As MEMS devices become ever more sensitive, even slight shifts in materials properties can be detrimental to device performance. Radiation-induced defects can change both the dimensions and mechanical properties of MEMS materials, which will be of concern to designers of MEMS for applications involving radiation exposure, such as those in a reactor environment or in space. We have performed atomistic simulations of the effect that defects and amorphous regions, such as could be produced by radiation damage, have on the elastic constants of silicon. We have then applied the results of the elastic constant shift calculations to a hypothetical MEMS device, and calculated the difference that would be generated by this effect.

This study reports on the microfrictional properties under reciprocating sliding of different types of commercially available diamond-like carbon (DLC) films, prepared using low and high frequency plasma-assisted chemical vapor deposition (PACVD) and the vacuum arc method. Silicon and sapphire balls were used as counterbodies. Friction-load curves suggest that, for applied forces in the N to mN regime, two properties have a strong influence on the microfriction: First, the chemical composition plays a dominant role and second, the film roughness. With silicon against DLC, microfriction of hydrogen-free DLC films was greater than the hydrogen containing films. With sapphire counterbodies, microfriction was inversely proportional to film roughness. For all films tested, microfriction was independent of the sliding velocity. Mild wear in the form of scratches was observed only on silicon, while no wear could be detected on any of the DLC films. These results illustrate the utility of implementing microtribological testing in a coating development for microsystems.

The aluminum nitride (AlN) process was successfully developed for as high frequency thin-film for bulk acoustic resonator applications. Columnar AlN was deposited on p-type (100) silicon substrate at 300–500°C using pulse direct current (DC) sputtering technique. Argon to nitrogen ratio was optimized to achieve stoichiometry at higher deposition rates of about 1000 Å/min at 1–4 kW DC power. The XRD of as-deposited and annealed AlN film shows preferred (002) orientations. The dry etching process was developed and etching rate about 3200 Å/min was achieved using Cl based chemistry. Film composition analysis was done using AES technique and stoichiometry was achieved.

Polycrystalline silicon carbide (poly-SiC) films were deposited by atmospheric pressure chemical vapor deposition (APCVD) at epitaxial growth temperatures on planar, 100 nm-thick polysilicon sacrificial layers using two recipes that included or excluded a pre-growth carbonization step. Poly-SiC films grown using the carbonization-based recipe exhibited a relatively high degree of (111) 3C-SiC texture and had uniform, well-defined, void-free poly-SiC/polysilicon interfaces. In contrast, poly-SiC films grown without carbonization were randomly oriented, had numerous poly-SiC inclusions that sometimes completely penetrated the polysilicon underlayer, and had a higher surface roughness than the films grown with carbonization. Analysis of micromechanical clamped-clamped (C-C) beam resonators fabricated from films grown using the two differing recipes shows that the carbonization step is needed to protect the thin polysilicon sacrificial layer from voids and inclusions and thus maintain the proper spacing between the drive electrodes and the resonant beams.

We describe the fabrication of self-aligned split gate electrodes on suspended multiwalled carbon nanotube structures. A suspended multiwalled carbon nanotube structure was used as an evaporation mask for the deposition of metal electrodes resulting in the formation of discontinuous wire deposition. The metal deposits on the nanotubes are removed with lift-off due to the poor adhesion of metal to the nanotube surface. Using Al sacrificial layers, it was possible to fabricate self-aligned contact electrodes and control electrodes nanometers from the suspended carbon nanotubes with a single lithography step. It was also shown that the fabrication technique may also be used to form nano-gaped contact electrodes. The technique should prove useful for the fabrication of nano-electromechanical systems.

The polysilicon elements of thermal actuators can reach temperatures high enough to cause permanent deformation. A fundamental understanding of the constitutive behavior is necessary for intelligent design and life prediction, but mechanical testing at high temperatures is especially challenging at the micron level.

