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Design, simulation, and fabrication of three-dimensional microsystem components using grayscale photolithography

Summary

Grayscale lithography is a widely known but underutilized microfabrication technique for creating three-dimensional (3-D) microstructures in photoresist. One of the hurdles for its widespread use is that developing the grayscale photolithography masks can be time-consuming and costly since it often requires an iterative process, especially for complex geometries. We discuss the use of PROLITH, a lithography simulation tool, to predict 3-D photoresist profiles from grayscale mask designs. Several examples of optical microsystems and microelectromechanical systems where PROLITH was used to validate the mask design prior to implementation in the microfabrication process are presented. In all examples, PROLITH was able to accurately and quantitatively predict resist profiles, which reduced both design time and the number of trial photomasks, effectively reducing the cost of component fabrication.
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Summary

Grayscale lithography is a widely known but underutilized microfabrication technique for creating three-dimensional (3-D) microstructures in photoresist. One of the hurdles for its widespread use is that developing the grayscale photolithography masks can be time-consuming and costly since it often requires an iterative process, especially for complex geometries. We discuss...

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Valleytronics: opportunities, challenges, and paths forward

Summary

A lack of inversion symmetry coupled with the presence of time-reversal symmetry endows 2D transition metal dichalcogenides with individually addressable valleys in momentum space at the K and K' points in the first Brillouin zone. This valley addressability opens up the possibility of using the momentum state of electrons, holes, or excitons as a completely new paradigm in information processing. The opportunities and challenges associated with manipulation of the valley degree of freedom for practical quantum and classical information processing applications were analyzed during the 2017 Workshop on Valleytronic Materials, Architectures, and Devices; this Review presents the major findings of the workshop.
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Summary

A lack of inversion symmetry coupled with the presence of time-reversal symmetry endows 2D transition metal dichalcogenides with individually addressable valleys in momentum space at the K and K' points in the first Brillouin zone. This valley addressability opens up the possibility of using the momentum state of electrons, holes...

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Optical Nondestructive Dynamic Measurements of Wafer-Scale Encapsulated Nanofluidic Channels

Published in:
Applied Optics, vol. 57, no. 15

Summary

Nanofluidic channels are of great interest for DNA sequencing, chromatography, and drug delivery. However, metrology of embedded or sealed nanochannels and measurement of their fill-state have remained extremely challenging. Existing techniques have been restricted to optical microscopy, which suffers from insufficient resolution, or scanning electron microscopy, which cannot measure sealed or embedded channels without cleaving the sample. Here, we demonstrate a novel method for accurately extracting nanochannel cross-sectional dimensions and monitoring fluid filling, utilizing spectroscopic ellipsometric scatterometry, combined with rigorous electromagnetic simulations. Our technique is capable of measuring channel dimensions with better than 5-nm accuracy and assessing channel filling within seconds. The developed technique is, thus, well suited for both process monitoring of channel fabrication as well as for studying complex phenomena of fluid flow through nanochannel structures.
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Summary

Nanofluidic channels are of great interest for DNA sequencing, chromatography, and drug delivery. However, metrology of embedded or sealed nanochannels and measurement of their fill-state have remained extremely challenging. Existing techniques have been restricted to optical microscopy, which suffers from insufficient resolution, or scanning electron microscopy, which cannot measure sealed...

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Fluidic microoptics with adjustable focusing and beam steering for single cell optogenetics

Published in:
Opt. Express, Vol. 25, No. 14, 10 July 2017, pp. 16825-16839.

Summary

Electrically controlled micron-scale liquid lenses have been designed, fabricated and demonstrated, that provide both adjustable focusing and beam steering, with the goal of applying them to optogenetic in vivo mapping of brain activity with single cell resolution. The liquid lens is formed by the interface between two immiscible liquids which are contained in a conically tapered lens cavity etched into a fused silica substrate. Interdigitated electrodes have been patterned along the sidewall of the taper to control the liquid lens curvature and tilt. Microlenses with apertures ranging in size from 30 to 80 μm were fabricated and tunable focusing ranging from 0.25 to 3 mm and beam steering of ± 1 degree have been demonstrated.
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Summary

Electrically controlled micron-scale liquid lenses have been designed, fabricated and demonstrated, that provide both adjustable focusing and beam steering, with the goal of applying them to optogenetic in vivo mapping of brain activity with single cell resolution. The liquid lens is formed by the interface between two immiscible liquids which...

