This paper discusses the use of laterally deformable optical nanoelectromechanical systems (NEMS) grating transducers for sensor applications. For very small changes in the spacing of the nanostructured grating elements, a large change in the optical reflection amplitude is observed, making this an ideal transducer element for detecting very small amounts of relative motion. These devices are also very sensitive to wavelength, and could thus be used as tunable elements for spectrometry, as well as communications or inertial sensing. This anomalous diffraction property was predicted in previous work; here, we experimentally verify operation of these devices and demonstrate a motion detection sensitivity of 10 fm/Hz1/2, comparable to the most sensitive MEMS transducer. As optical devices, these sensors have additional advantages over electrical sensors, including high immunity to electromagnetic interference and the possibility of integration with fiber optics to create a network of sensors with a single remote optical source and detector.
Flavio Pardo, Vladimir Aksyuk, Susanne Arney, H. Bair, Nagesh Basavanhally, David Bishop, Gregory Bogart, Cristian Bolle, J. Bower, Dustin Carr, H. Chan, Raymond Cirelli, E. Ferry, Robert Frahm, Arman Gasparyan, John Gates, C. Randy Giles, L. Gomez, Suresh Goyal, Dennis Greywall, Martin Haueis, R. Keller, Jungsang Kim, Fred Klemens, Paul Kolodner, Avi Kornblit, T. Kroupenkine, Warren Lai, Victor Lifton, Jian Liu, Yee Low, William Mansfield, Dan Marom, John Miner, David Neilson, Mark Paczkowski, C. Pai, A. Ramirez, David Ramsey, S. Rogers, Roland Ryf, Ronald Scotti, Herbert Shea, M. Simon, H. Soh, Hong Tang, J. Taylor, K. Teffeau, Joseph Vuillemin, J. Weld
As telecom networks increase in complexity there is a need for systems capable of manage numerous optical signals. Many of the channel-manipulation functions can be done more effectively in the optical domain. MEMS devices are especially well suited for this functions since they can offer large number of degrees of freedom in a limited space, thus providing high levels of optical integration.
We have designed, fabricated and tested optical MEMS devices at the core of Optical Cross Connects, WDM spectrum equalizers and Optical Add-Drop multiplexors based on different fabrication technologies such as polySi surface micromachining, single crystal SOI and combination of both. We show specific examples of these devices, discussing design trade-offs, fabrication requirements and optical performance in each case.
We are developing membrane mirrors for use in adaptive optics, particularly in astronomy and vision science. We have micro-fabricated membrane mirrors from single crystal silicon using wet chemical etching and reactive ion etching. Membrane size, tension and operating voltage were selected to allow greater deformation of the mirror surface at low operating voltage than previous membrane mirror designs. Mirror devices consist of independently fabricated membrane and electrode array chips that are flip chip bonded together. We have fabricated electrode arrays with 256 and 1024 electrodes, and active diameters ranging from 6-10 mm (comparable to the size of the human pupil). Membrane-electrode hybrids are mounted to ceramic packages, wire bonded, and driven by off chip, D/A electronics. These devices are milestones in the development of an electret membrane mirror.
Ian Johnston, Huma Ashraf, Jy Bhardwaj, Janet Hopkins, Alan Hynes, Glenn Nicholls, Serrita McAuley, Stephen Hall, Lilian Atabo, Gregory Bogart, Avi Kornblit, Anthony Novembre
The Advanced Silicon Etch (ASER) process has been used for silicon substrate etching for the manufacture of SCALPELR (SCattering using Angular Limitation Projection E-beam Lithography) masks. The current SCALPELR mask fabrication process uses an aqueous solution of KOH to etch the membrane support struts in 100 mm diameter, <100> crystalline silicon wafers. This technique is undesirable for the manufacture of large diameter masks with thicker substrates, as it limits the maximum printable die size. Inductively coupled plasma (ICP) etching, using the ASER process, provides the only alternative etch technique. This gives support struts with vertical profiles, yielding a higher printable area than with wet etching, and is ideal for etching the substrates of large diameter masks. In addition to this, and to the benefits of dry over wet etching, the ASER process allows the use of wafers of any crystal orientation and gives greater flexibility in pattern placement and geometry. This paper presents process optimization data based on 200 mm diameter wafers, using a system designed specifically for this application. The key aspects of this work have focused on etch rate, CD control and uniformity enhancement. Etch rate determines the economic feasibility of this approach, particularly with etch depths of approximately 750 micrometer. Uniform etching is required to minimize the time to clear the membranes, and the CD tolerances must be met so that structural integrity is maintained. The large exposed silicon areas, (> 40% global and > 80% local), the macro loading effects caused by the edge of the pattern, and the need for near vertical strut profile, make these requirements more difficult to achieve. Etch rate and uniformity achieved, exceed the minimum specification of > 2 micrometer/min and < +/- 6% respectively.
The SCALPEL lithography system combines the advantages of high resolution and wide process latitude of electron beam lithography with the throughput of a projection system. The SCALPEL approach has the potential to meet the minimum feature size requirements of future IC generations down to 50 nm.
Gregory Bogart, Anthony Novembre, Avi Kornblit, Milton Peabody, Reginald Farrow, Myrtle Blakey, Richard Kasica, James Liddle, Thomas Saunders, Chester Knurek, Ian Johnston
SCALPEL is a tue 4X reduction technology that capabilities on high resolution capabilities from electron beam exposure and high throughput capabilities from projection printing. Current mask blank fabrication for SCALPEL technology use widely available 100 mm, crystalline silicon wafers. The use of 100 mm crystalline wafers and a wet, through wafer etch process causes the patterned strut width to increase as the wafer is etched and must be accounted for in the mask blank fabrication process. In the wet etch process, a 100 micrometers wide strut grows to 800 micrometers at the strut-membrane interface. As a consequence, the maximum printable die size due to the wafer size and the decreased amount of open area between each strut is 8 X 8 mm. Additionally, crystal defects in the silicon wafer affect the wet etch process and contribute to mask blank failures. A partial solution for an increased die size is to increase the wafer size used to make the SCALPEL mask blank. A 200 mm wafer is capable of producing large die sizes. This can be further improved by dry etching of the grill structure to form struts with vertical sidewalls. As a result, due sizes of 25 X 25 mm or 16 X 32.5 mm can be produced depending on the grill pattern used. However, use of large wafers and dry etching for mask blank formation has significant issues that must be addressed. Among the issues to be addressed are etch chemistries, etch mask materials, and wafer handling.
Scattering with angular limitation projection electron beam lithography is a true 4X reduction technology that capitalizes on high resolution capabilities from electron beam exposure and high throughput capability from projection.
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