多组分免疫传感及其应用

多组分免疫传感是免疫分析领域的一个研究热点,具有分析通量高、所需时间短、样品消耗少、分析成本低等突出优点.目前多组分免疫传感多采用空间分辨或多标记物模式.该文综述了近十年来多组分免疫传感技术的进展及其应用,并对其发展前景进行了展望.     

Characterization of electrostatically coupled microcantilevers

The use of tightly packed arrays of probes can achieve the much desirable goal of increasing the throughput of scanning probe devices. However the proximity of the probes induces coupling in their dynamics, which increases the complexity of the overall device. In this paper we analyze and model the behavior of a pair of electrostatically and mechanically coupled microcantilevers. For the common case of periodic driving voltage, we show that the underlying linearized dynamics are governed by a pair of coupled Mathieu equations. We provide experimental evidence that confirms the validity of the mathematical model proposed, which is verified by finite element simulations as well. The coefficients of electrostatic and mechanical coupling are estimated respectively by frequency identification methods and noise analysis. Finally, we discuss parametric resonance for coupled oscillators and include a mapping of the first order coupled parametric resonance region.     

Characterization and displacement control of low surface-stress AlN-based piezoelectric micro-resonators

Micro-cantilevers and micro-bridges actuated by sputter-deposited aluminium nitride (AlN) thin films were measured with a scanning laser Doppler vibrometer up to 6 MHz, covering more than 10 resonance modes of different nature. A finite element model (FEM) was used to simulate the modal response of the micromachined structures. The comparison between experiment and simulation, regarding modal shapes and frequencies, resulted in an excellent agreement. An interferometric microscope was also used to study the static deflection of the structures. These measurements revealed a very low surface stress for the different micro-resonators. Finally, we point out how the amplitude of a given resonant mode can be controlled depending on the piezoelectric charge collected by the top electrode layout.     

Chemical sensing with micromolded plastic microcantilevers

This paper describes microcantilever sensors produced via injection molding. The injection mold design is novel in that it employs one floating and one fixed mold half, hence only necessitating high flatness on two surfaces (e.g., the mating surfaces of the mold), whereas the remainder of the mold can be machined to only moderate tolerances. The mold holds a sub-100 nanometer flatness error over the entire mold mating surfaces, needed to produce micro- and nanoscale parts. Micrometer-scale cantilevers are produced and characterized as a test case. Microcantilevers are fabricated from three different polymeric materials and have exceptional repeatability as evidenced by their measured first-mode bending resonant frequencies. As a precursor to biological sensing, gold-thiol chemical sensing results obtained with the injection-molded cantilevers are also presented and show values that agree with the literature. As a whole, this work shows that the polymeric microcantilever parts fabricated via injection molding are mechanical and functional equivalents to their silicon-type counterparts, and are cheaper and easier to manufacture. [1483].     

Cells adhered and cultured on microcantilevers

This paper shows a novel method to cultivate cells on a π-shape microcantilever inside a polydimethylsiloxane microfluidic system. Only one lithography step was needed to precisely align and pattern a poly(2-hydroxyethyl methacrylate) hydrogel microstructure, of size 200 × 200 μm, onto a silicon nitride microcantilever inside the PDMS microfluidic device. Gelatin was used as a sacrificial layer to resolve the issue of the microfluidic and hydrogel microstructure sticking together, successfully releasing the microcantilevers. BHK-21 cells were successfully laden and cultivated on the hydrogel microstructures of microcantilevers for 24 h. The optical system consisted of a He–Ne laser, a charge-coupled device camera, and a position-sensitive detector, which was used to measure the deflections of the microcantilevers due to the laden cells. The deflection increased continually during the cell-laden period. Meanwhile, the deflection increased with increasing cell concentration. By repeating the cell-laden and culture experiment three times, the magnitude and trend of deflection of microcantilevers were almost the same. It demonstrates that the microcantilever-based biochip has adequate stability and provides reliable measurement results for drug screening applications in the future.     

