Author
R. Khanna
Bio: R. Khanna is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Microelectromechanical systems & Deep reactive-ion etching. The author has an hindex of 9, co-authored 9 publications receiving 434 citations.
Papers
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TL;DR: In this paper, a single-crystal silicon micromachined air turbine supported on gas-lubricated bearings has been operated in a controlled and sustained manner at rotational speeds greater than 1 million revolutions per minute, with mechanical power levels approaching 5 W.
Abstract: A single-crystal silicon micromachined air turbine supported on gas-lubricated bearings has been operated in a controlled and sustained manner at rotational speeds greater than 1 million revolutions per minute, with mechanical power levels approaching 5 W. The device is formed from a fusion bonded stack of five silicon wafers individually patterned on both sides using deep reactive ion etching (DRIE). It consists of a single stage radial inflow turbine on a 4.2-mm diameter rotor that is supported on externally pressurized hydrostatic journal and thrust bearings. This work presents the design, fabrication, and testing of the first microfabricated rotors to operate at circumferential tip speeds up to 300 m/s, on the order of conventional high performance turbomachinery. Successful operation of this device motivates the use of silicon micromachined high-speed rotating machinery for power microelectromechanical systems (MEMS) applications such as portable energy conversion, micropropulsion, and microfluidic pumping and cooling.
148 citations
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TL;DR: In this article, the problems and the solutions presented in this paper are readily applicable to any microelectromechanical system project involving the fabrication of multi-stack structures of two or more wafers containing intricate geometries and large etched areas.
Abstract: Multi-stack wafer bonding is one of the most promising fabrication techniques for creating three-dimensional (3D) microstructures. However, there are several bonding issues that have to be faced and overcome to build multilayered structures successfully. Among these are: (1) chemical residues on surfaces to be bonded originating from the fabrication processes prior to bonding; (2) increased stiffness due to multiple bonded wafers and/or thick wafers; (3) bonding tool effects; (4) defect propagation to other wafer-levels after high-temperature annealing cycles. The problems and the solutions presented here are readily applicable to any microelectromechanical systems project involving the fabrication of multi-stack structures of two or more wafers containing intricate geometries and large etched areas.
76 citations
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01 Jan 2003TL;DR: In this article, the problems and the solutions presented in this paper are readily applicable to any microelectromechanical system project involving the fabrication of multi-stack structures of two or more wafers containing intricate geometries and large etched areas.
Abstract: Multi-stack wafer bonding is one of the most promising fabrication techniques for creating three-dimensional (3D) microstructures. However, there are several bonding issues that have to be faced and overcome to build multilayered structures successfully. Among these are: (1) chemical residues on surfaces to be bonded originating from the fabrication processes prior to bonding; (2) increased stiffness due to multiple bonded wafers and/or thick wafers; (3) bonding tool effects; (4) defect propagation to other wafer-levels after high-temperature annealing cycles. The problems and the solutions presented here are readily applicable to any microelectromechanical systems project involving the fabrication of multi-stack structures of two or more wafers containing intricate geometries and large etched areas.
73 citations
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TL;DR: In this paper, the problem of profile control of narrow trenches in the vicinity of wider topographic features, as well as for etching high aspect ratio, anisotropic trenches with depths in the 300-500μm range, and widths between 12 to 18μm.
Abstract: This paper reports solutions to the problem of profile control of narrow trenches in the vicinity of wider topographic features, as well as for etching high aspect ratio, anisotropic trenches with depths in the 300–500 μm range, and of widths between 12 to 18 μm. Additionally, specific operating conditions are discussed to address uniformity variations across dies with diameters in excess of 4200 μm.
55 citations
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TL;DR: A microelectromechanical system (MEMS) turbocharger has been designed, fabricated, and tested as part of a Massachusetts Institute of Technology program aimed at producing a microfabricated gas turbine engine for portable power applications as discussed by the authors.
Abstract: A microelectromechanical system (MEMS) turbocharger has been designed, fabricated, and tested as part of a Massachusetts Institute of Technology program aimed at producing a microfabricated gas turbine engine for portable power applications. A gas turbine engine requires high-speed high-efficiency turbomachinery operating at tip speeds of several hundred meters per second. This MEMS turbocharger serves to demonstrate these requirements. The turbocharger's silicon rotor, which is supported on hydrostatic gas thrust and journal bearings in a silicon stator housing, was spun to 480 000 rpm, corresponding to a tip speed of 200 m/s. This paper discusses critical fabrication processes that enabled the capabilities of this device. Operational issues and test results are also presented. The turbocharger's compressor demonstrated a pressure ratio of 1.21 at a mass flow rate of 0.13 g/s, with a combined compressor-turbine spool efficiency of 0.24. Under these conditions, the turbine produced about 5 W of power. Results from the simultaneous operation of a spinning rotor and burning combustor within the microscale turbocharger are also presented. Experimental results compare well with analytical models and computations.
