Many kinds of bulk hydrogen absorbing alloys undergo dramatic volume expansion when they absorb hydrogen. The maximum volume change varies with substances in the range of several to over twenty percents. Based on these phenomena, a new type of electrochemical microactuator has been designed. Bilayers of hydrogen absorbing alloy and nickel can generate a large bending and deliver high force, and it can work at very low voltage. As the first prototype, MmNi5 alloy film was chosen as the actuating medium, and it is deposited by sputtering method. The principle of this new microacturator and the microfabricating process of this bimorph are presented.
RIE is a promising way to fabricate high aspect ratio micro-structures and the PMMA is a widely used thick resist. In this paper, we developed a reactive ion etching of PMMA process in O2 plasma to fabricate micro-structures. High etch rate(0.5 micrometers /min) and smooth surface were achieved. In order to get high selectivity, We use Ni film as mask, which was patterned by photochemical etching. The etch results showed that vertical etch profile(base angle>88 degree(s)), high aspect ratio (5:1) and through-out etching of PMMA(100micrometers in thickness) could be obtained if select optimum etching conditions. We also found that the self-bias is one of the critical parameters during the process. If etching power was too high, the surface would be deformed due to the high energetic particles bombardment
A novel electrochemical actuation based on the hydrogen aborbing-desorping of metal is presented. The hydrogen aborbing-desorping of metal was accompanying with the volume swelling and shrinking, which could be used to convert electrical energy into mechanical energy. This type of actuation not only has usual advantages of electrochemical actuation such as long travel distance and acoustical quiet, but also there was no the concerns of gas leakage of those electrochemical actuation driven by the gas pressure built up by electrolysis of an aqueous electrolyte solution. In this work, a mischmetal (Mm)-Ni based alloy film, MmNi5, was prepared by sputtering method. The MmNi5 film was studied by x-ray diffraction method (XRD) and electrochemical method. It was found that the metal film had undergone phase transformation during its hydrogen absorbing and desorbing cycle, which was first time to be observed for the metal hydride film prepared by sputtering method. The further results of surface micromaching and scanning electron microscope (SEM) indicated that the hydrogen-induced actuation was applicable in MEMS.
The influence of easy axis orientation and bias field on magneto-impedance (MI) effect has been investigated in FeSiB amorphous films. The magnetic field corresponding to the maximum MI ratio shifts to a low value with the increase of the easy axis angle deviated from the transverse direction, and the sensitivity of MI change ratio to longitudinal field can be enhanced by applying a proper bias field along transverse direction.
The microstructures that have relatively large height, high aspect ratio are very important for improving micro-devices' characteristics. In this paper reactive ion etching (RIE) of PMMA to create high aspect ratio micro-structures was described. We use Ni film as mask, which was patterned by usual photochemical etching, then use O2RIE technology to etch PMMA thick film (100 micrometers ). During the etching process, O2 pressure, etching power are very important for the etching results. There are grass-like residues remained on the etched surface until the PMMA was over etched, this phenomena is caused by the micro-mask effect. With over etched, the grass-like residues can be eliminated. The etched surface is very smooth and the side wall is vertical. The etching depth can get up to higher than 100 (mu) M and the aspect ratio is 5.
Reactive Ion Etching is an effective method for etching of diamond films, in this paper, the influences of maskant, system pressure and the composition of reactive gas on the etch rate and etched surface of diamond were studied. A gas mixture of O2 and Ar was used as the reactive agent, the concentration of Ar in this mixture is in the range of 0 to 100% (V/V), and the etching result reveals that argon is not necessary. The system pressure plays the dominant effect on the etched surface and etched contours of diamond structures. The highest etch rate appears in the range of 60 - 100 Torr, very low and very high pressure both result in etch rate decreasing. The maskant plays an important role in etching process, it can be sputtered and re-deposited on the etched surface of diamond and act as a micro mask, results in rougher etched surface in some conditions. The optimum processing parameters were achieved, and combined this patterning process with conventional photolithography and sacrificial wet etching process, we have formed a new type of surface micromachining technique for fabrication of diamond MEMS structures. Typical MEMS structures such as cantilever beams, diamond micro hinge and diamond tips array have been fabricated successfully.
CVD diamond film is an attractive potential material for microelectronics and MEMS application, but patterning of diamond is one of the main difficulties hindering diamond electronics. In this paper, we studied the RIE process for precise patterning of diamond films. Ni/Cr, Cu/Cu or NiTi films were used as maskants, oxygen as reactive gas. The etching results showed that the NiTi film has high etching selectivity when used as mask for diamond etching and its is very convenient to be patterned by the special developed chemical etchant. Using O2 as main etching gas, the RIE can etch the diamond film effectively. The process parameters such as RF power, vacuum pressure have marked influence on the etching rate and the patterning of diamond film has been defined. Combined with sacrifice layer process and electroplating through mask technique, diamond micro hinge has been fabricated on silicon wafer.
A novel micropump actuated by NiTi/Si diaphragm has been developed. In order to optimize the actuating performance of the micropump, the dynamic actuating properties were studied in different actuating conditions such as different actuating currents, frequencies and duty cycles. The experimental result show that there is a maximum displacement when increasing the actuating current and frequency. The influence of duty cycle on maximum displacement when increasing the actuating current and frequency. The influence of duty cycle on maximum displacement with water flow and without water flow is different. The higher the displacement of the diaphragm is, the larger the flow rate is for a given frequency. The displacement of the pump diaphragm depends not only on the flow rate, but also on the moving frequency. The change of the resistance of NiTi strip indicates that the A - M phase transformation is completed partly during dynamic actuating processes. The maximum flow rate of 360 (mu) l/min was obtained in about 50Hz with 1:1 duty cycle in our experiment.
The patterning of nickel-titanium SMA thin films was one of critical micromachining issues during developing SMA film devices, now, an excellent etchant for etching of Ni-Ti SMA thin films was developed, therefore, this problem can be solved by photochemical etching easily. The etchant is based on the dilute hydrofluoric acid with several kinds of additives. The etching process is operated at room temperature with the etching rate of (1-5)micrometers /Min. The etched surface is very smooth and the edge of patterned SMA line is exactly the same as that of patterned photoresist. The etch factor is above 1.5 and might be enlarged furthermore. The etchant is stable and the repeatability is also good. This patterning method is compatible with IC processes, so it is easy to design and fabricate any magic pattern for MEMS applications.
A novel micropump actuated by thin film shape memory alloy has been designed, fabricated and tested. It is one of the membrane reciprocating micropumps which is driven by shape recoverable force of NiTi thin film and biasing force of Si membrane. The micropump is composed of a deformable chamber and two Si flap check valves. The structure of pump is simple. The pump was manufactured by Si surface and bulk micromachining technologies, Au-Si eutectic and epoxy bonding. The outer dimension of the micropump is 6*6*1.5 mm/mm/mm. The NiTi/Si composite actuator has an area of 3*3mm/mm with a thickness of 20micrometers Testing result show that the pump has extremely good performance, such as high pumping yield, low power consumption high working frequency. All these advantages are attributed to the patterning of NiTi thin film used as self-heating element and optimizing design of NiTi/Si actuated structure.
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