Design principle of micromechanical probe with an electrostatic actuator for friction force microscopy

It is important to understand friction force in micro/nano mechanical devices both at high sliding speed and with high lateral resolution. Dual-axis friction force microscopes that can provide high lateral resolution and accuracy have been proposed; however, the sliding speed is limited by the probe scan speed. While a micro mechanical probe (MMP) with an electrostatic actuator can overcome this problem, details of probe design have not been established yet. This paper presents the principle of the mechanical design for an MMP with high force sensitivity and sufficient drive force. The dimensions of the double cantilever beam control the spring constants, resonant frequencies, and drive force. The use of an actuated MMP enables accurate friction force microscopy at high sliding speeds, which is required for the design of micro/nano mechanical devices.     

A bidirectional magnetic microactuator using electroplatedpermanent magnet arrays

A novel bidirectional magnetic microactuator using electroplated permanent magnet arrays has been designed, fabricated and characterized. To realize a bidirectional microactuator, CoNiMnP-based permanent magnet arrays have been fabricated first on a silicon cantilever beam using a new electroplating technique. In the fabricated permanent magnets, the vertical coercivity and retentivity have been achieved up to 87.6 kA/m (1100 Oe) and 190 mT (1900 G), respectively by applying magnetic field during electroplating. A prototype bidirectional magnetic microactuator has been realized by integrating an electromagnet with a silicon cantilever beam, which has permanent magnet arrays on its tip. By applying a do current of 100 mA and altering its polarity, bidirectional motion on the tip of the cantilever beam has been successfully achieved in the deflection range of ±80 μm     

Asymmetric Dielectric Trilayer Cantilever Probe for Calorimetric High-Frequency Field Imaging

Multimaterial, microelectromechanical systems-based cantilever probes were developed for high-frequency magnetic field imaging. The basic configuration of the probe consists of a cantilever beam fabricated using surface micromachining and bulk micromachining techniques with dielectric silicon nitride and silicon oxide materials on a silicon wafer. A gold patterned metallization at the tip of the cantilever provides a source of eddy current heating due to the perpendicular component of the high-frequency magnetic field. This thermally absorbed power is converted to mechanical deflection by a multimaterial trilayer cantilever system. The deflection is measured with a beam-bounce optical technique employed in atomic force microscopy systems. We discuss the modeling, design, fabrication, and characterization of these field imaging probes     

A fully integrated surface micromachined magnetic microactuatorwith a multilevel meander magnetic core

A fully integrated magnetic microactuator using surface micromachining techniques is presented. To achieve this device, low-resistance meander conductors located in a single plane were interwoven with multilevel meander magnetic cores. This `wrapped' solenoid (with the core wrapped around the conductor) was fabricated in a fully integrated fashion. A magnetic microactuator was realized by incorporating a surface micromachined nickel-iron cantilever beam as part of the magnetic circuit of the core. The nickel-iron cantilever beam was 2.5 μm thick, 25 μm wide, and 780 μm long, and the magnetic circuit contained seventeen turns of meander-type solenoid coils. Cantilever beam tip deflection of 6 μm in the vertical direction was achieved when a DC voltage less than 1 V (and resulting drive current of 800 mA) was applied to the coils. This fully integrated multilevel topology offers advantages in a variety of micromagnetic applications, where actuators can be fabricated on the same substrate with an integrated circuit and actuated with low voltages     

Thermally actuated microprobes for a new wafer probe card

A new type of MEMS microprobe was designed and fabricated which can be used for a nest generation wafer probe card. A prototype MEMS probe card consisting of an array of microprobes individually actuated by bimorph heating to make contact with the test chip was also fabricated. This probe card is called the CHIPP (Conformable, HIgh-Pin count, Programmable) card and can be designed to contact up to 800 I/O pads along the perimeter of a 1-cm² chip with a microprobe repeat distance of approximately 50 μm. Microprobes for a prototype CHIPP probe card have been fabricated with a variety of cantilever structures including Al-SiO₂, W-SiO₂ and Al-Si bimorphs, and with the resistive heater placed either inside or on the surface of the cantilever. Ohmic contacts between tips and bond pads were tested with contact resistance as low as 250 mΩ. The deflection efficiency varies from 5.23-9.6 μm/mW for cantilever lengths from 300-500 μm. The maximum reversible deflection is in the range of 280 μm. The measured resonant frequency is 8.16 kHz for a 50×500 μm device and 19.4 kHz for a 40×300 μm device. Heat loss for devices operating in air was found to be substantially higher than for vacuum operation with a heat loss ratio of about 2/1 for a heater inside the structure, and 4.25/1 for a structure with the heater as an outer layer of the cantilever     

