Advanced Materials Research Vols. 60-61

Abstract: Differing with the traditional way to perform electroporation (EP) by using the DC electrical pulse, this paper proposes a new EP system by applying continuous DC voltages to generate proper EP electric field strengths utilizing the shape change of the channel. The fabrication of chip and set-up of system are clearly described and simulations also carried out utilizing CFD-ACE to study the electric field strength distribution and the time span when fluid passes through different electric field strengths. The fabrication of the proposed EP system is quite simple and low-cost.

Abstract: Micro cantilevers in atomic force microscopy are important force sensors in nano research, and the spring constant is one of the most important parameters of the cantilevers. Normal testing methods are not suitable for the spring constant detecting of micro cantilevers according to the strict scale of the cantilevers, and new methods are needed to the study of micro cantilevers. A method for detecting of spring constant of micro cantilevers based on combining the numerical simulation and frequency measurements is presented in this paper. The new method involves four steps, the first step is developing the vibration model of the micro cantilever studied immersed in air and determine the fluid parameters in the model during dynamic tests in atomic force microscopy presented in this paper; the second step is analyzing the vibration behavior of the corresponding cantilevers with the same geometry but different young’s modulus. The third step is measuring the natural frequencies of the micro cantilevers and comparing the experimental results with the numerical results to determine the young’s modulus of the cantilever. The last step is conducting the young’s modulus to the cantilever FEA model for determination of its spring constant. Experiments on a NSC cantilever have been done to validate the method presented in this paper.

Abstract: Gold nanostructures were synthesized at room temperature under irradiation of a fluorescent lamp in mixture of gold seeds smaller than 10 nm, HAuCl4, and poly(vinylpyrrolidone) (PVP). N,N'-dimethylformamide (DMF), water or ethylene glycol (EG) was used as solvent respectively. The products were characterized by transmission electron microscopy, X-ray diffraction and absorption spectra, and the results indicated that under light irradiation at ambient, the reducibility of the three solvents for HAuCl4 ranked as: EG> water> DMF, all far weaker than that of PVP; PVP also prevented the nanostructures from precipitating; gold seeds seemed to impose an autocatalytic effect to facilitate the reduction of HAuCl4; light irradiation was essential for high-yield production of gold particles; the above factors influenced the morphology and size of the gold structures, and led to formation of particles within nano or micron scale in shape of spheroid, rod or plate.

Abstract: A fixed microelectrode device for cell stimulation has been designed and fabricated using micro-electromechanical systems (MEMS) technology. Dielectrophoretic forces obtained from non-uniform electric fields were used for manipulating and positioning osteoblasts. The experiments show that the osteoblasts experience positive dielectrophoresis (p-DEP) when suspended in iso-osmotic culture medium and exposed to AC fields at 5 MHz frequency. This work will help to investigate the mechanisms underlying Wolff’s law of bone growth dynamics at the cellular level. The methods used can also be developed to control osteoblast metabolism and ultimately enhance bone repair processes.

Abstract: An excellent pressure sensor based a simple fabrication technology is presented. Differently from the present prevailing fabrication process of silicon piezoresistive pressure sensor: platinum is used as the sensing material, with a smaller but acceptable sensitivity and much simpler processes; adhesive bonding with SU-8 is used as an alternative choice to anodic bonding, and we choose a vacuum hot plate to avoid using a bonding machine. To achieve a successful bonding, it is found that pre-bake time and pumping time are the most important factors. Bonding quality is evaluated by inspection through the glass with 95% of the area successfully bonded and the failed area in the edge of the wafers. The measured bonding strength is 17.34 MPa. The Pressure-Voltage characteristic test results display a good linearity within 0.2% and especially a good precision within 0.035% in square fitting. The temperature drifting is also tested and the TCO is 1250 ppm/(°C FSO). The long-term stability of the sensor at a constant pressure is a fluctuation within 40 Pa (0.098% FSO) in 7 days. Both the simple fabrication process and the excellent performance of the sensor suggest that this sensor is a much good choice in measuring atmospheric pressure.

