**3. Results and discussions**

186 Dielectric Material

higher 20%.

three samples is measured by SAIKAWA ET-100. The industrial required elongation rate is

**Figure 6.** The schematic diagram of the thin wire plasma annealing system

Diameter of copper wire (mm) 0.2 Dielectric thickness (mm) 2.5 Dielectric material Glass Gap length (mm) 4.9 Reactor length (mm) 100

Gas Ar/He/N2

Gas mass low (l/min) 5 Applied voltage frequency (kHz) 45 Velocity of copper wire (m/min) 30

**Figure 7.** Cylindrical DBD reactor

**Table 1.** Experimental setup parameters

#### **3.1. Dielectric permittivity measurement**

The dependence of the dielectric permittivity on the frequency in APDBD annealing system is measured by electrode contact and CLR as shown in Figure 9. Dielectric material is placed sandwich in two aluminum electrodes, high voltage, high frequency function generator is used as power supply. Table 3 shows the experiment equipment be used in this study.

As shown in Figure 9, the dependence of dielectric permittivity on the dielectric voltage V is expressed via capacitance C as

$$V = \frac{I}{j \cdot o \cdot \text{C}} \tag{l}$$

where parallel capacitor C is expressed by

$$\mathbf{C} = \frac{\boldsymbol{\varepsilon}\_r \cdot \boldsymbol{\varepsilon}\_0 \cdot \mathbf{S}}{d},\tag{2}$$

where S is area of dielectric, d is discharge gap, εr and ε0 is the dielectric and free-space permittivity, respectively. From equation (1) and (2) the dielectric permittivity (3) can be expressed as

$$
\varepsilon\_r = \frac{d}{\varepsilon\_0 \cdot S} \cdot \frac{I}{o\nu} \cdot \frac{1}{V} \,. \tag{3}
$$

Effect of Dielectric in a Plasma Annealing System at Atmospheric Pressure 189

**Figure 10.** Dependency of dielectric permittivity on frequency

**Figure 11.** The dependence of elongation rate on frequency

0

5

10

Elongation rate

 [%]

15

20

**3.3. Dependence of annealing temperature on dielectric material** 

In this part, the effects of dielectric's material on annealing condition are observed. Figure 12 shows the comparison of the elongation rate with the dielectric substances. This result shows that the elongation rate strongly depends on the dielectric materials. The elongation rate using

32.5 35.0 37.5 40.0 42.5 45.0 47.5

Frequency [kHz]

**3.2. Dependence of annealing temperature on frequency** 

Figure 11 shows the experiment result, the dependence of elongation rate on frequency. The result shows the weakly positive relation between the elongation rate and the input frequency. When the frequency increases from 30 kHz to 40 kHz, the elongation rate slightly increases. Thus, we estimate that frequency has no effect on the annealing temperature.

For comparison, the CRL meter also is used to measure the dielectric permittivity as shown in Figure 9.

**Figure 9.** The schematic diagram of the dielectric permittivity measurement

From equation (3), the dependence of dielectric permittivity on frequency was shown in Figure 10. The results show that the dielectric permittivity in the APDBD decreases when frequency increases. At 45kHz, the dielectric permittivity of BN and Al2O3 are 12.9 and 6.79, respectively. Moreover, Table 4 shows the comparison of the dielectric permittivity at three measurement methods; our analysis, LCR, and literature. The results also show that at low frequency, the dielectric permittivity is higher than that literature however, at high frequency they are nearly the same.



**Table 3.** Equipment used

**Table 4.** Comparison dielectric permittivity between measurement and literature

**Figure 10.** Dependency of dielectric permittivity on frequency

188 Dielectric Material

expressed as

in Figure 9.

where S is area of dielectric, d is discharge gap, εr and ε0 is the dielectric and free-space permittivity, respectively. From equation (1) and (2) the dielectric permittivity (3) can be

> 0 <sup>1</sup> . *<sup>r</sup> d I S V*

 

For comparison, the CRL meter also is used to measure the dielectric permittivity as shown

From equation (3), the dependence of dielectric permittivity on frequency was shown in Figure 10. The results show that the dielectric permittivity in the APDBD decreases when frequency increases. At 45kHz, the dielectric permittivity of BN and Al2O3 are 12.9 and 6.79, respectively. Moreover, Table 4 shows the comparison of the dielectric permittivity at three measurement methods; our analysis, LCR, and literature. The results also show that at low frequency, the dielectric permittivity is higher than that literature however, at high

> Electrode contact LCR Literature [20, 21] BN Al2O3 BN Al2O3 BN Al2O3

6.8\* 8.1 10 31.7 22.9 4.95 4.76

**Table 4.** Comparison dielectric permittivity between measurement and literature

(3)

**Figure 9.** The schematic diagram of the dielectric permittivity measurement

Function generation NF Corporation model WF1973 Oscilloscope Agilent Technologies DSO 1024A High voltage probe Agilent Technologies N 2863A LCR meter Agilent Technologies Ul732A

Dielectric permittivity ε<sup>r</sup>

1 5.95 4.82

100 7.19 5.46 7.83 5.12

frequency they are nearly the same.

**Table 3.** Equipment used

45 12.9 6.79

Frequency f [ kHz]

#### **3.2. Dependence of annealing temperature on frequency**

Figure 11 shows the experiment result, the dependence of elongation rate on frequency. The result shows the weakly positive relation between the elongation rate and the input frequency. When the frequency increases from 30 kHz to 40 kHz, the elongation rate slightly increases. Thus, we estimate that frequency has no effect on the annealing temperature.

**Figure 11.** The dependence of elongation rate on frequency

#### **3.3. Dependence of annealing temperature on dielectric material**

In this part, the effects of dielectric's material on annealing condition are observed. Figure 12 shows the comparison of the elongation rate with the dielectric substances. This result shows that the elongation rate strongly depends on the dielectric materials. The elongation rate using BN is higher rate than using SiO2. According to a comparison of properties of some dielectric materials (SiO2, Al2O3, BN and glass), we acknowledge that dielectric with higher dielectric constants is more effective to reach the annealing temperature as shown in Table 5. Physical characteristics of the dielectric, such as thermal expansion and melting point, are also important. For example, from our experiment the alumina can be suddenly broken with long duration annealing using a water-cooled electrode due to its large thermal expansion. For the best annealing result, boron nitride is an excellent choice for the dielectric material.

Effect of Dielectric in a Plasma Annealing System at Atmospheric Pressure 191

driven through the reactor, the chatter motion changes the discharge gap length and heating point on the wire surface and consequently, the annealing result. Moreover, when the thin copper wire is annealed in a wide reactor, discoloration and unevenness occur on the wire surface due to the streamer length density reduction. To obtain a steady discharge state, it is usually necessary to reduce discharge gap length. However, decreasing the reactor gap

reduces the discharge volume and consequently, the annealing temperature.

**Figure 13.** The dependence of elongation rate on dielectric thickness

**Figure 14.** The dependence of elongation rate on dielectric size

0 1 2 3 4 5 6 7 8 9 10 11

Dielectric radius [mm]

0

5

10

Elongtion rate [%]

15

20

25

**Figure 12.** The dependence of elongation rate on dielectric material


**Table 5.** Material properties of dielectric
