基于NEMS技术的介电泳芯片及其关键工艺问题的研究

结合信息技术、生物技术与纳米技术的发展,提出一种基于NEMS技术的“三维纳隙网格阵列微电极生物传感器“设计,用于生物样品在蛋白或细胞水平上的介电泳分离和检测.重点针对传感器制作的关键工艺问题,创新性地提出了一种利用反应离子刻蚀侧向钻蚀效应实现纳隙薄金属悬臂梁结构的理论和方法,此方法对电容式生物传感器的制作有普遍的实践意义.     

Rapid fabrication of nanoparticles array on polycarbonate membrane based on positive dielectrophoresis

We report here a rapid formation of island arrays with nanoparticles on and within polycarbonate (PC) membrane based on positive dielectrophoresis (p-DEP). For the fabrication of the patterning device, PC membranes with 10 μm thickness and 100, 200 or 400 nm pore size were sandwiched by an upper bare ITO substrate and a lower disk array ITO electrode which was defined by insulation layer of negative photoresist. A suspension of 190 nm diameter polymethylmethacrylate (PMMA) particles containing rhodamine 6G (R6G) fluorescent molecules was introduced into the device between the upper ITO and the PC membrane. AC electric signal (typically 20 Vpp, 70 kHz) was then applied to the ITO, resulting in the formation of island patterns with high electric fields gradient regions on and in the PC membrane. Particles patterns with island shape were assembled on membrane within 1 s after applying AC electric field. The electrodes can be used repeatedly as the template of subsequent patterning. Although, particles islands were only formed on the PC membrane with 100 and 200 nm diameter pores, the particles penetrated the membrane with 400 nm pores to form patterns on the back surface. Since the strong electric fields were formed at the edges of disks, particles on the back surface were the projection of the disk array of ITO to form ring shapes. The unique structure with particles was explained based on the simulation of electric field distribution. The present proposal offers a procedure to fabricate particle arrays with extremely simple, rapid and highly reproducible manner.     

一种具有广泛适应性的微机械加工方法研究

研究了一种具有广泛适应性的微机械制造方法,该方法可用于制备各种不同的器件,包括硅微陀螺仪、加速度计、剪切应力传感器以及光开关等.利用该方法,制备了硅微陀螺仪,并给出了所制备的硅微陀螺仪的性能测试结果,同时分析了利用该制备方法制备各种不同器件时,工艺流程对器件性能的影响,重点讨论了硅-玻璃阳极键合、减薄工艺以及深刻蚀所形成的侧壁质量,包括侧壁垂直度、侧壁杂质等因素对器件性能的影响.     

基于介电泳的电极阵列电场仿真研究

介电泳方法被广泛地应用于微纳颗粒的分离和操纵中,实现介电泳操作的关键是设计满足所需电场分布的电极阵列.针对目前在微电极阵列设计中尚缺乏简单有效的电场解析方法的现状,提出一种基于格林公式的电极阵列电场的解析方法.首先介绍了传统介电泳和行波介电泳的概念和计算模型,分析了介电泳过程与电极上所施加的交变电压的频率和幅度的关系,然后在确立电极电势的边界条件的基础上,采用基于格林公式的电场解析方法,建立了非均匀电场的解析模型,得出不同条件下的电极阵列电场分布的仿真结果,最后利用FEMLAB有限元仿真软件对解析模型进行了对比仿真, 验证了该解析模型的可行性.基于格林公式的电场解析求解方法能够有效地提高电极阵列设计中的针对性以及缩短电极设计的时间.     

Design and fabrication of a SU-8 based electrostatic microactuator

Comb-drive microactuator is widely used in MEMS devices and traditionally is made of silicon as structural material using silicon-based fabrication technology. Recent development in UV lithography of SU-8 has made it possible to fabricate the ultra high aspect ratio microstructures with excellent sidewall quality. In this paper, we report a low cost alternative to the silicon-based comb drive by using cured SU-8 polymer as structural material. The microactuator was designed to have a integrated structure without assembly or bonding. A unique integration fabrication process was successfully developed based on UV lithography of SU-8 and selectively metallizing SU-8 polymer structures. Preliminary experimental results have proved the feasibility of the microactuator and the fabrication technology.     

