Search

We report on a method to reproducibly batch fabricate single-crystal silicon cantilevers with dimensions an order of magnitude smaller than conventional cantilevers, i.e., with lengths between 10 and 35μm, a width of 4μm, and a thickness of 0.2μm. The cantilevers are attached to support chips specially tailored for use in a scanning force microscope. The resonance frequencies are0.2 – 2 MHz, the spring constants about 0.05−1N∕m, and the quality factors 1.5−3.0×104. The resulting thermal force noise is 1−2×10−16N∕Hz at room temperature in vacuum. These cantilevers allow an enhancement of the measurement speed of more than one order of magnitude, and 2−5× better force sensitivity. After annealing in ultrahigh vacuum and measuring at liquid helium temperature, the thermal force noise of these cantilevers is expected to be further reduced down to 10−18N∕Hz.

We present a hybrid probe for scanning near-field optical microscopy (SNOM), which consists of a micromachined photoplastic tip with a metallic aperture at the apex that is attached to an optical fiber, thus combining the advantages of optical fiber probes and micromachined tips. The tip and aperture are batch fabricated and assembled to a preetched optical fiber with micrometer centering precision. Rectangular apertures of 50 nm X 130 nm have been produced without the need of any postprocessing. Topographical and optical imaging with a probe having an aperture of 300 nm demonstrate the great potential of the photoplastic probe for SNOM applications. © 2001 American Institute of Physics.

A new probe made entirely of plastic material has been developed for scanning probe microscopy. Using a polymer for the cantilever facilitates the realization of mechanical properties that are difficult to achieve with classical silicon technology. The new cantilever and tip presented here are made of an epoxy-based photoplastic. The fabrication process is a simple batch process in which the integrated tip and the lever are defined in one photolithography step. The simplicity of the fabrication step, the use of a polymer as material, and the ability to reuse the silicon mold lead to a soft low-cost probe for scanning force microscopy. Imaging soft condensed matter with photoplastic levers, which uses laser beam deflection sensing, exhibits a resolution that compares well with that of commercially available silicon cantilevers.

Multiple single-lever probes for scanning force microscopy arranged in a cassette design and made of a low-stiffness photoplastic material have been developed and successfully tested by imaging DNA molecules. The new concept consists of a column of a one-dimensional array of cantilevers with integrated tips, the first of which is used for imaging and the others are spares in case the first one becomes degraded. When this happens, the lever is mechanically removed from the chip so that the next spare becomes ready for scanning. The probes are fabricated of a photoplastic material, which allows simple batch fabrication and facilitates realization of specific mechanical properties for cantilevers - such as low stiffness - that are very difficult to achieve with classical silicon technology. The batch fabrication process, based on spin coating and subsequent near-ultraviolet exposure and development steps of the photoplastic SU-8, results in well-controlled and uniform mechanical properties of the probes within the same chip, as well as for different chips over a 4 in. wafer. Successful images of soft, condensed-matter samples were taken using these cassette probes, making consecutive readdressing of the same DNA molecule with two different cantilevers possible. Thus, a worn-out cantilever can be replaced by a new fresh one with only small positional adjustments and without any changes in the operating conditions. This ease of operation was provided by the cassette concept and the excellent uniformity of the mechanical cantilever characteristics.

We report on recent advances in micro fabrication technology using micromolding and high aspect ratio structuring of photopolymer. The direct application is the realization of components for millimeter-size, ultrasonic piezoelectric motors. A new fabrication process using a thick epoxy-based material (SU-8) and the electroplating of nickel is demonstrated. Photopolymer structures have also been realized and released using a positive tone resist as sacrificial layer. The main advantages over past fabrication methods are better design flexibility, simplicity of the fabrication process, the capability to combine metallic materials (Ni) with polymeric materials ( SU-8), and the use of positive tone resist as a sacrificial layer. (C) 1998 Elsevier Science S.A. All rights reserved.

We have developed a sensitive method for real-time mass sensing in a fluid using a microfabricated array of nanomechanical cantilevers actuated at their resonance frequencies. The sensor platform consists of a streptavidin layer immobilised onto gold-coated cantilevers and interacts with biotin-labeled latex beads. The addition of mass involved with this process decreased the resonance frequency. By monitoring frequency spectra of higher harmonics we measured a mass sensitivity of 3.3 Hz/pg. Our data demonstrate that the sensitivity can be increased by operating the cantilever at higher harmonics.

We report on recent advances in micro fabrication technology using micromoulding and high-aspect ratio structuring of photopolymer. The direct application is the realization of components for millimeter-size, ultrasonic piezoelectric motors. A new fabrication process using a thick epoxy-based material (SU-8) and the electroplating of nickel is demonstrated. Photopolymer structures have also been realized and released using a positive tone resist as sacrificial layer. The main advantages over past fabrication methods are better design flexibility, simplicity of the fabrication process, the capability to combine metallic materials (Ni) with polymeric materials (SU-8), and the use of positive tone resist as a sacrificial layer.

