Page 210 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

190 MICROSTEREOLITHOGRAPHY FOR MEMS

Monitor Photopolymerizable resin
Focused beam

CCD camera

X-scan stage
X-scan mirror

Shutter
Attenuator

Ti: sapphire laser

Argon ion laser

Figure 7.23 Optical setup for the two-photon MSL system. From Maruo and Kawata (1998)

1-2
1
- 1.0-
3
5- 0.8-
u
I 0.4-
< 0.2-
0.0 I I I I I I I 1
350 400 450 500 550 600 650 700 750
Wavelength (nm)

Figure 7.24 Absorption spectrum of the two-photon resin

and the Z-stage (Sigma Optics) were 0.3 and 0.5 urn, respectively. The peak beam power
in the resin was about 3 kW with a repetition of 76 MHz and pulse width of 130 fs at
a wavelength of 770 nm. The resin used was SCR-500, which is a mixture of urethane
acrylate oligomers or monomers and photoinitiators. The absorption spectrum of this resin
is shown in Figure 7.24. The resin is transparent at 770 nm, meaning that polymerisation
cannot take place by one-photon absorption.
Some high aspect ratio and extremely fine 3-D microstructures have been fabricated
using two-photon MSL, as shown in Figure 7.25 (Maruo and Kawata 1998). The lateral