Design and development of a novel paddle test structure for the mechanical behavior measurement of thin films application for MEMS

A new technique was developed for studying the mechanical behavior of thin films on substrate applications for micro-electro-mechanical system (MEMS). The test structure was designed on novel “paddle” cantilever beam coated thin film specimens with dimensions of a few hundred to 50 nm. This beam has a triangle shape that provides a uniform plane strain distribution. Standard clean room processing was used to prepare the paddle sample. The experiment can be operated using the electrostatic force to deflect the “paddle” cantilever beam and measure the mechanical response of the sample with surface deposited thin film. A capacitance measurement is used to observe the deflection of the cantilever plate on the other side of the sample with respect to the electrostatic force on the one side. The measured strain was then converted through this capacitance measurement to conduct mechanical behavior studies on the coated thin film. Both system performance experiments and calculations were studied to verify the design concepts. The residual thin film stress measurements were performed and compared with the calculated results from three different forces exerted on the “paddle” cantilever beam, including the force due to the film, compliance force, and electrostatic force.     

Measurement of static and dynamic mechanical behavior of micro and nano-scale thin metal films: using micro-cantilever beam deflection

We present the results of a novel micro-beam deflection test used to investigate the static and dynamic mechanical behavior of submicron-thick metal films. The method demonstrated in this study allows researchers to observe the motion of micro and nano-scale thin films responding to electrostatic loads, by means of laser reflection measurements at frequency rates of up to 500 Hz. Researchers fabricated a supporting frame and a novel triangular shaped “paddle” beam designed to provide uniform plane stress distribution while undergoing deflection. A simple geometric calculation, based on cantilever deflection, enabled the degree of strain to be determined, which in turn provided the Young’s modus for aluminum film of a given thickness. We also studied the dynamic behavior using the dynamic frequency response of the beam, generated by electrostatic forces under various loads and vacuum pressure conditions. Our results showed that air damping has a significant influence on the free damping behavior of specimens, and only a minor influence on damping frequency. We determined the loss angle and frequency using sweep frequency and free damping methods, which were very consistent with paddle resonant frequencies. The loss angle obtained from a simple silicon micro-beam was 2.001 × 10^−4°using the free damping method and 2.23 × 10^−4°using the sweep frequency method. The dynamic response loss mechanism measured in this experiment provides incentive for the further study of grain boundary motion and dislocation motion in thin films.     

Fabrication of cantilever with self-sharpening nano-silicon-tip for AFM applications

A simple, high yield method for the fabrication of cantilever with nano-silicon-tip by wet etching for atomic force microscopy (AFM) applications is described in this paper. The nano-silicon-tips with well controlled dimensions are fabricated by self-sharpening anisotropic wet etching technologies using a special pentagon etch mask design. The spring constant of the cantilever according to demand can be easily realized by changing the design of the etch mask and tuning the etching time in the fabrication process. A fabrication yield as high as 90 % has been realized for the AFM probes on 2 inch wafers. The height of tips on the cantilever is 10–15 μm, and the apex of each nano-silicon-tip typically has a radius of curvature of 5–10 nm. The cantilever’s spring constant can be well controlled within the range of 0.8–120 N m^?1. The fabricated AFM probes are capable of generating high quality AFM image comparable with the commercial probes available in our lab.     

Resonant Magnetic Field Sensor With Frequency Output

This paper presents a novel type of resonant magnetic field sensor exploiting the Lorentz force and providing a frequency output. The mechanical resonator, a cantilever structure, is embedded as the frequency-determining element in an electrical oscillator. By generating an electrical current proportional to the position of the cantilever, a Lorentz force acting like an additional equivalent spring is exerted on the cantilever in the presence of a magnetic field. Thus, the oscillation frequency of the system, which is a function of the resonator's equivalent spring constant, is modulated by the magnetic field to be measured. The resonant magnetic field sensor is fabricated using an industrial CMOS process, followed by a two-mask micromachining sequence to release the cantilever structure. The characterized devices show a sensitivity of 60 kHz/Tesla at their resonance frequency$f_0= 175~ kHz$and a short-term frequency stability of 0.025 Hz, which corresponds to a resolution below 1$~mu T$. The devices can thus be used for Earth magnetic field applications, such as an electronic compass. The novel resonant magnetic field sensor benefits from an efficient continuous offset cancellation technique, which consist in evaluating the frequency difference measured with and without excitation current as output signal. 1676     

Dynamic characteristics of voltage induced reciprocated bending in double cantilever configuration of asymmetric comb drive MEMS

The dynamic characteristics of an electrostatically actuated double cantilever beam, often found in asymmetric comb drive microstructures, have been investigated in the present paper. A coupled electromechanical problem is formulated and solved to obtain different performance parameters like pull-in voltage, frequency response etc. Effects of various critical factors on the dynamic pull-in characteristics have been discussed elaborately. It has been further observed through extensive studies that, the dynamic pull-in characteristics differ considerably from the static characteristics for the double beam configuration. Finally, these observations have been supported by experimental results with a fabricated (in SOIMUMPS process) double cantilever based microstructure, using a simple in-house developed low cost test set up. A typical case of design of a closed loop MEMS (microelectromechanical systems) capacitive accelerometer has also been discussed where the present study finds ready applications to predict the dynamic pull-in characteristics more accurately than the conventional lumped model.     