Using c‐axis La2CuO4 thin films, we first demonstrate that the electrochemical oxidation mainly occurs along the c axis. Then we induce oxygen‐rich regions electrochemically into an otherwise oxygen‐deficient matrix. On a microscopic scale the extra oxygen introduced creates metallic and/or superconducting regions in the insulating matrix. Contrary to other lithographic techniques in which large amounts of material are either removed or deposited, this technique does not induce significant height differences.

Briefly reports on advances in the fabrication technology of components for millimeter size ultrasonic piezoelectric motors. A very large height to width aspect ratio with good lateral patterning resolution is required for the active component in acoustic mode conversion. A new fabrication process using a thick epoxy-based material (SU-8) and the electroplating of nickel is demonstrated. The main advantages over past fabrication methods are better flexibility in the design, simplicity of the fabrication process and the combination of metallic materials (Ni) with polymeric materials (SU-8). The mechanical properties of SU-8 have been measured using free cantilever beam structures.

Detailed investigations of the limits of a new negative-tone near-UV resist (IBM SU-8) have been performed. SU-8 is an epoxy-based resist designed specifically for ultrathick, high-aspect-ratio MEMS-type applications. We have demonstrated that with single-layer coatings, thicknesses of more than 500 /spl mu/m can be achieved reproducibly. Thicker resist layers can be made by multiple coatings, and we have achieved exposures in 1200-/spl mu/m-thick, double coated SU-8 resist layers. We have found that the aspect ratio for near-UV (400 nm) exposed and developed structures can be greater than 18 and remains constant in the thickness range between 80 and 1200 /spl mu/m. Vertical sidewall profiles result in good dimensional control over the entire resist thickness. To our knowledge, this is the highest aspect ratio reported for near-UV exposures and resist thicknesses. These results will open up new possibilities for low-cost LIGA-type processes for MEMS applications. In addition, the SU-8 material has interesting mechanical properties which also makes it attractive for photoplastic device fabrication.

This paper describes the characterization of a home-made negative photoresist developed by IBM. This resist, called SU-8, can be produced with commercially available materials. Three blends were prepared for this article and some of its optical and mechanical properties are presented. One of its numerous advantages is the broad range of thicknesses which can be obtained in one spin: from 750 nm to 450 mu m with a conventional spin coater. The resist is exposed with a standard UV aligner and has an outstanding aspect ratio near 15 for lines and 10 for trenches. These ratios combined with the electroplating of copper allow the fabrication of highly integrated electromagnetic coils.

Sequential position readout from a microfabricated array of eight cantilever-type sensors silicon technology! is demonstrated. In comparison with single sensors we find that mechanical disturbances from noise, such as from vibrations, turbulent gas flow, or abrupt pressure changes, can be effectively removed in array sensors by recording difference signals with respect to reference cantilevers. We demonstrate that chemically specific responses can be extracted in a noisy environment using a sensor to detect specific chemical interactions and an uncoated cantilever as reference.

Nanoelectromechanical (NEM) switches have the potential to complement or replace traditional CMOS transistors in the area of ultra-low power digital electronics. This paper reports the demonstration of the first ring oscillator built using cell-level digital logic elements based on curved NEM switches. The NEM switch has a size of 5x3 mu m(2), an air gap of 60 nm and is coated with amorphous carbon (a-C) for reliable operation. The ring oscillator operates at a frequency of 6.7 MHz and confirms the simulated inverter propagation delay of 25 ns. The successful fabrication and measurement of this demonstrator is a key milestone on the way towards an optimized, scaled technology with sub-nanosecond switching times, lower operating voltages and VLSI implementation.

We have fabricated ultra-small, -fast, and -sensitive single-crystal silicon cantilevers, allowing at least a factor of 10 improvement in sensitivity and a factor of 20-50 enhancement in speed. Two methods allowing a good control of lever length and a miniaturized support chip were developed. These ultra-small cantilevers have excellent mechanical properties and are suitable for use in scanning force microscopes.

Digital circuits based on nanoelectromechanical (NEM) relays hold out the potential of providing an energy efficiency unachievable by conventional CMOS technology. This paper presents a detailed analysis of the operating characteristics of fabricated curved cantilever NEM relays using a comprehensive physical model. The mode of energy distribution within the electrical and mechanical operational domains of the relay is described in detail and the energy saving achievable by the technique of body-biasing is quantified. The analysis further reveals that the latency in a relay can be much larger or much smaller than the nominal mechanical delay depending on the point of actuation in the oscillation of the beam that takes place after pull-out. The methods that can utilize this phenomenon to reduce the latency of relay-based circuits are discussed, thus addressing one of the biggest challenges in NEM relay-based design.