Page 186 - An Introduction to Microelectromechanical Systems Engineering

Summary 165

attenuator from Lightconnect has a dynamic range (attenuation range) of 30 dB, a
wavelength dependence of attenuation of 0.25 dB, and a polarization-dependent
loss of 0.2 dB. The total insertion loss, which includes losses from fiber coupling, is
0.7 dB. The response time of the device is, as expected from the GLV, quite fast,
measuring 40 µs. The actuation voltage between the membrane and substrate is less
than 8V. The company also provides a specification for reliability: in excess of 100
billion cycles for wear out. While wear out is very subjective and not quantified, it
reflects the projected reliability of this device where displacements are very small
(λ /4 400 nm) and friction is nonexistent.
0
The fabrication is very similar to that of the GLV with a few exceptions. First,
lithography followed by an etch defines the reference posts with a height of 2.32
µm. A thin (20–60 nm) layer of silicon dioxide is thermally grown. A layer of sacrifi-
cial polysilicon or amorphous silicon is deposited. This layer must be optically
smooth, as any defects will subsequently imprint the moveable membrane. Holes
are etched through the sacrificial layer to allow for the anchor points to the sub-
strate. Silicon nitride is then deposited as the membrane material. It may be stochio-
metric or silicon rich. A lithographic step followed by an etch step pattern the
nitride layer into the desired membrane layout. Finally, xenon difluoride (XeF )
2
removes the sacrificial layer of silicon to release the membrane. A subsequent
evaporation step deposits a thin gold layer across the entire surface, ensuring high
reflectivity in the infrared.

Summary

This chapter reviewed a number of commercially available products with applica-
tions in imaging, displays, and fiber-optical telecommunications. The applications
are very diverse but share the common use of MEMS technology to manipulate
light. While MEMS have proven to be vital for the operation of the aforementioned
products, it remains an enabling technology and a means to an end. It is impera-
tive to understand the final application in order to assess the importance and
applicability of MEMS for that particular application.

References

[1] Cole, B. E., R. E. Higashi, and R. A. Wood, “Monolithic Two-Dimensional Arrays of
Micromachined Microstructures for Infrared Applications,” in Integrated Sensors, Micro-
actuators, & Microsystems (MEMS), K. D. Wise (ed.), Proceedings of the IEEE, Vol. 86,
No. 8, August 1998, pp. 1679–1686.
[2] Van Kessel, P. F., et al., “A MEMS-Based Projection Display,” in Integrated Sensors,
Microactuators, & Microsystems (MEMS), K. D. Wise (ed.), Proceedings of the IEEE, Vol.
86, No. 8, August 1998, pp. 1687–1704.
[3] Bloom, D. M., “The Grating Light Valve: Revolutionizing Display Technology,” Proc.
SPIE, Projection Displays III, Vol. 3013, San Jose, CA, February 10–12, 1997,
pp. 165–171.
[4] Chen, Y., et al., “Metro Optical Networking,” Bell Labs Technical Journal, January–
March 1999, pp. 163–186.
[5] Tomsu, P., and C. Schmutzer, Next Generation Optical Networks, Upper Saddle River, NJ:
Prentice Hall, 2002, pp. 68–70.