (SNR) and the output SNR. According to definition of noise factor of micro channel plate, noise mechanism and test principle, noise factor of filmed MCP test system is established in order to study the technical way to reduce noise factor of MCP. Because the input surface of the MCP is covered with ion barrier film to block the feedback ions, which have a great impact on the noise factor of the MCP. Hence, noise factor of filmed MCP and un-filmed MCP is measured respectively, and noise factors with different materials and different filmed thickness are measured too. Relationships between noise factor and filmed thickness, noise factor and output SNR of image intensifier have been obtained. That is valuable to reduce the noise of filmed MCP.
Rb+, Cs+ and other alkali metal ions in the Micro-channel Plate（MCP）channel, under the action of an electric field, leave out of the channel wall of MCP, and accelerate to input surface of channel along the opposite direction of the electric field to form ion feedback-induced noise. The feedback ions will cause great harms, it will bombard the cathode surface, resulting in decreased cathode sensitivity, reducing tube life, so you must take measures to reduce ion feedback-induced noise. This paper analyzes how to reduce ion feedback-induced noise from five aspects of the MCP materials, etching, annealing in hydrogen, high-temperature baking and electron scrubbing. Through the utilization of mixed alkali effect of suppressing mutual diffusion and decreasing internal network cavity to improve structure of MCP glass wall, the diffusion coefficient of each ion is reduced; the content of Al2O3 is reduced to reduce the Na+, K+ diffusion losses; etching process is optimized, except for the acid corrosion, the alkali corrosion, special acid etching and vacuum baking process are used; annealing in hydrogen technology is also optimized, the time of annealing in hydrogen was chosen on 270 ~ 350 minutes; and the vacuum baking and electron scrubbing are handled before manufacturing. By the above methods the ion feedback-induced noise is reduced.
First proximity voltage is the voltage between the cathode of Low Light Level image intensifier and the input surface of
Micro-channel plate（MCP）. There are so many factors influencing the image intensifier performance, and the first
proximity voltage is one of the most important factors that can not be ignored. Based on the theory analysis and test of
different proximity voltage on the gain、signal-to-noise ratio and equivalent background noise, this test has studied on the
important performance of Gen III image intensifier effected by the proximity voltage. By the experimental study, the
increase of first proximity voltage to a certain extent can improve gain、signal-to-noise ratio and equivalent background
noise at the same time. The main cause of this phenomenon is that the increase of proximity voltage can enlarge the
incident electron energy, and then improve the quantum efficiency of the incident electron; meantime, stray electron
produced by field emission at the action of the electric field of filmed-MCP will lead to equivalent background
deterioration. Ultimately we conclude that: 1) Signal to noise is proportional to the square of he cathode sensitivity,
increases with the first collision energy of the incident electron, especially at 200-500ev. 2)In the increasing process of
voltage from 300v to 800v, the gain of filmed-MCP increases rapidly, but lower again when Upk increases further because
of gain self-saturation; lgG and lgUpk are linear relationship, thus the curve can intuitively demonstrate the relationship
between them. 3) Stray electron produced by field emission at the action of the electric field of filmed-MCP will lead to
equivalent background deterioration, but will not exceed the requirements of technical specifications（2.5×10-7lx）.
In order to solve the design of screen structure and the compatibility of it with the performance of the
tube, we test the LE of screen in different structure and draw the LE curve. By certain methods of
analysis, we get more information about screen performance. The curve with more information has
great signification, thus it can improve the screen structure and process design. An optimal operating
voltage can be find in the LE curve for each type of structure screen, thus it can match the performance
of the entire tube.
As the development of Gen III Image Intensifier, photocathode sensitivity, spatial static resolution and
signal-to-noise ratio of the devices are continuously improved except for the view effect. However, for
most devices, the equivalent background illumination (EBI) is excessive, and considerable part is more
than an order of magnitude. Many factors have an effect on the EBI of the Gen III Image Intensifier. By
academic analysis and experiment research, it is demonstrated that: It is the thermal electron emission
of photocathode, dark current, gain of micro-channel plate (MCP) with ion barrier film(IBF), electric
field strength between MCP and photocathode and the light feedback of phosphor that lend to the EBI,
but for the phosphor screen made by the normal process, because of the aluminum film, EBI caused by
the optical feedback is slightly lower, which can not cause the excessive EBI. For the MCP with IBF
after normal processing, even the first focused voltage is added to 350V, the EBI does not exceed the
highest value of 1.66×10-7 allowed by national military standard. Needless to say the photocathode is
the focus factor of the EBI after excluding the phosphor screen, the MCP and other influencing factors.
It is believed that the thermal electron emission of photocathode leads to the excessive EBI. Finally,
without reducing the photocathode sensitivity, by optimizing activation technics, i.e., reduce CsO
quantity, and aging test disposal, the thermal electron emission is weaken, the EBI is becoming lower,
most of the products satisfy with request of technical standard in this index. That is valuable to
accelerate the engineering of Gen III Image Intensifier.