Microelectromechanical Structure Research Articles

Piezoelectrically actuated ultrananocrystalline diamond tip array integrated with ferroelectric or phase change media for high-density memory

A compact large density memory piezoactuated storage device and process for its fabrication provides an integrated microelectromechanical (MEMS) and/or nanoelectromechanical (NEMS) system and structure that features an integrated large density array of nanotips made of wear-resistant conductive ultrananocrystalline diamond (UNCD) in which the tips are actuated via a piezoelectric thin film integrated with the UNCD tips. The tips of the special piezoactuated storage device effectively contact an underlying metal layer (top electrode) deposited on a polarizable ferroelectric layer that is grown on top of another metal layer (bottom electrode) to form a ferroelectric capacitor. Information is imprinted in the ferroelectric layer by the polarization induced by the application of a voltage pulse between the top and bottom electrodes through the conductive UNCD tips. This integrated microelectromechanical (MEMS) and/or nanoelectromechanical (NEMS) system and structure can be efficiently used to imprint data in the ferroelectric layer for memory storage with high density in the gigabit (Gb) to terabit (Tb) range. An alternative memory media to the ferroelectric layer can be a phase change material that exhibits two orders of magnitude difference in electrical resistance between amorphous and crystalline phases.

Field-Concentrator-Based Resonant Magnetic Sensor With Integrated Planar Coils

This paper reports on a highly sensitive resonant magnetic microsensor with a shift of the mechanical resonance frequency f res depending quadratically on the magnetic flux density B to be measured. The sensor combines an electrostatically driven micromechanical resonator with a geometrically optimized planar magnetic concentrator with two narrow gaps. Sensitivities df res/dB of several megahertz per tesla are achieved without complex feedback and modulation electronics. When the device is operated in a switched auxiliary magnetic field using two integrated planar coils, the raw parabolic response of the sensor is translated into a resonance frequency difference proportional to B . For a coil current of plusmn120 mA, the device offers a sensitivity of 1.91 MHz/T and a resolution of 1.3 muT . In vacuum, a resolution of 400 nT is demonstrated. With these performance numbers, applications such as a microelectromechanical (MEM) compass for the measurement of the Earth's magnetic field can be envisaged. The fabrication process of the microsensor combines the following: 1) the micromachining of a silicon-on-insulator substrate for the MEM structure; 2) the attachment and structuring of a thin amorphous soft magnetic ribbon for the magnetic concentrator; and 3) the UV-laser ablation for the micropatterning of the concentrator gaps. Thermal effects due to high coil currents were analyzed in detail, as they play an important role in the reported microsensor design.

Micro-electroporation of mesenchymal stem cells with alternating electrical current pulses

Micro-electroporation is an electroporation technology in which the electrical field that induces cell membrane poration is focused onto a single cell contained in a micro-electromechanical structure. Micro-electroporation has many unique attributes including that it facilitates real time control over the process of electroporation at the single cell level. Flow-through micro-electroporation expands on this principle and was developed to facilitate electroporation of a large numbers of cells with control over the electroporation of every single cell. However, our studies show that when electroporation employs conventional direct current (DC) electrical pulses the micro-electroporation system fails, because of electrolysis induced gas bubble formation. We report in this study that when certain alternating currents (AC) electrical pulses are used for micro-electroporation it becomes possible to avoid electrolytic gas bubble formation in a micro-electroporation flow-through system. The effect of AC micro-electroporation on electrolysis was found to depend on the AC frequency used. This concept was tested with mesenchymal stem cells and preliminary results show successful electroporation using this system.

Bimorph mems devices

A micro-electromechanical dimensioned bimorph structure includes a first element layer structure, and a second element layer structure. The element layer structures are provided in various combinations, including piezoelectric/piezoelectric, antiferroelectric/antiferroelectric or antiferroelectric/piezoelectric. The layer thickness of the element structure is less than 100 μm. A bonding layer bonds the first element structure directly to the second element structure, and the bonding layer thickness is less than 10 μm. The bimorph structure can be made in various forms including a cantilever or a diaphragm. Microfluidic devices using the bimorph structures may also be constructed.

Electromechanical contact of microelectromechanical structure

Contact deformation of a membranelike microelectromechanical structure subjected to uniform mechanical pressure was analyzed by considering the effect of electric stress. Using the membrane theory, a closed-form solution of the contact deformation in an electric field was obtained. The contact size increases with the increase in the electric field intensity and is a linear function of the electrical voltage between the membrane and the rigid substrate if the membrane is only subjected to an electrical stress. Using the energy criterion, the adhesive contact between the membrane and the substrate in an electric field was also discussed. A lower bound of the contact size was obtained as a function of the electric stress and the adhesion energy.

