Micro and Nanosystems - Volume 10, Issue 2, 2018

As feature sizes of devices shrink every year, deposition and etching processes change to be very challenge, especially for sub-7 nm technology node. The acceptable variability of feature size is expected to be several atoms of silicon/germanium in the future. Therefore, Remote Plasma-Enhanced Atomic Layer Deposition (RPE-ALD) and Atomic Layer Etching (ALE) change to be more and more important in the semiconductor fabrication. Due to their self-limiting behavior, the atomic-scale fidelity could be realized for both of them in the processes. Compared with traditional Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD) methods, atomic-scale thickness controllability and good conformality can be achieved by RPE-ALD. Unlike conventional plasma etching, atomicscale precision and excellent depth uniformity can be achieved by ALE. The fundamentals and applications of RPE-ALD and ALE have been discussed in this paper. Using the combination of them, atomic-level deposition/etch-back method is also mentioned for achieving high quality ultra-thin films on three dimensional (3D) features.

An increasing impact of micromechanically governed uncertainties is nowadays foreseen due to the trend of progressively reducing the footprint of MEMS (microelectromechanical systems) devices. For polysilicon MEMS, the two major sources of uncertainties, as resulting from the microfabrication process, are linked to the polycrystalline morphology and to the etching. In this review, we summarize some of our recent results related to the statistical assessment of the aforementioned sources, on the basis of experimental data acquired via an on-chip testing device specifically designed to enhance such effects. Through standard electrostatic actuation and readout, the scattering in the response of a series of nominally identical cantilever structures is analyzed to determine characteristic features of etching defects, and of the overall stiffness of the polysilicon film constituting the movable parts of the tested devices.

Background: The hybrid photocatalysts constructed with various semiconductor and graphene can show dramatically enhanced photocatalytic activities. The separability of a photocatalyst from degraded pollutant aqueous solution is very important in some cases. Objective: The magnetic MnFe2O4 nanoparticles and reduced graphene oxide were used to construct magnetically separable (rGO)-MnFe2O4 hybrids with high photo- catalytic properties. Method: The pure MnFe2O4 nanoparticles and rGO/MnFe2O4 hybrid photocatalysts were synthesized with a facile hydrothermal process. Results: The nanoparticles showed great sunlight-excited photocatalytic and Fenton- like photocatalytic activities in the photodegradation of dye solution. Introducing rGO resulted in further enhancement of the activity compared to the nanoparticles. The effect of initial dye solution pH and H2O2 on the activities were also studied. The greater activities of the hybrids are ascribed to good interface charge transfer that was verified by the estimation of optical conductivity and band energy level. The hybrids also showed an magnetically separable performance from degraded pollutant solution. Conclusion: This work suggested a facile method to synthesize the magnetic MnFe2O4 nanoparticles and rGO/MnFe2O4 hybrids. The hybrids are an promising photocatalytic materials for environmental applications.

Background: The bulk production of Gold Nanoparticles (AuNPs) and their concentrated ink, with desirable properties such as morphology, purity, stability and final Au concentration, remains a challenge. Objective: (i) Synthesis of AuNPs through Ultrasonic Spray Pyrolysis (USP) from different precursors. (ii) Preparation of their concentrated ink and (iii) Test their feasibility for ink jet printing onto a glossy paper substrate. Method: Initially, two different start materials were used - precursor: Gold Chloride with its nanoparticles as C-AuNPs, and Gold Acetate with its nanoparticles as A-AuNPs stabilised with PVP40 in deionised water. The concentrated ink was prepared from both AuNPs, and filtered up to the [Au] of 1000 ppm. Ink-jet printing was performed, and the obtained patterns were analysed through SEM. Results: The [Au] in the obtained solutions, determined through ICP-OES analysis, was, for CAuNPs, about 100 ppm, and 150 ppm for A-AuNPs. In the case of C-AuNPs the solution was rose, and for A-AuNPs violet. TEM investigation revealed that C-AuNPs dominated in a circular shape with size about 18 nm; contrary to this, A-AuNPs were mostly in ellipsoid shape, with size in the longitudinal direction of about 36 nm. EDX analyses detected 99.9 wt. % of Au in both AuNPs, which is evidence that these were of high purity. Due to different AuNPs` sizes and [Au], the colloidal solutions showed maximum absorbance wavelength of 532 nm for C-AuNPs and 528 nm for A-AuNPs. SEM results showed that A-AuNPs were significantly better for printing on the paper substrate than C-AuNPs, due to their ellipsoidal shape, as the flow behaviour had been much smoother through the nozzle as compared to the circular shape. The printed area with A-AuNPs reflected in better incorporation of nanoparticles on the paper surface and high-density connectivity among AuNPs. Conclusions: C-AuNPs and A-AuNPs were synthesised successfully under optimum parameters of evaporation temperature, reaction temperature and gas flow rates. The spherical shape of C-AuNPs as compared to the ellipsoidal nature of A-AuNPs was due to the rapid sintering of Gold Chloride at a higher temperature of 300ºC as compared to Gold Acetate.

