Micro and Nanosystems - Volume 11, Issue 1, 2019

As the feature size of integrated circuit devices is shrinking to sub-7 nm node, the chip power dissipation significantly increases and mainly converted to the heat. Vertically Aligned Carbon Nanotube arrays (VACNTs) have a large number of outstanding properties, such as high axial thermal conductivity, low expansion coefficient, light-weight, anti-aging, and anti-oxidation. With a dramatic increment of chip temperature, VACNTs and their composites will be the promising materials as Thermal Interface Materials (TIMs), especially due to their high thermal conductivity. In this review, the synthesis, transfer and potential applications of VACNTs have been mentioned. Thermal Chemical Vapor Deposition (TCVD) has been selected for the synthesis of millimeter-scale VACNTs. After that, they are generally transferred to the target substrate for the application of TIMs in the electronics industry, using the solder transfer method. Besides, the preparation and potential applications of VACNTs-based composites are also summarized. The gaps of VACNTs are filled by the metals or polymers to replace the low thermal conductivity in the air and make them free-standing composites films. Compared with VACNTs- metal composites, VACNTs-polymer composites will be more suitable for the next generation TIMs, due to their lightweight, low density and good mechanical properties.

The main challenge in the commercialization of the RF-MEMS switches is their reliability, related to both the electrical and mechanical domains. The development of test standards and understanding the underlying physics of different failure modes has always been of major concern for the RF-MEMS designers. This paper reviews the different failure modes in the RF-MEMS switches like stiction, residual stress, cyclic fatigue, creep, wear and packaging in detail. The origin of these failure modes, their characterization procedure and respective solutions presented in the literature are presented to get a better understanding of the state of the art work done in the field RF-MEMS reliability for nearly past two decades.

Background: Metal dichalcogenides are important branch of functional materials, which have renewed great attention in academia and industry because of their various significant applications. Objective: The aim of the present study is to synthesize PbSe by solvothermal and investigate PbSe’s tribological properties. Results: The XRD pattern of the sample can be readily indexed as PbSe. The tribological properties of PbSe as additives in base oil were investigated using a UMT-2 ball-on-disc tribotester. Under the determinate conditions, the friction coefficient of the base oil containing 1.0 wt. % PbSe was lower than that of the base oil. A stable tribofilm on the rubbing surface could explain the improved tribological properties of PbSe as additives. Conclusion: PbSe nanoparticles have been synthesized successfully via solvothermal reaction. The preliminary tribological experimental results show that the PbSe could be a lubricant additive to the base oil and able to improve the tribological properties under the optimal concentration (1.0 wt. %). The result of tribological experiments demonstrated that the stable tribofilm with PbSe nanoparticles on the rubbing surface could benefit to decreasing surface friction.

Background: This paper presents a fundamental study of protein manipulation under the influence of dielectrophoretic (DEP) force for a lab-on-a-chip platform. Objective: Protein manipulation is dependent on the polarisation factor of protein when exposed to an electric field. Therefore the objective of this work is a microfluidic device and measurement system are used to characterise the human beta-2 microglobulin (β2M) protein via lateral attractive forces and vertical repulsive forces by means of DEP responses. Method: The manipulation of the β2M protein was conducted using a microfluidic platform with a tapered DEP microelectrode and the protein concentration was quantified based on a biochemical interaction using an Enzyme-Linked Immunosolvent Assay (ELISA). The protein distribution has been analysed based on the β2M concentration for each microfluidic outlet. Results: At 300 kHz, the protein experienced a negative DEP (nDEP) with of 83.3% protein distribution on the middle microchannel. In contrast, the protein experienced a positive DEP (pDEP) at 1.2 MHz with of 78.7% of protein on the left and right sides of the microchannel. Conclusion: This is concept proved that the tapered DEP microelectrode is capable of manipulating a β2M via particle polarisation, hence making it suitable to be utilised for purifying proteins in biomedical application.

Objective: This paper presents the effect of anode temperature and contact voltage on the breakdown arc of micro electrical contact pair under DC excitation. Methods: A rectangular micro electrical contact pair is considered. The resistance and capacitance of the contact pair are obtained for the materials Al, Cu, Au and Pt. The anode temperature is calculated based on the 3D heat equation. Pre-breakdown arc due to anode temperature is analyzed. Result: The breakdown voltage and breakdown electric field characteristics for the gap between 0.5μm and 30μm are reported. The electric field of micro electrical contact pair is analyzed mathematically. The calculated values of resistance, anode temperature and electric field are compared with the simulation results obtained using COMSOL multiphysics FEA software tool. The arc-less operating region of micro contact is identified. Four cases with the ratings 50V/5A, 50V/0.5A, 400 V/ 5A and 400V/0.5A have been considered for the analysis of arcless micro electrical contact. Conclusion: These results can be considered while designing arc-less micro electrical switches, micro relays and micro circuit breakers which can be applicable for the future DC electric power distribution, protection system and automobiles. Also these results can be considered when designing micro actuators, sensors and electrostatic devices.

