Biomedical Engineering Reference
In-Depth Information
Figure 4.29
The TMAH etching setup used for micromachining
water bath (from VWR Scientific, Model 1235 PC) was used to control the temperature
of the TMAH. To maintain the TMAH at 90
◦
C, the temperature of the water was set
to 95
◦
C. A condenser at the top of the container prevented evaporation of TMAH. The
condenser was kept cool by circulating the water at a flow rate of about 1 L min
-1
.The
samples were placed in a sample holder and inserted into the container. The previous
characterization tests showed that etch rates of silicon and thermal oxide are equal to
0.670 μmmin
-1
and 1.15 A
◦
min
-1
, respectively. Therefore, to etch 180 μm of silicon
(
<
100
>
direction), 4.5 hours were required. As previously mentioned, the sensor consists
of two parts. One part, which served as the support, was etched for 1.5 hours to obtain an
etch depth of 60 μm, while the top parts were maintained in TMAH for 4.5 hours to etch
through and release the hanging beams. Samples of etched parts, in which Figure 4.30a is
the top part with three beams and Figure 4.30b is the support, are shown in Figure 4.30.
Etched
cavity
(a) Top part
(b) Bottom part
Figure 4.30
Samples of micromachined silicones