Manipulation of ZnO nanostructures using dielectrophoretic effect

In this paper, the dielectrophoretic manipulation of the nanostructured zinc oxide (ZnO) with microfabricated electrodes and electrode arrays had been studied. The nanorod-like ZnO prepared by the chemical solution growth, with the length of 10 μm, was used as the manipulation target. The electrodes and electrode arrays were prepared by standard IC process. The SEM pictures have been used to examine and evaluate the manipulation results. The influences of the pattern of electrodes, the applied frequency, the concentration and the applied voltage on the dielectrophoretic manipulation effect have been investigated to research the manipulation of particles by dielectrophoresis. We succeeded in manipulating ZnO particles along the electric field and depositing them across the gaps between two electrodes by modulating different factors. It is concluded that the nanostructured ZnO can be manipulated by dielectrophoresis and both the positive dielectrophoretic effect and the negative dielectrophoretic effect can be observed. This manipulation technique is potential for lots of application such as the construction of micro/nano sensors and the nanoelectronic devices.     

Analytical formulation of electric field and dielectrophoretic force for moving dielectrophoresis using Fourier series

Electrokinetics manipulation and separation of living cells employing microfluidic devices require good knowledge of the strength and distribution of electric field in such devices. AC dielectrophoresis is performed by generating non-uniform electric field using microsize electrodes. Among the several applications of dielectrophoretic phenomenon, this present study considers the recently introduced phenomenon of moving dielectrophoresis. An analytical solution using Fourier series is presented for the electric field distribution and dielectrophoretic force generated inside a microchannel. The potential at the upper part of the microchannel has been found by solving the governing equation of the electric potential with specific boundary conditions. The solutions for the electric field and dielectrophoretic force show excellent agreement with the numerical results. Microdevices were fabricated and experiments were carried out with living cells confirming and validating the analytical solutions.     

Fundamental characteristics of printed gelatin utilizing micro 3D printer

Gelatin is useful for biofabrication, because it can be used for cell scaffolds and it has unique properties. Therefore, we attempted to fabricate biodevices of gelatin utilizing micro 3D printer which is able to print with high precision. However, it has been difficult to fabricate 3D structure of gelatin utilizing 3D printer, because a printed gelatin droplet on the metal plate electrode would spread before solidification. To clear this problem, we developed a new experimental set-up with a peltier device that can control temperature of the impact point. At an impact point temperature of 80 °C, the spreading of printed gelatin droplets was prevented. Therefore, we were able to print a ball gelatin. In addition, we were able to print a narrower gelatin line than at an impact point temperature of 20 °C.     

Simulation study of single‐cell‐gap transflective liquid crystal display with nonuniform potential

A single‐cell‐gap transflective liquid crystal display with a nonuniform electric potential is demonstrated. The top substrate has a top planar common electrode, a transparent dielectric layer with a general dielectric constant is coated on the bottom substrate, and two planar pixel electrodes with the same size are coated on the dielectric layer and the bottom substrate, respectively. With the different gaps between the two planar pixel electrodes and top planar pixel electrode, the nonuniform electric potential from the transmissive region (T region) to the reflective region (R region) is generated, while a bumpy reflector is coated under the bottom substrate. In this device, with the dielectric layer, the pixel and common electrodes generate a strong electric potential in the T region and a relatively weak electric potential in the R region. Consequently, the T and R regions accumulate the same optical phase retardation. The simulation results show that the display exhibits reasonably low operating voltage, high optical efficiency, and well‐matched voltage‐dependent transmittance and reflectance curves. Besides, the fabrication process and the driving mode of the transflective liquid crystal display are relatively simple, and it is suitable for mobile applications.     

Dielectrophoretic manipulation of nano-materials and its application to micro/nano-sensors

Dielectrophoresis is a potential technique which can be employed to align and manipulate nano-structured materials to the preset locations in fluid for electronic device applications in micro/nano-sensors and circuits. In this paper, with several home-made electrode pairs, we succeeded in manipulating the micro/nano-particles along the electric field and depositing them across the gaps between two electrodes. It is proven as a helpful experiment to assemble the nano-structures with precise arrangement. A relative humidity sensor, using the dielectrophoretically assembled self-grown nano-materials as a sensing element, was fabricated and the sensing properties were then tested. The sensitivity increased with the decline of the testing frequency. And a high humidity sensitivity of 146.90 kΩ/RH% was obtained with a testing frequency of 100 Hz. The relativity of the impedances measured at the same frequency was above −0.90. The relative standard deviations were small especially under a lower relative humidity level. The comparison between aligned and not-aligned nano-materials in the sensing structures was presented to verify the work of the dielectrophoresis. The detection result confirmed the feasibility of applying nano-materials located between the electrodes by dielectrophoresis as sensing elements to micro/nano-sensors.     