Abstract: In self-power sensor nodes, the capability of energy harvesting and storing of the solar micro-power system determines their lifetime and adaptability to the environment. As a load of solar cells, energy storage devices directly influence the output conversion efficiency of solar cells and output power of solar micro-power system. In this paper, the advantages and disadvantages of NiCD batteries, NiMH batteries, Polymer Lithium-ion batteries and Super-capacitors are analyzed based on features of the solar micro-power system. A hybrid storage system combined with Polymer Lithium-ion batteries and the super-capacitors is designed. Experimental results show that the power density of hybrid storage system is larger than that of Polymer Lithium-ion batteries. The capability of pulsing load is improved over 60%, and the energy storage loss is reduced.

Abstract: Resonant pressure sensor, whose thermal gradient field is changed by variations in electro-thermal excitation, then influences the resonant frequency of the sensor, so different thermal excitation will produce different thermal stress, and then influences the characteristic of the sensor. For the thermal excitation resonant pressure sensor at different voltages excitant will produce different thermal gradient field, then influences the frequency of the sensor. Taking the advantage of lock-in amplifier, which can detect weak signal, an open-loop test experiment about the resonance output signal is carried out by using the method of alternating current excitation and pick-up with two-octave component. The results show the relational about thermal excitant virtual value and resonant frequency of this silicon microstructure resonant pressure sensor. Analysis about the result of the experiment is given, which can provide certain theories basis for the optimum design of the related parameter of this sensor, and have an important advice for the peripheral circuit design.

Abstract: The gauge factor and nonlinearity of 80nm polysilicon nanofilms with different doping concentration were tested. The experimental results show that, from 8.1×1018cm-3 to 2.0×1020cm-3, the gauge factors first increase then decrease, which like the common polysilicon films (thickness is larger than 100nm). From 2.0×1020cm-3 to 7.1×1020cm-3, the gauge factors do not change with doping concentration almost, which can be explained by tunneling piezoresistive theory. When doping concentration is low than 4.1×1019cm-3, the nonlinearities are big, and the nonlinearities become small when doping concentration is high than 4.1×1019cm-3. The nonlinearity is related to the occupied condition of trapping states in grain boundary. The longitudinal gauge factor and nonlinearity are smaller than transverse ones. Take the gauge factor and nonlinearity both into consideration, the optimal doping concentration should be 4.1×1019cm-3. The conclusions are very useful for design and fabrication of polysilicon nanofilms piezoresistive sensor.

Abstract: The polysilicon nanofilms have significant piezoresistive characteristics. In this paper, an analysis of tunneling piezoresistive effect of p-type polysilicon nanofilms is presented based on the experimental data. The analysis results show that the tunneling piezoresistive effect is much remarkable than piezoresistive effect of neutral region, and the former is about 1.3 to 1.5 times of the latter. The higher is doping concentration, the more remarkable tunneling piezoresistive effect is. This advantage can be utilized to improve the temperature characteristics of polysilicon piezoresistive sensor.

Abstract: Packaging of MEMS has been identified as one of the most significant areas of research for enabling MEMS usage in product applications. In order to make MEMS a real-life opportunity, it is vital to explore and develop an understanding of the possibilities and limitations of MEMS packaging. This paper presents several packaging structures for RF MEMS switch which based on GaAs substrate. The return loss of X-band RF MEMS switch before and after packaged can be simulated by Ansoft HFSS. The results show that return loss of RF MEMS switch after packaging deteriorated at least 3dB compared with that of before. Thermal mismatch caused by the variation of the temperature in the packaging process will introduce additional thermo-elastic strain and geometric deformation into the mechanical structure. The influence on return loss of the RF MEMS switch is researched in this paper too. Considering that, return loss simulated by HFSS decreases from -16.38dB to -16.88dB. Then, some design guidelines of RF MEMS packaging derived from the simulation of HFSS are also concluded at the end of the article.