Multiwalled carbon nanotube-polyimide nanocomposite for MEMS piezoresistive pressure sensor applications

Multiwalled carbon nanotube (MWCNT)-polyimide (PI) nanocomposite was prepared with different MWCNT concentrations and characterized for their piezoresistive response. The morphology and mechanical behavior of the nanocomposite was investigated by scanning electron microscopy and force–displacement spectroscopy respectively. The surface conductivity of the nanocomposite was determined by atomic force microscopy in current mode. Studies reveal that this nanocomposite will be useful for strain-sensing element in micro electro mechanical system (MEMS)/nano electro mechanical system (NEMS) based piezoresistive pressure sensor applications. The study shows that the nanocomposite with 2 % MWCNT content is a unique piezoresistive sensing element for MEMS/NEMS pressure sensor.     

Photoresist-based integration of enzyme functionality into MEMS

We demonstrate the direct immobilization of glucose oxidase and lactate oxidase onto photoresists commonly used in microfabrication. The method allows for a cost-effective, facile inclusion of enzyme functionality into novel MEMS devices because it does not require any chemical or physical pre-treatment of surfaces, and it is largely compatible with existing fabrication technologies. We used fluorescence imaging and absorbance spectrometry to confirm attachment of the enzymes onto the photoresists and to determine their activity. In addition, the procedure was used to successfully integrate enzyme functionality into a photoresist-based biosensor. This further demonstrates the effectiveness of the approach, and opens a path towards other novel applications in MEMS research.     

High-aspect-ratio photolithography for MEMS applications

High-aspect-ratio photolithography using a commercially available positive photoresist and a conventional contact mask aligner with standard UV light source is described. A multiple coating process is developed to obtain a photoresist thickness up to 23 μm while maintaining a smooth photoresist surface. Intimate contact between the mask and wafer is found to be most critical for high-resolution photolithography. Vacuum contact is found to be well-suited for this purpose. Additionally, edge bead removal is found to be of significant importance for intimate contact between the mask and the substrate. Prebake, exposure, and development conditions are optimized for resolution and aspect ratio. Maximum prebake temperature still allowing the photoresist to be developed is found to be the optimal temperature for obtaining high resolution. Prebake time distribution is optimized for avoiding residual stress in the photoresist, as well as maintaining high resolution, when multiple coating is applied. Minimum linewidth and spacing of 3.5 μm and 2.5 μm, respectively, and a maximum aspect ratio of 7.7 have been achieved in a photoresist thickness of 23 μm. Postbake improves the chemical resistance to subsequent processes, for example, electroless nickel plating using the photoresist as a mold. However, postbake also causes pattern distortion, which can be severe at times. Therefore, optimal process and design conditions for minimizing the pattern distortion have been studied     

Porous polycrystalline silicon: a new material for MEMS

A new technique for the fabrication of thin patterned layers of porous polycrystalline silicon (polysilicon) and surface micromachined structures is presented. First, a multilayer structure of polysilicon between two layers of low-stress silicon nitride is prepared on a wafer of silicon. Electrochemical anodization with an external cathode takes place in an RF solution. A window in the outer nitride layer provides contact between the polysilicon and the HF solution; the polysilicon layer contacts the substrate through openings in the lower silicon nitride layer (remote from the upper windows). Porous polysilicon growth in the lateral direction is found at rates as high as 15 μm min^-1 in 12M (25%, wgt) HF to be controlled by surface-reaction kinetics. A change in morphology occurs when either the anodic potential is raised or the HF concentration is decreased, causing the polysilicon to be electropolished. The etch front advances proportionally to the square root of time as expected for a mass-transport-controlled process. Similar behavior is observed in HF anodic reactions of single-crystal silicon. Dissolution of the polysilicon layer is confirmed using profilometry and scanning electron microscopy. Enclosed cavities (chambers surrounded by porous plugs) are formed by alternating between pore formation and uniform dissolution. Porous polysilicon also forms over a broad-area layer of polycrystalline silicon that has been deposited without overcoating the silicon wafer with a thin film of silicon nitride. The resulting porous layer may be useful for gas-absorption purposes in ultrasonic sensors     

Design of MEMS switch for RF applications

Components like passive electronically scanned (sub) arrays, T/R modules, reconfigurable antennas etc., in RF applications are in need of MEMS switches for its re-configurability and polarization. This paper presents the analysis, design and simulation of a MEMS switch. The switch proposed in this paper is intended to work in the frequency range of 4–8 GHz. The proposed switch fulfills the switching characteristics concerning the five requirements loss, linearity, high switching speed, small size/power consumption, low pull down voltage following a relatively simple design, which ensures reliability, robustness and high fabrication yield. The switch implemented in this paper is based on the integration mode of operation and widely used in RF applications.     

