For power generation experiments, we develop a prototype
electret generator. Figure 3 shows the fabrication process of
the electret plate. Firstly, Cr/Au/Cr (10/100/10 nm in thickness)
thin films are deposited on a 0.7 mm-thick Pyrex wafer
using an EB evaporator, followed by patterning with standard
lithography and wet etching. Then, CYTOP (CTL-809M) is
spun-on at a rotational speed of 1,000 rpm for 20 seconds and
soft-baked at 100 ˚C for 30 minutes. This process is repeated
7 times to obtain a 20 µm-thick film, and is fully-cured at 185
˚C for 1.5 hours. Next, copper is evaporated and patterned as
the metal mask. Finally, the CYTOP film is etched by O2
plasma with 100 W RF power for 60-70 minutes. The counter
electrode is fabricated with a similar process. Figure 4 shows
the patterned electret film with guard electrodes. The width of
electret and guard electrodes is 150 µm, and the gap in beNeedle
voltage -8 kV
Grid voltage -600 V
Temperature 120 ˚C
Charge time 10 min.
Table 1. Condition of corona-charging.
Base electrode (Cr/Au/Cr)
CYTOP
Metal mask (Cu)
(a)
(b)
(c)
(d)
PYREX
Base electrode
CYTOP Guard electrode
Fig. 3. Fabrication process of the electret plate : (a) Deposit
and pattern base electrode (Cr/Au/Cr), (b) Spin-on and cure
CYTOP, (c) Deposit and pattern metal mask (Cu), (d) O2 plasma
etch and remove metal mask.
Fig. 4. Glass substrate with patterned electret.
Electret
Guard
electrode
- 281 -
tween is 30 µm. The total area of the electret is 10 x 20 mm2
.
The electret plate is then charged by corona discharge. The
condition of corona-charging is shown in Table 1. The temperature
during charging is kept at higher than the glass transition
temperature of CYTOP. Average surface voltage of about
-600 ~ -1000 V is obtained after this charging process.