This paper describes techniques for testing freestanding thin-film polysilicon specimens in tension at temperatures up to 700°C. Strain is measured directly on the specimens by laser interferometry from platinum markers. The complete stress-strain curve can be obtained as well as strain versus time for creep tests. Initial results show that polysilicon is ductile at temperatures above 500°C and can have a high creep rate.

Characteristics of selective anodization of p+-type Si have been studied. Temporal evolution of the etching front was visualized by periodic porosity modulated anodization. The etching front proceeded inside along the bottom of mask making its angle with the mask bottom face sharper and sharper. It was also found that the etching front proceeds forming a specifically angled facet. Selective anodization was applied to form Si micro-tips. Proper time of anodization for p+-type Si substrate with an n-type circular shape mask left a Si micro-tip formed on the substrate. A high resolution SEM observation revealed that the apex of the tip was composed of {110} facets.

A better understanding of the origin and evolution of the stresses is a crucial step in improving reliability of packaging systems for microelectromechanical systems (MEMS). Given its importance, we examine the stresses developed in hermetically packaged MEMS inertial sensors. For this purpose, an optical surface profilometer is employed to assess the stresses by measuring the curvature of dummy silicon dies (3.5×3.5 mm2) assembled in different types of packages and die attach adhesives. We also explore a temporal evolution of stresses during thermal exposure of the test packages in an effort to emulate actual packaging processes and device operation conditions. The result shows different levels of stresses generated from various adhesives and package types, and also a stress evolution during packaging processes. The mechanical stress data also show a good agreement with MEMS performance data obtained from actual accelerometers. Therefore, the stress data will not only be useful in better understanding performance of MEMS packages, but the testing protocol can also provide a diagnostic tool for very small packaging systems.

In our previous investigations [1, 2], we have demonstrated that the introduction of fatigue pre-crack ahead of a notch is required to measure reliable fracture toughness values even for micro-sized specimens. However, it is rather difficult to introduce a fatigue pre-crack into a micro-sized specimen as once a fatigue crack starts to grow then the fatigue fracture occurs within one thousand cycles and this makes it extremely difficult to control fatigue crack length. Therefore, a new fatigue pre-cracking method is required for measuring fracture toughness. In this investigation, a new fatigue pre-cracking method has been proposed for micro-sized specimens and fracture toughness tests were carried out for the micro-sized specimens with fatigue pre-crack. Micro-cantilever beam type specimens with dimensions of 10 × 10 × 50 μm3 were prepared from an electroless deposited Ni-P amorphous alloy thin film and notches were introduced by focused ion beam machining. Fatigue pre-cracks were introduced ahead of the notches by far-field cyclic compression method using a mechanical testing machine for micro-sized specimens (MFT2000). Fracture tests were also carried out using the testing machine. Fatigue pre-cracks with length of 0.2 μm were confirmed on the fracture surfaces ahead of the notches in the far-field cyclically compressed specimens. This indicates that the fatigue pre-cracking method developed in this investigation is promising for measuring accurate fracture toughness for micro-sized specimens for MEMS applications.

Although slow and dissipative, sputtered thin-film shape-memory alloys like equiatomic titanium-nickel can exert a large ohmically-excited force·displacement product when deployed in photolithographically micromachined actuators. They give energy densities far exceeding those typically produced by competing microactuator materials [1], and their size can probably be scaled down to the nanometer range (where the benefits of high surface to volume ratio are best exploited for speed and efficiency). But a large, energetic, and resettable actuation stroke is possible only if some agency has imparted a non-trivial initial plastic strain, of between one and five percent, to the martensite phase. Is not always obvious how this strain is to be achieved when discrete mechanical manipulation of the active element is difficult. Furthermore, for cyclic actuation, a resetting-force that periodically re-deforms the martensite during the cooling interval must arise naturally from mechanical elements in the design. Here, several methods responding these requirements are discussed in relation to various kinematic themes.

