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At least 127 records · Page 7Linked to original sources

arXiv2008

Fabrication of Miniaturized Variable-focus Lens Using Liquid Filling Technique

This paper describes a simple method for fabricating a variable-focus lens by using PDMS (polydimethylsiloxane) and filling with liquid for the variable-focus lens. The lens diameter of 2-mm was designed in this experiment and expected to reach the focal length in the range of 3 ~ 12 mm. The theoretical value between the liquid volume and the lens contact angle at different focal lengths were simulated and measured. The pumped-in volumes ranged from 200 to 1400 $μ$l, the contact angles ranged from 14.25 degrees to 49.02 degrees. Changing the deformation of PDMS film using different micro-fluidic volume produces the variable focal length from 4 10 mm in this experiment. The proposed method successfully fabricated a variable-focus lens. Bonding PDMS only once using no expensive instrument such as oxygen plasma was accomplished. The final objective is to insert the variable focus lens into portable optical imagery products.

cs.OH↗

arXiv2008

A Novel X-Axis Tuning Fork Gyroscope with "8 Vertical Springs-Proofmass" Structure on (111)-Silicon

A novel x-axis tuning fork MEMS gyroscope with "8 vertical springs-proofmass" structure for Coriolis effect detection is presented. Compared with the common single-plane springs, the 8 vertical springs, symmetrically located at the top and bottom sides, more stably suspend the large thick proofmass featuring large capacitance variation and low mechanical noise. A bulk-micromachining technology is applied to obtain the large proofmass and twins-like dual beams. During the fabrication process, the dimensions of the 8 vertical springs are precisely confined by thermal oxide protected limit trenches (LTs) sidewalls and the extreme slowly etched (111)-planes; therefore a small mismatch of less than 30 Hz is achieved before tuning. Initial test shows a sensitivity of 0.15mV/(deg/s) and rate resolution around 0.1deg/s under atmosphere pressure.

cs.OH↗

arXiv2008

Fabrication of MEMS Resonators in Thin SOI

A simple and fast process for micro-electromechanical (MEM) resonators with deep sub-micron transduction gaps in thin SOI is presented in this paper. Thin SOI wafers are important for advanced CMOS technology and thus are evaluated as resonator substrates for future co-integration with CMOS circuitry on a single chip. As the transduction capacitance scales with the resonator thickness, it is important to fabricate deep sub-micron trenches in order to achieve a good capacitive coupling. Through the combination of conventional UV-lithography and focused ion beam (FIB) milling the process needs only two lithography steps, enabling therefore a way for fast prototyping of MEM-resonators. Different FIB parameters and etching parameters are compared in this paper and their effect on the process are reported.

cs.OH↗

arXiv2008

Usage of Porous Al2O3 Layers for RH Sensing

At the Department of Electron Devices a cheap, more or less CMOS process compatible capacitive type RH sensor has been developed. Capacitive sensors are based on dielectric property changes of thin films upon water vapour uptake which depends on the surrounding media's relative humidity content. Because of the immense surface-to-volume ratio and the abundant void fraction, very high sensitivities can be obtained with porous ceramics. One of the ceramics to be used is porous Al2O3, obtained by electrochemical oxidation of aluminium under anodic bias. The average pore sizes are between 6...9 nm. In our paper we intend to demonstrate images representing the influence of the technological parameters on the porous structure and the device sensitivity.

cs.OH↗

arXiv2008

Modeling of large area hot embossing

Today, hot embossing and injection molding belong to the established plastic molding processes in microengineering. Based on experimental findings, a variety of microstructures have been replicated so far using the processes. However, with increasing requirements regarding the embossing surface and the simultaneous decrease of the structure size down into the nanorange, increasing know-how is needed to adapt hot embossing to industrial standards. To reach this objective, a German-Canadian cooperation project has been launched to study hot embossing theoretically by a process simulation and experimentally. The present publication shall report about the first results of the simulation - the modeling and simulation of large area replication based on an eight inch microstructured mold.

cs.OH↗

arXiv2008

Liquid Density Sensing Using Resonant Flexural Plate Wave Device with Sol-Gel PZT Thin Films

This paper presents the design, fabrication and preliminary experimental results of a flexure plate wave (FPW) resonator using sol-gel derived lead zirconate titanates (PZT) thin films. The resonator adopts a two-port structure with reflecting grates on the composite membrane of PZT and SiNx. The design of the reflecting grate is derived from a SAW resonator model using COM theory to produce a sharp resonant peak. The comparison between the mass and the viscosity effects from the theoretical expression illustrates the applications and the constraints of the proposed device in liquid sensing. Multiple coatings of sol-gel derived PZT films are adopted because of the cost advantage and the high electromechanical coupling effect over other piezoelectric films. The fabrication issues of the proposed material structure are addressed. Theoretical estimations of the mass and the viscosity effects are compared with the experimental results. The resonant frequency has a good linear correlation with the density of low viscosity liquids, which demonstrate the feasibility of the proposed device.