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Seismic barrier protection of critical infrastructure

Published in:
16th Annual IEEE Int. Symp. on Technologies for Homeland Security, HST 2017, 25-26 April 2017.

Summary

Each year, on average a major magnitude-8 earthquake strikes somewhere in the world. In addition, 10,000 earthquake related deaths occur annually, where collapsing buildings claim by far most lives. Moreover, in recent events, industry activity of oil extraction and wastewater reinjection are suspected to cause earthquake swarms that threaten high-value oil pipeline networks, U.S. oil storage reserves, and civilian homes. Earthquake engineering of building structural designs and materials have evolved over many years to minimize the destructive effects of seismic surface waves. However, even under the best engineering practices, significant damage and numbers of fatalities can still occur. In this paper, we present a novel concept and approach to redirect and attenuate the ground motion amplitudes caused by earthquakes by implementing an engineered subsurface seismic barrier – creating a form of metamaterial. The barrier is comprised of borehole array complexes and trench designs that impede and divert destructive seismic surface waves from a designated 'protection zone'. The barrier is also designed to divert not only surface waves in the aerial plane, but includes vertical 'V' shaped muffler structures composed of opposing boreholes to mitigate seismic waves from diffracting and traveling in the vertical plane. Computational 2D and 3D seismic wave propagation models developed at MIT Lincoln Laboratory suggest that borehole array and trench arrangements are critical to the redirection and self-interference reduction of broadband hazardous seismic waves in the vicinity of the structure to protect. The computational models are compared with experimental data obtained from large bench-scale physical models that contain scaled borehole arrays and trenches. These experiments are carried out at high frequencies, but with suitable material parameters and borehole dimensions. They indicate that effects of a devastating 7.0 Mw -magnitude earthquake can be reduced to those of a minor magnitude-4.5 or -5.5 Mw earthquake within a suitable protection zone. These results are very promising, and warrant validation in field scale tests.
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Summary

Each year, on average a major magnitude-8 earthquake strikes somewhere in the world. In addition, 10,000 earthquake related deaths occur annually, where collapsing buildings claim by far most lives. Moreover, in recent events, industry activity of oil extraction and wastewater reinjection are suspected to cause earthquake swarms that threaten high-value...

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High-resolution, high-throughput, CMOS-compatible electron beam patterning

Published in:
SPIE Advanced Lithography, 26 February - 2 March 2017.

Summary

Two scanning electron beam lithography (SEBL) patterning processes have been developed, one positive and one negative tone. The processes feature nanometer-scale resolution, chemical amplification for faster throughput, long film life under vacuum, and sufficient etch resistance to enable patterning of a variety of materials with a metal-free (CMOS/MEMS compatible) tool set. These resist processes were developed to address two limitations of conventional SEBL resist processes: (1) low areal throughput and (2) limited compatibility with the traditional microfabrication infrastructure.
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Summary

Two scanning electron beam lithography (SEBL) patterning processes have been developed, one positive and one negative tone. The processes feature nanometer-scale resolution, chemical amplification for faster throughput, long film life under vacuum, and sufficient etch resistance to enable patterning of a variety of materials with a metal-free (CMOS/MEMS compatible) tool...

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Electrically switchable diffractive waveplates with metasurface aligned liquid crystals

Published in:
Opt. Express, Vol. 24, No. 21, 17 October 2016, 24265-24273.

Summary

Diffractive waveplates and equivalent metasurfaces provide a promising path for applications in thin film beam steering, tunable lenses, and polarization filters. However, fixed metasurfaces alone are unable to be tuned electronically. By combining metasurfaces with tunable liquid crystals, we experimentally demonstrate a single layer device capable of electrically switching a diffractive waveplate design at a measured peak diffraction efficiency of 35%, and a minimum switching voltage of 10V. Furthermore, the nano-scale metasurface aligned liquid crystals are largely independent of variations in wavelength and temperature. We also present a computational analysis of the efficiency limits of liquid crystal based diffractive waveplates, and compare this analysis to experimental measurements.
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Summary

Diffractive waveplates and equivalent metasurfaces provide a promising path for applications in thin film beam steering, tunable lenses, and polarization filters. However, fixed metasurfaces alone are unable to be tuned electronically. By combining metasurfaces with tunable liquid crystals, we experimentally demonstrate a single layer device capable of electrically switching a...

