Preparation of Mesoporous Oxides for Mems Structures

ABSTRACTThe high porosity and uniform pore size provided by mesoporous oxide films offer interesting opportunities for MEMS devices that require low density and low thermal conductivity. This paper describes recent efforts at adapting mesoporous films for MEMS fabrication. Mesoporous SiO2 and Al2O3 films were prepared using block copolymers as the structure-directing agents, leading to films which were 70% porous and < 5 nm surface roughness. A number of etchants were investigated and good etch selectivity was observed with both dry and wet systems. Micromachining methods were used to fabricate cantilevers, micro bridges and membranes.

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Micromachining of mesoporous oxide films for microelectromechanical system structures

Journal of Materials Research ◽

10.1557/jmr.2002.0313 ◽

2002 ◽

Vol 17 (8) ◽

pp. 2121-2129 ◽

Cited By ~ 22

Author(s):

Jong-Ah Paik ◽

Shih-Kang Fan ◽

Chang-Jin Kim ◽

Ming C. Wu ◽

Bruce Dunn

Keyword(s):

Sacrificial Layer ◽

Oxide Films ◽

Average Diameter ◽

High Porosity ◽

Mems Devices ◽

Mesoporous Films ◽

Microelectromechanical System ◽

Mesoporous Oxide ◽

Structure Layer ◽

Mesoporous Oxides

The high porosity and uniform pore size of mesoporous oxide films offer unique opportunities for microelectromechanical system (MEMS) devices that require low density and low thermal conductivity. This paper provides the first report in which mesoporous films were adapted for MEMS applications. Mesoporous SiO2 and Al2O3 films were prepared by spin coating using block copolymers as the structure-directing agents. The resulting films were over 50% porous with uniform pores of 8-nm average diameter and an extremely smooth surface. The photopatterning and etching characteristics of the mesoporous films were investigated and processing protocols were established which enabled the films to serve as the sacrificial layer or the structure layer in MEMS devices. The unique mesoporous morphology leads to novel behavior including extremely high etching rates and the ability to etch underlying layers. Surface micromachining methods were used to fabricate three basic MEMS structures, microbridges, cantilevers, and membranes, from the mesoporous oxides.

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Rigid Polyurethane Foam: A Versatile Energy Efficient Material

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.678.88 ◽

2016 ◽

Vol 678 ◽

pp. 88-98 ◽

Cited By ~ 2

Author(s):

Harpal Singh

Keyword(s):

Thermal Conductivity ◽

Polyurethane Foam ◽

Weight Ratio ◽

Building Envelope ◽

Polymerization Reaction ◽

Low Density ◽

High Porosity ◽

Rigid Polyurethane Foam ◽

Low Thermal Conductivity ◽

Moisture Permeability

Rigid polyurethane foam (RPUF) is typically prepared by the reaction of an isocyanate, such as methyl diphenyl diisocyanate (MDI) with a polyol blend. During the polymerization reaction, a blowing agent expands the reacting mixture. The finished product is a solid, cellular polymer with a high thermal resistance. RPUF is an outstanding material for different applications. It has many desirable properties such as low thermal conductivity, low density, low water absorption, low moisture permeability, excellent dimensional stability, high strength to weight ratio. So, it is the best insulating material for industrial buildings, cold storages, telecom and defense shelters due to low thermal conductivity, low density, low moisture permeability and high porosity. It works to reduce heating and cooling loss, improving the efficiency of the building envelope. Thus, RPUF insulation in building envelopes brings additional benefits in energy savings, resulting in lower energy bills and protecting the environment by cutting CO2 emissions.

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Laser Melting of High Thermal Conductivity Steel (HTCS) Surface

Materials Science Forum ◽

10.4028/www.scientific.net/msf.890.380 ◽

2017 ◽

Vol 890 ◽

pp. 380-383 ◽

Cited By ~ 2

Author(s):

Norhafzan Bariman ◽

Syarifah Nur Aqida ◽

Fazliana Fauzun

Keyword(s):

Thermal Conductivity ◽

Surface Roughness ◽

Pulse Repetition Frequency ◽

Average Power ◽

High Thermal Conductivity ◽

Composition Analysis ◽

High Porosity ◽

Laser Melting ◽

Metallographic Study ◽

Modified Layer

This paper presents a laser melting of high thermal conductivity steel (HTCS) dies for surface properties modification due to die failures during operations. Sample were cut from as-received die without any defect or crack. Melting process was conducted using Nd:YAG laser system with pulse mode at 50 W average power. The laser beam was defocused to a spot size of 1 mm on the sample surface. Parameters controlled in this study were peak power of 800 and 1200 W, and pulse repetition frequency of 80 and 90 Hz. Metallographic study and chemical composition analysis were conducted using Hitachi TM3030Plus scanning electron microscope (SEM) and energy dispersive x-ray spectrometer (EDXS). Surface roughness was measured using Mitutoyo SURFTEST SJ-410 stylus profilometer. Hardness properties of the modified layer were characterized by Wilson Hardness tester at 100 N force. The metallographic study showed high porosity at partially melted zone (PMZ) area. From overall findings, laser processing parameter affected hardness properties and surface roughness of modified layer. Where the surface roughness value obtained is between 1.49 and 3.15 μm, while the hardness value is between 550.9 and 610.9 HV0.1. These findings are significant to parameters selection for hot stamping die surface repair and prolong its service.

