Collaborators

• M.G. Allen, Georgia Inst. of Tech.
• J.G. Brisson, MIT
• V. Bulovic, MIT
• D. J. Perreault, MIT
• A.H. Slocum, MIT
• C.R. Sullivan, Dartmouth
• M.S. Triantafyllou, MIT
• D.L. Trumper, MIT
• E.N. Wang, MIT

Graduate Students

• M. Araghchini, EECS
• W. Bosworth, ME
• S. Chang, EECS
• N. Farve, EECS
• V. Fernandez, ME
• S. Hou, EECS
• Z. Trimble, ME
• F. Yaul, EECS

Support Staff

• D. Bizi, Admin. Asst. I

Publications

F. Herrault, B. C. Yen, Z. S. Spakovszky, J. H. Lang and M. G. Allen; “Fabrication and performance of silicon-embedded permanent-magnet micro-generators,” IEEE/ASME Journal of Microelectromechanical Systems, 19, 4-13, February 2010.

M. Ryou, P. Cantillon-Murphy, J. H. Lang and C. C. Thompson; “A magnetic retrieval system for pancreaticobiliary stents: obviating the need for second endoscopy,” Gastrointestinal Endoscopy, 71, Issue 5, AB134, April 2010.

M. K. Ryou, P. Cantillon-Murphy, J. H. Lang and C. C. Thompson; “Transoral endoscopic creation of immediate cholecysto-gastrostomy using smart self-assembling magnets via endoscopic needle (SAMSEN),” Gastrointestinal Endoscopy, 71, Issue 5, AB242, April 2010.

M. K. Ryou, P. Cantillon-Murphy, D. E. Azagury, S. N. Shaikh, G. Ha, J. H. Lang, and C. C. Thompson; “Transoral endoscopic creation of immediate gastrojejunostomy using self-assembling magnets via endoscopic needle (SAMSEN),” Gastroenterology, 138, Issue 5, Supplement 1, S-113, May 2010.

M. K. Ryou, P. Cantillon-Murphy, S. Shaikh, D. Azagury, G. Ha, J. H. Lang and C. C. Thompson; “Harnessing the power of magnets: novel uses in advanced endoscopic therapies,” Gastrointestinal Endoscopy, 71, Issue 5, AB99, April 2010.  Also presented at American Society of Gastrointestinal Endoscopy Video Forum, New Orleans, LA, May 3, 2010.

M. McCarthy, J. Allison, D. Jenicek, A. Kariya, C. Koveal, J. H. Lang, J. G. Brisson and E. N. Wang; “High-performance air-cooled heat exchanger with an integrated capillary-pumped loop heat pipe,” in Proc. Twelfth Intersociety Conference on Thermo and Thermomechanical Phenomena in Electrical Systems, TT15-2, Las Vegas, NV, June 2-5, 2010.

S. Sato, S. Jovanovic, J. H. Lang and Z. S. Spakovszky; “Demonstration of a palm-sized 30-Watt air-to-power turbine generator,” in Proc. ASME International Gas Turbine Conference, GT-2010-22925, Glasgow, UK, June 14-18, 2010.

P. Cantillon-Murphy, M. Ryou, S. N. Shaikh, D. Azagury, M. Ryan, C. C. Thompson and J. H. Lang; “Magnetic retrieval system for stents in the pancreaticobiliary tree,” IEEE Transactions on Biomedical Engineering, 57, 2018-2025, August 2010.

A. Z. Trimble, J. H. Lang, J. Pabon and A. H. Slocum; “A device for harvesting energy from rotational vibrations,” Journal of Mechanical Design, 132, 91001/1-6, September 2010.

M. B. Read, J. H. Lang, A. H. Slocum and R. Martens; “Contact resistance in flat-on-flat and sphere-on-flat thin films,” in Proc. 56th IEEE Holm Conference on Electrical Contacts, pp. 348-355, Charleston, SC, October 4-7, 2010.

A. Murarka, C. Packard, F. Yaul, J. H. Lang and V. Bulovic; “Micro-contact printed MEMS,” Proc. IEEE Workshop on Micro Electro Mechanical Systems, pp. 292-295, Cancun, Mexico, January 23-27, 2011.

M. Ryou, P. Cantillon-Murphy, D. Azagury, S. N. Shaikh, G. Ha, I. Greenwalt, M. B. Ryan, J. H. Lang and C. C. Thompson; “Smart self-assembling magnets for endoscopy (SAMSEN) for transoral endoscopic creation of immediate gastrojejunostomy (with video),” Gastrointestinal Endoscopy, 73, 353-359, February 2011.

