Microelectromechanical Systems Elements Research Articles

High‐performance MEMS shutter display with metal‐oxide thin‐film transistors and optimized MEMS element

AbstractActive matrix prestressed microelectromechanical shutter displays enable outstanding optical properties as well as robust operating performance. The microelectromechanical systems (MEMS) shutter elements have been optimized for higher light outcoupling efficiency with lower operation voltage and higher pixel density. The MEMS elements have been co‐fabricated with self‐aligned metal‐oxide thin‐film transistors (TFTs). Several optimizations were required to integrate MEMS process without hampering the performance of both elements. The optimized display process requires only seven photolithographic masks with ensuring proper compatibility between MEMS shutter and metal‐oxide TFT process.

Surface topography and nanomechanical/tribological behaviour of ultrathin nitride films on silicon

Abstract Surface topography and roughness characteristics were studied based on the analysis of three dimensional atomic force microscopy images of several multilayer ultrathin-film samples. TiN, CrN and NbN (200 nm thick) were deposited on single crystal n-type silicon without or with a 200 nm thick underlayer of silicon dioxide or silicon nitride. The nitride films were deposited by physical vapour deposition technique and the underlayer films by plasma-enhanced chemical vapour deposition. Nanomechanical studies and nanotribological tests were also conducted to investigate the properties of such films as possible candidates for protective layers on rubbing elements of micro-electromechanical systems. The effect of the underlayer on the surface properties and the mechanical/tribological behaviour was evaluated as well.

Mechanically Robust Free-Standing Single-Walled Carbon Nanotube Thin Films With Uniform Mesh-Structure by Blade Coating

Carbon nanotubes (CNTs) have garnered tremendous attention as building blocks for self-supporting membranes owing to remarkable developments in the manufacturing technology of high-quality CNT films. CNT films are expected to be applied in a wide range of applications, such as ultrafiltration membranes and as switching or sensing elements in micro electromechanical systems. However, the main challenge has been in fabricating CNT films by versatile and scalable processes suitable for industrial production retaining lab-scale high-performances. In this work, we succeed in fabricating macroscale (10-cm square) free-standing CNT films with thicknesses as low as 200 nm showing tensile strengths of ~ 166 MPa by simple, versatile, and scalable blade-coating of CNT suspensions. Our study demonstrates that it is possible to control CNT film bundle size distribution and pore structure by controlling the CNT dispersibility and entanglement in the suspensions. We find that controlling bundle size distribution, pore structure uniformity and packing can lead to 5-fold, 4-fold and 3-fold higher tensile strengths, fracture strain and Young’s modulus, respectively compared to films with poorer uniformity and packing.

3D Printed MEMS Technology-Recent Developments and Applications.

Microelectromechanical systems (MEMS) are of high interest for recent electronic applications. Their applications range from medicine to measurement technology, from microfluidics to the Internet of Things (IoT). In many cases, MEMS elements serve as sensors or actuators, e.g., in recent mobile phones, but also in future autonomously driving cars. Most MEMS elements are based on silicon, which is not deformed plastically under a load, as opposed to metals. While highly sophisticated solutions were already found for diverse MEMS sensors, actuators, and other elements, MEMS fabrication is less standardized than pure microelectronics, which sometimes blocks new ideas. One of the possibilities to overcome this problem may be the 3D printing approach. While most 3D printing technologies do not offer sufficient resolution for MEMS production, and many of the common 3D printing materials cannot be used for this application, there are still niches in which the 3D printing of MEMS enables producing new structures and thus creating elements for new applications, or the faster and less expensive production of common systems. Here, we give an overview of the most recent developments and applications in 3D printing of MEMS.

AOI strategies for defects identification of micro-electro mechanical system elements

The structures of micro-electro mechanical system (MEMS) components are considerably fine, and their quality control (QC) is typically achieved using visual inspection with high-labour intensity. The manual detection approach is inefficient (low yield) and limited to the discrimination ability of the human eye in each individual, and thus, bears inconsistent quality problems. Furthermore, a 100% overall inspection requirement for critical parts can barely be achieved by human inspection. This paper proposes an automated optical inspection (AOI) to replace labour visual inspection. The proposed approach provides a high-recognition rate, and enhances the detection efficiency for QC practical industry purposes, which has made it an indispensable key technology in recent developments. Because of the high complexity of MEMS structures, the manufactured parts often consist of defects such as breaks, fillet, Ag paste, scratches, particles and chips. These microdefects on an MEMS device easily cause damage and even malfunction in the entire module, and therefore, developing effective detection techniques is crucial for emerging MEMS applications. Binarisation processing has previously been adopted, and frequently results in confusion caused by illegible image problems. This paper proposes a systematic approach by applying a colour charge-coupled device, in which the characteristics of light reflectance for different colours of light (at various wavelengths) are used, with the PatInspect method for image comparison and the Sobel gradient edge detection method for processing the structure boundary. The benchmark tests for the present AOI strategy revealed that the normal confusing defects were effectively detected as a result. Working cases are provided, showing that the detection efficiency, requiring only 8 s for each die in completing the identification process involved, is up to the industry standard.

