Optimization design of multi-material micropump using finite element method

This paper presents a micropump fabricated from low cost materials with specific goal of cost reduction. The micropump does not require any valve flap and comprises one plastic pump polyether–ether–ketone (PEEK) body, one metal diaphragm, and three piezoelectric ceramics to form piezoelectrically actuated diaphragm valves. The valve actuation simplifies micropump structural designs and assembly processes to make the pump attractive for low cost bio-medical drug delivery applications. A detailed optimization design of geometric parameters of the piezoelectrically actuated diaphragm is undertaken by use of 3D finite element method (FEM) to maximize piezoelectric actuation capability and ensure actuation reliability. An optimized geometric dimensional design: the ratio of thicknesses between the piezoelectric ceramics and the metal diaphragm, and the lateral dimension of the piezoelectric ceramic, is obtained through simulations. Based on the optimized design, a good agreement has been reached between simulated and measured strokes of the micropumps. The tested results show that the micropump has a high pump flow rate for air, up to 39 ml/min, and for water, up to 1.8 ml/min, and is capable of ensuring diaphragm’s maximum stress and strain is within material strength for reliable work.     

A surface-tension driven micropump for low-voltage and low-power operations

In this paper, we first report a micropump actuated by surface tension based on continuous electrowetting (CEW). We have used the surface-tension-induced motion of a mercury drop in a microchannel filled with an electrolyte as actuation energy for the micropump. This allows low voltage operation as well as low-power consumption. The micropump is composed of a stack of three wafers bonded together. The microchannel is formed on a glass wafer using SU-8 and is filled with electrolyte where the mercury drop is inserted. The movement of the mercury pushes or drags the electrolyte, resulting in the deflection of a membrane that is formed on the second silicon wafer. Another silicon wafer, which has passive check valves and holes, is stacked on the membrane wafer, forming inlet and outlet chambers. Finally, these two chambers are connected through a silicone tube forming the complete micropump. The performance of the fabricated micropump has been tested for various operation voltages and frequencies. We have demonstrated actual liquid pumping up to 70 /spl mu/l/min with a driving voltage of 2.3 V and a power consumption of 170 /spl mu/W. The maximum pump pressure is about 800 Pa at the applied voltage of 2.3 V with an operation frequency of 25 Hz.     

A low-temperature thin-film electroplated metal vacuum package

This paper presents a packaging technology that employs an electroplated nickel film to vacuum seal a MEMS structure at the wafer level. The package is fabricated in a low-temperature (<250/spl deg/C) 3-mask process by electroplating a 40-/spl mu/m-thick nickel film over an 8-/spl mu/m sacrificial photoresist that is removed prior to package sealing. A large fluidic access port enables an 800/spl times/800 /spl mu/m package to be released in less than three hours. MEMS device release is performed after the formation of the first level package. The maximum fabrication temperature of 250/spl deg/C represents the lowest temperature ever reported for thin film packages (previous low /spl sim/400/spl deg/C). Implementation of electrical feedthroughs in this process requires no planarization. Several mechanisms, based upon localized melting and Pb/Sn solder bumping, for sealing low fluidic resistance feedthroughs have been investigated. This package has been fabricated with an integrated Pirani gauge to further characterize the different sealing technologies. These gauges have been used to establish the hermeticity of the different sealing technologies and have measured a sealing pressure of /spl sim/1.5 torr. Short-term (/spl sim/several weeks) reliability data is also presented.     

Design, fabrication, and measurement of high-sensitivity piezoelectric microelectromechanical systems accelerometers

Microelectromechanical systems (MEMS) accelerometers based on piezoelectric lead zirconate titanate (PZT) thick films with trampoline or annular diaphragm structures were designed, fabricated by bulk micromachining, and tested. The designs provide good sensitivity along one axis, with low transverse sensitivity and good temperature stability. The thick PZT films (1.5-7 /spl mu/m) were deposited from an acetylacetonate modified sol-gel solution, using multiple spin coating, pyrolysis, and crystallization steps. The resulting films show good dielectric and piezoelectric properties, with P/sub r/ values >20 /spl mu/C/cm/sup 2/, /spl epsiv//sub r/>800, tan/spl delta/<3%, and |e/sub 31,f/| values >6.5 C/m/sup 2/. The proof mass fabrication, as well as the accelerometer beam definition step, was accomplished via deep reactive ion etching (DRIE) of the Si substrate. Measured sensitivities range from 0.77 to 7.6 pC/g for resonant frequencies ranging from 35.3 to 3.7 kHz. These accelerometers are being incorporated into packages including application specific integration circuit (ASIC) electronics and an RF telemetry system to facilitate wireless monitoring of industrial equipment.     