Simulation of SiO2-based piezoresistive microcantilevers

This article uses finite element design for optimization of piezoresistive Si covered SiO₂ microcantilevers. The maximum resistance changes were systematically investigated by varying piezoresistor geometries and doping concentration. Our simulation results show that both cantilever deflection displacement and ΔR/R change decrease when the thickness of piezoresistors increases; the highest sensitivity can be obtained when the piezoresistor length is approximately 2/5 of the SiO₂ cantilever length; increase of both Si width and leg width result in decrease in cantilever deflection and sensitivity; the sensitivity of cantilevers with lower doping concentrations is more significant than those with higher doping concentrations. Temperature control is critical for thin piezoresistor in lowering the S/N ratio and increasing the sensitivity.     

AlN陶瓷微热板MEMS传感器阵列设计与工艺实现

针对陶瓷基微热板MEMS器件难以微加工,器件表面加热Pt膜使用普通正性光刻胶难以实现光刻剥离的工艺难点问题,提出了激光微加工和柔性机械剥离相结合的微加工方法。以AlN陶瓷为衬底基片,采用激光微加工技术实现热隔离刻蚀体加工,刻蚀梁宽可达0.2 mm。采用柔性机械剥离工艺制备方法解决普通正性光刻胶形成倒梯形凹槽Pt膜难实现图形化问题,可在复杂表面特性的陶瓷基衬底上实现Pt膜剥离线宽10μm。同时利用有限元法进行传感器阵列设计和热结构仿真,验证设计工艺的可行性。     

Electro-optical characterization of IC compatible microcantilevers

The aim of this work is to simulate and optically characterize the piezoelectric performance of complementary metal oxide semiconductor (CMOS) compatible microcantilevers based on aluminium nitride (AlN) and manufactured at room temperature. This study should facilitate the integration of piezoelectric micro-electro-mechanical systems (MEMS) such as microcantilevers, in CMOS technology. Besides compatibility with standard integrated circuit manufacturing procedures, low temperature processing also translates into higher throughput and, as a consequence, lower manufacturing costs. Thus, the use of the piezoelectric properties of AlN manufactured by reactive sputtering at room temperature is an important step towards the integration of this type of devices within future CMOS technology standards. To assess the reliability of our fabrication process, we have manufactured arrays of free-standing microcantilever beams of variable dimension and studied their piezoelectric performance. The characterization of the first out-of-plane modes of AlN-actuated piezoelectric microcantilevers has been carried out using two optical techniques: laser Doppler vibrometry (LDV) and white light interferometry (WLI). In order to actuate the cantilevers, a periodic chirp signal in certain frequency ranges was applied between the device electrodes. The nature of the different vibration modes detected has been studied and compared with that obtained by a finite element model based simulation (COMSOL Multiphysics), showing flexural as well as torsional modes. The correspondence between theoretical and experimental data is reasonably good, probing the viability of this high throughput and CMOS compatible fabrication process. To complete the study, X-ray diffraction as well as d₃₃ piezoelectric coefficient measurements were also carried out.     

Selective modal excitation in coupled piezoelectric microcantilevers

We study in detail the first vibration modes of a piezoelectric resonator based on two coupled micro-cantilevers, also known as tuning-forks. A multiple electrode geometry lying on a layer of piezoelectric AlN allows the selective excitation of different modes, including in-plane modes. A complete optical characterization of the devices in the z- and also the x-direction has been performed employing a Doppler vibrometer. The measurements confirm the excitation and inhibition of different modes depending on the actuation signals distribution on the electrodes. The influence of the dimensions of the resonator on the coupling between the microcantilevers has also been studied. Quality factors above 4,300 have been measured for the first anti-phase in-plane mode.     

Stability and bifurcation characteristics of viscoelastic microcantilevers

Microsystem Technologies - The stability and bifurcations of viscoelastic microcantilevers is investigated via the Kelvin–Voigt scheme and the modified couple stress (MCS) theory. All the...     