介电泳操控纳米材料及其在微纳传感器中的应用

要将纳米结构作为功能元件应用在微纳传感器、纳米电路等系统中,首先要解决材料的定位操作问题.在自行设计的几种电极的基础上,采用介电泳技术对SiO2微纳米材料进行操控,可以实现材料的沿电场方向的排布和电极间的跨接,为解决纳米结构的定位操作做了有益的尝试.初步测试了采用介电泳技术操控自行生长的ZnO纳米结构制作而成的湿度传感器的基本特性并取得很好的响应,表明介电泳技术可以很好得实现纳米材料在传感器领域中的应用.     

Synergistic effects of micro/nano modifications on electrodes for microfluidic electrochemical ELISA

Microfluidic electrochemical sensing has been considered to be highly efficient. However, we showed, by using numerical simulations in this study, that a planar electrode formed on the bottom of a microchannel is exposed to only a small fraction of analytes in amperometric detection. We also showed that three-dimensional (3D) micropillar electrodes significantly improve the detection current. The practical performance was evaluated using 3D micropillar electrodes fabricated by photolithography. The output current increased as the diameters of the micropillars decreased, as predicted by the simulations. It is noteworthy that the current enhancements obtained with the 3D electrodes were larger than those expected from an increase in the surface area. Further increase in current was achieved by electrical deposition of nanoporous gold-black onto the surface of the 3D electrode: when a 3D electrode with micropillars 30 μm in diameter was used, the output current was approximately 20 times that obtained with a 2D electrode without modification. The applicability of the micropillar electrodes was demonstrated in electrochemical enzyme-linked immunosorbent assay (ELISA) of bone metabolic marker proteins. Although an increase in the surface area of the electrode leads to more noise in general, there is no significant difference in the signal-to-noise ratio between the modified 3D electrode and the 2D electrode without modification in the ELISA experiments. This nanoporous micropillar electrode could potentially be a useful component for the development of on-site diagnosis systems.     

A MEMS-based pyramid micro-needle electrode for long-term EEG measurement

The microelectromechanical systems process including cutting, isotropic wet-etching and sputtering was used to fabricate a pyramid micro-needle electrode, which could be applied in long-term electroencephalogram (EEG) measurement. A penetrating testing and comfort survey was presented to optimize the parameters of applying force and penetrating depth in order to make user comfort, safe and free of pain and bleeding. To investigate the performance of the micro-needle electrode, three micro-needle electrodes with different arrays were deployed to perform skin–electrode contact impedance experiments. Moreover, the impedances in time domain were measured to verify the feasibility of long time measurement. At last, EEG signals were recorded directly by three pairs of standard wet/micro-needle electrodes and the power spectrum density (PSD) was presented between standard wet electrode and micro-needle electrode to estimate signal quality. Based on the results of EEG signals and the PSD, the micro-needle electrode can be as a biopotential electrode for recording EEG with low skin–electrode contact impedance.     

Polymer-based cantilevers with integrated electrodes

An innovative release method of polymer cantilevers with embedded integrated metal electrodes is presented. The fabrication is based on the lithographic patterning of the electrode layout on a wafer surface, covered by two layers of SU-8 polymer: a 10-/spl mu/m-thick photo-structured layer for the cantilever, and a 200-/spl mu/m-thick layer for the chip body. The releasing method is based on dry etching of a 2-/spl mu/m-thick sacrificial polysilicon layer. Devices with complex electrode layout embedded in free-standing 500-/spl mu/m-long and 100-/spl mu/m-wide SU-8 cantilever were fabricated and tested. We have optimized major fabrication steps such as the optimization of the SU-8 chip geometry for reduced residual stress and for enhanced underetching, and by defining multiple metal layers [titanium (Ti), aluminum (Al), bismuth (Bi)] for improved adhesion between metallic electrodes and polymer. The process was validated for a miniature 2/spl times/2 /spl mu/m/sup 2/ Hall-sensor integrated at the apex of a polymer microcantilever for scanning magnetic field sensing. The cantilever has a spring constant of /spl cong/1 N/m and a resonance frequency of /spl cong/17 kHz. Galvanometric characterization of the Hall sensor showed an input/output resistance of 200/spl Omega/, a device sensitivity of 0.05 V/AT and a minimum detectable magnetic flux density of 9 /spl mu/T/Hz/sup 1/2/ at frequencies above 1 kHz at room temperature. Quantitative magnetic field measurements of a microcoil were performed. The generic method allows for a stable integration of electrodes into polymers MEMS and it can readily be used for other types of microsensors where conducting metal electrodes are integrated in cantilevers for advanced scanning probe sensing applications.     

