Selected papers from the latest issue:
Sharp silicon tips with different aspect ratios in wet etching/DRIE and surfactant-modified TMAH etching
27 January 2012, 22:07:35
Publication year: 2012
Source: Sensors and Actuators A: Physical, Available online 27 January 2012
Bin Tang, Kazuo Sato, Miguel A. Gosálvez
A simple, high yield method of surfactant-modified wet anisotropic etching for the fabrication of sharp silicon tips is proposed in the applications of scanning probe microscope (SPM) and vacuum microelectronics. The formation of this new tip has been explained as the change in the local etch rate brought about by the strong adsorption of surfactant molecules in the apex of a silicon tip. In order to understand this point, the different etch rates of the same orientations tested on the hemispherical silicon (with curvature) and flat samples (no curvature) are investigated, and the adsorption thicknesses (or densities) of surfactants on various silicon surfaces measured by an ellipsometer are obtained. Tips with different aspect ratios (0.8:1 and 6:1) have been successfully fabricated on silicon (100) and (111) by the combination of etching in pure tetramethylammonium hydroxide (TMAH) or deep reactive ion etching (DRIE) and etching in surfactant-modified TMAH solutions, having the advantages of good uniformities, low temperatures, low costs and complementary metal oxide semiconductor (CMOS)-compatible. The apex of each resultant tip after the treatment in surfactant-added wet etchants typically can have a radius of curvature of 4∼5 nm on silicon (100) or even ≤2 nm on silicon (111) without any subsequent oxide sharpening process.
Source: Sensors and Actuators A: Physical, Available online 27 January 2012
Bin Tang, Kazuo Sato, Miguel A. Gosálvez
A simple, high yield method of surfactant-modified wet anisotropic etching for the fabrication of sharp silicon tips is proposed in the applications of scanning probe microscope (SPM) and vacuum microelectronics. The formation of this new tip has been explained as the change in the local etch rate brought about by the strong adsorption of surfactant molecules in the apex of a silicon tip. In order to understand this point, the different etch rates of the same orientations tested on the hemispherical silicon (with curvature) and flat samples (no curvature) are investigated, and the adsorption thicknesses (or densities) of surfactants on various silicon surfaces measured by an ellipsometer are obtained. Tips with different aspect ratios (0.8:1 and 6:1) have been successfully fabricated on silicon (100) and (111) by the combination of etching in pure tetramethylammonium hydroxide (TMAH) or deep reactive ion etching (DRIE) and etching in surfactant-modified TMAH solutions, having the advantages of good uniformities, low temperatures, low costs and complementary metal oxide semiconductor (CMOS)-compatible. The apex of each resultant tip after the treatment in surfactant-added wet etchants typically can have a radius of curvature of 4∼5 nm on silicon (100) or even ≤2 nm on silicon (111) without any subsequent oxide sharpening process.
An array of 100 μm x 100 μm Dielectric Elastomer Actuators with 80% Strain for Tissue Engineering Applications
27 January 2012, 22:07:35
Publication year: 2012
Source: Sensors and Actuators A: Physical, Available online 27 January 2012
Samin Akbari, Herbert Shea
Biological cells modulate their behavior, express genes, proliferate or differentiate in response to mechanical strains ranging from 1 to 20%. There currently exists no technique to apply strain to many targeted individual cells in a larger culture in order to perform parallelized high throughput testing. Dielectric Elastomer Actuators (DEAs) are compliant devices capable of generating large percentage strains with sub-second response time, ideally suited by their compliance for cell manipulation. We report an array of 100 μm x 100 μm DEAs reaching up to 80% in-plane strain at an electric field of 240 V/μm. The miniaturized DEAs are made by patterning 100 μm wide compliant ion-implanted gold electrodes on both sides of a 30 μm thick polydimethylsiloxane (PDMS) membrane. We report the important effect of uniaxial prestretch of the membrane on the microactuators’ performance; the largest strain is achieved by prestretching uniaxially by 175%. Each actuator is intended to have a single cell adhered to it in order to periodically stretch the cells to study the effect of mechanical stimulation on its biochemical responses. To avoid short-circuiting all the top electrodes by the conductive saline cell growth medium, a 20 μm thick biocompatible PDMS layer is bonded on the actuators. In this configuration, 37% strain is achieved at 3.6 kV with sub-second response. This device can be used as a high throughput single cell stretcher to apply relevant biological periodic strains to individual cells in a single experiment
Source: Sensors and Actuators A: Physical, Available online 27 January 2012
Samin Akbari, Herbert Shea