CMOS MEMS Fabrication Technologies and Devices.

This paper reviews CMOS (complementary metal-oxide-semiconductor) MEMS (micro-electro-mechanical systems) fabrication technologies and enabled micro devices of various sensors and actuators. The technologies are classified based on the sequence of the fabrication of CMOS circuitry and MEMS elements, while SOI (silicon-on-insulator) CMOS MEMS are introduced separately. Introduction of associated devices follows the description of the respective CMOS MEMS technologies. Due to the vast array of CMOS MEMS devices, this review focuses only on the most typical MEMS sensors and actuators including pressure sensors, inertial sensors, frequency reference devices and actuators utilizing different physics effects and the fabrication processes introduced. Moreover, the incorporation of MEMS and CMOS is limited to monolithic integration, meaning wafer-bonding-based stacking and other integration approaches, despite their advantages, are excluded from the discussion. Both competitive industrial products and state-of-the-art research results on CMOS MEMS are covered.

The fluid flow through the related element system of technical device such as pipe–hydraulic resistance–pipe

In this paper the stationary flow through the pipe–hydraulic resistance–pipe element system have been investigated to determine how the liquid flow rate depends on the differential pressure applied to the system and the system geometry. The Navier–Stokes equations are solved numerically in axially symmetric geometry by the finite element method at irregular computational grid. It was found that the area of the non-linear pressure drop in the element system is localized at length of three inlet radii which allowed to build a model of arbitrary length of the system with a fixed length of hydraulic resistance. The pipe equivalent for the element system with hydraulic resistance have been constructed. A method for constructing a computer model for the element system, which later will enable to make calculations of whole technical device work in real time, have been proposed. This study is particularly relevant for the hydraulic elements of microelectromechanical systems, since it allows to optimize the geometry of the element system to obtain the necessary operating parameters of the technical device.

Micro/nano-mechanical structure fabricated by transfer printing

A fabrication of micro-electro-mechanical systems (MEMS) generally involves complicated conventional semiconductor processes. Simply micro/nano-structuring process is a technical issue on further wide range of MEMS application. This study proposes to apply transfer printing to fabricate a mechanical structure for MEMS elements. Some metals (Au, Cu and Ni) are previously deposited to be thin-films on a micro-ridged poly-dimethyl-siloxane (PDMS) stamp, while a micro-grooved SU-8 is prepared as a substrate. Contact-and-release process allows the metal thin-film to be locally transferred from the micro-ridges of stamp to the micro-grooved substrate. The transferred Au and Ni thin-films successfully form to be an ultra-thin fixed beam, “cross-linked structure”, of which the thickness is less than 100 nm. The fabricated structure is applicable to a nano-scale mechanical oscillator. The production yield of fixed beam increases with thin-film thickness and highly-dense of thin-film. The micro-roughness and hydrophobicity of stamp enhance the production yield of ultrathin fixed beam. These experimental results clearly indicate that the proposed process is dominated by an adhesion force between the stamp and the thin-film as well as the mechanical strength of the thin-film. Nevertheless, it is confirmed the transfer printing process is effective for a fabrication of MEMS element.

Reliability assessment of a MEMS microphone under mixed flowing gas environment and shock impact loading

In this work the reliability of a Micro-Electro-Mechanical Systems (MEMS) microphone is studied through two accelerated life tests, mixed flowing gas (MFG) testing and shock impact testing. The objective is to identify the associated failure mechanisms and improve the reliability of MEMS devices. Failure analyses are carried out by using various tools, such as optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS). Finite element analysis is also conducted to study the complex contact behaviors among the MEMS elements during shock impact testing. The predicted failure sites are in agreement with the experimental findings.

Dual-Polarized Partially Reflective Surface Antenna With MEMS-Based Beamwidth Reconfiguration

A partially reflective surface (PRS) antenna design enabling 1-bit dynamic beamwidth control is presented. The antenna operates at X-band and is based on microelectromechanical systems (MEMS) technology. The reconfigurable PRS unit cell monolithically integrates MEMS elements, whose positions are chosen to reduce losses while allowing a considerable beamwidth variation. The combined use of the proposed PRS unit cell topology and MEMS technology allows achieving low loss in the reconfigurable PRS. In addition, the antenna operates in dual-linear polarization with independent beamwidth control of each polarization. An operative MEMS-based PRS unit cell is fabricated and measured upon reconfiguration, showing very good agreement with simulations. The complete antenna system performance is rigorously evaluated based on full-wave simulations and the unit cell measurements, demonstrating an 18° and 23° variation of the half-power beamwidth in the E-plane and the H-plane, respectively. The antenna radiation efficiency is better than 75% in all states of operation.

