Wafer-level vacuum package of two-dimensional micro-scanner

Microsystem Technologies - We present wafer-level vacuum package of two-dimensional (2-D) micro-scanner based on glass-silicon anodic bonding. To form the sacrificial gap for evacuating air in the...     

Design, fabrication, and operation of submicron gap comb-drivemicroactuators

Making submicron interelectrode gaps is the key to reducing the driving voltage of a micro comb-drive electrostatic actuator. Two new fabrication technologies, oxidation machining and a post-release positioning method, are proposed to realize submicron gaps. Two types of actuator (a resonant type and a nonresonant type) with submicron gaps were successfully fabricated and their operational characteristics were tested experimentally. The drive voltage was found to be lower than that of existing actuators. The stability of comb-drive actuators is discussed     

Design and modeling of a novel electromechanical optical micro-scanner

Microsystem Technologies - This article presents a design principle of a novel small-sized compliant optical micro-scanner with two translational (X, Y) and a rotational (θz) degree of...     

用于器件级真空封装的MEMS加速度传感器的设计与制作

设计了一种可用于器件级真空封装的三明治电容式MEMS加速度传感器.该传感器被设计为四层硅结构,其中上下两层为固定电极,中间两层为硅-硅直接键合的双面梁-质量块结构的可动电极.利用自停止腐蚀工艺在中间质量块键合层上腐蚀出2个深入腔内的V型抽气槽,使得MEMS器件在后续的封装中能够实现内部真空.为防止V型抽气槽在划片中被水或硅渣堵塞,采用双面划片工艺.划片后,器件的总尺寸为6.8mm ×5.6mm ×1.72 mm,其中,敏感质量块尺寸为3.2mm×3.2mm ×0.86mm,检测电容间隙2.1 μm.对器件级真空封装后的MEMS加速度传感器进行了初步测试,结果表明:制作的传感器的谐振频率为861 Hz,品质因数Q为76,灵敏度为1.53 V/gn,C-V特性正常,氦气细漏＜1×10-9 atm-cm3/s,粗漏无气泡.     

Design,fabrication, and test of a peristaltic micropump

The design, fabrication, and electrical characterization of a novel peristaltic thermopneumatic microfluidic (PTMF) pump for next-generation implantable medical treatment. To satisfy the demands of an implantable system, the PTMF pump design presented here includes biocompatibility, simple integration with microfluidics, bidirectionality, and particle tolerance. Test devices were fabricated with both silicon micromachining and soft lithography (polydimethylsiloxane micromolding). The effects of process parameters, specifically those related to silicon wet etch and metal deposition, on the performance of the microheaters in a peristaltic microfluidic pump. The thermal resistance of the microheaters is strongly dependent upon the relative thermal isolation, which impacts maximum pumping speed (from a few Hertz to kilo-Hertz). Thermal isolation is shown not to be an issue in the pump design given the spacing of the neighboring microheaters.     

Design and fabrication of submicrometer, single crystal Siaccelerometer

A lateral accelerometer has been designed, simulated, and fabricated using a 3-mask high-aspect ratio technology. Electron beam lithography and high-density plasma etching in an inductively coupled plasma source enabled aspect ratios >30 to be achieved. This makes possible beams with very small spring constants. Combining the ability to measure very small displacement of a proof mass due to narrow capacitive gaps between comb fingers, a highly sensitive accelerometer can be obtained. The fabricated accelerometer with 1 μm beams and 0.2 μm comb gaps had a spring constant of 0.127 N/m, which is close to the calculated values of 0.146 N/m. Based on the capacitance measurements, the accelerometer sensitivity is calculated to be 6.3 fF/g. Reducing the beam width to 0.4 μm lowered the spring constant to 0.03 N/m, and an improved equivalent sensitivity of 79.2 fF/g is calculated. The minimum detectable acceleration is on the order of a few microgravity over a range of hundreds of gravities     

Design, fabrication and testing of sandwich coupled inductors

A planar coupled inductor having sandwich coil structure is fabricated using MEMS microfabrication techniques. The structure of the inductor coil is designed to achieve high coupling and high winding number with a relatively small coil area. In this work, the structure is fabricated by bonding two planar on-chip coil fabricated on two different substrates. This method can replace the conventional via connections that cause various problems in output pads interconnection. The functionality of the fabricated device was tested, while the basic characteristics of the fabricated coil were measured at wide range of operating frequency using cascade GSG probe and compared with the simulation. For measurements up to 1?GHz, three resonance frequencies, inductance of 35?nH and resistance of as low as 25?Ω were observed. The results show that the proposed technique is a promising alternative method for fabricating a simple and cost effective 3-D coupled inductors.     

Design, fabrication, and testing of a prototype micro-thermophotovoltaic system

The design, fabrication and testing of a novel prototype micro-thermophotovoltaic (micro-TPV) system is first described in this paper. The system is made of a SiC emitter, a simple nine-layer dielectric filter and a GaSb photovoltaic cell array. When the flow rate of hydrogen is 4.20 g/h and the H/sub 2//air ratio is 0.9, the micro-TPV system is able to deliver an electrical power output of 1.02 W in a microcombustor of 0.113 cm/sup 3/ in volume. The open-circuit electrical voltage and short-circuit current are 2.28 V and 0.59 A, respectively. This paper makes it possible for us to replace batteries with micro-TPV systems as the power of micro mechanical devices in near future.     