S. Sato, S. Jovanovic, J. H. Lang and Z. S. Spakovszky; “Demonstration of a palm-sized 30-Watt air-to-power turbine generator,” ASME Journal of Engineering for Gas Turbines and Power, accepted for publication.

A. Sprunt, A. H. Slocum and J. H. Lang; “Fracture fabrication of precision single-crystal silicon surfaces for MEMS devices,” Precision Engineerin, accepted for publication.

A novel sensing technology for unmanned undersea vehicles (UUVs) is under development. The project is inspired by the lateral line sensory organ in fish, which enables some species to form three-dimensional maps of their surroundings ^{[1] [2]} . The canal subsystem of the organ can be described as an array of pressure-sensors ^[3] . The lateral line allows fish to perform a variety of actions, from tracking prey ^[4] to recognizing nearby objects ^{[2] [5]} .  Similarly, by measuring pressure variations on a vehicle surface, an engineered pressure-sensor array allows the identification and location of obstacles for navigation. Several strain-gauge-based approaches to the sensing element are being tested. The two types presented here are silicon- and polymer-based technologies.

Both sensor designs share the following features. The array consists of thin diaphragms. Each sensor has an empty cavity behind the membrane connected via a common backplane to the others.  A set of strain gauge resistors on the diaphragms responds to pressure changes. When the sensor is placed in a Wheatstone bridge, the resulting output voltage can be used to determine the change in resistance in the strain gauges and thus the pressure difference between the two sides of the diaphragm. The two technologies differ chiefly in how strain is measured.  In the silicon-based approach, the shape of the resistor is altered slightly by strain. In the polymer-based approach, the distances between conducting particles embedded in the material adjusts as strain is applied.

The amplified voltage output bridges with strain-gauge resistors on diaphragms of various sizes as was measured as a function of applied pressure.  Generally, larger diaphragms are more stable and more sensitive, whereas small diaphragms maintain linearity over a wider range and are more physically robust. The deflections of the centers of silicon diaphragms are measured as functions of applied pressure.  Although larger diaphragms exhibit non-linear behavior, there are no hysteretic effects, thus enabling their usage for static and dynamic pressure sensing.

For the conductive polymer strain-gauge patterned onto a PDMS membrane, the resistances of the strain gauges are measured against the segment length. The resulting linear fit demonstrates consistency of resistivity across the patterned structure. Finally, observing output voltage in response to dynamic pressure applied with a syringe connected to the sensor indicates a bandwidth fast enough for underwater sensing.

1. J. C. Montgomery, S. Coombs, and C. F. Baker, “The mechanosensory lateral line system of the hypogean form of Astyanaxfasciatus,” Environmental Biology of Fishes, vol. 62, pp. 87-96, 2001.
2. C. von Campenhausen, I. Riess, and R. Weissert, “Detection of stationary objects by the blind cave fish Anoptichthys jordani (Characidae),” Journal of Computational Physiology A, vol. 143, pp. 369-374, 1981.
3. S. Coombs, “Smart skins: Information processing by lateral line flow sensors,” Autonomous Robots, vol. 11, pp. 255-261, 2001.
4. K. Pohlmann, J. Atema, and T. Breithaupt, “The importance of the lateral line in nocturnal predation of piscivorous catfish,” Journal of Experimental Biology, vol. 207, pp. 2971-2978, 2004.
5. T.J. Pitcher, B. L. Partridge, and C. S. Wardle, “A blind fish can school,” Science, vol. 194, pp. 963-965, 1976

Figure 1: Schematics of buried toroidal inductors in silicon. Left: 3-D rendering. Right: cross-sectional view. (For clarity, the polymer via layer is not represented.)

Passive components, namely inductors, transformers, and capacitors, are often the largest and most expensive components in power electronic circuits, and the magnetic components (inductors and transformers) are often responsible for a large portion of the power loss. As operating frequencies are increase, the physical size of the passive components can, in theory, be correspondingly reduced while maintaining or improving efficiency. However, increases in frequency also increase the severity of several losses. Realizing the potential for miniaturization and ultra-high efficiency requires new magnetic component designs, fabrication strategies, and materials.