28 citations
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TL;DR: The history, current state of the art, and ongoing challenges for compact (less than a few cubic centimeters) magnetic power generation systems in the microwatts to tens of watts power range are discussed.
Abstract: This paper discusses the history, current state of the art, and ongoing challenges for compact (less than a few cubic centimeters) magnetic power generation systems in the microwatts to tens of watts power range. These systems are of great interest for powering sensor networks, robotics, wireless communication systems, and other portable electronics. The paper considers the following topics. 1) The theoretical and practical implications of miniaturizing magnetic power generators. 2) The design and performance of previously demonstrated devices, which are summarized and compared. 3) Ongoing challenges for implementation, including integrated high-performance hard magnetic materials, microscale core laminations, low-friction bearings, high-speed rotor dynamics, and compact, high-efficiency power converters.
536 citations
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TL;DR: A review of micro/nanoscale adhesion, friction, and wear studies of materials and lubrication studies for MEMS/NEMS and BioMEMS/BioNEMS is presented in this article.
358 citations
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25 Aug 2005TL;DR: In this paper, a digital camera including a plurality of arrays of photo detectors, including a first array of photo detector to sample an intensity of light of a first wavelength and a second array of camera sensor to sample a second wavelength, is described.
Abstract: There are many, many inventions described herein. In one aspect, what is disclosed is a digital camera including a plurality of arrays of photo detectors, including a first array of photo detectors to sample an intensity of light of a first wavelength and a second array of photo detectors to sample an intensity of light of a second wavelength. The digital camera further may also include a first lens disposed in an optical path of the first array of photo detectors, wherein the first lens includes a predetermined optical response to the light of the first wavelength, and a second lens disposed in with an optical path of the second array of photo detectors wherein the second lens includes a predetermined optical response to the light of the second wavelength. In addition, the digital camera may include signal processing circuitry, coupled to the first and second arrays of photo detectors, to generate a composite image using (i) data which is representative of the intensity of light sampled by the first array of photo detectors, and (ii) data which is representative of the intensity of light sampled by the second array of photo detectors; wherein the first array of photo detectors, the second array of photo detectors, and the signal processing circuitry are integrated on or in the same semiconductor substrate.
334 citations
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TL;DR: In this article, a set of experiments was designed and performed to fully characterize the sensitivity of surface morphology and mechanical behavior of silicon samples produced with different DRIE operating conditions, and the data was then fitted to response surfaces to model the dependence of response variables on dry processing conditions.
Abstract: The ability to predict and control the influence of process parameters during silicon etching is vital for the success of most MEMS devices. In the case of deep reactive ion etching (DRIE) of silicon substrates, experimental results indicate that etch performance as well as surface morphology and post-etch mechanical behavior have a strong dependence on processing parameters. In order to understand the influence of these parameters, a set of experiments was designed and performed to fully characterize the sensitivity of surface morphology and mechanical behavior of silicon samples produced with different DRIE operating conditions. The designed experiment involved a matrix of 55 silicon wafers with radius hub flexure (RHF) specimens which were etched 10 min under varying DRIE processing conditions. Data collected by interferometry, atomic force microscopy (AFM), profilometry, and scanning electron microscopy (SEM), was used to determine the response of etching performance to operating conditions. The data collected for fracture strength was analyzed and modeled by finite element computation. The data was then fitted to response surfaces to model the dependence of response variables on dry processing conditions.
279 citations
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TL;DR: Here, strategies that have been developed over the past two decades that seek to enable such millimeter to nanoscale 3D fabrication and patterning are reviewed, specifically in a biologically inspired, more deterministic form, known as self-folding.
Abstract: Despite the fact that we live in a 3D world and macroscale engineering is 3D, conventional submillimeter-scale engineering is inherently 2D. New fabrication and patterning strategies are needed to enable truly 3D-engineered structures at small size scales. Here, strategies that have been developed over the past two decades that seek to enable such millimeter to nanoscale 3D fabrication and patterning are reviewed. A focus is the strategy of self-assembly, specifically in a biologically inspired, more deterministic form, known as self-folding. Self-folding methods can leverage the strengths of lithography to enable the construction of precisely patterned 3D structures and “smart” components. This self-assembly approach is compared with other 3D fabrication paradigms, and its advantages and disadvantages are discussed.
Frontispiece images reprinted with permission from References25,55,138,80, copyrights 2009, Nature Publishing Group, 2006 and 2007, IOP Publishing, 2001, Conference of Photopolymer Science and Technology, and with permission from Adam Cohen, Microfabrica Inc.
250 citations