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Broadband Optical Switch Based on Liquid Crystal Dynamic Scattering

Published in:
Optics Express, vol. 24, no. 13

Summary

This work demonstrates a novel broadband optical switch, based on dynamic-scattering effect in liquid crystals (LCs). Dynamic-scattering-mode technology was developed for display applications over four decades ago, but was displaced in favor of the twisted-nematic LCs. However, with the recent development of more stable LCs, dynamic scattering provides advantages over other technologies for optical switching. We demonstrate broadband polarization-insensitive attenuation of light directly passing thought the cell by 4 to 5 orders of magnitude at 633 nm. The attenuation is accomplished by light scattering to higher angles. Switching times of 150 μs to 10% transmission have been demonstrated. No degradation of devices is found after hundreds of switching cycles. The light-rejection mechanism is due to scattering, induced by disruption of LC director orientation with dopant ion motion with an applied electric field. Angular dependence of scattering is characterized as a function of bias voltage.
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Summary

This work demonstrates a novel broadband optical switch, based on dynamic-scattering effect in liquid crystals (LCs). Dynamic-scattering-mode technology was developed for display applications over four decades ago, but was displaced in favor of the twisted-nematic LCs. However, with the recent development of more stable LCs, dynamic scattering provides advantages over...

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Wafer-scale aluminum nanoplasmonic resonators with optimized metal deposition

Published in:
ACS Photonics, Vol. 3, No. 5, 18 May 2016, pp. 796-805.

Summary

Spectroscopic ellipsometry is demonstrated to be an effective technique for assessing the quality of plasmonic resonances within aluminum nanostructures deposited with multiple techniques. The resonance quality of nanoplasmonic aluminum arrays is shown to be strongly dependent on the method of aluminum deposition. Three-layer metal-dielectric-metal nanopillar arrays were fabricated in a complementary metal-oxide semiconductor (CMOS) facility, with the arrays of nanopillars separated from a continuous metal underlayer by a thin dielectric spacer, to provide optimum field enhancement. Nanostructures patterned in optimized aluminum, which had been deposited with a high temperature sputtering process followed by chemical mechanical planarization, display different resonance and depolarization behavior than nanostructures deposited by the more conventional evaporation process. Full plasmonic band diagrams are mapped over a wide range of incidence angles and wavelengths using spectroscopic ellipsometry, and compared for aluminum nanostructures fabricated with two methods. The resonators fabricated from optimized aluminum exhibit a narrower bandwidth of both plasmonic resonance and depolarization parameters, indicating a higher quality resonance due to a stronger localization of the electric field. The optimized wafer-scale aluminum plasmonics fabrication should provide a pathway towards better quality devices for sensing and light detection in the ultraviolet and blue parts of the spectrum.
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Summary

Spectroscopic ellipsometry is demonstrated to be an effective technique for assessing the quality of plasmonic resonances within aluminum nanostructures deposited with multiple techniques. The resonance quality of nanoplasmonic aluminum arrays is shown to be strongly dependent on the method of aluminum deposition. Three-layer metal-dielectric-metal nanopillar arrays were fabricated in a...

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Nanochannel fabrication based on double patterning with hydrogen silsesquioxane

Published in:
J. Vac. Sci. Technol. B, Microelectron. Process. Phenon., Vol. 33, No. 2, March 2015, 020601.

Summary

A double patterning process is presented to pattern sub-35 nm wide channels in hydrogen silsesquioxane with near 100% pattern densities. Using aligned electron beam lithography, each side of the nanochannel structure is patterned as a separate layer. A 50000 uC/cm^2 high-dose anneal is applied to the first layer after exposure. Channels with widths below ~60 nm are shown to exhibit footing with standard tetramethyl ammonium hydroxide developers. This problem is resolved by adding surfectant during the development of the final channel structure. The resulting process produced channels
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Summary

A double patterning process is presented to pattern sub-35 nm wide channels in hydrogen silsesquioxane with near 100% pattern densities. Using aligned electron beam lithography, each side of the nanochannel structure is patterned as a separate layer. A 50000 uC/cm^2 high-dose anneal is applied to the first layer after exposure...

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