一种高灵敏度硅微机械陀螺的设计与制造

设计与制造了一种高灵敏度的硅微机械陀螺。陀螺用静电来驱动,用连接成惠斯顿电桥的压阻式力敏电阻应变计来检测。主梁、微梁 质量块结构实现了高灵敏度。比较硬的主梁提供了一定的机械强度,并且提供了高共振频率。微梁很细,检测时微梁沿轴向直拉直压。力敏电阻应变计就扩散在微梁上,质量块很小的挠动就能在微梁上产生很大的应力,输出很大的信号。5V条件下,陀螺检测部分的理论灵敏度达到27.45mV/gn。压阻式四端器件用来监测驱动振幅,可以反馈补偿压阻的温度系数。检测模态的Q值达260使陀螺能在大气下工作。陀螺利用普通的n型硅片制造,为了刻蚀高深宽比的结构,使用了深反应离子刻蚀(DRIE)工艺。     

Mechanical and tribological characterization of a thermally actuated MEMS cantilever

The temperature effect on the mechanical and tribological behaviors of a microelectromechanical systems cantilever is experimentally investigated using an atomic force microscope. A nonlinear variation of the bending stiffness of microcantilevers as a function of temperature is determined. The variation of the adhesion force between the tip of atomic force microscope (AFM) probe (Si₃N₄) and the microcantilever fabricated in gold is monitored at different temperatures. Using the lateral mode operation of atomic force microscope, the influence of temperature on friction coefficient between the tip of AFM probe and microcantilever is presented. Finite element analysis is used to estimate the thermal field distribution in microcantilever and the axial expansion.     

一种用于高密度信息存储中数据读取的新方法的 理论和实验研究

通过测量压电悬臂梁的等效电容来检测悬臂梁的振动信息,以应用于基于扫描探针技术的高密度信息存储中进行数据读取.在压电悬臂梁的PZT压电层上施加交流电场使其工作在共振状态,并使其自由端与存储介质进行周期性的接触.当悬臂梁的自由端扫描到数据点时,其自由端的振幅和所受到的外力将发生变化,进而引起PZT压电层的介电常数发生变化.因此,通过检测悬臂梁上压电层的等效电容变化,便可以得到悬臂梁的振幅改变量,从而实现了对存储介质上数据的读取.实验结果表明,该可以实现1nm的位移检测分辨率.     

Tilting Micromirror With a Liquid-Metal Pivot

In this paper, we have developed a new micromirror with a compact footprint which can be rapidly tilted to large angles. The micromirror is supported by a liquid-metal drop (LMD) with low vapor pressure and is rotated by an electrostatic torque. A torsional spring model is proposed to predict the equivalent torsional constant of the LMD and the resonant frequency of the mirror. Micromirrors (1 mmtimes1 mmtimes25 mum) and actuating electrodes are microfabricated with a centralized wetting area surrounded by a nonwetting parylene area to confine the LMD. Our measurements of the mirror show the average snap-down voltage of ~ 79 V and the resonant frequency of 165 Hz. A single mirror is actuated to steer a laser beam with a maximum deflected angle of 23.6deg. A 1times3 mirror array is demonstrated for light switching, and has greater than 1 : 64 idle/deflection contrast. We also test the stability of the mirror to mechanical shake up to 56 g (g = 9.807 m/s²). The prototype mirror has 3.6 million cycles of operation     

Finite element modeling and experimental proof of NEMS-based silicon pillar resonators for nanoparticle mass sensing applications