Micromachining of diamond film for MEMS applications

We realized two diamond microdevices: a movable diamond microgripper and a diamond probe for an atomic force microscope (AFM), consisting of a V-shaped diamond cantilever and a pyramidal diamond tip, using a microfabrication technique employing semiconductive chemical-vapor-deposited diamond thin film. The microgripper was fabricated by patterning the diamond thin film onto a sacrificial SiO ₂ layer by selective deposition and releasing the movable parts by sacrificial layer etching. The diamond AFM probe was fabricated by combining selective deposition for patterning a diamond cantilever with a mold technique on an Si substrate for producing a pyramidal diamond tip. The cantilever was then released by removing the substrate. We report the initial results obtained in AFM measurements taken using the fabricated diamond probe. These results indicate that this diamond probe is capable of measuring AFM images. In addition, we have developed the anodic bonding of diamond thin film to glass using Al or Ti film as an intermediate layer for assembly. This bonding technique will allow diamond microstructures to be used in many novel applications for microelectromechanical systems     

Design of a packaging-friendly double-topology RF MEMS switch for space applications

Microsystem Technologies - This article presents the results of the research, design and a series of manufacturing steps of an RF-MEMS switch to be used in space communication systems. Design and...     

MEMS multi-vibrating ring gyroscope for space applications

Microsystem Technologies - This paper presents the design of a novel multi-ring vibratory gyroscope. The design incorporates two sets of rings, inner and outer, separated by a set of perforated...     

Low-noise MEMS vibration sensor for geophysical applications

The need exists for high-sensitivity, low-noise vibration sensors for various applications, such as geophysical data collection, tracking vehicles, intrusion detectors, and underwater pressure gradient detection. In general, these sensors differ from classical accelerometers in that they require no direct current response, but must have a very low noise floor over a required bandwidth. Theory indicates a capacitive micromachined silicon vibration sensor can have a noise floor on the order of 100 ng/√Hz over 1 kHz bandwidth, while reducing size and weight tenfold compared to existing magnetic geophones. With early prototypes, we have demonstrated Brownian-limited noise floor at 1.0 μg/Hz, orders of magnitude more sensitive than surface micromachined devices such as the industry standard ADXL05     

Design of a novel step structure RF MEMS switch for K-band applications

Microsystem Technologies - In this paper, we have design a proposed step structure RF MEMS switch for K-band applications. The non-uniform meander structure is implemented for both optimized and...     

Multiport RF MEMS switch for satellite payload applications

Microsystem Technologies - Design, fabrication and characterization of a novel RF switch is proposed in this paper. The multiport RF MEMS switch provides a single input multiple output novel...     

Low cost anodic bonding for MEMS packaging applications

Anodic bonding of Pyrex 7740 glass to bare silicon and oxidized silicon wafer is presented for micro electro mechanical systems (MEMS) device packaging. Experimentally it has been observed that anodic bonding process parameters are varying with different 3D structures. The effects of bonding temperature and voltage are discussed by keeping the temperature constant and varying the voltage. The bonding interface has been studied by scanning electron microscope observations. Effective parameters for MEMS structure such as bonding temperature, voltage has been discussed.     

Silicon isotropic and anisotropic etching for MEMS applications

In MEMS technology there is an increasing interest in developing high aspect ratio silicon columns having rounded corners, slightly positive tapered shafts, sharp tips, and smooth surfaces. A precise control of the profile can be used for different applications, such as for molds used in polymer hot embossing processes, micro needles used for drug delivery and blood sampling, and neural probes used for controlling motor or sensory prosthetic devices. The mixture of hydrofluoric acid (HF) and nitric acid (HNO₃) is an isotropic etchant and is used in MEMS technology to etch silicon. We present a novel way of isotropically and anisotropically etch MEMS structures using the HF–HNO₃ etchant. The shape and size of the structure is controlled by the dynamics of acid solution to yield highly repeatable and reproducible needle geometry.     

A MEMS reconfigurable DGS resonator for K-band applications

A MEMS reconfigurable defected-ground-structure (DGS) resonator using two-dimensional (2-D) periodic DGS for coplanar waveguide (CPW) transmission line and RF MEMS series-resistive switches is proposed. The introduced MEMS reconfigurable DGS resonator has approximately a fixed bandwidth of 8.1 GHz over a wideband frequency range (K-band). The proposed structure can be designed easily for other frequency bands by changing the number of unit-cells of the 2-D PDGS. A cascaded two parallel-resonance circuit model for the MEMS reconfigurable DGS resonator has been introduced as well. The equivalent circuit parameters extraction methods have also been derived. Simulations based on the proposed circuit model are in a very good agreement with the electromagnetic (EM) simulations, which suggests that the MEMS reconfigurable DGS resonator is an inductive controlled reconfigured structure. The structure is designed in CPW environment on a high-resistivity silicon substrate. It is therefore suitable for monolithic integration with standard IC process.     