Development of an Electrohydrodynamic Injection Micropump and Its Potential Application in Pumping Fluids in Cryogenic Cooling Systems

Cryogenic cooling has become a widely adopted technique to improve the performance of electronics and sensors. A potential application of an electrohydrodynamic (EHD) pumping system is its use in pumping fluids in cryogenic cooling systems. In this paper, we present the results of a theoretical/experimental investigation to study the feasibility of using an EHD injection micropump for pumping liquid nitrogen. First, the mechanisms of charge transport and ionization phenomenon in cryogenic liquids are discussed. Next, the design and fabrication of an EHD injection micropump that employs an array of interdigitated saw-tooth/plane electrodes are described. Finally, experimental results and observations are presented. An asymmetric saw-tooth/plane geometry was designed to achieve a strong inhomogeneous electric field. Each emitter electrode had a base width of 10$mu$m. Each tooth on the emitter electrode had a base length of 10$mu$m with a tip angle of 60$^circ$. The collector electrode consisted of a planar strip with a width of 10$mu$m. The gap between emitter and collector electrodes was 20$mu$m. The distance between each neighboring stage (a pair of emitter and collector electrodes) was 40$mu$m. The patterned area was 10 mm by 20 mm allowing approximately 200 stages to be fabricated along the length of the micropump. The maximum pressure head achieved by this micropump in the absence of a net flow was 550 and 205 Pa for 3M's HFE-7100 thermal fluid and liquid nitrogen, respectively. Also, the maximum mass flow rate was 3.9 g/min at the generated pressure of 180 Pa during a closed loop test with HFE-7100.hfillhbox[1063]     

Laser-induced fluorescence visualization of ion transport in a pseudo-porous capacitive deionization microstructure

In this paper, a microfluidic experimental set-up is introduced to study the ionic transport in an artificial capacitive deionization (CDI) cell. CDI is a promising desalination technique, which relies on the application of an external electric field and high surface area porous electrodes for ion separation and storage. Photolithography and deep reactive ion etching were used to fabricate a micro-CDI channel with pseudo-porous electrodes on a silicon-on-insulator substrate. Laser-induced fluorescence was performed using cationic Sulforhodamine B (SRB) fluorescent dye to measure ion concentration within the bulk solution and more importantly, within the porous electrodes during the desalination process, with an average normalized root mean square deviation of 8.2 %. Using this set-up, electromigration of ions within the electrode was visualized and the effect of applied electric potential on bulk solution concentration distribution is quantified. In addition, SRB and Fluorescein were used together to visualize anion and cation concentrations simultaneously. The method presented in this study can be used for solution concentrations up to approximately 0.7 mM. The ionic concentration profiles obtained by this approach can be used to test and validate the existing electrosorption models, and pseudo-porous electrodes can be modified to observe the effects of pore size, shape and distribution on electrosorption performance. Furthermore, with proper modifications, the microfabricated structure and experimental set-up can be used for CDI-on-a-chip applications and bio-separation devices.     

Fabrication and characterisation of bulk micromachined ZnO energy transducer with interdigitated electrodes

The proposed research work deals with the design, fabrication and characterisation of a ZnO cantilever energy transducer on Si(c) without the use of SOI wafers, thereby, reducing the cost of fabrication. The energy transducer is operated in the longitudinal mode through the interdigitated electrodes. This is for the first time, we have attempted to fabricate a cantilever transducer with interdigitated electrodes on Si(c) in our lab. The design frequency has been chosen in the range of 700–1000 Hz for a typical tire pressure monitoring system application in mind. The experimentally obtained frequency is 876.25 Hz and d₃₃ was calculated as 3.9 pC/N from the measurements. The experimental results are further validated by simulation and the feasibility of its application as energy harvester is demonstrated. The fabrication process is being optimised to fabricate devices with higher piezoelectric coefficients.     

