Key Engineering Materials Vol. 503

Abstract: Two kinds of fabrication schematics of micro perforated panel (MPP) based on MEMS technology is expatiated in the article. MPP has been widely used to reduce noise, and theory reveals that better ability of sound absorption of the MPP will be getting by means of reducing the diameters and increasing the dense of the perforators properly. Small error of the dimension will decline the sound absorption seriously on such a scale. MEMS technology is applied to fabricate the micro perforated panel which is hard to be realized utilize machine. The parameters are calculated based on the theory of Maa D-Y to obtain a kind of wide band, high sound absorption structure. The computer simulation is also conducted to forecast the capability of the MPP and the experiment result shows the accordance with the simulations.

Abstract: In previous research, in order to simulate the 3D structure of MEMS device, we developed a software named Virtual Process which can help the designer to testify his/her design by comparing the simulation result with real requirements. As Virtual Process could only find out the difference in structure, we put forward a new method, which can compare the functions of the device to verify the simulation result. In this paper, we take hydrophobicity as an example to show the comparison between the results of simulation and experiment. The hydrophobicity is expressed by contact angle, which is measured by certain device in reality. In this case, this paper put forward a method to calculate the contact angle to verify the hydrophobicity of black silicon. Besides, we put forward a method combining micro/nano dual-scale DRIE to realize the simulation of black silicon before the calculation. As a result, the contact angle of black silicon between our calculating method and the actual value is only 7° .

Abstract: The precision lapping and polishing Si wafer is presented. Three-step lapping Si wafer and two-step polishing Si wafer are adopted within this processing. The Al2O3 abrasive of 20μm, 9μm and 3μm is used to lap wafer, then precision polishing is done with lapping agent of CeO2 and SF1. The thickness of the Si wafer can be controlled accurately, the flatness can be controlled within 3μm, and the roughness can be controlled under 1nm. The stress can be decreased evidently, even the thickness of the Si wafer is thinned down to 60μm, it is still flat.

Abstract: The commutation of pressure, electro-osmosis and acoustic methods is usually adopted to realize the drive of microfluid in microsystem. However, the above methods do not have a very ideal controllability. In view of the above situation, the paper proposes a kind of microfluid-driven method according to physical mechanism of wave-vortex interaction. In the method the microfluid-driven control is realized sympathetic vibration between forced wave and unstable wave in the vortex layer to intensify or destroy nonlinear stability of vortex or to regulate quasi-vortex energy flow in the boundary layer, in which the forced wave is produced by applying tangential simple harmonic motion with specific frequency and amplitude to the outside of flowing passage or flowing body. The paper demonstrates the method theoretically, and then uses an experiment to prove its availability. By using de-ionized water, straight round glass with the diameter of Φ18~Φ20μm, the experiment of separation is carried out successfully. The method has very broad applying prospect for the activity retention in the process of cell injection and transfer in the biomedical field and the fuel transfer in the micro propeller.

Abstract: This paper presents a micro-fluidic inertial switch with varying rectangular cross section, which employs the moving mercury droplet in the micro-channel to close a switch. Combining the Young-Laplace formula with the structure, the formula of the threshold g-value is derived. The influence of design parameters of microchannel on the threshold g-value is analyzed. Based on the VOF approach containing contact angle effects, the dynamic behavior of mercury droplet in the microchannel is simulated using Fluent. The response time is predicted through simulation with the contact angles ranging from 130° to 170°. In addition, the dynamic process of inertial switch is simulated, and the result indicates that the selected design parameters can achieve reliable switching under given threshold g-value.

Abstract: In this paper, we improved the design of a membrane peristaltic micropump. The pump was driven by a rotating motor with magnetically attracted steel balls on top. The size of the micropump was significantly reduced to realize small flow rate and high pressure, to serve for precision delivering applications. Testing results showed that the pump can realize small flow rate from 0.93 to 12.73 μL/min, with very high linearity. The back pressure could reach more than 83 kPa until the PDMS (polydimethylsiloxane) channel structure was destroyed under high pressure. The pulsation problem of the peristaltic pump was also mentioned, as well as the possible solution to deliver a certain amount of small sample volume.

Abstract: Due to its simple structure, low consumption of energy but strong driving forces, Electrowetting on Dielectric (EWOD) is used most frequently in digital microfluidics for manipulation and control of droplets. In this paper, the internal mechanism of EWOD is explained though establishing the geometric model of the unipolar board structure digital microfluidic chip. And the boundary conditions of equations are determined. Three coupling physical fields: electric field, flow field and temperature field in the digital microfluidic chip are simulated and analyzed. With the electric field equation coupled, Navier-Stokes equations and energy equation of the temperature control, the numerical simulation of the chip is conducted. The results show that the internal flow of micro-droplets is counterclockwise and swirling flow. The external flow velocity of micro-droplet is greater than the internal velocity. In addition, micro-droplets near the electrode applied temperature are higher than the internal temperature. Surface micromachining technologies are employed to fabricate the chip. Experimental results show that the droplet can be driven in a velocity of 25cm/s. It will possibly provide an effective solution to the manipulation of droplets.

Abstract: Piezoelectric thin films cantilevers with a central Si mass are designed for harvesting vibration energy applications. Through the theoretic analyzer and MATLAB simulation, the displacement, resonance frequency and maximum stress dependent of the different structure parameters of micro-power device are obtained. It shows that increasing the quality of mass and the length of microcantilever, decreasing the width and thickness of microcantilever can realize the low-frequency resonance and maximum power in actual design. The static and mode analysis of the theory model are done by using Ansys 11.0. The results can provide guidance for the design and fabrication process of micro power generator.

Abstract: (Pb,La)(Zr,Ti)O₃ antiferroelectric thick films were prepared on Pt (111)/ Ti/SiO₂/Si (100) substrates by a sol-gel process. The effects of single annealing and multistep annealing on the structures and electric properties of the films were investigated. The crystal orientation and structure of the antiferroelectric thick films were studied. The thick films by multistep annealing have higher (100)-preferred orientation than them by single annealing. The surface of the films was more smooth, compact and uniform by single annealing. The antiferroelectric nature of the (Pb,La)(Zr,Ti)O₃ antiferroelectric thick films by various sintering procedures was demonstrated by P(polarization)-E(electric field) and C(capactitance)-E(electric field). The temperature dependent of the dielectric constant and loss was measured under the frequency 1, 10, and 100 kHz and comparing with traditional signal annealing, the films have phase transition from antiferroelectric state to paraelectric state by multistep annealing.

Abstract: Stress gradient of a thin film along its thickness direction has important influence on performance of MEMS/NEMS devices. The measuring method based on curvature radius is a usual method for extracting film stress gradient. In this paper the error of the method has been analyzed using Finite Element Analysis software Coventorware, and the current theory has been modified according to FEA results to enhance its accuracy. Simulating results indicated that the accuracy of the method has been increased observably after correcting.