Key Engineering Materials Vols. 562-565

Abstract: Because fabrication errors have a great influence on micro-springs elastic coefficient, and it is difficult to reduce the influence through fabrication process methods at this stage, the authors propose solutions through design process to reduce the sensitivity of Elastic coefficient of fabrication errors. The authors derived error propagation formula through multivariate function Taylor series expansion method, and made a quantitative analysis of the influence of fabrication errors, then summarized the influence rules of the size parameters on dispersibility of elastic coefficient K, finally proposed the method to degrade device performance dependent on the fabrication precision.

Abstract: This paper proposed a removal analysis and a contouring strategy of accurate micro-WEDM processing for an aerodynamic micro-air journal bearing for micro-gas turbine engine. It is designed based on aerodynamic theory and can be self-acting by the compressed air pressure. The rotor is stably rotated in a relatively low speed which is below one hundred thousand revolutions per minute, and is much lower than other references. The extended and trimmed tool path is adopted in this paper, and the cusp at the corner of the micro-air journal bearing is obtained by this method which is better than the common arc tool path. The inner and outer diameter of the micro-air journal bearing with a satisfactory shape and good surface quality is 1.068mm and 1.165mm, respectively. The minimum radius at the bottom of wedged-structure is 15.9μm. The kerf of the blanking is 43μm, and the machining discharge gap is 18μm under this machining conditions. The MRR calculated by experimental data is 0.00144mm²/min.

Abstract: In this paper, we report the fabrication and characteristics of the top-gated thin film transistors (TFTs) with nanopolysilicon as active layers. The nanopolysilicon thin films were deposited on SiO₂ layers by LPCVD and the SiO₂ layers were grown on the single silicon substrates. Then the nanopolysilicon thin film transistors with different thin film thicknesses and different channel width length radios were fabricated by CMOS technology, in which the thicknesses of channel layers were 90nm and 120nm, and the channel width length radios were 160μm/160μm, 320μm/160μm and 640μm/160μm, respectively. The experiment results show that drain current is in proportion to channel width length radio. In addition, when the thickness of the nanopolysilicon thin film is 90nm and the channel width length radio is 640μm/160μm, the on/off current radio reaches 10⁶.

Abstract: In this study, Tin Oxide (SnO₂) inverse opal was fabricated by infiltrating SnO₂ sol-gel precursor solution into Poly Styrene (PS) spheres crystal template which was generated via evaporative deposition self-assembling, then was heat treating at 500°C for two hours in controlled atmosphere box furnaces. PS spheres crystal template was characterized by Scanning electron microscope and Ultraviolet-visible-near infrared absorption spectrometer. The SnO₂ inverse opal was characterized by Scanning electron microscope, Energy Diffraction Spectrum, X Ray Diffraction. The large-area, highly ordered SnO₂ inverse opal was achieved in this paper.

Abstract: A new fabrication method to produce low residual stress PECVD SiNx layers at high frequency (13.56 MHz) was developed. High frequency up to 60W is employed in this new method to fabricate low stress SiNx. By adjusting the composition of reactant gases, process vacuum and the chamber temperature, the residual stress can be lower to-0.28 MPa, and high deposition rate up to 240 nm/min can be achieved. In addition, this paper investigated the influence of other important parameters on the results, such as pressure, power and gases flow rates. Moreover, by using the optimal process, the refractive index is ranged from 1.98 to 2.20, and the uniformity of run to run wafers is about ±3% for 4 inch wafers. Finally, a typical FBAR (film bulk acoustic wave resonator) structure using these low stress PECVD SiNx layers as solid layer and mask indicated that these layers are compatible in IC technology and suitable for using in fabricating MEMS(microelectromechanical systems) devices.

Abstract: Fabrication of a novel in-plane field emission diode structure is presented. Sub-micro metal tips were obtained using a two-step lithography method. The Minimum width of the metal tips was less than 100nm, and the minimum spacing of 145.7nm was obtained. The I-V characters in atmospheric environment before and after the silicon etching were measured.

Abstract: Superhydrophobic surface have many applications such as drag reduction in the micro-electromechanical systems. A novel method of fabricating superhydrophobic surface is proposed using the simple wet chemical etching in this paper. Firstly, the surface of steel disc is polished by abrasive paper and then treated with chemical etching. Secondly, the surface of steel is modified with 1H,1H,2H,2H-Perfluorooctyltrimethoxysilane. The superhydrophobic surface was obtained on the stainless steel surface. Finally, the effects of the etching time and etching solution concentration were analyzed to the superhydrophobic performance. The experimentation results show that superhydrophobic performance is the best when the HCl concentration is 2mol/L, the etching time is 20 minute respectively. The water contact angle (CA) of the rotor surface is 152°. The water droplets are hardly able to stick to the steel surface．

Abstract: The requirement for fabrication of the nanometer-scale structures has grown up recently due to the advance in the development of the nanoscale electronic-devices or bio-devices. Scanning tunneling microscope (STM)-based electric lithography is one of the potential fabrication approaches to produce nanoscale structures on a variety of materials. This study of the STM-based electric lithography intends to fabricate flat-bottomed and lamellar structures on the graphite surface, which differs from the conventionally fabricated tapered structures. The formation and the comparison of both the lamellar and tapered structures are obtained by applying distinct STM tip geometries in the STM-based electric lithography. On the basis of the experimental results, it is found that the formation of lamellar structures should be attributed to the local electrochemical reaction, while the generation of tapered structures is resulted from the dielectric breakdown in the tip-sample gap.

Abstract: A new method for drilling micro-hole called EDM-ECM combined processing is proposed in this paper. This method consists of EDM shaping and ECM finishing, and they are carried out in sequence on the same machine tool with the same electrode but different dielectric medium. Micro-hole drilling experiment was done by micro-EDM, micro-ECM and EDM-ECM combined processing. The results show that the machining efficiency is improved by 9.2 times compared to conventional micro-ECM, and machining precision and shape accuracy of micro-hole are much better. The surface quality and mechanical property of the workpiece are improved, since the recast layer and surface defects generated by EDM are removed completely by ECM finishing. It proves that this combined machining method is possible and useful in the field of micro-hole drilling.