Metal Cantilever Research Articles

Nano-Electromechanical Displacement Sensing Based on Single-Walled Carbon Nanotubes

We present a nano-electromechanical system based on an individual single-walled carbon nanotube (SWNT) demonstrating their potential use for future displacement sensing at the nanoscale. The fabrication and characterization of the proposed nanoscaled transducer, consisting of a suspended metal cantilever mounted on top of the center of a suspended SWNT, is presented and discussed. The displacement of the nanoscale cantilever is detected via the electromechanically induced change in conductance of the strained SWNT. A relative differential resistance sensitivity (for a metallic SWNT) of up to 27.5%/nm was measured and a piezoresistive gauge factor of a SWNT of up to 2900 was extracted.

Metallic NEMS components fabricated from nanocomposite Al–Mo films

We have fabricated fully released nano-electro-mechanical system (NEMS) cantilevers ofvarious geometries from metallic alloy nanocomposite films. At thicknesses of 4.3 and20.0 nm, these are the thinnest released metal cantilevers reported in the literatureto date. Such device dimensions are very difficult to achieve using conventionalmetal films. We were able to overcome this limitation by using room-temperatureco-sputtering to synthesize nanocomposite alloy films of Al–Mo. A systematicinvestigation of microstructure and properties as a function of Mo content resulted in anoptimum film composition of Al–32 at.%Mo with a unique microstructure comprisinga dense distribution of nano-scale Mo crystallites dispersed in an amorphousAl-rich matrix. These films were found to exhibit unusually high nanoindentationhardness and a very significant reduction in roughness compared with pure Al,while maintaining resistivity in the metallic range. A single-anchored cantilever5 µm long, 800 nm wide and 20 nm thick showed a resonance frequency of 608 kHz, yielding aYoung’s modulus of 112 GPa, in good agreement with a reduced modulus of 138 GPameasured by nanoindentation.

High voltage thin film transistors integrated with MEMS

The integration of high voltage thin film transistors with a released MEMS process onto the same substrate is demonstrated. High voltage transistors capable of 800 V actuation voltage are used to actuate released metal cantilevers and membranes with a low temperature fabrication process (<350 °C) on glass substrates. This demonstration is an important step towards realizing MEMS arrays with integrated addressable drivers for applications which require high voltage, such as electrostatic MEMS devices on low temperature substrates (e.g. glass or flex). High voltage thin film transistors (HVTFT) provide the unique property of easily controlling high voltage (50–800 V) using a standard input voltage range (0–20 V). To our knowledge, this is the first demonstration of integrated HVTFT actuating released MEMS structures.

Finite-Element Analysis of the Frequency Response of a Metallic Cantilever Coupled With a Piezoelectric Transducer

This paper is devoted to modeling the dynamic response of an electromechanical system consisting of a piezoelectric transducer glued on part of the upper surface of a metallic cantilever. The piezo works both as vibration sensor and as actuator, and the system is the basis of many vibration-control devices of current interest. A three-dimensional (3D) finite-element method (FEM) model that reproduces the physical system is proposed, and its advantages with respect to an analytical approach and to one-dimensional (1D) and two-dimensional (2D) FEM models are discussed. In sensor mode, the frequency response in terms of the voltage at the electrodes is drawn; while in actuator mode, the frequency response of acceleration and displacement at the free end of the cantilever is calculated. The 3D model has been verified through the comparison with the results from the experiment carried out at the University of L'Aquila, Italy. Furthermore, experimental inaccessible quantities such as stresses at the piezo-cantilever interface are computed in both modes as a preliminary step in the study of delamination phenomena and their impact on the performance of the system in vibration-control applications.

Modeling microwave behaviors of series cantilever MEMS switch

Simple and effective model is demanded which enables the design and structural optimization of the microwave MEMS switch efficiently. For this purpose the microwave behaviors of series metal cantilever MEMS switch have been modeled by “simple” circuit in this paper. The microwave characteristics have been calculated and compared with the experiment data based on the developed model. The results show that the microwave characteristics of series metal cantilever MEMS switch can be described very well with this model. Based on this model, the influences of the structural parameters of the switch on the microwave characteristics have been discussed extensively.

