Biomedical Engineering Reference
In-Depth Information
Si
Si
3
N
4
FIGURE 1.11
Micromachining. of. a. cantilevered. tip.. (From. Folch,. A.,. M.S.. Wrighton,. and. M.A..
Schmidt,.“Microfabrication.of.ultra-sharp.Si.tips.on.Si3N4.cantilevers.for.atomic.force.microscopy,”.
J. Microelectromech. Syst.
,.6,.303,.1997..Figure.contributed.by.the.author.)
underetching a silicon nitride square atop a Si layer, which itself is resting on a cantilever made
of silicon nitride). And that is a relatively simple device!
Micromachining processes oten include many such photolithography/etching steps, but
unfortunately, the structural materials that are (traditionally) “allowed” are very few—mostly
(crystalline or amorphous) silicon, silicon oxide, and silicon nitride. Yet, it is remarkable how
many structures can be manufactured with just a few combinations of materials and chem-
istries. Using electrochemical deposition of metals and ceramics, and planarization processes
borrowed from the integrated circuit chip industry, multilayer devices with arbitrary 3-D geom-
etries that incorporate moving parts (gears, tweezers, etc.) with 2-μm resolution are possible
(
Figure 1.12
). However, the processing cost of the irst wafer ranges from $10,000 to $100,000,
depending on the complexity of the device (the cost per device can be lowered if there are several
devices per wafer and as production proceeds).
Three-way mechanical switch
500 µm Microfluidic valve
500 µm
Microconnectors with 3-1
mechanical switch
Energy-harvesting mechanism
1 mm
500 µm
FIGURE 1.12
State-of-the-art.of.3-D.micromachining..The.structures.are.made.of.ceramics..Images.
courtesy.of.Microfabrica,.Inc..(Note:.the.igure.is.not.meant.to.endorse.Microfabrica's.technology.
over.other.competing.technologies.)