Objective: This paper discusses analytically and by simulation, a novel disk and ring-shaped piezoelectric micromechanical acoustic resonators in which asymmetric Lamb wave (A0) mode is induced in a thin-film aluminum nitride (AlN)-on-silicon structure. Method: The piezoelectric resonators are designed and simulated at two-port state by the aid of FEM tool. An analytical investigation is carried out in order to study the propagation of asymmetric lamb wave in a cylinder structure. Circular electrodes are utilized for excitation of intended order of asymmetric acoustic Lamb wave (A0) in the structures. Due to the significance of feedthrough capacitances in the piezoelectric MEMS resonators in high-frequency applications, these capacitances are calculated and extracted. Several electrodes and tethers configurations are introduced and simulated by FEM simulation in order to study distortion of resonator structures. Result: Stress-free nodal zones close to the resonators outer edge are identified and support tethers, which are used to anchor the resonators, are connected to those points by applying the notch method. Connecting anchoring tethers to stress-free nodal zones considerable decreased tether deformation leading to lower loss for resonators. The prototype models of structures work at 307 MHz and 318 MHz for the disk-shaped and ring-shaped resonators, respectively. Numerous transient and harmonic analysis have been carried out in order to study resonators behavior at the fundamental mode and their spurious electrical response. Conclusion: The proposed structures in this paper can be a promising choice for different applications ranging from RF filter, RF oscillators, RF micromachined circuits and physical and biochemical sensors.

Background: Electromagnetic wave absorbers that has near perfect performance have been studied since 2008, various one dimensional and two dimensional structures have been optimized. High absorption at certain frequency can be easily realized. However, high absorption that covers broad band is relatively hard to realized. Method: In this paper, a nickel nanograting is designed by using rigorous coupled wave analysis theory. The effect of grating height and grating width on absorption performance is analyzed physically by using equivalent medium theory and Fabry-Pérot resonate theory. Results: Because of the intrinsic absorption character and the influence of F-P resonance, TM absorption shows periodically increase with the increasing of metal thickness. Absorption of the TE polarization slightly increases with the increasing of grating height. Peak absorption of TM polarization light can be gotten when DC of 0.52 is chosen, however, absorption performance of TE polarization light degrades seriously. In this paper, DC of 0.19 is chosen. Conclusion: A one dimensional nickel grating based broadband absorber is analyzed in this paper. The proposed absorber has good absorption performance over the visible band, and shows no clear degradation over a wide incident angle (-40° to 40°).