Design, fabrication, and testing of micromachined silicone rubbermembrane valves

Technologies for fabricating silicone rubber membranes and integrating them with other processes on silicon wafers have been developed. Silicone rubber has been found to have exceptional mechanical properties including low modulus, high elongation, and good sealing. Thermopneumatically actuated, normally open, silicone rubber membrane valves with optimized components have been designed, fabricated, and tested. Suspended silicon nitride membrane heaters have been developed for low-power thermopneumatic actuation. Composite silicone rubber on Parylene valve membranes have been shown to have low permeability and modulus. Also, novel valve seats were designed to improve sealing in the presence of particles. The valves have been extensively characterized with respect to power consumption versus flow rate and transient response. Low power consumption, high flow rate, and high pressure have been demonstrated. For example, less than 40 mW is required to switch a 1-slpm nitrogen flow at 33 psi. Water requires dose to 100 mW due to the cooling effect of the liquid     

Design, fabrication, and testing of a bistable electromagneticallyactuated microvalve

A bistable electromagnetically actuated microvalve was designed, processed, and tested. The valve was designed to control a water flow of 0.05-0.5 μs from a reservoir at a pressure of 1-2000 Pa. The two valve components were fabricated in silicon, the upper piece comprises an electroplated gold coil, and the lower piece is an Ni/Fe alloy beam. The bistable capability was achieved by balancing the elastic forces on the beam with the magnetic forces due to a 46-μm-thick rolled magnetic foil. The design includes the flow through the orifice, squeeze film damping due to beam motion, beam elasticity, and electromagnetics. The microvalve was tested for power consumption, flow rate, time response, Ni/Fe alloy composition, and magnetic foil properties. The valve operates at 1-2 V in both air and water     

Design, fabrication, and testing of VDP MEMS pressure sensors

In this paper, a four-terminal piezoresistive sensor commonly known as a van der Pauw (VDP) structure is presented for its application to MEMS pressure sensing. In a recent study, our team has determined the relation between the biaxial stress state and the piezoresistive response of a VDP structure by combining the VDP resistance equations with the equations governing silicon piezoresistivity and has proposed a new piezoresistive pressure sensor. It was observed that the sensitivity of the VDP sensor is over three times higher than the conventional filament type Wheatstone bridge resistor. To check our theoretical findings, we fabricated several (100) silicon diaphragms with both the VDP sensors and filament resistor sensors on the same wafer so both the sensor elements have same doping concentration. Several diaphragms had VDP sensors of different sizes and orientations to find out their geometric effects on pressure sensitivity. The diaphragms were subjected to known pressures, and the pressure sensitivities of both types of sensors were measured using an in-house built calibration setup. It was found that the VDP devices had a linear response to pressure as expected, and were more sensitive than the resistor sensors. Also, the VDP sensors provided a number of additional advantages, such as its size independent sensitivity and simple fabrication steps due to its simple geometry.     

A design method of comb-drive actuators for linear tuning characteristics in mechanically tunable optical filters

A new method is proposed in design of comb-drive actuators for specific voltage-displacement characteristics with finger gaps as the design parameters. The design method proposed by the author previously is further refined by adopting a more accurate model which considers fringe electric fields. The proposed method is applied to design comb-drive actuators with an aim to achieve linear tuning characteristics in mechanically tunable optical add-drop filters with microring resonators. To make an assessment of the accuracy of the proposed design method, three-dimensional electrostatic numerical analysis is conducted to obtain capacitances of the designed comb-drive actuators as functions of the moving finger displacement. Obtained capacitances are used to find the tuning characteristics (resonant wavelength vs. voltage) of the filter, in combination with the results from the author’s other work where a relationship between the resonant wavelength and the displacement of an index modulator was studied. It is found that by employing the actuators designed by the proposed method, the maximum deviation from linearity (MDL) can be reduced by 17.2 % points (from 25.7 % of the conventional design to 8.5 % of the new design). MDL is further reduced to 4.4 % by making a few modifications in the design.

     

Design and characteristics of a-Si-based micro-bolometers with shared-anchor structure in vacuum packaged systems

This paper reports the design and fabrication of an a-Si-based micro-bolometer using a new pixel design to enhance the fill factor through use of shared-anchor structures, which enable a one-anchor-per-unit-pixel scheme. The proposed micro-bolometer was fabricated in 64 × 64 arrays with 25 μm pixel size. The design increased the fill factor by 10 % compared to that of the unshared-anchor design owing to the mechanical flatness of the shared-anchor structure. The fabricated bolometer showed enhancements in responsivity from 1.08 × 10⁵ to 1.23 × 10⁵ V/W and an increased thermal time constant of 10 ms at a 30 Hz chopping frequency. From the measurement results, there were no mechanical, electrical, or thermal crosstalk problems between adjacent pixels with the increased fill factor compared to the unshared-anchor design.     