Analysis of intrinsic damping in vibrating piezoelectric microcantilevers

The intrinsic damping of a piezoelectric microcantilever is studied under high vacuum conditions, where the influence of fluid damping on the quality factor is negligible. This paper investigates three major intrinsic damping effects, which are anchor loss, thermoelastic damping (TED) and coating loss. Since the different damping mechanisms generally appear mixed with each other, it is difficult to separate them experimentally. Anchor loss and TED are investigated by using a combination of both analytical and numerical methods, while the coating loss mechanism is explored by measuring a series of cantilevers being coated by a piezo-electrode stack with 20–100 % coverage of the beam length. Finally, experimental validations are conducted on different structures of piezoelectric microcantilevers, showing a good qualitative match with the analytical findings.     

Vibration characterisation of AFG microcantilevers in nonlinear regime

Microsystem Technologies - The large-amplitude vibrations of axially functionally graded (AFG) microcantilevers is investigated for the first time. Due to a harmonic base-displacement, the AFG...     

Fabrication and micromechanical characterization of polycrystalline diamond microcantilevers

The exceptional chemical, mechanical and thermal properties of diamond make this material the ideal choice for resonant MEMS. Micro-cantilevers designed for biochemical applications have been fabricated using CVD diamond. In this work, the mechanical properties of these cantilevers were investigated by two different techniques: bending test using a Contact Surface Profilometer and resonant test, using a Laser Doppler Vibrometer. The Young’s Modulus of diamond thin film was estimated by these two tests. For the resonance test, the estimated values are comprised between 930 and 1300 GPa while bending test gives values between 950 and 1030 GPa. The load–displacement characteristics and the fracture point (or ultimate stress) have also been investigated.     

Using electric actuation and detection of oscillations in microcantilevers for pressure measurements

Response characteristics of a microcantilever, such as resonant frequency, amplitude, phase and quality factor, can be used for absolute pressure measurements in the range of 10⁻⁴ to 10³ Torr. To this end, it would be very convenient to have the resonance of the microcantilever actuated and detected electrostatically. Herein, we report the nonlinear dynamics of microcantilevers under varying pressure and different gases using the harmonic detection of resonance (HDR) technique [J. Gaillard, M.J. Skove, R. Ciocan, A.M. Rao, Electrical detection of oscillations in 340 microcantilevers and nanocantilevers, Rev. Sci. Instrum. 77 (2006) 073907]. The HDR technique exploits nonlinearities in the cantilever-counter electrode system to allow electrostatic actuation and detection of the responses of the microcantilever to the pressure and gas composition. In particular, the 2nd and 3rd harmonics of the measured charge on the cantilever are investigated. The microcantilever demonstrates a quality factor of 10,000 at 10⁻³ Torr, and a usable response in the range from 10⁻³ to 10³ Torr. The use of different harmonics can enable us to adjust the range of pressures over which the sensor has an efficacious response, enhancing its sensitivity to a particular environment. The experimental results are in reasonable agreement with theoretical calculations, despite the nonlinearities involved.     

Water diffusion in polymer nano-films measured with microcantilevers

We present a method to measure the absorption of water molecules from the liquid and the vapour phase into polymer nano-films and the diffusion inside these films. Film thickness can be down to 45 nm. To demonstrate the possibilities of this method we use polymer films that are deposited on the upper side of a silicon cantilever by plasma polymerization of norbornene. When a microdrop of water is deposited onto the initially straight cantilever, the drop causes the cantilever to bend while it evaporates. Evaporation of such small water drops usually takes less than a second. An upwards bending is due to capillary forces and a downwards bending is due to the diffusion of water into the polymer film – and the consequent volume expansion (swelling) of the film. The magnitude of the capillary forces and the extent of swelling continuously change during drop evaporation. When drop evaporation is over the cantilever returns to its initial straight position. We simulate the time dependent bending with a numerical model that qualitatively agrees with the experiment. From the time dependence of cantilever bending we are able to determine the diffusion coefficient of water in the thin polymer film.     