Reversible electrostatic control of micromechanical structure tunneling characteristics

We report on a submicrometer thick, surface nanomachined curvature-free metallic cantilever with an insulated contact tip applied as a micromechanical contact tunneling device. A technique for modulating the tunneling current characteristics based on an elastic compressible contact surface model is demonstrated by changing the effective tunneling area for asperities via change in electrostatic pressure. The electrostatic pressure comes from the excess potential applied on the gate after the cantilever has been switched on. This allows the gate voltage to independently modulate the characteristics of the tunneling barrier that the electrons must cross in a reversible manner. Preliminary measurements show a reasonably good agreement with the Hertzian contact force law.

Niagara Cantilever

The first modern metal cantilever bridge in the United States, using erection methods that were to be utilized in most future cantilever bridges, was by C. C. Schneider across the Niagara Gorge in 1883. The Niagara, saw in order, John Roebling’s Railroad Suspension Bridge, Samuel Keefer’s Honeymoon Suspension Bridge, Edward Serrell’s Lewiston-Queenston Suspension Bridge, Schneider’s cantilever, Leffert Buck’s arch bridge at the falls as well as Buck’s arch built under Roebling’s suspension bridge. Schneider’s bridge had a useful life of over 40 years during a period when rolling stock on the railroads was increasing rapidly. The speed of erection of a new style bridge coupled with its performance makes it one of the most innovative and significant bridges built in the world at the time.

Editorial

Electrical nanoprobing inside scanning electron microscopy (SEM) systems has become a routinely used characterization technique for electrically measuring prototypes of the most advanced nanoelectronics device structures. Tungsten wire needles with a sharpness of about 50–100 nm are commonly used as probe tips in these measurements. They suffer unfortunately from tip oxidation effects and need to be initialized. Moreover, they are too soft to directly probe on semiconductor materials such as Si and Ge. Therefore, harder probe tips are required which can withstand high pressures (in GPa range) and oxidation. In order to meet these requirements, we have developed doped diamond tips and integrated them into metal cantilevers. They have an in-plane geometry which allows direct visibility in the SEM system of both the area to be contacted and the tip apex. Furthermore, the probes are mounted at the end of a metal wire which ensures compatibility with existing nanoprobing systems and allows for convenient probe handling. This paper describes the probe concept and discusses the probe fabrication process in detail. Manufactured probes are presented and their suitability for measurements on a Ge calibration structure is demonstrated. Our work shows that the developed diamond nanoprobes overcome the disadvantages of existing tungsten wire probes and enable the probing of semiconductor materials.

Development of a microwave microelectromechanical systems switch

A novel microwave microelectromechanical systems switch with a coplanar waveguide structure has been developed. The switch consists of a freestanding metallic cantilever and an electromagnet. A permanent magnetic film was deposited on top of the cantilever. By supplying a dc current to the electromagnet, the magnetic field generated would attract or repel the permanent magnetic film on top of the cantilever, causing it to make or break contact with a bottom electrode. An all-electrodeposition method has been used to improve the mechanical properties of the cantilever. The deposition process of the cantilevers has been optimized to improve the adhesion of the cantilever to the substrate and to minimize the switching dc power. Using commercially available electromagnet, a voltage of 2 V (dc power of about 15 mW), is sufficient to actuate the switches. Similar switching power was observed using an improved hand wound electromagnet. The on-state dc resistance of the switches is generally less than 2 Ω. At 10 GHz, the on state insertion loss due purely to the switches is about 0.1 dB and off state isolation is greater than 20 dB. Repeated operations of the switches showed no sign of performance degradation in a conventional room environment.

Sputtered Tantalum as a Structural Material for Surface Micromachined RF Switches

Micro-electro-mechanical systems (MEMS) are batch fabricated miniature systems with both electrical and non-electrical (e.g. mechanical) functionalities. Examples of such MEMS are miniature mechanical switches, acceleration sensors, gyroscopes etc… RF-MEMS devices are an emerging class of MEMS devices used for RF signal processing in telecommunication applications. For example, metal surface micro-machined switches are a promising alternative for current solid state switches or mechanical reed relays due to their potential for miniaturization, integration and improved performance. RF-MEMS switches normally consist of a metal bridge or cantilever electrode, which can be pulled in towards a bottom electrode by electrostatic forces [1]. The bridge material is often chosen to be Al or an Al-alloy because of its low resistivity [2]. During each switch cycle the metal top electrode goes through a mechanical stress cycle. These successive stress cycles might lead to reliability problems such as fatigue and/or creep. This is certainly the case for Al, which is known to have a low creep resistance [3]. Several alternatives have been investigated as alloying Al with other materials [4], or replacing Al with metals having better mechanical properties, specifically low creep, such as Tungsten (W) or Tantalum (Ta). Especially high melting point materials are interesting alternatives as the creep resistance is expected to increase with the melting point [5]. If we consider surface micromachined RF switches, the pull in voltage and sheet resistance are two important parameters that should be taken into consideration while selecting the switch material. In general, the pull in voltage depends on mean stress, lateral dimensions, layer thickness and Young's modulus. In case of stress free films, a material having a low Young's modulus is preferred for low pull-in voltage. As W is known to have high intrinsic stress [6], and a higher Young's modulus compared to Ta [7], it is instructive to consider Ta as a structural material for surface micromachining applications.