Sequential Field-Flow Cell Separation Method in a Dielectrophoretic Chip With 3-D Electrodes

This paper presents a sequential dielectrophoretic field-flow separation method for particle populations using a chip with a 3-D electrode structure. A unique characteristic of our chip is that the walls of the microfluidic channels also constitute the device's electrodes. This property confers the opportunity to use the electrodes' shape to generate not only the electric field gradient required for dielectrophoretic force but also a fluid velocity gradient. This interesting combination gives rise to a new solution for the dielectrophoretic separation of two particle populations. The proposed sequential field-flow separation method consists of four steps. First, the microchannel is filled with the mixture of the two populations of particle. Second, the particle populations are trapped in different locations of the microfluidic channels. The population, which exhibits positive dielectrophoresis (DEP), is trapped in the area where the distance between the electrodes is the minimum, while the other population that exhibits negative DEP is trapped in locations of maximum distance between electrodes. In the next step, increasing the flow in the microchannels will result in an increased hydrodynamic force that sweeps the cell population trapped by positive DEP out of the chip. In the last step, the electric field is removed, and the second population is swept out and collected at the outlet. For theoretical and experimental exemplification of the separation method, a population of viable and nonviable yeast cells was considered.     

Polyimide micro-channel arrays for peripheral nerve regenerative implants

Mechanical guidance is one way in which regenerating axons can be directed towards an appropriate target. In this paper, we present the design and fabrication process of a three-dimensional (3D) device comprising a bundle of parallel micro-channels, which can be used as a 3D regenerative implant for peripheral nerve repair. The skeleton of the device is entirely made of flexible polyimide films. Gold micro-electrodes and micro-channels of photosensitive polyimide are patterned directly on polyimide substrates. After fabrication, the 2D electrode channel array is rolled into a 3D channel bundle fitting the peripheral nerve.The efficiency with which axons enter the 2D channel array was evaluated in vitro as a function of channel width, spacing and pitch. Axon outgrowth is maximised when micro-channels are wide (>30 μm), and when the array transparency (the channel width to pitch ratio) is at least 50%. To ensure the metallic electrodes remain functional in the rolled device, substrate thickness and micro-channel height must also be optimized to position the metal film in the neutral plane of the rolled structure. Electrodes embedded in the implant polyimide structure are robust to rolling. Their impedance at 1 kHz in Ringer solution is of the order of 1 MΩ on flat samples, and changes little when the same samples are rolled and inserted into 1.5 mm inner diameter tube. Such 3D, electrode channel devices on polymer not only provides a novel technological approach to physical guidance of regenerating neurons in vivo but also enables the fabrication of an electrode implant with direct electrical communication with multiple groups of nerve fibres in a regenerating peripheral nerve.     

Particle streaming and separation using dielectrophoresis through discrete periodic microelectrode array

This study presents a particle manipulation and separation technique based on dielectrophoresis principle by employing an array of isosceles triangular microelectrodes on the bottom plate and a continuous electrode on the top plate. These electrodes generate non-uniform electric fields transversely across the microchannel. The particles within the flowing fluid experience a dielectrophoretic force perpendicular to the fluid flow direction due to the non-uniform electric fields. The isosceles triangular microelectrodes were designed to continuously exert a small dielectrophoretic force on the particles. Particles experiencing a larger dielectrophoretic force would move further in the perpendicular direction to the fluid flow as they traveled past each microelectrode. Polystyrene microspheres were used as the model particles, with particles of ∅20 μm employed for studying the basic characteristics of this technique. Particle separation was subsequently demonstrated on ∅10 and ∅15 μm microspheres. Using an applied sinusoidal voltage of 20 V_pp and frequency of 1 MHz, a mean separation distance of 0.765 mm between them was achieved at a flow rate of 3 μl/min (~1 mm/s), an important consideration for high throughput separation capability in a micro-scale technology device. This unique isosceles triangular microelectrodes design allows heterogeneous particle populations to be separated into multiple streams in a single continuous operation.