Piezoelectric bimorph microphone built on micromachined parylene diaphragm

This paper describes a novel bimorph piezoelectric microphone built on a micromachined parylene diaphragm with two ZnO films of opposite c-axis orientations. Both the sensitivity and signal-to-noise ratio (SNR) of the bimorph parylene-diaphragm microphone have been demonstrated to be much higher than those of a conventional unimorph silicon-nitride-diaphragm microphone.     

Characteristic studies of the piezoelectrically actuated micropump with check valve

This study presents the design and fabrication of a novel piezoelectric actuator for a micropump with check valve having the advantages of miniature size, light weight and low power consumption. The micropump is designed to have five major components, namely a piezoelectric actuator, a stainless steel chamber layer with membrane, two stainless steel channel layers with two valve seats, and a nickel check valve layer with two bridge-type check valves. A prototype of the micropump, with a size of 10 × 10 × 1.0 mm, is fabricated by precise manufacturing. The check valve layer was fabricated by nickel electroforming process on a stainless steel substrate. The chamber and the channel layer were made of the stainless steel manufactured using the lithography and etching process based on MEMS fabrication technology. The experimental results demonstrate that the flow rate of micropump accurately controlled by regulating the operating frequency and voltage. The flow rate of 1.82 ml/min and back pressure of 32 kPa are obtained when the micropump is driven with alternating sine-wave voltage of 120 Vpp at 160 Hz. The micropump proposed in this study provides a valuable contribution to the ongoing development of microfluidic systems.     

Encapsulated submillimeter piezoresistive accelerometers

While micromachined accelerometers are widely available and used in various applications, some biomedical applications require extremely small dimensions (相似文献   

InP-based optical waveguide MEMS switches with evanescent coupling mechanism

An optical waveguide MEMS switch fabricated on an indium phosphide (InP) substrate for operation at 1550 nm wavelength is presented. Compared to other MEMS optical switches, which typically use relatively large mirrors or long end-coupled waveguides, our device uses a parallel switching mechanism. The device utilizes evanescent coupling between two closely-spaced waveguides fabricated side by side. Coupling is controlled by changing the gap and the coupling length between the two waveguides via electrostatic pull-in. This enables both optical switching and variable optical coupling at voltages below 10 V. Channel isolation as high as -47 dB and coupling efficiencies of up to 66% were obtained with switching losses of less than 0.5 dB. We also demonstrate voltage-controlled variable optical coupling over a 17.4 dB dynamic range. The devices are compact with 2 /spl mu/m/spl times/2 /spl mu/m core cross section and active area as small as 500 /spl mu/m/spl times/5 /spl mu/m. Due to the small travel range of the waveguides, fast operation is obtained with switching times as short as 4 /spl mu/s. Future devices can be scaled down to less than 1 /spl mu/m/spl times/1 /spl mu/m waveguide cross-sectional area and device length less than 100 /spl mu/m without significant change in device design.     

A hybrid PZT-silicon microvalve

A low-voltage, low-power microvalve for compact battery-powered portable microfluidic platforms is designed, fabricated and experimentally characterized. The microvalve employs laser-machined piezoelectric unimorphs mechanically linked to surface micromachined nickel structures anchored on corrugated Si/sub x/N/sub y/-Parylene composite membrane tethers. The Parylene layer also serves as a compliant sealing layer on the valve seat for reducing the leakage in the off state. A mechanical linking process to connect the bulk piezoelectric unimorphs to micromachined diaphragms in a self-aligned manner has been developed. The design enables large strokes (2.45 /spl mu/m) at low-actuation voltages (10 V) consuming a comparatively low switching energy (678 nJ). The dependence of the measured flow rates on the modulated clearance over the orifice was found to be in good agreement with the theory of laminar flow in the low (1-100) Reynolds number regime. The microvalve was experimentally characterized for both gas and liquid flows. For example, at 10 V unimorph actuation, a gas flow rate of 420 /spl mu/L/min at a differential pressure of 9.66 kPa was measured. The off-state leakage rate for 0 V actuation is estimated to be 10-20 /spl mu/L/min. Typical flow rates with pulse width modulated (PWM) actuation with 50% duty cycle at 20 V/sub pp/ (1 kHz) were measured to be 770 /spl mu/L/min at 6.9 kPa for gases and 2.77 /spl mu/L/min at 4.71 kPa for liquids.     