Thin-film silicon MEMS DNA sensors

Thin-film microelectromechanical molecular sensors are fabricated at temperatures below 110°C on glass substrates. The microelectromechanical structure consists of a surface micromachined bilayer bridge of phosphorous-doped hydrogenated amorphous silicon and aluminum. There is specific binding of DNA to hydroxylated bridge surfaces through silanization chemistry. Microbridges are electrostatically actuated and the resonance frequency measurements are performed in vacuum in the initial state after fabrication, after surface functionalization and after DNA immobilization. The sensor is able to detect the functionalization molecular layer and the DNA molecules attached to the surface through a shift in its resonance frequency.

Measurement of residual stresses in micromachined structures in a microregion

The use of a focused ion beam equipment is reported to find out the in-plane residual stress value of a microelectromechanical system structure by performing a local stress release. The ion beam column is used to mill stress-release slots of a few microns, whereas the scanning electron column captures micrographs of the milled area before and after the stress release process. The displacement component perpendicular to the slot is obtained from digital image correlation analysis of the captured high-resolution micrographs. The fitting of the experimental results with an analytical model together with the independent determination of the Young’s modulus allows one to find the residual stress value of the layer under study to a very good accuracy.

A diffraction-based optical method for the detection of in-plane motion of Lamb waves

This paper describes a laser optical technique that allows the detection of in-plane motion of Lamb waves. This interference-based laser optical technique includes a tiny square indentation with a width of about 30 micron on the sample surface and a relatively simple optical arrangement. The current technique is applied for the detection of in-plane motions of Lamb waves propagating in a 70-micron thick brass plate. Measurement of So mode dominated by in-plane motion in the low fd (frequency times thickness) regime is successfully demonstrated with the current technique. With the indentation replaced by a microreflector in a microelectromechanical (MEMS) structure, this technique is applicable for the detection of in-plane motion in MEMS structures.

Silicon nanoelectronics and beyond: An overview and recent developments

This year marks the 40th anniversary of the invention of the first beam-lead device by Lepselter et al. Lepselter and coworkers proposed a method of fabricating a new semiconductor device structure and its application to high-frequency silicon switching transistors and ultra-high-speed integrated circuits. Beam-lead technology, also known as air-bridge technology, has established itself for its unsurpassed reliability in high-frequency silicon switching transistors and ultra-high-speed integrated circuits for telecommunications and missile systems. The beam-lead device became the first example of a commercial microelectromechanical structure (MEMS). Since its inception, MEMS has taken advantage of the evolving silicon technology, resulting in today’s nano-electromechanical structure and nano-optomechanical structure. In this paper, an overview of recent developments of silicon nanoelectronics is presented.

Thin Film Silicon Microbridges for DNA Detection

AbstractThin-film MEMS molecular sensors are fabricated at temperatures below 110°C on glass substrates. The microelectromechanical structure consists of a surface micromachined bilayer bridge of phosphorous-doped hydrogenated amorphous silicon and aluminum with a patterned SiO2 layer on the top. Specific binding of DNA to functionalized SiO2 on the bridge is confirmed using fluorescence microscopy. Microbridges are electrostatically actuated and the resonance frequency measurements are performed in vacuum in the initial state after fabrication, after the chemical functionalization of the SiO2surface and after DNA immobilization. The sensor is able to detect the functionalization molecular layer, the cross-linker molecular layer, and the DNA molecules attached to the surface through a shift in its resonance frequency. The binding of molecules to the surface results in a shift of the resonance frequency due to contributions from surface stresses and mass loading.

Recovering image resolution in reconstructing digital off-axis holograms by Fresnel-transform method

The resolution of amplitude and phase reconstruction of images from digital holograms by the Fresnel transformation method is limited by the pixel width in the reconstructed image plane. The reconstruction pixel depends on distance, wavelength, and number of pixels in the hologram. The spatial frequencies, in the reconstructed image, are band limited by the size of the reconstruction pixel. Undersampling can occur, in the image plane, in the reconstructed amplitude and/or wrapped phase maps. Recovery of reconstructed undersampled spatial frequencies, is possible by the fictitious enlargement of the digital hologram. Correct profile reconstruction of a silicon microelectromechanical structure is demonstrated, applying the proposed method.

Study of electrothermal V-beam actuators and latched mechanism for optical switch

We present new optical switch devices based on a bi-stable microelectromechanical structure driven by two sets of one-directional movable electrothermal V-beam actuators. In conjunction with the movement translation link structure, or T-shaped end of the switch body, and buckle springs, the first V-beam actuator set can drive the in-plane moving reflective shutter from one rest position to the second stable position, while the second V-beam actuator set is able to drive the reflective shutter back to the original rest position. The transmission state of the optical switch device could be one of these bi-stable positions, and the switching state will be the counter position. Thus, the bi-directional motion capability is realized by using a pair of V-beam actuator sets with opposite directions of motion. We have optimized the design of V-beam actuators according to the application requirements. The preliminary results prove the application feasibility.