Design, fabrication and measurement of ultra-precision micro-structured freeform surfaces

Due to the geometry complexity and high precision requirement, there still possess a lot of challenges in the design, manufacturing and measurement of ultra-precision micro-structured freeform surfaces (e.g. microlens array) with submicrometer form accuracy and surface finish in nanometer range. Successful manufacturing of ultra-precision micro-structured freeform surface not only relies on the high precision of machine tools, but also largely depends on comprehensive consideration of advanced optics design, modelling and optimization of the machining process, freeform surface measurement and characterization.This paper presents the theoretical basis for the establishment of an integrated platform for design, fabrication, and measurement of ultra-precision micro-structured freeform surfaces. The platform mainly consists of four key modules, which are Optics Design Module, Data Exchange Module, Machining Process Simulation and Optimization Module and Freeform Measurement and Evaluation Module. A series of experiments have been conducted to evaluate the performance of the platform and its capability is realized through a trial implementation in design, fabricating and measurement of a microlens array. The results predicted by the system are found to agree well with the experimental results. These show that the proposed integrated platform not only helps to shorten the cycle time for the development of microlens array components but also provides an important means for optimization of the surface quality in ultra-precision machining of micro-structured surfaces. With this successful development of the system, optimal machining parameters, the best cutting strategy, and optimization of the surface quality of the ultra-precision freeform surfaces can be obtained without the need for conducting time-consuming and expensive cutting tests.     

Design,fabrication and testing of a piezoelectric energy microgenerator

This article presents the design, fabrication and characterization of a micromachined energy harvester utilizing aluminium nitride (AlN) as a piezoelectric thin film material for energy conversion of random vibrational excitations. The harvester was designed and fabricated using silicon micromachining technology where AlN is sandwiched between two electrodes on top of a silicon cantilever beam which is terminated by a silicon seismic mass. The harvester generates electric power when subjected to mechanical vibrations. The generated electrical response of the device was experimentally evaluated at various acceleration levels. A maximum power of 34.78 μW was obtained for the device with a seismic mass of 5.6 × 5.6 mm² at an acceleration value of 2 g. Various fabricated devices were tested and evaluated in terms of the generated electrical power as well as the resonant frequency.     

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.     

Design and fabrication of medical micro-nebulizer

The application of a spray device to treat respiratory disease has long been known to be effective. Clinical studies have shown that the finer the droplet size, the deeper position of trachea that can be reached. With the aim of enhancing the curative effect, this study proposes a new design of micro-nebulizer, integrating a piezoelectric actuator, micro-nozzle plate, and the cavity of the micro pump to achieve a high-quality atomizing effect. In this research, we built a novel portable micro-nebulizer device with a changeable and cleanable medication chamber, which can generate a spray droplet of less than 4.04 μm in size (sauter mean diameters, SMD) and has a nebulizer rate of 0.5 ml/min. The device has an electrical requirement of drive voltage only 3 V, with a low power consumption of 1.2 W and an optimal operation frequency of 120 kHz. According to the simulations and experiments, it can be inferred that the droplet size distribution of the micro-nebulizer described in this research is finer and more uniform than that of the current conventional devices; furthermore, the system power consumption is lower than that of the ultrasonic-type nebulizer.     

Simple and cost-effective fabrication of two-dimensional plastic nanochannels from silica nanowire templates

Nanofluidic systems are attracting a great deal of interest due to their fundamental significance and potential applications in chemistry, biology and physics. However, high fabrication cost, expensive equipments and complicated fabrication process of most current fabrication techniques prevent lots of researchers from entering the nanofluidic field. Here we present a quick, simple and cost-effective method for fabricating two-dimensional (2D) nanochannel in polycarbonate (PC) substrates. Silica nanowires, taper-drawn from commercially available single-mode fiber were used as templates and embedded in the PC substrate by hot embossing. The nanochannels were created after removing the nanowires by hydrofluoric acid (HF) etching. Poly(dimethylsiloxane) (PDMS) was used to seal the nanochannel reversibly. Nanochannels with widths range from 100 to 900 nm and lengths up to several millimeters were obtained. Various nanostructures including integrated micro and nanochannels, nanochannel array, bent nanochannel and cross-shaped nanochannel were fabricated and characterized by fluorescent microscope, scanning electron microscope (SEM) and atomic force microscope (AFM).     

Design,fabrication and characterization of a low-noise Z-axis micromachined gyroscope

This paper presents the design, fabrication and characterization of a low-noise Z-axis micromachined gyroscope. A triple-mass scheme is adopted to obtain a decoupled mode and matched vibration structure. The gyroscope was fabricated based on a 30-μm silicon on insulator wafer. A DRIE, lag-effect-based, dicing-free process was used to easily and rapidly create the gyroscope devices without requiring normal dicing. The fabricated gyroscopes were vacuum packaged (pressure of approximately 2,000 Pa) and tested. The measured power spectral density of the noises is as low as 17.5 μV/√Hz, and the resolution of the fabricated gyroscope is 7.1 × 10–4°/s/√Hz (2.52°/h/√Hz).