Study of an innovative one-sided actuating piezoelectric valveless micropump with a secondary chamber

Previous studies have indicated that a one-sided actuating piezoelectric micropump (OAPMP) combined with two valves may enhance the liquid flow rate to 4.1 ml/s and make it possible to reach the maximum pump head of 9807 Pa in a limited space. In this study, an innovative one-sided actuating piezoelectric valveless micropump (OAPMP-valveless) has been developed to actuate fluid at a higher flow rate in one direction by adding a secondary chamber. The secondary chamber plays a key role in the application of the valveless micropump: the flow rate of the pump can reach 0.989 ml/s by adding a secondary chamber. The maximum pump head is 1522.5 Pa when using the 0.3 mm-thick secondary diaphragm and the 0.5 mm-thick primary diaphragm. In addition, if a nozzle/diffuser element is applied to the OAPMP-valveless with a secondary chamber, the flow rate can be further improved to 1.183 ml/s at a frequency of 150 Hz. A three-dimensional numerical model of the valveless micropump has been built to compare the measured results with the simulated results.     

Low-voltage, large-scan angle MEMS analog micromirror arrays with hidden vertical comb-drive actuators

This paper reports on novel polysilicon surface-micromachined one-dimensional (1-D) analog micromirror arrays fabricated using Sandia's ultraplanar multilevel MEMS technology-V (SUMMiT-V) process. Large continuous DC scan angle (23.6/spl deg/ optical) and low-operating voltage (6 V) have been achieved using vertical comb-drive actuators. The actuators and torsion springs are placed underneath the mirror (137/spl times/120 /spl mu/m/sup 2/) to achieve high fill-factor (91%). The measured resonant frequency of the mirror ranges from 3.4 to 8.1 kHz. The measured DC scanning characteristics and resonant frequencies agree well with theoretical values. The rise time is 120 /spl mu/s and the fall time is 380 /spl mu/s. The static scanning characteristics show good uniformity (相似文献   

A micromechanical flow sensor for microfluidic applications

We fabricated a microfluidic flow meter and measured its response to fluid flow in a microfluidic channel. The flow meter consisted of a micromechanical plate, coupled to a laser deflection system to measure the deflection of the plate during fluid flow. The 100 /spl mu/m square plate was clamped on three sides and elevated 3 /spl mu/m above the bottom surface of the channel. The response of the flow meter was measured for flow rates, ranging from 2.1 to 41.7 /spl mu/L/min. Several fluids, with dynamic viscosities ranging from 0.8 to 4.5/spl times/10/sup -3/ N/m, were flowed through the channels. Flow was established in the microfluidic channel by means of a syringe pump, and the angular deflection of the plate monitored. The response of the plate to flow of a fluid with a viscosity of 4.5/spl times/10/sup -3/ N/m was linear for all flow rates, while the plate responded linearly to flow rates less than 4.2 /spl mu/L/min of solutions with lower dynamic viscosities. The sensitivity of the deflection of the plate to fluid flow was 12.5/spl plusmn/0.2 /spl mu/rad/(/spl mu/L/min), for a fluid with a viscosity of 4.5/spl times/10/sup -3/ N/m. The encapsulated plate provided local flow information along the length of a microfluidic channel.     