Characterization of Bi-Stable Micromechanism Based on Buckle Spring and Electrothermal V-Beam Actuators

We present a novel bi-stable microelectromechanical structure driven by a pair of one-directional movable electrothermal V-beam actuators for applications need latch functions, like optical switch and relay. In conjunction with the T-shaped end and buckle spring, the first V-beam actuator set can drive the in-plane moving reflective mirror from transmission state to switching state, while the second V-beam actuator set is able to return the reflective mirror from position of switching state to position of transmission state. Thus the bi-directional motion capability is realized by using a pair of V-beam actuator sets with opposite moving direction. The preliminary results prove its application feasibility.

Long Wavelength-Tunable VCSELs With Optimized MEMS Bridge Tuning Structure

In this letter, we present the first demonstration of a long wavelength-tunable vertical-cavity surface-emitting laser (VCSEL) using a monolithically integrated bridge tuning microelectromechanical system structure. The use of such a tuning structure allows for better wavelength tuning repeatability and wider tuning range as compared to cantilever-based tunable VCSELs. The devices show tuning ranges over 22 nm with peak output power of 1.3 mW in continuous-wave operation at 15/spl deg/C. The bridge structure has a mechanical resonant frequency of 80 kHz. The transmission test through 300-km single-mode fiber (SMF-28) using the tunable VCSEL under mechanical vibration below 10 KHz and 10-G acceleration shows little bit-error-rate degradation.

The design and assembly of surface-micromachined optical switch for optical add/drop multiplexer application

An assembly process including: flip-chip bonding, microelectromechanical (MEMS) structure release, and atomic layer deposition (ALD) is proposed to integrate a surface micromachined optical switch for optical add/drop multiplexer (OADM) applications. In the current optical switch designs, pre-stressed beams were used to pop up the micromirror and an electrode (substrate) under the beams was designed to perform ON/OFF function of the optical switch. In order to achieve desired popped-up angle for precise optical switching, a flip-chip bonding technique is applied to a mechanical stopper with an accurate joint height that can be used to constrain the movement of the micromirror. A conformal thin layer of dielectric material (Al/sub 2/O/sub 3/) coated on the surfaces of device through an ALD coating process is used to improve vertical actuation force, as well as electrical isolation. Experiments indicate that the micromirrors fabricated by the present assembly process can achieve desired angle that meet the requirements of the proposed OADM configuration.

Single-pole-double-throw switch based on toggle switch

A single-pole-double-throw (SPDT) switch based on the toggle switch, a new type of radio frequency (RF) microelectromechanical (MEMS) switch structure for low voltage actuation, high broadband application and enhanced power capability, is presented. Electromagnetic simulation results are discussed and the fabrication process and measurement results are given. The SPDT switch exhibits low insertion loss (<0.5 dB at 20 GHz) and high isolation (>28 dB at 30 GHz).

Controlled placement of an individual carbon nanotube onto a microelectromechanical structure

We report on the precise placement of a single carbon nanotube (CNT) onto a microlectromechanial system (MEMS) structure. Using a hybrid atomic force microscope/scanning electron microscope (AFM/SEM) system, an individual multiwalled CNT was retrieved from a cartridge by the AFM tip, translated to a MEMS device, and then placed across a gap between an actuating and a stationary structure. Progress toward a resistance versus stress/strain measurement on a CNT will be discussed, including SEM images of a MEMS structure we have designed specifically for such a measurement.

MEMS and Si micromachined circuits for high-frequency applications

RF micromachining and microelectromechanical structure (MEMS) technology promise to provide an innovative approach in the development of effective and low-cost circuits and systems. This technology is expected to have significant application in the development of low-cost antenna arrays and reconfigurable apertures, due to its potential to support novel systems architectures. This paper presents a brief history and the state-of-the-art in the development of RF MEMS devices, with primary emphasis on switches and Si-micromachined circuit components for use in high-performance high-density on-wafer packaged circuits.

Controlled placement of an individual carbon nanotube onto a microelectromechanical structure

Controlled placement of an individual carbon nanotube onto a microelectromechanical structure

Water Dispersible Silanes for Wettability Modification of Polysilicon

The objective of this research has been to develop the chemistry and techniques for the application of hydrophobic coatings on polysilicon substrates from aqueous media with the ultimate goal of applying these techniques for preventing or reducing release as well as in use stiction in microelectromechanical structure devices. In this paper, the results obtained from a chemical system consisting of a water dispersible silane and a cationic surfactant are presented. Key experimental variables that have been investigated are the concentration of reactive silane and cationic surfactant, type of oxidation pretreatment, pH of the silane dispersion, and curing temperature. © 2001 The Electrochemical Society. All rights reserved.