cs.OH↗

arXiv2008

Design, Fabrication and Characterization of a Piezoelectric Microgenerator Including a Power Management Circuit

We report in this paper the design, fabrication and experimental characterization of a piezoelectric MEMS microgenerator. This device scavenges the energy of ambient mechanical vibrations characterized by frequencies in the range of 1 kHz. This component is made with Aluminum Nitride thin film deposited with a CMOS compatible process. Moreover we analyze two possible solutions for the signal rectification: a discrete doubler-rectifier and a full custom power management circuit. The ASIC developed for this application takes advantage of diodes with very low threshold voltage and therefore allows the conversion of extremely low input voltages corresponding to very weak input accelerations. The volume of the proposed generator is inferior to 1mm3 and the generated powers are in the range of 1$μ$W. This system is intended to supply power to autonomous wireless sensor nodes.

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arXiv2008

A complete study of electroactive polymers for energy scavenging: modelling and experiments

Recent progresses in ultra low power microelectronics propelled the development of several microsensors and particularly the self powered microsystems (SPMS). One of their limitations is their size and their autonomy due to short lifetime of the batteries available on the market. To ensure their ecological energetic autonomy, a promising alternative is to scavenge the ambient energy such as the mechanical one. Nowadays, few microgenerators operate at low frequency. They are often rigid structures that can perturb the application or the environment; none of them are perfectly flexible. Thus, our objective is to create a flexible, non-intrusive scavenger using electroactive polymers. The goal of this work is to design a generator which can provide typically 100 ?W to supply a low consumption system. We report in this paper an analytical model which predicts the energy produced by a simple electroactive membrane, and some promising experimental results.

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arXiv2008

Step-up converter for electromagnetic vibrational energy scavenger

This paper introduces a voltage multiplier (VM) circuit which can step up a minimum voltage of 150 mV (peak). The operation and characteristics of this converter circuit are described. The voltage multiplier circuit is also tested with micro and macro scale electromagnetic vibrational generators and the effect of the VM on the optimum load conditions of the electromagnetic generator is presented. The measured results show that 85% efficiency can be achieved from this VM circuit at a power level of 18 ?W.

cs.OH↗

arXiv2008

Gas Damping Coefficient Research for MEMS Comb Linear Vibration Gyroscope

Silicon-MEMS gyroscope is an important part of MEMS (Micro Electrical Mechanical System). There are some disturb ignored in traditional gyroscope that must be evaluated newly because of its smaller size (reach the level of micron). In these disturb, the air pressure largely influences the performance of MEMS gyroscope. Different air pressure causes different gas damping coefficient for the MEMS comb linear vibration gyroscope and different gas damping coefficient influences the quality factor of the gyroscope directive. The quality factor influences the dynamic working bandwidth of the MEMS comb linear vibration gyroscope, so it is influences the output characteristic of the MEMS comb linear vibration gyroscope. The paper shows the relationship between the air pressure and the output amplified and phase of the detecting axis through analyzing the air pressure influence on the MEMS comb linear vibration gyroscope. It discusses the influence on the frequency distribute and quality factor of the MEMS comb linear vibration gyroscope for different air pressure.

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arXiv2008

Comparison of Two Low-Power Electronic Interfaces for Capacitive Mems Sensors

The paper discusses the importance and the issues of interfacing capacitive sensors. Two architectures applicable for interfacing capacitive sensors are presented. The first solution was designed to interface a capacitive humidity sensor designed and built for a humidity-dependent monolithic capacitor developed at Budapest University of Technology and Economics. The second case presents the possible read-out solutions for a SOI-MEMS accelerometer. Both of the architectures were built and tested in a discrete implementation to qualify the methods before the integrated realization. The paper presents a detailed comparison of the two methods

cs.OH↗

arXiv2008

High Efficiency 3-Phase Cmos Rectifier with Step Up and Regulated

This paper presents several design issues related to the monolithic integration of a 3-phase AC to DC low voltage, low power rectifier for 3-phase micro source electrical conditioning. Reduced input voltage operation (down to 1V), high efficiency, and output voltage regulations are implemented, based on commercially available CMOS technology. Global design and system issues are detailed. The management of start-up sequences under self supplied conditions as well as output voltage regulations are specifically addressed. Simulation results, practical implementation and validation are presented. They are based on the association of three micro elements : a 3-phase micro-generator, a stand alone 3-phase AC to DC integrated rectifier, and an output voltage conditioner based on a commercially available IC.