Effect of trimethylsilane flow rate on the growth of SiC thin-films for fiber-optic temperature sensors

We have investigated the effect of trimethylsilane ([(CH/sub 3/)/sub 3/SiH] or 3MS) flow rate on the growth of SiC thin-film on single-crystal sapphire substrate for fiber-optic temperature sensor. The SiC film thickness was in the range of 2-3 /spl mu/m. The variation of the 3MS flow rate affected the structural properties of the SiC films. This, in turn, changed the optical properties and temperature sensing performance of the sensors. Optical reflection from the SiC thin-film Fabry-Pe/spl acute/rot interferometers showed one-way phase shifts in resonant minima on all measured samples. Linear fits to the resonant minima (at 660 to 710 nm) versus temperature provide the corresponding thermal expansion coefficient, /spl kappa//sub /spl phi//, of 1.7-1.9/spl times/10/sup -5///spl deg/C. With the optimized 3MS flow rate, the SiC temperature sensor exhibits a temperature accuracy of /spl plusmn/2.8/spl deg/C from 22 to 540/spl deg/C. The short-term SiC sensor stability at 532/spl deg/C for two weeks shows a very small standard deviation of 0.97/spl deg/C.     

A piezoelectric microvalve for compact high-frequency, high-differential pressure hydraulic micropumping systems

A piezoelectrically driven hydraulic amplification microvalve for use in compact high-performance hydraulic pumping systems was designed, fabricated, and experimentally characterized. High-frequency, high-force actuation capabilities were enabled through the incorporation of bulk piezoelectric material elements beneath a micromachined annular tethered-piston structure. Large valve stroke at the microscale was achieved with an hydraulic amplification mechanism that amplified (40/spl times/-50/spl times/) the limited stroke of the piezoelectric material into a significantly larger motion of a micromachined valve membrane with attached valve cap. These design features enabled the valve to meet simultaneously a set of high frequency (/spl ges/1 kHz), high pressure(/spl ges/300 kPa), and large stroke (20-30 /spl mu/m) requirements not previously satisfied by other hydraulic flow regulation microvalves. This paper details the design, modeling, fabrication, assembly, and experimental characterization of this valve device. Fabrication challenges are detailed.     

一种基于MEMS技术的压电微泵的研究

介绍了一种基于MEMS技术的压电微泵。该微泵利用聚二甲基硅氧烷(PDMS)作为泵膜,使用了一个主动阀和一个被动阀,并利用压电双晶片作为驱动部件。压电双晶片和PDMS泵膜的组合可以产生较大的泵腔体积改变和压缩比,显著降低了加工成本,并提高了成品率。对压电微泵的输出流量进行了测试,结果显示:电压、频率以及背压对流量均有显著影响。在100 V,25Hz的方波驱动下,该压电微泵的最大输出流量为458μL/m in,最大输出压力为6 kPa。     

Design and fabrication of a valveless micropump based on low temperature co-fired ceramic tape technology

Low temperature co-fired ceramic (LTCC) tape technology has been widely studied in microsystems and microfluidic devices. The current study presented the manufacturing process of a simple and inexpensive micropump which is made of LTCC. The components of micropump including fluidic channels, diaphragm, chamber, and planar diffuser valves were integrated in one LTCC module. Geometries of these components were designed based on numerical analysis. The finite element analysis was used to characterize the displacement of a piezoelectric actuator and the computational fluid dynamics was applied to design the diffuser. The performance of the micropump was optimized and performance of the designed micropump was carefully examined in the experiments. The data revealed that the performance of a micropump can be significantly increased by adding a pair of pockets. Overall, the study demonstrated that LTCC tape technology is a simple and reliable method to fabricate a valveless micropump.     

Uncooled multimirror broad-band infrared microbolometers

A new generation of microbolometers were designed, fabricated and tested for the NASA CERES (Clouds and the Earth's Radiant Energy System) instrument to measure the radiation flux at the Earth's surface and the radiant energy now within the atmosphere. These detectors are designed to measure the earth radiances in three spectral channels consisting of a short wave channel of 0.3 to 5 /spl mu/m, a wide-band channel of 0.3 to 100 /spl mu/m and a window channel from 8 to 12 /spl mu/m each housing a 1.5 mm x 1.5 mm microbolometers or alternatively 400 /spl mu/m x 400 mm microbolometers in a 1 /spl times/ 4 array of detectors in each of the three wavelength bands, thus yielding a total of 12 channels. The microbolometers were fabricated by radio frequency (RF) magnetron sputtering at ambient temperature, using polyimide sacrificial layers and standard micromachining techniques. A semiconducting YBaCuO thermometer was employed. A double micromirror structure with multiple resonance cavities was designed to achieve a relatively uniform absorption from 0.3 to 100 /spl mu/m wavelength. Surface micromachining techniques in conjunction with a polyimide sacrificial layer were utilized to create a gap underneath the detector and the Si/sub 3/N/sub 4/ bridge layer. The temperature coefficient of resistance was measured to be -2.8%/K. The voltage responsivities were over 10/sup 3/ V/W, detectivities above 10/sup 8/ cm Hz/sup 1/2//W, noise equivalent power less than 4 /spl times/ 10/sup -10/W/Hz/sup 1/2/ and thermal time constant less than 15 ms.     