Biological cells modulate their behavior, express genes, proliferate or differentiate in response to mechanical strains ranging from 1 to 20%. There currently exists no technique to apply strain to many targeted individual cells in a larger culture in order to perform parallelized high throughput testing. Dielectric Elastomer Actuators (DEAs) are compliant devices capable of generating large percentage strains with sub-second response time, ideally suited by their compliance for cell manipulation. We report an array of 100 μm x 100 μm DEAs reaching up to 80% in-plane strain at an electric field of 240 V/μm. The miniaturized DEAs are made by patterning 100 μm wide compliant ion-implanted gold electrodes on both sides of a 30 μm thick polydimethylsiloxane (PDMS) membrane. We report the important effect of uniaxial prestretch of the membrane on the microactuators’ performance; the largest strain is achieved by prestretching uniaxially by 175%. Each actuator is intended to have a single cell adhered to it in order to periodically stretch the cells to study the effect of mechanical stimulation on its biochemical responses. To avoid short-circuiting all the top electrodes by the conductive saline cell growth medium, a 20 μm thick biocompatible PDMS layer is bonded on the actuators. In this configuration, 37% strain is achieved at 3.6 kV with sub-second response. This device can be used as a high throughput single cell stretcher to apply relevant biological periodic strains to individual cells in a single experiment
Highlights
► Fabrication and characterization of an array of 100 μm x 100 μm dielectric elastomer actuators, generating up to 80% in-plain strain. ► Presenting an effective method to pattern 100 μm wide compliant electrodes by low energy ion implantation, addressing the lack of suitable fabrication techniques to pattern μm scale compliant electrodes on silicone membranes. ► Fabrication of two layer actuators showing up to 37% strain for cell stretching applications to allow high throughput mechanotransduction studies in single cell levelGAMMA AND eLECTRON BEAM IRRADIATION EFFECTS ON The Resistance of mICROMACHINED Polycrystalline silicon BEAMS
27 January 2012, 22:07:35
Publication year: 2012
Source: Sensors and Actuators A: Physical, Available online 24 January 2012
Lei Wang, Jieying Tang, Qing-An Huang
This paper reports gamma and electron beam irradiation effects on the resistance of polycrystalline silicon beams in MEMS. Displacement damage, injection annealing, and thermal spike are identified as causes of the gamma and electron beam irradiation effect on polycrystalline silicon. Radiation effect on grain neutral regions and grain boundary of polycrystalline silicon are also discussed. Co60 irradiation test and Electron beam irradiation were performed to identify the radiation effects on polycrystalline silicon beams. Resistances were measured by a Keithley Semiconductor Characterization with hardware modules of 4200-scs to reveal the gamma and electron irradiation effect on resistance of the microbridges. The reason for the change of the resistance was analyzed by the theory of radiation effects in solids, and the gamma and electron beam irradiation effects which induce this change were discussed.
Source: Sensors and Actuators A: Physical, Available online 24 January 2012
Lei Wang, Jieying Tang, Qing-An Huang
This paper reports gamma and electron beam irradiation effects on the resistance of polycrystalline silicon beams in MEMS. Displacement damage, injection annealing, and thermal spike are identified as causes of the gamma and electron beam irradiation effect on polycrystalline silicon. Radiation effect on grain neutral regions and grain boundary of polycrystalline silicon are also discussed. Co60 irradiation test and Electron beam irradiation were performed to identify the radiation effects on polycrystalline silicon beams. Resistances were measured by a Keithley Semiconductor Characterization with hardware modules of 4200-scs to reveal the gamma and electron irradiation effect on resistance of the microbridges. The reason for the change of the resistance was analyzed by the theory of radiation effects in solids, and the gamma and electron beam irradiation effects which induce this change were discussed.
Development of on-chip vacuum generation by gas-liquid phase transition
27 January 2012, 22:07:35
Publication year: 2012
Source: Sensors and Actuators A: Physical, Available online 24 January 2012
K. Sugiyama, Y. Ukita, Y. Takamura
In this paper, we developed on-chip vacuum generation technique using gas-liquid phase transition. Fabricated quartz chip was composed simply of a structural vacuum chamber and a diaphragm for pressure measurement by laser displacement meter. Efficient reduction of pressure in the chamber was accomplished by the phase transition with the simple design of the fabricated chip. The pressure was reduced by decreasing the temperature of low boiling point liquid filled into the chamber after closing its valve. The lowest pressure attained to 50.8kPa(diethyl ether) or 23.2 kPa(water) at 7 min from atmospheric pressure by using diethyl ether and water, respectively. The highest performance of micro vacuum pump was achieved. The absolute pressure below 25 kPa was maintained about 20 min due to low leakage of the fabricated chip.
Source: Sensors and Actuators A: Physical, Available online 24 January 2012
K. Sugiyama, Y. Ukita, Y. Takamura
In this paper, we developed on-chip vacuum generation technique using gas-liquid phase transition. Fabricated quartz chip was composed simply of a structural vacuum chamber and a diaphragm for pressure measurement by laser displacement meter. Efficient reduction of pressure in the chamber was accomplished by the phase transition with the simple design of the fabricated chip. The pressure was reduced by decreasing the temperature of low boiling point liquid filled into the chamber after closing its valve. The lowest pressure attained to 50.8kPa(diethyl ether) or 23.2 kPa(water) at 7 min from atmospheric pressure by using diethyl ether and water, respectively. The highest performance of micro vacuum pump was achieved. The absolute pressure below 25 kPa was maintained about 20 min due to low leakage of the fabricated chip.
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