22P006-O
Ignition Characteristics Relating with Shape of Floating Electrodein Micro ICP source
マイクロ誘導結合プラズマ源に導入した浮遊電極の形状と点火特性
H. Asano, Y. Yokoyama, H. Matsuyama, R. Sato, S. Kumagai and M. Sasaki
浅野博敬, 横山佳弘, 松山弘樹, 佐藤龍仁, 熊谷慎也, 佐々木実
Dept. of Advanced Science and Technology, Toyota Technological Institute,2-12-1, Hisakata, Tenpaku-ku, Nagoya 468-8511, Japan
豊田工業大学 〒468-8511 名古屋市天白区久方2-12-1
The micro-plasma can generate the local high-density plasma without using the vacuum system. MEMS
technique will be applied for realizing the small plasma source. Inductively coupled plasma (ICP) issuitable, since its density is higher using the small number of elements. The difficulty is the ignition. We
have reported that the floating electrode can enhance the ignition. Some electrode shapes in 2-different
setups are examined with the feasibility of the combination with MEMS structures.

1. Introduction
Micro-plasma source is expected to match with
MEMS devices since the atmospheric pressure
decreases the characteristic length down to mmlevel. In addition, saving power and gas
consumptions are also expected. Among manyplasma setups, ICP is attractive since it cangenerate higher plasma density using the fewer
number of elements. However, the ignition of ICP
is troublesome. We have first reported that theignition can be easier by introducing the floating
electrode using a prototype setup of the glass
epoxy substrate with the milled gas channel [1].
Although the effect of the floating electrode isclear, there are many unknown factors especiallyfor introducing this technique in MEMS devices.
In this study, two different plasma setups withMEMS elements are examined especially relating
to the floating electrode.
2. Experimental setups
Two different ICP setups are tried using 100MHz
power source. The magnetic field occurs around thecurrent path. The floating wire electrode receives
this field and the inductively generated voltage isconsidered to triger the ignition. Figure 1(a) is theplaner type. ICP coil is U-shaped one-turn coil. The
center region is the trench of the gas channel, insidewhich MEMS floating electrode is introduced.
Figure 1(b) is the tube type. The spiral coil is
combined with the gas tube. The floating wire isplace near to the spiral coil. The capillary and thefloating wire are integrated to one MEMS element.
3. Devices
Figure 2 shows the fabricated floating electrodefor the setup of Fig. 1(a). The original Si wafer is

100 MHzHe

floating wire
plasmacover glass

2mm coil

Hglassepoxy
substrate(a)
100MHzHcoil

He
capillary(b)

1mm
plasmafloating wire

Fig. 1: Schematic drawing of setups for generating
micro plasma. (a) Planer-type using U-shaped ICPcoil. (b) Tube type using spiral ICP coil.

200-mm thick, and the through Si etching is carriedout for the fabrication. The structures are 20-mm
wide beams. About 900 nm-thick Al is deposited on
Si for the electrical conduction. 18 different shapes
are prepared being connected to thick Si frame.
The electrode shape can be grouped with C-shape,spiral, and loop with bow-tie (two triangular tips
facing each other). C-shaped electrode is neither
stably obtained nor mechanically handled.
Figure 3 shows the device chip for the setup ofFig. 1(b) integrating the floating wire and thecapillary tube. The size is 8x3 mm2. The center60spiralIgnition power [W]C shapeloop withbow-tiegap

q50
200um gap spiral
100um gap spiral

40

100um 90deg. bow-tie
100um 60deg. bow-tie

30300um 60deg. bow-tie
100um 30deg. bow-tie

20
2.5

4.0

4.5

5.0

5.5

6.0

Fig. 4: Ignition power against 6 different electrodeschanging He gas flow rate.
100mm

thermally shrinking tube

O30Fig. 2: MEMS floating
electrodes for setting inside U-shaped coil in Fig.
1(a). The magnified image is the loop with bow-tie.

bow-tie

3.5

He gas flow rate [m/s]24mmｌoop with bow-tie

3.0

tube

MEMS device

spiraltwin spiral

bow tie
bow-tie

Fig. 5: Photo of the ignition. The ignition point is
considered at the bow-tie.

Fig. 3: MEMS device of the floating electrodeintegrated with the gas flow channel.

has the dependence on He gas flow rate having its
valley at about 3.5 m/s. The spiral electrode shows
the higher ignition power compared with the loop
electrode with the bow-tie. The minimum value inour experiment is 28 W. The gap between bow-tie
is 100 mm and the cone angle is 30O.
Figure 5 shows the photo of the ignition using
the electrode shown in Fig. 3. The ignition is
obtained only for the loop electrode with thebow-tie. The bow-tie is at the end of the loop at theupstream of the gas flow. The gap between bow-tie
is 90 mm and the cone angle is 60O. The ignition
power is 138 W. He gas flow is 49 ml/min. The
average gas flow speed is similar to that of Fig. 4.

trench is the gas flow channel. The floating
electrode is Al film pattern on the top surface faced
to the gas channel. 8 different electrode shapes aredesigned. The floating electrode is grouped by loopwith bow-tie and spiral. The bow-tie positions are at
the center or the end of the loop.
4. Results
Figure 4 shows the ignition power using theelectrode as shown in Fig. 2. The ignition power

Acknowledgments
This research was supported by MEXT "TokaiRegion Nanotechnology Manufacturing Cluster inthe knowledge Cluster Initiative (the second stage)"and the program for forming strategic research
infrastructure (S0801058).
References[1] S. Kumagai, H. Matsuyama, Y. Yokoyama, M. Hori,M. Sasaki, Jpn. J. Appl. Phys. 50 (2011) 08JA02.