As the switching frequencies of the power electronics rise and the size of the magnetics fall, new fabrication strategies for the magnetics become possible. In particular, with sufficiently small volume the magnetics can be embedded in the substrate of the power circuit or within a secondary substrate and flip-bonded above the power circuit. Moreover, toroidal magnetics fabricated in this manner provide the self-shielding necessary to mitigate electromagnetic interference, and they can be fabricated using standard MEMS bulk fabrication processes. The purpose of this work is to develop the analyses, design rules and fabrication processes necessary for the implementation and demonstration of such embedded magnetics that enable high-frequency operation and realize small size and low loss.

The work carried out here focuses on toroidal inductors such as that shown schematically in Figure 1. It is anticipated that all conductors in the figure will be fabricated from electroplated copper. The labeling in the figure suggests that the inductor is buried in the power electronics chip itself. Fabrication within a separate insulating substrate is under study, too.

It has been known for several decades that polymers doped with conducting particles, for example silicone nickel nano-particles, will exhibit a dramatically decreasing resistivity as the polymer is compressed. It is possible that the conductivity will vary by 12 orders of magnitude over a 40% strain ^[1] . Such composites conduct via tunneling from particle to particle, and the tunneling currents grow exponentially as the particles become closer together. These composites have already been used in applications from tactile sensors to fuses.

In this study we use the composites as the active element in an electronically-controlled switch. The Squeezable electronically controlled switch, referred to here as a “squitch,” is shown in Figure 1. In this embodiment, the squitch is a three-terminal device, with its terminals labeled as per the comparable terminals in a MOSFET. The central component of the device is the doped polymer labeled “Squitch Material” connected to drain and source electrodes. As fabricated, the squitch material would be a poor conductor, permitting little if any electron current to flow from the source to drain. That is, the resistance of this conduction path would be very large, putting the squitch in an off state. By applying voltage to the gate electrode, either positive or negative, an electric field is developed between the gate and the source. This electric field causes the gate to be attracted to the source, thereby compressing the squitch material. As the squitch material is compressed in the vertical direction, it begins to conduct, putting the squitch in an on state.

Thus, the squitch is a voltage controlled conductor, much the same as a FET or a BJT but with very large on-to-off conduction ratio and subthreshold swing (S) < 60 mV/dec, which allows for more aggressive supply voltage scaling and improvement in the energy efficiency.

1. D. Bloor, K. Donnelly, P. J. Hands, P. Laughlin, and D. Lussey, “A metal–polymer composite with unusual properties,” J. of Phys. D: Appl. Phys., 38 (2005) 2851–2860.

It is desirable to extend the functionality of MEMS to different form factors including large area arrays of sensors and actuators, and to various substrate materials, by developing a means to fabricate large-area suspended thin films. Conventional photolithography-based MEMS fabrication methods limit the device array size and are incompatible with flexible polymeric substrates. We present a new method for fabricating thin (140-nm-thick) suspended metal films in MEMS using micro-contact printing. These films can be utilized in pressure sensors, microphones, deformable mirrors, tunable optical cavities, and large-area arrays of MEMS sensors.

Our approach to MEMS fabrication involves the use of a stamp and a donor viscoelastic transfer pad that is coated with an organic release layer and a thin film of metal. The stamp consists of a layer of patterned polydimethylsiloxane (PDMS) atop a glass slide that is coated with a layer of electrically conducting indium tin oxide (ITO). The surface of this patterned PDMS stamp is placed in contact with the thin metal film on the donor transfer pad, and then the stamp is rapidly peeled away, picking up the metal film. The metal film ends up bridging the gaps in the patterns of the PDMS stamp, forming a capacitive MEMS structure. A continuous film of metal is lifted onto the stamp only if the stamp is peeled off the transfer pad rapidly.

This process avoids the use of solvents and etchants, eliminating the need for deep reactive-ion etching and other harsh chemical treatments. Solvent absence during fabrication also avoids the detrimental effects of MEMS stiction that can result during wet processing. MEMS fabrication on flexible polymeric substrates is also possible due to the absence of elevated temperature processing.

Thin films up to 0.78 mm² in area have been fabricated using the aforementioned process, as shown in Figure 1. These MEMS devices are actuated electrostatically to demonstrate the deflection of 25-μm-diameter films (see Figure 2).

1. A. Murarka, C. Packard, F. Yaul, J. Lang, and V. Bulovic, “Micro-contact printed MEMS,” in 2011 IEEE 24th International Conference on Micro Electro Mechanical Systems (MEMS), pp. 292-295, 23-27 Jan. 2011.
2. C. Packard, A. Murarka, E. W. Lam, M. A. Schmidt, and V. Bulovic, “Contact-printed microelectromechanical systems,” Advanced Materials, vol. 22, pp. 1840–1844, 2010.