Key Engineering Materials Vols. 645-646

Abstract: To assemble easily damaged micro-parts safely in interference fit way, the assembly process is designed and the interaction force in assembly process is analyzed. The pose of micro-parts is aligned based on calibration of three microscopic vision systems from different directions. In addition, a control strategy based on feedback of vision and force is proposed to assemble safely. In the case of two micro-parts just contact, position of micro-part is adjusted based on force information to compensate pose alignment error and keep force in safe range. When micro-part is deformed as increased contact force, position of micro-part is adjusted based on force in the interference fit process and deformation of micro-part. Experimental results demonstrate the effectiveness of proposed methods.

Abstract: A novel Bar TSV(B-TSV) structure, formed by two semi-cylinders combining with a quadrangular is studied in this paper. This B-TSV structure extends the TSV design options by introducing new design parameters. The scalable electrical model of B-TSV is proposed and the effects of design parameters, such as the side length of quadrangular and the minimum distance between TSVs are investigated and concluded by a 3D electromagnetic solver. Performance comparison between B-TSV and the traditional cylindrical one is also provided by simulation under the Ground-Signal-Ground configuration. Simulation results show that B-TSV has better performance than the traditional one, and can be used to increase the TSV array density without degrading the electrical performance of TSV system.

Abstract: There are several factors that affect heat transfer of heat pipe, for example, structure dimension, filling ratio and vacuum degree of charging. This paper studied the thermal conductivity of micro flat heat pipes (MFHPs) with different structure dimension and with different filling ratio, when the charging vacuum degree of MFHP was decided. When electric power was 2W or 4W, MFHPs with parallel grooves and nonparallel grooves, charged by working fluid with different filling ratio, were carried out. And the filling ratio is 30%, 40% and 50%, respectively. The better thermal performance of MFHP can be evaluated by lower thermal resistance and higher effective thermal conductivity. The experiment results show that MFHP has the highest effective thermal conductivity when the filling ratio is 40%; and the thermal performance of MFHP with nonparallel structure in axial direction is better than that of MFHP with parallel structure.

Abstract: Effective field emitting angle plays an important role when investigating field emission characters. In this work, effective field emitting angle is introduced for Spindt-type emitter to relate spatial variation of current density along tip’s surface to emission current. The effects of various parameters on effective field emitting angle are analyzed. The results show that effective field emitting angle decreases exponentially as half angle increases, decreases quadratically as radius of gate aperture increases, but increases logarithmically as gate voltage increases linearly. It is also found that effective field emitting angle increases first and then decreases with emitter’s height increasing. Similar trends can be also found with insulator height. Grid thickness nearly has no effect on the effective field emitting angle.

Abstract: A method of fabricating convex plate-shaped micro electrode was proposed based on the electrochemical etching principle. The square sectional electrodes were prepared in advanced using wire-EDM, The micro cylindrical electrode was fabricated firstly by using the eletrochechemical etching method. Then the top end was insulated to protect it from etching. Then the convex plate-shaped micro electrode was obtained in subsequent etching. Comparative experiments in drilling micro-hole in stainless steel with the thickness of 1mm were done by using the cylindrical and convex plate-shaped micro electrode. Results shows that the better locality, smaller side-gap and hole taper could be obtain by using convex plate-shaped micro electrode.

Abstract: In recent years, pulsed laser processing technology is widely used in MEMS device manufacturing, aerospace technology, precision instrument manufacturing and circuit board processing. According to the characteristics of nanosecond laser, this paper designs a novel nanosecond pulsed laser micromachining system with PMAC card as its core unit. The system can achieve automation control of laser parameters and movement pattern of motion system by software, which can easily realize automatic processing of point, line, and plane structure in micron scale. In this paper, several groups of experiments are taken to test the reliability and accuracy of the machining system and find the group to obtain the best processing result.