飞行器用高精度小量程石英微加速度计研究

为满足对振动环境下10 Hz以下低频小量程加速度信号的高精度测量需求,提出了一种基于石英微工艺的新型窄带宽MEMS加速度计,其敏感元件采用变间距式差分电容梳齿结构。采用有限元分析手段,对敏感元件质量块尺寸、梳齿长度、U型梁刚度、盖板结构、阻尼和带宽等参数进行了综合优化设计。敏感元件采用石英晶片经湿法腐蚀体工艺制作,加速度计样机经过了实际性能测试和环境适应性试验,带宽为8.9 Hz,非线性度约为0.7%,可以满足飞行器小量程低频加速度参数的测量需求。     

Robust optimization using a gradient index: MEMS applications

This paper discusses a simple and effective robust optimization formulation and illustrates its application to MicroElectroMechanical Systems (MEMS) devices. The proposed formulation improves robustness of the objective function by minimizing a gradient index (GI), defined as a function of gradients of performance functions with respect to uncertain variables. The level of constraint feasibility is also enhanced by adding a term determined by a constraint value and the gradient index. In the robust optimal design procedure, a deterministic optimization for performance improvement is followed by a sensitivity analysis with respect to uncertainties such as MEMS fabrication errors and changes of material properties. During the process of the deterministic optimization and sensitivity analysis, dominant performances and critical uncertain variables are identified to define the GI. Our approach for robust design requires no statistical information on the uncertainties and yet achieves robustness effectively. Two MEMS application examples including a micro accelerometer and a resonant-type micro probe are presented.     

高性能微机械陀螺接口电路研究

微机械陀螺输出信号非常微弱,从系统角度对其接口电路进行研究,采用闭环驱动,通过改善驱动信号稳定性及陀螺输出端接口电路,系统性能得到较大提高,改善后系统灵敏度9.8 mV/(o)·s-1,非线性度0.43%,分辨率达180°/h.     

A MEMS affinity glucose sensor using a biocompatible glucose-responsive polymer

We present a MEMS affinity sensor that can potentially allow long-term continuous monitoring of glucose in subcutaneous tissue for diabetes management. The sensing principle is based on detection of viscosity changes due to affinity binding between glucose and poly(acrylamide-ran-3-acrylamidophenylboronic acid) (PAA-ran-PAAPBA), a biocompatible, glucose-specific polymer. The device uses a magnetically driven vibrating microcantilever as a sensing element, which is fabricated from Parylene and situated in a microchamber. A solution of PAA-ran-PAAPBA fills the microchamber, which is separated from the surroundings by a semi-permeable membrane. Glucose permeates through the membrane and binds reversibly to the phenylboronic acid moiety of the polymer. This results in a viscosity change of the sensing solution, which is obtained by measuring the damped cantilever vibration using an optical lever setup, allowing determination of the glucose concentration. Experimental results demonstrate that the device is capable of detecting glucose at physiologically relevant concentrations from 27 mg/dL to 324 mg/dL. The glucose response time constant of the sensor is approximately 3 min, which can be further improved with device design optimization. Excellent reversibility and stability are observed in sensor responses, as highly desired for long-term, stable continuous glucose monitoring.     

Laterally moving bistable MEMS DC switch for biomedical applications

In this paper, we have designed a bistable microelectromechanical switch for an implantable lead electrode multiplexer application. Fabrication is based on a single mask process. State changes require an 18 V pulse to the actuators consuming only 0.2 nJ energy. The switch does not consume any energy in either the ON or the OFF state. Total chip size including bond pads is approximately 1.5 mm /spl times/ 1.5 mm. The initial contact resistance is below 5 /spl Omega/ with a contact force in the order of 10 /spl mu/N. The contact resistance stays consistently below 30 /spl Omega/ for the first 40 000 cycles. Breakdown voltage between the two contact members in OFF state is 300 V. We plan to further investigate applicability of this switch in the biomedical field.     

BPN a new thick negative photoresist with high aspect ratio for MEMS applications

The BPN is a negative photoresist, sensitive in the UV at 365 nm and was previously dedicated for Wafer Level Packaging (WLP) applications. This photoresist offer the advantage of forming thick layers, however, it suffers from low aspect ratio (2:1 declared by the supplier). This work reports the optimization of BPN’s technological process enabling forming 30–160 μm thick molds for electroplating purposes. Our results revealed an aspect ratio as high as 16:1 while having vertical sidewalls using conventional photolithography.