Background: Glipizide is an oral anti-diabetic drug used for the treatment of type II diabetes. Eudragit polymers are widely used for the sustained and targeted release of drugs. Encapsulated glipizide microparticles were developed using Oil-in-Water emulsion using Eudragit RS 100 -RL 100 in combination for sustained release of glipizide and its characterization for drug release and kinetics study. Objective: To develop glipizide loaded microparticles using combination of Eudragit RS 100 -RL 100 and to characterize for drug polymer interaction, surface morphology and drug release. Method: A 32 full factorial design was utilized for the preparation of microparticles and to understand the effect of input variable on output variables. The microparticles were characterized by Fourier Transform Infrared Spectroscopy for compatibility of drug and polymer, X-Ray diffractometer for crystallinity, Field emission scanning electron microscope for morphology study and in vitro drug release behaviour. Results: Percentage encapsulation efficiency and drug loading were obtained in the range of 45.5- 98.92% and 9.5-24.72% respectively. FTIR reveals the absence of chemical interaction between drug and polymer. XRD showed a reduction in crystallinity of drug. FE-SEM displayed spherical, nonaggregated porous microparticles. In vitro drug release studies showed sustained release of drug over a period of 12 h. Conclusion: The microparticles developed by this method were spherical and porous. The absence of drug-polymer interactions was confirmed by FTIR. Distribution of the drug within the polymers was confirmed by XRD. In vitro drug release studies showed sustained release of drug from encapsulated microparticles.

Background: Micromixers having various simple and complex microchannels is an inevitable part of almost all the microfluidic devices and circuitries nowadays. Particularly the metallic micromixers are very important for many chemical and process industries. Fabrication of metallic microchannels still remains a challenging task. Objective: The work focuses on the fabrication of microchannels of different geometries and intrinsic features on metals. Here, an alternate approach for fabricating microchannel in metals is demonstrated which is easy and doesn't demand a very high level of expertise. Method: The fabrication is carried out using Wire-Cut Electric Discharge Machine (WEDM) and Electric Discharge Machine (EDM) and accomplished in two stages: 1) Micro-tool fabrication in WEDM; 2) Microchannel machining in EDM. Parametric investigation of the processes is also carried out for understanding the influence of different parameters in microfabrication. Results: Different serpentine micromixer configurations are fabricated on copper and aluminum. Open channel configuration of metallic micromixers of average microchannel width 400 μm is fabricated as per the design. During micro-tool fabrication in WEDM, parametric conditions: pulse on time 25 μs, pulse off time 6 μs, input current 1 A and wire feed rate 75 mm/min gave optimal results among the investigated parametric combinations. During the second stage of microfabrication using EDM, the effect of input parameters, viz. input current, pulse on time and pulse off time on the output parameters viz. machining time, overcut, edge deviation and tool depletion are investigated. Results highlight the importance of careful selection and control of all these process parameters for manufacturing metallic microchannels by EDM. Conclusion: The proposed method is able to give rise to micro-features like microchannel on metals with reasonable ease and accuracy. The fabricated micromixers can be used for Lab on Chip (LOC), Point of Care (POC) devices or/and microreactors. The metallic micromixers can be used to handle various corrosive species and reagents which the conventional polymeric substrate can't handle. Thus it can lead to further advancement in the field of microfluidics.

Background: Nanomaterials for medical applications, preparations with silver and copper nanoparticles attract special attention. Silver has stronger antimicrobial properties than does penicillin, biomycin and a number of other antibiotics. Nanoparticles of copper and copper oxide also exert a pronounced antibacterial effect. Objective: Further development and creation of medicines based on silver and copper nanoparticles require selecting a method for synthesis of nanoparticles that would ensure production of various nanomaterial compositions. Method: The method of electron beam evaporation and deposition of materials in vacuum opens up wide possibilities. The idea of using this approach is the possibility of simultaneous evaporation and deposition of mixed molecular flows of two substances onto a substrate. Results: The paper presents the results of investigation of the structure of porous condensates of Ag-NaCl and Cu-NaCl composition; chemical and phase compositions and dimensions of nanoparticles, produced from the vapour phase by EBPVD method. Silver and copper nanoparticles in a porous matrix have considerable sorption capacity relative to oxygen and moisture. Along to concentration change, phase composition of nanoparticles can be also controlled by heat treatment of the initial condensate produced at low condensation temperatures. Silver and copper nanoparticles can be converted into stable colloidal systems. Conclusion: Physical synthesis of silver and copper nanoparticles by EBPVD method allowed producing nanostructured material in the form of a dry substance for preparation of the required colloidal solutions. TGA method provides an indication of the processes of transformation in Ag-O system. Ag2O decomposes at the temperature of 460°C. Controlling the activity (size) of nanoparticles allows creating various compositions of nanomaterials, based on copper.