Electron transmittance characteristics of MCP ion barrier film
DeLong Jiang, Kui Wu, Qingduo DuanMu, Ye Li, Guozheng Wang,
Yanjun Gao, Lichen Fu, Jingquan Tian
Changchun University of Science and Technology, Changchun, Jilin, 130022, P.R.China
ABSTRACT
The MCP ion barrier film in low-light-level imaging tube and its process techniques were introduced in this paper. The
electron transmittance of this film was studied. The results of half field-of-view testing comparisons and the concept of
dead voltage were presented. The dead voltage curve and the relation between dead voltage and thickness of film were
tested. The composition of film was analyzed by XPS.
Keywords: microchannel plates, without pollution film forming process, electron transmission characteristics, dead
voltage, UV photoelectric method
1. INTRODUCTION
Microchannel Plates (MCP) is a two-dimension array-type channel electron intensifier that is lumped by millions of
single channel electronic multipliers (CEM). It has a cellular structure. Fig.1 shows its basic structure and principle of
single channel electronic multiplier. It has already widely applied to the extremely faint optical signal detector,
low-light-level image device, electron, ion, UV ray, X ray and γ ray detectors because of its advantages such as high
gain, low noise, high resolution, wide band, low power consumption, long life and self-saturation effect, etc. In the third
generation low-light-level image intensifier (Fig. 2), high density electron cloud is formed in MCP output end. Residual
gas molecules are ionized to positive ions with the action of back proximity field intensity and they are feedbacked to
photocathode, which destroyed the structure of Cs-0 activate layer on surface of negative electron affinity subgroup GaAs photocathode, reduced sensitivity of photocathode, shortened life of the device, formed an ion spot on
output screen and made the background deteriorative. So we deposit a dielectric film of 3-4nm on MCP input surface,
call that ion barrier film (or electron transmission film). Most electrons can transmit it and it can prevent positive ions
feedback to the front proximity area effectively in order to avoid positive ions bombarding the photocathode, lengthen
device life and improve image background.1, 2
ⅢⅤ
channel
channel wall
output surface
electrode
input electrons
output electrons
input surface
electrode
braided curent
Figure 1: Microchannel plate and single channel
electron multiplier.
Figure 2: The third generation low-light-level image intensifier.
1.photocathode 2. front proximity area 3. MCP with film
4. back proximity area 5. screen 6. fiber-optic image inverter
2. LAYER PREPARATION TECHNOLOGY
In middle of the 1990s, ion barrier film was made on input surface of MCP by adopting traditional process (direct
current or magnetron sputtering) method and it was used in developing the third generation image intensifier.3
Advanced Materials and Devices for Sensing and Imaging II, edited by
Anbo Wang, Yimo Zhang, Yukihiro Ishii, Proceedings of SPIE Vol. 5633
(SPIE, Bellingham, WA, 2005) · 0277-786X/05/$15 · doi: 10.1117/12.573854
Downloaded from SPIE Digital Library on 28 Mar 2012 to 192.16.192.183. Terms of Use: http://spiedl.org/terms
443
→
Technological process: deposit an organic film carrier on the input surface of MCP
sputter aluminium film on film
carrier
forced oxidize
deprive the organic film carrier. The organic film carrier is kept intimate contact with
MCP all the time of whole course. It is extremely serious in polluting MCP especially C pollution while decomposing
and depriving the film. For this reason new process without pollution film forming was developed in recent years.
Technological process: sputter aluminium film on self-sustained organic film carrier (MCP nonintervention process)
adhere aluminium film to the input surface of MCP (the organic film carrier is not contact with MCP directly). It is
oxidized and the organic film carrier is deprived at the same time. The probability polluted by the organic matter in the
ion barrier film and MCP channel is lowest at the whole process.
→
→
→
3. ELECTRON TRANSMITTANCE CHARACTERISTICS OF FILM
3.1 Experiment of half field-of-view comparison
On MCP input surface, half of it coat Al2O3 film, the remaining half have no film. We adopt UV photoelectric method4
to test the characteristic of MCP .We observe and contrast through the experiment and so we can judge thickness of film
layers (d), dead voltage (Ve), uniformity of film layers, having flaw and needle hole or not, etc. Fig.3 and Fig.4 show
the principle of UV photoelectric method device and the relation between luminance distribution of screen and the input
electronic energy in the experiment of half field-of-view comparison. Fig.4 shows that when input voltage Vin<150V,
the output screen that was corresponded with film area is almost not illuminated. When Vin>150V, the luminance of
output screen increased linearly with the increase of electronic input energy. When Vin>700V, the luminance of output
screen with film and without film were basically corresponded. Fig.5 shows the relation among output current and input
energy at film area or without film area. It presents the same regular as the compared result of the luminance of output
screen.
UV light source
Photocathode
Vin
MCP
Vs
Screen
Figure 3: Pattern for principle of UV photoelectronic method.
Figure 4: Relations between screen output brightness distribution
and input electron energy of half film MCP.