Design and fabrication of PZT microcantilevers with freestanding structure

For developing freestanding piezoelectric microcantilevers with low resonant frequency, some critical mechanical considerations, especially cantilever bending, were given in this study. Two strategies, using piezoelectric thick films and adding a stress compensation layer, were calculationally analyzed for mitigating the cantilever bending, and then was applied for the fabrication of PZT freestanding microcantilevers. (100) oriented PZT thick films with the thickness of 6.93 μm were grown on the Pt/SiO₂/Si substrate by chemical solution deposition (CSD), and the SiO₂ layer with the thickness of 1.0 μm was kept under the PZT layer as a stress compensation layer of the freestanding microcantilevers. The freestanding microcantilevers fabricated with the micromachining process possessed the resonant frequency of 466.1 Hz, and demonstrated no obvious cantilever bending.     

Release processing effects on laser repair of stiction-failed microcantilevers

Undesirable adhesion in microelectromechanical systems (MEMS) is referred to as stiction and is a principal failure mechanism in surface-micromachined MEMS devices. Previous investigations demonstrated repairing stiction-failed polycrystalline silicon MEMS structures released from isopropyl alcohol (IPA) using Nd:YAG laser irradiation and predicting the laser repair process using a thermomechanical model. The current paper reports the effectiveness of the laser repair process and corresponding thermomechanical model predictions for microcantilevers that have failed during four release treatments: water, IPA, octadecyltrichlorosilane (OTS), and supercritical CO/sub 2/ drying. Model predictions and experimental measurements of the laser repair process are also provided for MEMS devices that failed due to contact during electrostatic actuation. The results indicate that the laser repair process is very effective for both failure modes and that the thermomechanical model predicts the laser repair of microcantilevers that failed during release much better than for microcantilevers that failed due to subsequent contact.     

Experimental characterization of electrostatically actuated in-plane bending of microcantilevers

Experimental validation of numerical models developed by the authors to predict the static behaviour of microelectrostatic actuators is described. Cantilever microbeams, currently used in connection with RF-MEMS and micro-scale material testing were analysed. A set of microcantilevers, bending in the plane of the wafer, i.e. in the same plane as the profiling system’s target, was tested. This differs from the popular case of out-of-plane microbeams, usually studied in the literature. Geometry nonlinearity caused by large deflection of the microbeam was investigated and nonlinear coupled formulation of electromechanical equilibrium was performed. Coupled-field analysis was implemented using the Finite Element Method (FEM), to predict displacements and pull-in voltage measured by Fogale Zoomsurf 3D, subsequently plotting the displacement-versus-voltage curve to complete model validation. FEM nonlinear analysis, based on iterative approach with mesh morphing, and FEM non-incremental approach, including a special element proposed by the authors, are compared to the linear solution and to experimental results. Geometry nonlinearity appears relevant in microbeam modelling and requires a nonlinear solution of the coupled problem. Investigative work, which compared the results of 2D and 3D models to experimental data, revealed that some three dimensional effects are significant in model validation, but the 2D approach may be effective in predicting static behaviour provided that at least a microbeam thickness equivalent is adopted.     

Mechanical properties of microcantilevers: Influence of the anticlastic effect

Measurements of Young's modulus of microstructures are frequently based on dynamic tests on microbeams. The aim of this work is evaluating if the accuracy of these measurements is affected significantly by the anticlastic effect. A nonlinear model of cantilever's dynamic behavior is thus developed and applied to some characteristic cases. The obtained results show that, even if the introduced nonlinearity is small enough to allow a modal approach to be still applied, the anticlastic effect has a meaningful influence on measurement accuracies as it is evidenced by the dependence of the resonant frequency on vibration amplitudes. The proposed treatise permits determining the appropriate range of excitation amplitudes to be used during the experiments and consequently to reduce appreciably the intervals of uncertainty of the measurements.