Design and Electrical Characterization of Wafer-level Micro-package for GaAs-based RFMEMS Switches

Packaging of Micro-Electro-Mechanical system (MEMS) at wafer-level is one of the critical areas for its application, as the MEMS elements are delicate and can easily get damaged during wafer scribing or packaging process. We describe here a novel approach for wafer-level encapsulation of GaAs-based RFMEMS switches. EM simulation of the proposed microcaps has been carried out to study the effect of encapsulation on the switch performance. Both GaAs and Pyrex glass-based caps have been fabricated and the switches were encapsulated. The performance of the packaged switches has been characterized and the measured results show a close agreement with EM simulation.

Electrodeposition of Cobalt Nanowires

and DAESA concentration was 1 mL/L.Key Words : Cobalt, Electroplating, Nanowire, Additive, Super-fillIntroductionMetal nanowires have been widely studied for applicationin semiconductor devices and MEMS (Micro Electro-Mech-anical System) elements. Nanowires of magnetic materialssuch as nickel, iron, cobalt, and alloys of them are one of themost widely investigated structures because of their possibleapplications in high density magnetic recording media,sensor elements, and building blocks in biological transportsystems.

Biostability of an implantable glucose sensor chip

Surface materials of an implantable microelectronic chip intended for medical applications were evaluated with respect to their long-term stability in bio-environments. The sensor chip shall apply in a glucose monitor by operating as a microviscosimeter according to the principle of affinity viscosimetry. A monolithic integration of a microelectromechanical system (MEMS) into the sensor chip was successfully performed in a combined 0.25 μm CMOS/BiCMOS technology. In order to study material durability and biostability of the surfaces, sensor chips were exposed to various in vitro and in vivo tests. Corrosional damage of SiON, SiO2 and TiN surfaces was investigated by optical microscopy, ellipsometry and AFM. The results served for optimizing the Back-end-of-Line (BEoL) stack, from which the MEMS was prepared. Corrosion of metal lines could significantly be reduced by improving the topmost passivation layer. The experiments revealed no visible damage of the actuator or other functionally important MEMS elements. Sensor chips were also exposed to human body fluid for three month by implantation into the abdomen of a volunteer. Only small effects were observed for layer thickness and Ra roughness after explantation. In particular, TiN as used for the actuator beam showed no degradation by biocorrosion. The highest degradation rate of about 50 nm per month was revealed for the SiON passivation layer. These results suggest that the sensor chip may safely operate in subcutaneous tissue for a period of several months.

Device Process Integration: A New Device Fabrication Approach

Microelectromechanical systems (MEMS) devices have gained considerable attention in medical and automotive applications due to their vast advantages in fault detection. However, the cost for MEMS devices has been a challenge for the device manufacturing industry due to the final packaging of the devices. It is considered expensive compared with device fabrication in certain applications. Majority of MEMS devices are still housing traditional packaging methods due to difficulty in handling and yield loss. The advanced interconnect solutions based on thin silicon carrier and through silicon via are being developed to interconnect integrated circuits and other devices at high densities. Can such technologies be used for MEMS device interconnections? It is really a challenge for MEMS designers and engineers due to the MEMS elements present in the devices. In this paper, we present a device fabrication process to realize interconnects that are fabricated prior to the MEMS elements are defined and processed in the device wafer. The interconnects are filled by doped polysilicon and device wafers with such prefabricated vertical interconnects can be used as the starting wafers for any device processing including optoelectronic and MEMS. The process details and their characterization are elaborated along with the physical and electrical analysis of such interconnections.

Vacuum ultraviolet smoothing of nanometer-scale asperities of Poly(methyl methacrylate) surface

Smoothing of the nanometerscale asperities of a poly(methyl methacrylate) (PMMA) film using vacuum ultraviolet (VUV) with the wavelength λ = 123.6 nm was studied. The exposure time and the residual air pressure in a working chamber were varied during the process of VUV treatment. A nanostructured sur� face of PMMA film is used as a sample to be exposed. The nanostructured surface of the PMMA film was obtained by treating the initially smooth spincoated film in oxygen radiofrequency plasma. The degree of VUV exposure is estimated using changes in the morphology and roughness of the nanostructured surface, which were determined by atomicforce microscopy (AFM). Recognition of morphological surface features on the AFMimages and determination of main geometri cal characteristics of these features are performed by using virtual featureoriented scanning method. It is discovered by morphology and Fourier spectra that the nanostructured surface of the PMMA film is partially ordered. The developed VUV smoothing procedure can be used to treat the electronb eam, UV, and Xray sensitive PMMA resists, PMMA elements of micro� electromechanical systems, biomedical PMMA implants, as well as to certify nanotechnological equipment incorporating UV radiation sources. DOI: 10.1134/S1027451010010015