We report the use of Raman spectroscopy to characterize the bending stresses in a deep reactive-ion etched, single-crystal, silicon flexure of length 2950 μm, width 480 μm, thickness 150 μm, and fillet radius 65 μm, subjected to a tip displacement of 69.5 μm. The spectral resolution of the measurement was 0.02 cm-1, which corresponds to a stress resolution of ∼10 MPa, and the spatial resolution was ∼1 μm. Line scans were performed across the thickness, at several locations along the length, of the flexure. The changes in the Raman shift were converted to stress values, assuming a uniaxial stress state, without the use of any fitting parameters. A comparison of the measured values with the predictions of analytical and numerical models indicates agreement to within 25–35 MPa (or ∼15%) at locations sufficiently distant from the root. At the root itself, the complex nature of the stress distribution precludes unambiguous stress determination using spectroscopic measurements.

Micromachined actuators based on the electrostrictive P(VDF-TrFE) copolymer, which possesses a high strain (∼5%) and high elastic energy density (∼ 1 J/cm3), have been designed and fabricated. The performance of the devices have been characterized and modeled in terms of the properties of the copolymer and dimensions of the devices. The experimental results on the device responses under high AC fields (electrostrictive mode), weak AC fields in DC field biased state, and frequency dependence, are very close to the modeling results. Due to the large field induced strain and high frequency capability of the electrostrictive P(VDF-TrFE), the device possesses the capability of operation at non-resonance mode with high displacement and force output, and hence, the device is capable to be used over a broad frequency range. For example, for a device of 1 mm lateral dimension, the displacement output can reach more than 50 μm and the ratio of the displacement/applied voltage is more than 20 nm/Vrms. Furthermore, over more than 3 frequency decades (up to 100 kHz), the dispersion of the displacement is less than 20%. The observed performance of the devices indicates that this class of the electrostrictive P(VDF-TrFE) based micro-actuators is attractive for micropumps and valves.

The accurate determination of residual stress/strain in thin films is especially important in the emerging field of MicroElectroMechanical Systems (MEMS). In this article, a focused ion beam (FIB) moiré method is proposed and demonstrated to measure the strain in MEMS structures. This technique is based on the advantages of the FIB system in nano-fabrication, imaging, in-situ deposition, and fine adjustment. Nano-grating lines with 70 nm width and 140 nm spacing are directly written on the top of the MEMS structures by ion milling without the requirement of an etch mask. The FIB moiré pattern is formed by the interference between a prepared specimen grating and FIB raster scan lines. The strain of the MEMS structures is derived by calculating the average spacing of moiré fringes. Since the local strain of a MEMS structure itself can be monitored during the process, the FIB moiré technique has many potential applications in the mechanical metrology of MEMS. As an example, the strain distribution along the sticking MEMS structures, and the contribution of surface oxidization and mass loading to the cantilever strain is determined by this FIB moiré technique.

This paper introduces a new microfabrication technique, Ultraprecision Manufacturing of Self-Assembled Micro-Systems (UPSAMS), which combines ultraprecision micromachining (milling/turning/drilling/grinding) with sacrificial/structural multi-layer manufacturing processes to produce self-assembled, 3-D microsystems and associated mesoscale interfaces from a variety of materials for MEMS applications. With this process, a new class of microsystems can be developed that is highly three dimensional, precisely machined, and automatically assembled.

This paper reviews some of our recent work on a new class of photonic component that uses electrowetting pumps and microfluidic channels for dynamic tuning of the characteristics of optical waveguides. These pumps exploit the ability to alter the contact angle of conductive liquids situated on top of a dielectric layer with appropriately patterned underlying electrodes. By applying different voltages to opposite sides of a conductive fluid plug, the contact angle imbalance created between the ends of the liquid drives fluid motion toward the higher field regions [1]. In our design, this electrically controlled, fully reversible motion of fluids contained within recirculating channels is used to alter the effective indices of waveguide modes of three different types of optical fiber structures: fiber Bragg and long period gratings and etched or tapered fiber. Our systems operate non-mechanically and have excellent optical performance, including low insertion and polarization-dependent losses. These characteristics suggest a promising potential for electrowetting-based microfluidic tuning of optical fiber devices and other photonic components.