Fine ZnO patterning with controlled sidewall-etch front slope

This paper describes a wet-etching technique that solves the major difficulty of fine patterning a c-axis oriented polycrystalline ZnO film. The technique uses aqueous NH/sub 4/Cl with electrolytically added copper ions and convection flow, and for the first time, allows the ZnO film to be etched 1) with controlled etch rate ratio between the vertical and horizontal etch rates and 2) with controlled etch-front slope. The ratio between the vertical and horizontal etch rates is as high as 20 to 1, while the angle between the sidewall etch-front surface and the substrate surface can be electrically controlled between 73/spl deg/ and 106/spl deg/. Also, ZnO films can now be patterned to fine features (even sub-/spl mu/m level) with a wet etchant. The electroless galvanic etching technique described in this paper produces uniform etching over a large area (larger than 3" in diameter).     

Fabrication and measured performance of a first-generation microthermoelectric cooler

The measured performance of a column-type microthermoelectric cooler, fabricated using vapor-deposited thermoelectric films and patterned using photolithography processes, is reported. The columns, made of p-type Sb/sub 2/Te/sub 3/ and n-type Bi/sub 2/Te/sub 3/ with an average thickness of 4.5 /spl mu/m, are connected using Cr/Au/Ti/Pt layers at the hot junctions, and Cr/Au layers at the cold junctions. The measured Seebeck coefficient and electrical resistivity of the thermoelectric films, which were deposited with a substrate temperature of 130/spl deg/C, are -74 /spl mu/V/K and 3.6/spl times/10/sup -5/ /spl Omega/-m (n-type, power factor of 0.15 mW/K/sup 2/-m), and 97 /spl mu/V/K and 3.1/spl times/10/sup -5/ /spl Omega/-m (p-type, power factor of 0.30 mW/K/sup 2/-m). The cooling performance of devices with 60 thermoelectric pairs and a column width of 40 /spl mu/m is evaluated under a minimal cooling load (thermobuoyant surface convection and surface radiation). The average cooling achieved is about 1 K. Fabrication challenges include the reduction of the column width, implementation of higher substrate temperatures for optimum thermoelectric properties, and improvements of the top connector patterning and deposition.     

A micromachining process for die-scale pattern transfer in ceramics and its application to bulk piezoelectric actuators

This paper reports on a batch mode planar pattern transfer process for bulk ceramics, glass, and other hard, brittle, nonconductive materials suitable for micromachined transducers and packages. The process is named LEEDUS, as it combines lithography, electroplating, batch mode micro electro-discharge machining (/spl mu/EDM) and batch mode micro ultrasonic machining (/spl mu/USM). An electroplating mold is first created on a silicon or metal wafer using standard lithography, then using the electroplated pattern as an electrode to /spl mu/EDM a hard metal (stainless steel or WC/Co) tool, which is finally used in the /spl mu/USM of the ceramic substrate. A related process (SEDUS) uses serial /spl mu/EDM and omits lithography for rapid prototyping of simple patterns. Feature sizes of 25 /spl mu/m within a 4.5/spl times/4.5 mm/sup 2/ die have been micromachined on glass-mica (Macor) ceramic plates with 34 /spl mu/m depth. The ultrasonic step achieves 18 /spl mu/m/min. machining rate, with a tool wear ratio of less than 6% for the stainless steel microtool. Other process characteristics are also described. As a demonstration, octagonal and circular spiral shaped in-plane actuators were fabricated from bulk lead zirconate titanate (PZT) plate using the LEEDUS/SEDUS process. A device of 20 /spl mu/m thickness and 450 /spl mu/m/spl times/420 /spl mu/m footprint produces a displacement of /spl ap/2/spl mu/m at 40 V.