cs.OH↗

arXiv2008

Silicon on Nothing Mems Electromechanical Resonator

The very significant growth of the wireless communication industry has spawned tremendous interest in the development of high performances radio frequencies (RF) components. Micro Electro Mechanical Systems (MEMS) are good candidates to allow reconfigurable RF functions such as filters, oscillators or antennas. This paper will focus on the MEMS electromechanical resonators which show interesting performances to replace SAW filters or quartz reference oscillators, allowing smaller integrated functions with lower power consumption. The resonant frequency depends on the material properties, such as Young's modulus and density, and on the movable mechanical structure dimensions (beam length defined by photolithography). Thus, it is possible to obtain multi frequencies resonators on a wafer. The resonator performance (frequency, quality factor) strongly depends on the environment, like moisture or pressure, which imply the need for a vacuum package. This paper will present first resonator mechanisms and mechanical behaviors followed by state of the art descriptions with applications and specifications overview. Then MEMS resonator developments at STMicroelectronics including FEM analysis, technological developments and characterization are detailed.

cs.OH↗

arXiv2008

Copper Planar Microcoils Applied to Magnetic Actuation

Recent advances in microtechnology allow realization of planar microcoils. These components are integrated in MEMS as magnetic sensor or actuator. In the latter case, it is necessary to maximize the effective magnetic field which is proportional to the current passing through the copper track and depends on the distance to the generation microcoil. The aim of this work was to determine the optimal microcoil design configuration for magnetic field generation. The results were applied to magnetic actuation, taking into account technological constraints. In particular, we have considered different realistic configurations that involve a magnetically actuated device coupled to a microcoil. Calculations by a semi-analytical method using Matlab software were validated by experimental measurements. The copper planar microcoils are fabricated by U.V. micromoulding on different substrates: flexible polymer (Kapton) and silicate on silicon. They are constituted by a spiral-like continuous track. Their total surface is about 1 mm2.

cs.OH↗

arXiv2008

Ni-MH battery modelling for ambient intelligence applications

Mobile devices, like sensor networks and MEMS actuators use mobile power supplies to ensure energy for their operation. These are mostly batteries. The lifetime of the devices depends on the power consumption and on the quality and capacitance of the battery. Though the integrated circuits and their power consumption improve continually, their clock frequency also increases with the time, and the resultant power consumption seems not to vary, or slightly increase. On the other hand, the properties of batteries are developing much slower, necessitating the optimization of their usage on system level.

cs.OH↗

arXiv2008

Analysis of polysilicon micro beams buckling with temperature-dependent properties

The suspended electrothermal polysilicon micro beams generate displacements and forces by thermal buckling effects. In the previous electro-thermal and thermo-elastic models of suspended polysilicon micro beams, the thermo-mechanical properties of polysilicon have been considered constant over a wide rang of temperature (20- 900 degrees C). In reality, the thermo-mechanical properties of polysilicon depend on temperature and change significantly at high temperatures. This paper describes the development and validation of theoretical and Finite Element Model (FEM) including the temperature dependencies of polysilicon properties such as thermal expansion coefficient and Young's modulus. In the theoretical models, two parts of elastic deflection model and thermal elastic model of micro beams buckling have been established and simulated. Also, temperature dependent buckling of polysilicon micro beam under high temperature has been modeled by Finite Element Analysis (FEA). Analytical results and numerical results using FEA are compared with experimental data available in literature. Their reasonable agreement validates analytical model and FEM. This validation indicates the importance of including temperature dependencies of polysilicon thermo-mechanical properties such as Coefficient of Thermal Expansion (CTE) in the previous models.

cs.OH↗

arXiv2008

Parameter Identification of Pressure Sensors by Static and Dynamic Measurements

Fast identification methods of pressure sensors are investigated. With regard to a complete accurate sensor parameter identification two different measurement methods are combined. The approach consists on one hand in performing static measurements - an applied pressure results in a membrane deformation measured interferometrically and the corresponding output voltage. On the other hand optical measurements of the modal responses of the sensor membranes are performed. This information is used in an inverse identification algorithm to identify geometrical and material parameters based on a FE model. The number of parameters to be identified is thereby generally limited only by the number of measurable modal frequencies. A quantitative evaluation of the identification results permits furthermore the classification of processing errors like etching errors. Algorithms and identification results for membrane thickness, intrinsic stress and output voltage will be discussed in this contribution on the basis of the parameter identification of relative pressure sensors.

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arXiv2008

New Horizontal Frustum Optical Waveguide Fabrication Using UV Proximity Printing

This paper presents a novel method to fabricate the horizontal frustum structure as a planar optical waveguide by using the proximity printing technique. A horizontal frustum optical waveguide with a both lateral and vertical taper structure was produced. The orthogonal and inclined masks with the diffraction effect were employed in lithography process. This method can precisely control each horizontal frustum optical waveguide geometric profile in the fabrication process. The horizontal frustum optical waveguide and its array with the same inclined angle were generated. The beam propagation simulation software (BPM_CAD) was used to modeling the optical performance. The simulation results reveal that the mode profile matched into horizontal frustum optical waveguide and fiber from the laser diode. The optical loss of horizontal hemi-frustum structure of optical waveguides was less than 0.2dB. The horizontal hemifrustum waveguide will be used for fiber coupling on boards for further optical communication systems.

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