Advanced Materials Research Vols. 60-61

Abstract: A new low cost high performance PMMA micropump, developed for microfluidic system, is presented. According to the orifice flow theory, a diffuser/nozzle structure is fabricated with precision milling process, and packaged with the film-sealing at the condition of thermal bonding process. The size parameter of the diffuser/nozzle structure is 2.5mm *150µm, 8° conical angle, the volume of PMMA micropump is 14×14×2.5 mm3. And experimental results show that the PMMA micropump can produce a maximum back pressure of 1906.1Pa and a maximum flow rate of 564µL/min under 220 V, 500Hz squired wave power supply.

Abstract: In this paper, an effective method is presented to improve thickness uniformity in nickel electroforming process. In most electroforming processes, thickness ratio of edge to center is 2.5~4 and the shape of the electroforming zone is naturally a concave. Dividing conductive zone of electroforming structure to redistribute current density was applied to improve electroforming uniformity. Theoretical analysis and experimental results verify that a proper dividing method can improve the electroforming uniformity effectively. In the experiment, the thickness ratio of edge to center decreases from 2.91 to 1.88.

Abstract: An integrated micro xy-stage is designed and fabricated for application in nanometer-scale operation and nanometric positioning precision. This device integrates the functions of both actuating and sensing in the same silicon ship and is mainly composed of a silicon-based xy-stage, electrostatics comb actuator and a displacement sensor. In this paper a robust control strategy based on single neuron adaptive PID control theory is developed for silicon-based xy-stage, considering electrical, mechanical, and stiffness models. Single neuron adaptive PID control enables compact realization of a robust controller tolerant of device characteristics variation, types of inherent instabilities, and improving dynamical characteristics. The experimental results verified that the controller is more suitable for the silicon integrated micro xy-stage, under which the settling time is less than 2.5ms and the repeatability error is better than ±24.9nm. In addition, the presented control scheme is simple to implement in practical application.

Abstract: Model order reduction is an effective method to generate macromodels for system-level simulation. But it is difficult to deal with the electro-mechanical-damping coupling problems. So we presents a new approach to model the capacitive microaccelerometers with squeeze film damping and electrostatic effects using model order reduction (MOR) method. In this approach, the mechanical, squeeze film damping and electrostatic domains of the devices are modeled separately and then coupled at system-level. The macromodel for squeezed film damping effects could account for slip condition of the flow at low pressure and edge effects. In addition, some important parameters are preserved as symbol. The extracted macromodels are translated into the hardware description language and imported into a circuit simulator. An accelerometer is used to demonstrate the feasibility and efficiency of the proposed approach. Numerical simulation results show that the extracted macromodel can dramatically reduce the computation cost while capturing the device behavior accurately.

Abstract: In the paper, an attitude and heading reference system based on MIMU/magnetometers with moderate accuracy is presented. To meet the requirements of the real-time measurement, a master/slave CPU structure is proposed in order to improve the data refresh rate effectively. In the algorithm part, an adaptive extended Kalman filter equation is applied in the system, where the filter equation uses three tilt angles of attitude and three bias errors for the gyroscopes as state vectors, the measurements of three accelerometers and magnetometers are used to drive the state update. When the system is in dynamic mode, the measured values of the accelerometers consist of the gravity vector and the dynamic accelerations, an adaptive extended Kalman filter tunes its gain automatically based on the system dynamics sensed by the accelerometers to yield optimal performance. The experiment result shows that the attitude and heading angle errors are within 0.2 deg and 0.5 deg respectively in stationary mode, and the result can reflect the attitude angles reasonably in dynamic mode.

Abstract: . A Bulk RF MEMS switch is present in this paper. The beam structure and transmission line are separated fabricated on silicon and gallium arsenide (GaAs) wafer. The beam structure, up electrode, contact and anchor are fabricated on the silicon wafer. And transmission line and down electrode are made on the GaAs substrate. Two parts of the switch are bonded together by wafer bonding using gold layer as seed. The total area of the switch is 600 um X 600 um.

Abstract: We report our efforts towards fabricating nanomechanical resonators patterned by optical lithography in silicon nitride. Optical lithography has advantages of low cost and high efficiency over electron-beam lithography. Double clamped beam resonators with thickness 150nm, length and lateral dimensions 20um, 800nm have been designed. Through utilizing reactive ion etching and controlling gas flow, reaction time of CF4 and O2 plasma and power of the upper and lower electrode, nanomechanical resonators with lateral dimensions within 200nm are demonstrated.

Abstract: This paper presents a kind of fine polishing technique that adopts three-step polishing procedure and keeping-wafer-wet method. In order to remove the damaged layer created by lapping process or improve surface condition of silicon wafer, polishing process is needed. In this paper, techniques of improving the surface roughness of silicon are studied, three different polishing processes are presented, and optimum condition has been attained. Experiments of Si-Si bonding are also performed, and results show that after polishing ends, keeping surface of wafer wet is necessary to avoid slurry agglomerating.

Abstract: Quadrature error and Coriolis offset are main errors of micro-gyroscopes which caused by manufacturing imperfections. They deteriorate the overall performance of micro-gyroscopes. For inside sense outside drive frame micro-gyroscope, quadrature error and Coriolis offset have their own characters. Based on the mechanical analysis of inside sense outside drive frame micro-gyroscope in imperfect condition, the dynamic equations of condition with quadrature error and Coriolis offset are investigated, and an equivalent electrical model with quadrature error and Coriolis offset is presented. It is convenient to observe the effect of quadrature error and Coriolis offset by equivalent electrical model simulating. Three conditions are simulated and compared. The results indicate that the Coriolis offset reduces the amplitude of instantaneous displacement to a very small extent. Its effect can be neglected. Quadrature error causes an error displacement with the amplitude much bigger than the prefect displacement’s amplitude. It is the overwhelming error in ISOD frame micro-gyroscope.

Abstract: The MEMS fluxgate magnetic sensor which is characterized by its small mass, smart volume, high sensitivity and outstanding temperature stability, is often applied on the measurements of weak magnetic fields, such as the geomagnetic field. Therefore, it is widely utilized in the field of aeronautics and aerospace field, especially in Nano-/Pico- satellites. MEMSMag, a novel type of micro fluxgate magnetic sensor (MFGM), which exploits magnetic fluxgate principle, was designed and microfabricated, Based on MEMS technology. The micro sensor probe has symmetrical geometry, and is flexible for electrical connection. MEMSMag would be easily assembled into a 3-axis subminiature magnetometer and will be applied to measure vector of the weak geomagnetic field. The microfabrication process was developed. The UV lithography technology in combination with thick negative hard-cured technology was exploited in the microfabrication. The original samples were produced with the dimension of 1 1 100 . The primary tests have been done. The integrity, conductivity and resist test, as well as transformer effect measurement were completed. The statistics, analysis and conclusion of the experimental results have been obtained.