12
-9
Iout/10 A
300
-9
200
250
1-d=4nm,Ve =200V
2-d=5nm,Ve =255V
3-d=7nm,Ve =360V
200
150
without film
with film
100
1
10
2
9
8
3
150
11
d/nm
Iout/10 A
3.2 Electron transmission characteristics of the whole film MCP5, 6
Relation between output electric current and input electronic energy of the whole film MCP was measured through
experiments, as is shown in Fig.6. Here we introduce the concept of dead voltage that is used to describe the ability that
7
6
100
5
50
50
4
Vin/V
0
200 400 600 800 1000 1200
Figure 5: The relation curve between
output current and input electron
energy of filmed and unfilmed area.
444
Vin/V
V e/V
3
0
0
0
200 400 600 800 1000 1200
Figure 6: The relation curve between
output current and input electron
energy of the whole film MCP (the
dead voltage curve).
100
200
300
400
500
Figure 7: The relation curve between
dead voltage and film thickness.
Proc. of SPIE Vol. 5633
Downloaded from SPIE Digital Library on 28 Mar 2012 to 192.16.192.183. Terms of Use: http://spiedl.org/terms
ion barrier film prevents electron from transmitting it. Ve provided here is the intersecting point of the reverse extension
line of the straight part of the curve and the voltage axle, which is exactly the value of the dead voltage of the film
which thickness is given definitely. If electronic energy is greater than the dead voltage, the probability of transmitting
film increase rapidly. So dead voltage can be regarded as a probable measurement of film thickness. Fig.7 presents the
relation of film thickness and dead voltage. It is nonlinear that mainly because outer electrons of the film atoms and free
electrons scatter with input electrons. High-energy electrons directly transmitting and inside secondary electrons that
scattered to transmit form the input electron-stream of MCP. The higher incident electronic energy, thinner film or lower
density of materials of film is, the greater probability of directly transmitting film and smaller scattering is. So there are
a group of curves shown in Fig.6.
3.3 Electrical characteristic of MCP with film
In the two processes of MCP film making, we have adopted UV photoelectric method to measure electron gains,
volume resistance and dark current change of MCP with film by contrast to those without film. The dates are given in
table 1. The gains reduction results from the film blocking electron and C polluting the surface. The increase of volume
resistance is caused by structural changes of surface and conducting layers. The reason why dark current is decreased is
that the increasing of potential barrier which is caused by structural changes of the surface.
Table 1: Change of electron gains, volume resistance and dark current when MCP with film or not.
Decrease of gain (%)
(VMCP=900V)
Traditional
process
New
process
～
5～10
15 20
Increase of volume resistance (%)
(VMCP=500V)
15
～20
Decrease of dark current (%)
(VMCP=1000V)
<10
<10
<5
4. COMPOSITION ANALYSIS ON FILM
The analysis results in X-ray Photoelectronic Spectrum (XPS) show that films prepared by traditional process and new
one all have O, Al, C, N, etc. We found that film interior composition of O and Al is the same basically as the surface
after analyzing by Ar ion deep etching. It is indicated by binding energy (peak position of characteristic) and atom
concentration of elements that Al exists as oxide of Al3+ in film, namely Al2O3. At the meantime we found that there
were less carbon content in new process than traditional process. The ratio of their atom concentrations is 10.71: 6.51.
Fig.8 shows the XPS analysis chart.
Figure 8: The XPS analysis of the film surface on filmed MCP.
(a) Sample from conventional process. (b) Sample from new process
5.CONCLUSION
(1) Al exists as oxide of Al3+ in ion barrier film. According to structure and atom concentrations, we conclude that the
Proc. of SPIE Vol. 5633
Downloaded from SPIE Digital Library on 28 Mar 2012 to 192.16.192.183. Terms of Use: http://spiedl.org/terms
445
film is Al2O3.
(2) Dead voltage is an important parameter to evaluate the electron transmittance characteristics of ion barrier film. Its
value is a kind of indirect method to predicate film thickness too.
(3) Half field-of-view comparison is a direct-vision and feasible method to judge film exists or not, thickness and
homogeneity of layer, etc. There are practical meanings.
(4) Ion barrier film without pollution forming process is scientific and feasible. It has wide application prospects for not
only pollution is light but also the film has a little effect on MCP characteristic.
(5) In order to attribute ion being blocked ability by MCP ion barrier film quantitatively, it is imperative to measure ion
transmittance.
REFERENCES
1. M J Iosue, Phoenix A Z, Night vision device and method, [J]. U.S. Patents, US6198090B1, 2001.
2. Zou Yisong, The electric vacuum image device and theory analysis, (M). Beijing, The publishing house of national
defense industry, 1989, § 2.1, § 6.1
3. Tian Jingquan, Jiang Delong, et al., Non-crystalline Al2O3 electronic transmission film of MCP, [J]. Electronic
Journal, 1996, 24(8):1-5
4. Tian Jingquan, Zhang Baifu, et al., UV-Photomethod for mesurement of MCP characteristic Parameters, [J]. SPIE,
1990, 1230: 228-230
5. Csorba P I., Recent advancements in the field of image intensification: the generation 3 wafer tube, [J]. Applied
Optics, 1979,18(14): 2440-2444
6. Timoty W Sinor and Joseph P Estrare, An Analysis of electron Scattering in thin dielectric used as ion barriers in
Generation III image tubes, [J]. SPIE, 2003, 4096: 23-32
446
Proc. of SPIE Vol. 5633
Downloaded from SPIE Digital Library on 28 Mar 2012 to 192.16.192.183. Terms of Use: http://spiedl.org/terms