Background: Grooves may inevitably occur on the surface of the friction pair caused by severe wear or residual stress, which will play an important role on the reliability of machine parts during operation. Objective: The effect of the micro-grooves perpendicular to sliding direction on the wear performance of the friction pairs should be studied. Method: Micro-grooves can be machined on discs of friction pairs using electrical discharge machining. On-line visual ferrograph method was used to monitor the wear process to research the wear rate changing characteristic. Profilemeter and metallurgical microscope were used to observe the wear scars. Results: Comparing to the non-groove test, i) in one-groove test, wear volume and rate were approximate the same, and the wear scar was smooth, ii) when the grooves more than 4, the test running-in stage will be obviously prolonged, particularly for the test with 8 grooves on the disc, the duration of running-in stage is 4 times than that without grooves on specimen, and the wear rate and volume increase significantly, and then decrease with fluctuation, iii) the abrasive wear can be avoid with the debris stagnating in the groove, however, fatigue wear will significantly emerge. Conclusion: Abrasive wear can be avoided and smooth running-in surfaces can be obtained with proper amount of initial radial micro-grooves.

Background: Electrothermal microactuators are very promising for wide range of Microelectromechanical Systems (MEMS) applications due to the low voltage requirement and large force produced. Method: A new optimized V-beam electrothermal micro actuator was implemented in variable optical attenuator. In this work, Particle Swarm Optimization (PSO) technique is proposed to design the Vshaped beam. Result: The approach has successfully improved both angular displacement & output force of the microactuator. Entropy generation rate was used as optimization criteria.

Background: Nickel grating absorber has been studied and shows good absorption property in the visible band. In order to further improve the absorption performance, reflection should be reduced, and anti-reflection layer should be added upon or under the gratings. Method: In this paper, the dielectric layer is added between and upon the nickel gratings. Equivalent medium theory is used to analyze the role of dielectric layer on absorption mechanism of nickel gratings. photoresist is used to illustrate the possible practical usage of the proposed method. Results: Absorption efficiency of TM (transverse magnetic) and TE (transverse electric) polarization show growing trend with the increase of refractive index of the dielectric material. PMMA and TU7 are chosen as the dielectric material. The simulation results show that TM absorption reduced slightly in visible band, and improved by up to 86% in the near infrared region. TE absorption shows up to 79% improvement in the whole visible to near infrared waveband. Conclusion: Nickel grating based broadband absorber is analyzed in this paper. Dielectric layer is added upon the gratings, and act as the anti-reflection layer. The refractive index and layer thickness is analyzed by using equivalent medium theory. Dielectric material that has high refractive index is more desired. The designed nickel grating shows high absorption property from 450nm to 800nm for both TM and TE polarization.

Background: Micro-positioning platform is a device with high accuracy of positioning and a certain range of motion. Accuracy of the micro-positioning mechanism is ensured by using a flexible hinge to replace the traditional motion pair. Objective: A two-dimensional micro-positioning platform is proposed in this study. It is necessary to find out how the geometric parameters affect the output displacement of the amplification structure component. Thus, this paper aims to build up the relation model of stiffness and geometric parameters. Method: A novel method for building the relational model of parameters and output displacement is introduced on the basis of the superposition principle of small deformation and the principle of deflection. Firstly, the amplification structure is divided into different units according to the section shape and force. Secondly, the parametric model of integral deflection curve of the amplification structure is solved. The method is based on the flexibility matrix of the flexible hinge unit and the differential equation of the deflection curve of the rectangular unit. Finally, the parametric model of output displacement is established by using the integral deflection curve equation and geometric relationship between adjacent deformations of the compliant structure. Result: It is shown that the output displacements by analysis method are close to the results achieved by the ANSYS software, with a maximal difference of 15.3%. The reason is that the integral deflection curve is not smooth at some special points, which is verified by finite element analysis.

The transformation from the development of enabling technology to mass production of consumer-centric semiconductor products has empowered the designers to consider characteristics like robustness, compactness, efficiency, and scalability of the product as implicit pre-cursors. The Carbon Nanotube Field Effect Transistor (CNFET) is the present day technology. In this manuscript, we have used CNFET as the enabling technology to design a 1-bit Full Adder (1b-FA16) with overflow detection. The proposed 1b-FA16 is designed using 16 transistors. Finally, the proposed 1b-FA16 is further used to design a Ripple Carry Adder (RCA), Carry Look Ahead Adder (CLA) circuit and RCA with overflow bit detection. Methods and Results: The proposed 1b-FA16 circuit was designed with CNFET technology simulated at 32 nm with a voltage supply of +0.9 V using the Cadence Virtuoso CAD tool. The model used is Stanford PTM. Comparison of the existing full adder designs with the proposed 1b-FA16 design was done to validate the improvements in terms of power, delay and Power Delay Product (PDP). Table 2, shows the results of comparison for the proposed 1b-FA16 with the existing full adder designs implemented using CNFET for parameters like power, delay and power delay product. Conclusion: It can be concluded that the proposed 1b-FA16 yielded better results as compared to the existing full adder designs implemented using CNFET. The improvement in power, delay and power delay product was approximately 11%, 9% and 24% respectively. Hence, the proposed circuit implemented using CNFET gives a substantial rate of improvements over the existing circuits.