Integrating diamond pyramids into metal cantilevers and using them as electrical AFM probes

Si cantilevers with conductive diamond pyramids have recently shown the highest dynamic range in scanning spreading resistance microscopy (SSRM). The use of metal cantilevers would significantly reduce fabrication costs because fewer process steps are required. Furthermore, smaller diamond pyramids, which are commonly sharper, could be used. Therefore, we have developed a procedure for metal cantilevers with diamond pyramids based on a peel-off concept which gives a yield of ∼70%. This paper discusses the fabrication of sharp diamond pyramids and their integration into metal cantilevers. SSRM measurements on Si device structures are presented. A peel-off procedure with higher yield is currently under development.

Electrical characterization of single-walled carbon nanotubes with Scanning Force Microscopy

In this work, a study of the possibilities of the Scanning Force Microscope (SFM) for studying transport properties of carbon nanotubes (CNTs) was done. Single-walled carbon nanotubes were deposited on SiO 2. Afterwards, using a mask, the surface was covered with gold, so that some of the carbon nanotubes in the surface stick out underneath the gold. In those areas, topographies and electrical measurements with metallic cantilevers have been carried out. We have developed simultaneous force vs. distance and current vs. distance data along the uncovered length of the nanotubes. In addition, current vs. voltage data was acquired at the maximum loading force during the indentation process. We found that the current rises abruptly when the tip touches the carbon nanotube and it is compared with similar experiments on the gold surface by the carbon nanotube.

Terahertz field characterization using Fabry–Perot-like cantilevers

We show that a Fabry–Perot-like tunneling cantilever consisting of two parallel thin metallic cantilevers joined at their free ends is able to sense the power of an incoming terahertz (THz) field. An array of such microstructures, with linearly varying distances between the two parallel cantilevers, can measure simultaneously the power and frequency of the THz field in the bandwidth 1.2–58 THz.

A metallic microcantilever electric contact probe array incorporated in an atomic force microscope

We present the realization and performance of a multiprobe microcontactor made of an array of metallic microcantilevers inserted in an atomic force microscope (AFM). This instrument permits simultaneous AFM imaging and electrical characterization of nanoscale devices. It is therefore well adapted for future generations of molecular devices. The probes are 2-μm-wide metallic cantilevers that are brought in contact with 3 μm×3 μm metallic pads of a nanocircuit using a nanopositioning table. The performance of the instrument, tested on mesoscopic metallic wires and carbon nanotubes, shows that the reproducibility of the electrical contact between the probes and the circuit is better than 99.2%.

Microfabricated small metal cantilevers with silicon tip for atomic force microscopy

Atomic force microscopy with small cantilevers is faster due to higher resonant frequencies and has a lower noise level. We report a new process to microfabricate small metal cantilevers with integrated silicon tips. This process is used to fabricate gold cantilevers that are 13-40-/spl mu/m long, 5-10-/spl mu/m wide, and 100-160-nm thick. The tip is first formed at the free end of a sacrificial oxide cantilever. The cantilever layer of the desired metal is then deposited on the nontip side of the sacrificial oxide cantilever. The oxide layer is removed to form the cantilevers with tips on them in a batch process. The highly stressed cantilevers are rapid thermal annealed for 60 s at 300/spl deg/C to relieve the stress. The gold cantilevers have been characterized through their thermal spectra and used to image in tapping mode. The process can be used, not only for gold, but also for any metal or compound that can withstand removal of sacrificial oxide cantilevers.