Abstract: Although the nanostructure machining by AFM probe assisted with laser has gain a great progress, few studies has been done on the optical fiber probe guiding the continuous laser to irradiate on AFM probe to machining nanostructure. Using this technology to create nanodot and nano-groove was presented in this paper. The law of how the experiment parameters influenced the results was summarized in the paper. The scale of nanodot is about 450nm, and nano-groove is about 40nm. When the fabrication is completed, the wear of the AFM probe was observed by SEM and drew a conclusion. In the method of nano machining by AFM Probe combining with a CW Laser, there will be a combined field to achieve the fabrication, and the method is better than mechanical characterization with AFM probe.

Abstract: In this paper, we present two metamaterial absorbers (MMA) at mid-infrared using multi-resonant structures. The dual band MMAs employ the typical metal/dielectric/metal structure with 80 nm gold ground plane at the bottom, 190 nm SiO₂ dielectric spacer in the middle and periodic gold patterns on top. The top resonant structure in MMA1 consists of a gold cross resonator ringed by four gold split-ring resonators (SRR) at the ends of the cross, while in the unit cell of MMA2, gold SRRs are placed at the four quadrants of the cross resonator. MMA1 shows two absorption peaks of 90.3% and 88.4% at 4.17μm and 4.86μm respectively, and the absorption peaks of MMA2 are observed to be 72.4% at 3.90μm and 48.0% at 5.66μm.

Abstract: In some areas such as micro-mechanical, ultra-precision machining, nanotechnology, the high-precision positioning and very fine vertical scanning motion are needed urgently. Therefore, the Z-axis micro-displacement driving control technology has become the key technology in these areas. The piezoelectric ceramics actuator and stepper motor were integrated into hybrid linear actuator in Z-axis nanopositioning stage, and this can simplify the structure of the drive system. By calculating the gravity center of the vertical scanning system, and using single counterweight, a new one-arm bridge type structure was built. Appropriate tension and current sensors were also equipped in order to real-time monitor the drive status. It is feasible to balance the weight with this simplified system structure, and also guarantee the driving control accuracy of nanopositioning stage. Besides, in the structural design, the Abbe error can be reduced greatly by placing the stage center, grating ruler and displacement measurement centerline on the same line with grating reading head. The driving travel of nanopositioning stage is 150mm, and driving resolution is 1nm. The designing method introduced gives a scientific method and practical reference for the development of z-axis driving control system.

Abstract: The elastic mechanical properties of silicon nanocantilevers are of prime importance in biotechnology and nanoelectromechanical system (NEMS) applications. In order to make these applications reliable, the exact evaluation of the effect of the undercut on the mechanical properties of silicon nanocantilevers is essential and critical. In this paper, a numerical-experimental method for determining the effect of the undercut on resonant frequencies and Young’s modulus of silicon nanocantilevers is proposed by combining finite element (FE) analysis and dynamic frequency response tests by using laser Doppler vibrometer (LDV) as well as static force-displacement curve test by using an atomic force microscope (AFM). Silicon nanocantilevers test structures are fabricated from silicon-on-insulator (SOI) wafers by using the standard complementary metal-oxide-semiconductor (CMOS) lithography process and anisotropic wet-etch release process based on the critical point drying, which inevitably generating the undercut of the nanocantilever clamping. Combining with three-dimensional FE numerical simulations incorporating the geometric undercut, the dynamic resonance tests demonstrate that the undercut obviously reduces resonant frequencies of nanocantilevers due to the fact that the undercut effectively increases the nanocantilever length by a correct value ΔL. According to a least-square fit expression including ΔL, we extract Young’s modulus from the measured resonance frequency versus the effective length dependency and find that Young’s modulus of a silicon nanocantilever with 200-nm thickness is close to that of bulk silicon. However, when we do not consider the undercut ΔL, the obtained Young's modulus is decreased 39.3%. Based on the linear force-displacement response of 12μm long and 200nm thick silicon nanocantilever obtained by using AFM, our extracted Young’s modulus of the [110] nanocantilever with and without undercut is 169.1GPa and 133.0GPa, respectively. This error reaches 21.3%. Our work reveals that the effect of the undercut on the characterization of the mechanical properties of nanocantilevers with dynamic and static test must be carefully considered.