We have designed and developed a calorimeter that is capable of measuring the heat released by ultrathin films in the temperature range from 77 to 1050 K. Semiconductor processing techniques are used to fabricate the microreactors. The symmetric design of the Pt heaters in the microreactor channel provide a good temperature profile across the active region of the membrane making it suitable for accurate calorimetric measurements. The low thermal mass of our system allows for a high sensitivity. The effective heat capacity of the microcalorimeters with a 200 nm SixNy membrane is 0.14 μJ/K at room temperature. In high vacuum heating rates of 2×106 K/s have been achieved. Under these conditions the microcalorimeter works as an adiabatic scanning calorimeter and therefore heat capacity is directly obtained from the input power. A thermal characterization of the microcalorimeters in the transient state and calorimetric measurements on indium thin films and films made of CdSe nanocrystals are briefly discussed to show the potentiality of the microreactors.

In this work, we investigate the possibility of using pulsed laser annealing to locally tailor the physical properties of Si1-xGex (18% < × < 90%) prepared by low pressure chemical vapor deposition (LPCVD) at 400°C. Films which were amorphous as deposited showed, after laser annealing, strong {111} texture and a columnar grain microstructure and an average resistivity of 0.7 mΩ.cm. AFM showed that the first few laser pulses result in a noticeable reduction in surface roughness, which is proportional to the pulse energy. However, a large number of successive pulses dramatically increases the surface roughness.

This paper focuses on recent developments in the localised characterisation of the mechanical properties of Microsystems and MEMS devices and structures. Conventional indentation techniques provide a highly powerful method for measuring the load and depth response of bulk and coated materials, but can also be used to measure the mechanical properties of very small micro-machined silicon structures. Beam structures, such as are used for accelerometers, need to be characterised in terms of the number of cycles to failure, the spring constant or the energy required to bend the beam by a required amount. Such localised testing needs to be adapted to work at various distances from the origin of the beam with a positioning accuracy of less than a micron. Initial studies have proved to be highly repeatable. A range of examples is presented which covers a range of application areas, including accelerometer beam structures, microswitches and printer head structures. The basic instrumental concepts are explained together with the modifications required for testing small structures in a localised way.

Micro-relief surfaces including grating structures, greytone/micrographic features and microramps have been fabricated with depth features of up to 30 μm. Grey scale lithography has been used to produce the microstructures by a single UV exposure into a layer of thick resist. Arrays of the pixelated microstructures have formed the security features on the surface of optically variable devices. Each of the microstructures was designed to provide an intended optical effect in features such as portraits, symbols and lettering which comprised a larger image (typically 2.5 × 3 cm). An essential part of the process has been the determination of the optimum conditions for coating of the thick resist (AZ P4620) as a function of spin speed and exposure.

Stress adjustment and improvement of electrical characteristics in film bulk acoustic wave resonator (BAW) have been successfully carried out in 1.8GHz range by using a multi-layer structure of ZnO / Al2O3 / SiO2. The BAW resonator, designed on secondary harmonics at about 1.8GHz, has Al / ZnO / Al / Al2O3 / SiO2 structure. ZnO and SiO2 thin films have a negative and a positive temperature coefficient of sound velocity, respectively. So temperature coefficient of frequency (TCF) of the BAW resonator can be controlled by the thickness ratio of ZnO and SiO2 thin films. Since both ZnO and SiO2 have compressive stress, and Al2O3 has tensile one, the stress of the membrane is reduced by combining these thin films so that the membrane can avoid deformation. The BAW resonator, with thickness of ZnO / Al2O3 / SiO2=1.2 /0.45/1.25 microns, was designed by finite element method (FEM) simulation and fabricated. The value of quality factor (Q factor) and the TCF of the BAW resonator were realized over 1000 and −20 ppm/degree C, respectively. The Q of ZnO / Al2O3 / SiO2 structure was higher than that of ZnO / SiO2 one with keeping small TCF.