Anelastic Creep Phenomena in Thin Metal Plated Cantilevers for MEMS

ABSTRACTDuring the past several years, we have developed high displacement sensitivity tunneling accelerometers using surface micromachining and metal electroplating techniques. These devices consist of a Au tunneling tip fabricated below a 1-2 μm thick metal cantilever beam of electroplated Ni or Au. A thin film of e-beam evaporated Au on the underside of the cantilever serves as the tunneling counter electrode. In operation, a 100mV bias is applied across the tunneling gap. A larger turn-on voltage is also applied between the cantilever and a control electrode, located on the substrate, to deflect the cantilever and maintain a constant tunneling current of 1 or 10 nA. Typical deflections of the end of 100 μm-long and 250 μm-long cantilevers are 0.5μm during operation. We have observed that the turn-on voltage decreases over time for most devices with a larger drop observed for the Au cantilevers. In all cases, the initial decay of the turn-on voltage was almost completely recoverable after the device was turned off for 24 hrs. This decay was not found to be strongly dependent on the magnitude of the tunneling current, but could be significantly reduced by pre-stressing the cantilever before operation. Finally, a vacuum anneal at 100°C influences the measured temperature dependence of the turn-on voltage. The observed effects appear to be consistent with fatigue and creep phenomena in the cantilevers. These effects are reversible at room temperature and are dependent on the stress and temperature history of the devices. A comparison is made between metal plated and all-Si structures.

Large deformations of rigid-viscoplastic cantilevers under impulsive loading

The problem of a ductile metal cantilever structure (not necessarily initially straight) subjected to dynamic loads leading to deformations of the order of the dimensions of the structure is considered. The material is treated as rigid-viscoplastic; in this idealization elastic effects are ignored, and the dependence of the yield stress on the rate of strain is taken into account. The problem is first analysed as one of impulsive loading, using the concepts of the mode approximation technique. A new algorithm for the determination of mode shapes is presented, together with an algorithm for the time integration of the motion in which the geometry of the structure is updated. Applications of the method are described for impulsive loading, and extended to the pipe-whip problem where the loading is in the form of a pulse which acts in the direction of the tangent at the tip of the cantilever structure at each instant.

Centripetal accelerometer

A force transducer can easily be made by attaching a strain gauge to a metal cantilever and applying a force F to the free end (Kuhl). A mass m fastened to the free end of this cantilever makes an accelerometer. This can be mounted on a turntable at a radius R to provide a convincing demonstration of the centripetal force relationship F=m nu 2/R=mR omega 2 where nu is the tangential velocity and omega is the angular velocity.

A Cantilever Mounted Resilient Pad Gas Thrust Bearing

A gas thrust bearing consisting of flat sector shaped pads mounted on resilient metallic cantilever beams is described and analyzed. Compliance and stiffness of the bearing assembly are discussed and the effects of bearing design parameters on performance are shown. A design example is presented and a special case where zero axial movement of the runner can be obtained is pointed out.

Dos obras de Welton Becket (EE. UU.)

Nassau Veterans Memorial Coliseum . It is oval in shape and can house sports competitions and gymnastic events, musical productions, circuses and it can be used to show films as well as for expositions, meetings and conventions. From the plaza, entrance is achieved through a mirrored gallery circumscribing the building and that communicates with the interior corridor that sorrounds the court. It holds more than 11,000 people and there are telescopic platforms that unfold at court-level and portable chairs that increase this capacity to a total of 16,500. The building is covered by a steel frame, limited on the outside by a wide metallic cantilever. The whole system is supported by 32 large concrete columns, in U shape, that show on the exterior facade. The Coliseum has theatrical lighting and sound installations which adapt it to each of the different types of events the building can be used for. Under the adjacent plaza a large underground exhibition hall has been set up to serve the Coliseum. More than 5,000 m 2 in area, this space can be subdivided by folding panels as needed. Bullock’s Shopping Center in Northridge . The main feature of this large department store is that it has been treated entirely as a stage for the various goods that are on display there. Moreover, its design has broken with the traditional box shape typical of this type of building, replacing it with a polyhedral volume for a more dynamic effect. Great importance has been given in this building to architectonic spaces as well as the lighting system and the decor. Thus, the different areas are given more or less importance by means of the various lighting effects, while the decoration and architectonic forms differentiate and limit the various display areas. A system of ornaments and mobile partitions gives the unit great flexibility thus permitting modifications as per the needs of each particular moment.