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Thermophysical Properties of Multifunctional Syntactic Foams Containing Phase Change Microcapsules for Thermal Energy Storage

Polymers ◽

10.3390/polym13111790 ◽

2021 ◽

Vol 13 (11) ◽

pp. 1790

Author(s):

Francesco Galvagnini ◽

Andrea Dorigato ◽

Luca Fambri ◽

Giulia Fredi ◽

Alessandro Pegoretti

Keyword(s):

Thermal Conductivity ◽

Energy Storage ◽

Phase Change ◽

Epoxy Resin ◽

Storage Modulus ◽

Thermal Energy ◽

Thermal Energy Storage ◽

Neat Epoxy ◽

Low Density ◽

Syntactic Foams

Syntactic foams (SFs) combining an epoxy resin and hollow glass microspheres (HGM) feature a unique combination of low density, high mechanical properties, and low thermal conductivity which can be tuned according to specific applications. In this work, the versatility of epoxy/HGM SFs was further expanded by adding a microencapsulated phase change material (PCM) providing thermal energy storage (TES) ability at a phase change temperature of 43 °C. At this aim, fifteen epoxy (HGM/PCM) compositions with a total filler content (HGM + PCM) of up to 40 vol% were prepared and characterized. The experimental results were fitted with statistical models, which resulted in ternary diagrams that visually represented the properties of the ternary systems and simplified trend identification. Dynamic rheological tests showed that the PCM increased the viscosity of the epoxy resin more than HGM due to the smaller average size (20 µm vs. 60 µm) and that the systems containing both HGM and PCM showed lower viscosity than those containing only one filler type, due to the higher packing efficiency of bimodal filler distributions. HGM strongly reduced the gravimetric density and the thermal insulation properties. In fact, the sample with 40 vol% of HGM showed a density of 0.735 g/cm3 (−35% than neat epoxy) and a thermal conductivity of 0.12 W/(m∙K) (−40% than neat epoxy). Moreover, the increase in the PCM content increased the specific phase change enthalpy, which was up to 68 J/g for the sample with 40 vol% of PCM, with a consequent improvement in the thermal management ability that was also evidenced by temperature profiling tests in transient heating and cooling regimes. Finally, dynamical mechanical thermal analysis (DMTA) showed that both fillers decreased the storage modulus but generally increased the storage modulus normalized by density (E′/ρ) up to 2440 MPa/(g/cm3) at 25 °C with 40 vol% of HGM (+48% than neat epoxy). These results confirmed that the main asset of these ternary multifunctional syntactic foams is their versatility, as the composition can be tuned to reach the property set that best matches the application requirements in terms of TES ability, thermal insulation, and low density.

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Cavity-BOX SOI: Advanced Silicon Substrate with Pre-Patterned BOX for Monolithic MEMS Fabrication

Micromachines ◽

10.3390/mi12040414 ◽

2021 ◽

Vol 12 (4) ◽

pp. 414

Author(s):

Marta Maria Kluba ◽

Jian Li ◽

Katja Parkkinen ◽

Marcus Louwerse ◽

Jaap Snijder ◽

...

Keyword(s):

Complex Geometry ◽

Pressure Sensors ◽

Silicon On Insulator ◽

Test Case ◽

Mems Devices ◽

Device Layer ◽

Mems Fabrication ◽

Silicon Islands ◽

Design Freedom ◽

Deep Brain

Several Silicon on Insulator (SOI) wafer manufacturers are now offering products with customer-defined cavities etched in the handle wafer, which significantly simplifies the fabrication of MEMS devices such as pressure sensors. This paper presents a novel cavity buried oxide (BOX) SOI substrate (cavity-BOX) that contains a patterned BOX layer. The patterned BOX can form a buried microchannels network, or serve as a stop layer and a buried hard-etch mask, to accurately pattern the device layer while etching it from the backside of the wafer using the cleanroom microfabrication compatible tools and methods. The use of the cavity-BOX as a buried hard-etch mask is demonstrated by applying it for the fabrication of a deep brain stimulation (DBS) demonstrator. The demonstrator consists of a large flexible area and precisely defined 80 µm-thick silicon islands wrapped into a 1.4 mm diameter cylinder. With cavity-BOX, the process of thinning and separating the silicon islands was largely simplified and became more robust. This test case illustrates how cavity-BOX wafers can advance the fabrication of various MEMS devices, especially those with complex geometry and added functionality, by enabling more design freedom and easing the optimization of the fabrication process.

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The Equivalent Thermal Conductivity of the Micro/Nano Scaled Periodic Cubic Frame Silver and Its Thermal Radiation Mechanism Analysis

Energies ◽

10.3390/en14144158 ◽

2021 ◽

Vol 14 (14) ◽

pp. 4158

Author(s):

Haiyan Yu ◽

Haochun Zhang ◽

Heming Wang ◽

Dong Zhang

Keyword(s):

Thermal Conductivity ◽

Thermal Radiation ◽

Cell Size ◽

Near Infrared ◽

High Porosity ◽

Mechanism Analysis ◽

Infrared Band ◽

Spectral Radiation ◽

Radiation Mechanism ◽

Equivalent Thermal Conductivity

Currently, there are few studies on the influence of microscale thermal radiation on the equivalent thermal conductivity of microscale porous metal. Therefore, this paper calculated the equivalent thermal conductivity of high-porosity periodic cubic silver frame structures with cell size from 100 nm to 100 µm by using the microscale radiation method. Then, the media radiation characteristics, absorptivity, reflectivity and transmissivity were discussed to explain the phenomenon of the radiative thermal conductivity changes. Furthermore, combined with spectral radiation properties at the different cross-sections and wavelength, the radiative transmission mechanism inside high-porosity periodic cubic frame silver structures was obtained. The results showed that the smaller the cell size, the greater radiative contribution in total equivalent thermal conductivity. Periodic cubic silver frames fluctuate more in the visible band and have better thermal radiation modulation properties in the near infrared band, which is formed by the Surface Plasmon Polariton and Magnetic Polaritons resonance jointly. This work provides design guidance for the application of this kind of periodic microporous metal in the field of thermal utilization and management.

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