Characterization of Stiction Accrual in a MEMS

Stiction remains one of the chief reliability concerns for microelectromechanical systems (MEMS) devices. In this paper, we quantify and analyze the rate of accrual of stiction in a standard MEMS device under a set of controlled temperature and humidity splits. An accelerated aging system was employed to more rapidly induce stiction in the MEMS. Optical characterization techniques were used to study the progression of stiction. The stiction accrual was quantified in terms of stiction equivalent energy, which provides compensation for mechanical fatigue in the devices due to long periods of operation. The fastest accrual of stiction was seen in the 90degC, 80% relative humidity (RH) split with approximately 80% of the MEMS elements failing within 4.4 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> cycles (10 h) with 2.7 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-14</sup> Joules of stiction equivalent energy while the 60degC, 20% RH showed the least stiction accrual rate with less than 2% failure for 2.26 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cycles (1500 h). In general, the stiction was seen to increase with an increase in humidity while mechanical fatigue showed an increase with an increase in temperature. Atomic force microscopy topography imaging was used to assess physical wear at the contacting areas. The results revealed that there were not any discernable changes in the surface profile due to long periods of actuation.

Review of Device and Reliability Physics of Dielectrics in Electrostatically Driven MEMS Devices

After decades of improving semiconductor-device reliability, dielectric failure rates resulting from surface-charge accumulation, dielectric breakdown, and charge injection have been reduced to an almost imperceptible range. However, the influence of dielectric properties and behavior on device performance in microelectromechanical systems (MEMS) is still poorly understood and a substantial contributor to device failure. The difference is primarily due to two factors. First, the characteristic length scale and electrical stress of dielectrics in MEMS are often an order of magnitude or more than in semiconductor devices. Lateral dimensions of tens of micrometers increase the probability of including defect sites, and higher applied voltages increase the probability of dielectric breakdown. Second, dielectrics in MEMS are often designed to fulfill multiple functions, often with no equivalent in semiconductor devices. The use of dielectrics as structural material puts substantial emphasis on material properties other than the classic dielectric properties. The use of freestanding elements in MEMS causes large interfacial surfaces between the dielectric and air which in turn provides various charge trap mechanisms. The same surfaces, when allowed to come in contact, could lead to a failure mechanism called stiction, where the surfaces cannot be separated after contact. This paper provides a review of the most prevalent failure mechanisms resulting from the use of dielectrics in electrostatically driven MEMS devices and methods to characterize both their material properties and impact on reliability performance.

Practical applications of the chemical strain effect in ionic and mixed conductors

Abstract The chemical strain effect in solids is the deviation from linear elasticity due to the association and dissociation of point defects. Although to date this effect has been observed and studied only in Ce0.8Gd0.2O1,9, one may expect that it will be found in other ionic and mixed conductors containing a large concentration of point defects. In this work, some practical applications of materials exhibiting the chemical strain effect are discussed. Based on the example of Ce0.8Gd0.2O1,9, mechanical structures built from these materials should exhibit exceptional mechanical stability and are therefore very attractive for use as components of solid oxide fuel cells (SOFC) or other devices subjected to large and frequent temperature variations. The ability of these materials to withstand large strain without accumulating large stress also makes them potentially useful as flexible elements in micro-electromechanical systems (MEMS).

Microfriction analysis of novel two-dimensional electrostatic comb device

Constructed by a two-dimensional micro-electrostatic comb actuator fabricated by bulk micromachined process, a novel test device on chip was designed to study the phenomena of the microfrictions in the side wall between movable micro-electromechanical system elements. The general analytic expressions of the applied voltages, displacement, the static friction coefficient and the geometry parameters were established. It was found that the displacement was linear to Uy2, so the friction coefficient could be obtained by fitting them. And larger nb and l2 could help to decrease Uy and to increase the displacement.

Stress control structures for microelectromechanical systems using structural mechanics approach

A method of stress control in microelectromechanical systems (MEMS) devices is presented that consists of creating counterbalancing structures to position stressed layers at the neutral plane of the device, eliminating the bending momentum acting on the device. Upon metallization, many MEMS elements such as silicon membranes show substantial bow under the stress developed as a result of the difference in the thermal expansion coefficients of a metal and silicon. The proposed membranes with the counterbalancing structures remain flat in the entire test temperature range (25–150°C). The method gives material-independent solution to stress-induced curvature problems in a variety of ultrathin devices.