The potential use of nanoelectromechanical systems (NEMS) created in silicon nanopillars (SiNPLs) is investigated in this work as a new generation of aerosol nanoparticle (NP)-detecting device. The sensor structures are created and simulated using a finite element modeling (FEM) tool of COMSOL Multiphysics 4.3b to study the resonant characteristics and the sensitivity of the SiNPL for femtogram NP mass detection in 3-D structures. The SiNPL arrays use a piezoelectric stack for resonance excitation. To achieve an optimal structure and to investigate the etching effect on the fabricated resonators, SiNPLs with different designs of meshes, sidewall profiles, heights, and diameters are simulated and analyzed. To validate the FEM results, fabricated SiNPLs with a high aspect ratio of approximately 60 are used and characterized in resonant frequency measurements where their results agree well with those simulated by FEM. Furthermore, the deflection of a SiNPL can be enhanced by increasing the applied piezoactuator voltage. By depositing different NPs [i.e., gold (Au), silver (Ag), titanium dioxide (TiO₂), silicon dioxide (SiO₂), and carbon black NPs] on the SiNPLs, the decrease of the resonant frequency is clearly shown confirming their potential to be used as airborne NP mass sensor with femtogram resolution level. A coupling concept of the SiNPL arrays with piezoresistive cantilever resonator in terms of the mass loading effect is also studied concerning the possibility of obtaining electrical readout signal from the resonant sensors.     

Design and static modeling of a semiconductor polymericpiezoelectric microactuator

The design of a semicircular polymeric piezoelectric actuator is presented, the models for its deflection and force are derived, and the results of the experiments used to verify the models are reported. The design is a polymeric piezoelectric bimorph formed in a semicircular shape instead of the standard straight cantilever beam bimorph design. The deflection model is adopted from the straight cantilever beam model and relates the free deflection as a function of the applied voltage field. The force model is developed using Castigliano's second theorem. Two experiments were conducted to verify the model: force-voltage and force-deflection. The models show that a bimorph formed in a semicircular shape produces significantly more force than a straight cantilever beam bimorph of the same length without a significant sacrifice in deflection     

多晶硅双端固支梁高周循环下疲劳特性的分析

多晶硅固支梁是MEMS器件中较常见的可动部件,通过静电激励的方式对其进行疲劳振动加载;所用结构为面外运动结构,为了测试样品的加速疲劳特性,通过在固支梁面内引入缺陷的方式来增大应力水平值;器件在经历了1.72×1011次循环之后,微梁的谐振频率、振动幅度发生了较大偏移,其谐振频率的偏移量达到14.531 kHz,器件性能发生了严重的退化.研究结果表明,利用谐振频率的改变来表征材料性能的退化是一种准确、可行的方法,同时本文进一步分析指出,器件上引入凹槽缺陷的方法确实可起到加速疲劳的作用;可利用此方法制作不同应力水平幅度的结构进行振动载荷疲劳加载实验,从而得到固支梁结构疲劳加速因子.     

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 and Analysis of Microcantilevers for Biosensing Applications

We have analyzed the detection of microcantilevers utilized in biosensing chips. First, the primary deflection due to the chemical reaction between the analyte molecules and the receptor coating, which produces surface stresses on the receptor side is analyzed. Oscillating flow conditions, which are the main source of turbulence in cantilever based biosensing chips, are found to produce substantial deflections in the microcantilever at relatively large frequency of turbulence. Then mechanical design and optimization of piezoresistive cantilevers for biosensing applications is studied. Models are described for predicting the static behavior of cantilevers with elastic and piezoresistive layers. Chemo-mechanical binding forces have been analyzed to understand issues of saturation over the cantilever surface. Furthermore, the introduction of stress concentration regions during cantilever fabrication has been discussed which greatly enhances the detection sensitivity through increased surface stress, and novel microcantilever assemblies are presented for the first time that can increase the deflection due to chemical reaction. Finally an experiment was made to demonstrate the shift of resonant frequency of cantilever used as biosensor. The relation between resonant frequency shift and the surface stress was analyzed.     

Determination of exposure to engineered carbon nanoparticles using a self-sensing piezoresistive silicon cantilever sensor

A novel MEMS-based cantilever sensor with slender geometry is designed and fabricated to be implemented for determining personal exposure to carbon engineered nanoparticles (NPs). The function principle of the sensor is detecting the cumulative mass of NPs deposited on the cantilever surface as a shift in its resonant frequency. A self-sensing method with an integrated full Wheatstone bridge on the cantilever as a piezoresistive strain gauge is introduced for signal readout replacing optical sensing method. For trapping NPs to the cantilever surface, an electrostatic field is used. The calculated equivalent mass-induced resonant frequency shift due to NPs sampling is measured to be 11.78?±?0.01?ng. The proposed sensor exhibits a mass sensitivity of 8.33?Hz/ng, a quality factor of 1,230.68?±?78.67, and a temperature coefficient of the resonant frequency (TC _f ) of ?28.6?ppm/°C. These results and analysis indicate that miniaturized sensors based on self-sensing piezoresistive microcantilever can offer the performance to fulfill the requirements of real-time monitoring of NPs-exposed personnel.