A special micro-tensile tester was used to carry out tensile tests of thin copper films on substrates. The elastic strain in the film was measured in-situ using x-ray diffraction and the total strain with an external strain gage. From the elastic strains the stresses in the films were calculated and stress-strain curves were obtained. It was observed that the flow stress increases with decreasing film thickness. The method was also applied to investigate the mechanical behavior of films under cyclic loading.

We propose electroless metallization as a method for conformal metal deposition microelectromechanical systems (MEMS). The intrinsically conformal nature of electroless deposition makes it ideal for coating high aspect ratio (greater than 50:1) structures frequently fabricated with micromachining techniques We take advantage of the selective nature of the deposition to obtain self-aligned electrical isolation. We minimize the metal film roughness for potential applications in RF and optics. Given the specific MEMS metallization requirements, we determined the ideal concentrations of additives and surfactants in order to provide good electrical isolation, low roughness and high film reliability. Our depositions were done using seed layers as well as through direct chemical activation of the silicon surface. Characteristics such as resistivity [ 1 ], morphology [ 1 ], microstructure [ 2 ], and electrochemical behavior [ 3 ] have already been reported in the literature; our paper is focused on the specific requirements for MEMS applications.

Ferroic materials are ideally suited for actuators in MEMS applications. Ferro- elastic materials, i.e. shape memory alloys (SMAs), produce a significant, o. o. 104 microstrain, phase transformation induced thermoelastic eigenstrain. Rare earth based ferromagnetic materials possess large, o.o. 103 microstrain, saturation magnetostriction which can be developed at fields of the order of mT readily achieved in MEMS geometries. This paper discusses the essentials of the thermoelastic stress evolution in SMA/Substrate bimorphs and of the development of rare earth based ferromagnetic multilayers. SMA actuationunder the constraint of a substrate and the optimization of the multilayers are emphazized.

Thin films of PZT have been deposited using a solution deposition method onto platinized silicon substrates. The effects of process variables, including sintering time and solution molarity, have been investigated on the resulting microstructure and electrical properties. As utilizing piezoelectric thin films in geometries for MEMS applications requires load to be transferred between the film and an underlying membrane, the adhesion of these films has been examined using nanoindentation techniques. Delaminations occur at the PZT-Pt interface, suggesting that these films may be susceptible to interfacial failure with repeated bending. Longer firing times are shown to improve the adhesion of the films, but increase the surface roughness and grain size. Film hardnesses range between 4 and 6.8 GPa; for sintering times beyond 5 minutes at 700 °C the hardness appears relatively constant. Electrical properties are shown to degrade with tine at elevated temperatures.

Two techniques for dry etching of sol-gel lead zirconate titanate (PZT 52/48) thin films were investigated: reactive ion etching and argon ion milling. Etched profiles were characterized by scanning electron microscopy. For reactive ion etching, a parallel plate etcher was used with HC2ClF4, an environmentally safe etch gas, in a process described by other researchers. Etch rates were measured and compared as a function of electrode shield material (ardel, graphite, alumina) and RF input power (100 to 500 W). These etch rates varied from 10 to 100 nm/min. Reactive ion etched sidewall angles 12° off normal were consistently produced over a wide range of RF powers and etch times, but overetching was required to produce a clean sidewall. For argon ion milling, a 300 mA/500 V beam 40° off normal to the substrate operating in a 72 mPa argon pressure was used. These ion milling conditions produced an etch rate of 250 nm/min with a sidewall slope angle of about 70°. The ion milling etch rate for sol-gel PZT was significantly faster than rates reported for bulk PZT. The 500 nm thick PZT films used in this study were prepared by the sol-gel process that used methoxyethanol solvent, spin coating on t/Ti/SiO2 silicon substrates, and rapid thermal annealing for 30 s at 650 °C for crystallization of the perovskite phase.

Many MEMS devices require piezoelectric excitation and readout to actuate and sense motion of mechanical structures. Aluminum nitride is advantageous for MEMS fabrication because it is compatible with silicon integrated circuit foundry impurity contamination requirements, can be deposited at low temperatures, provides a high piezoelectric coefficient, and is easily patterned using conventional photolithographic techniques. In this work, AIN thin films were deposited on silicon substrates for use in a MEMS silicon membrane ultrasonic resonator. The ultrasonic resonator is configured as a gravimetric sensing device for chemical detection. Issues of concern with regard to device performance and yield include the maximization of the electromechanical coupling constant (k2), film stress control, and film uniformity; these issues were addressed through a central composite design set of experiments to resolve the film property responses as a function of the deposition parameters. Film characterization was conducted with x-ray diffraction, spectroscopic ellipsometry, and surface profilometry. Optimization of film deposition parameters improved sensor performance and enabled further device miniaturization with the use of thinner films.

Development of ceramic microcomponents can open up the current silicon-based MEMS technology to new applications, especially for use in high temperature, chemically reactive environments. We report a study of sol-gel technologies applied to the fabrication of microcomponents. Organic/inorganic hybrid materials, particularly silica-based hybrids, were developed by sol-gel processing. A weak silica network was made possible by using acid catalyst, low functionality organic precursor in the sol preparation. Since the weak network has a high tendency to collapse, the result is a denser material. Incorporation of organic ligands modifies the surface chemistry of gel network so that a greater drying stress was developed and a denser hybrid structure was achieved without high temperature treatment. In addition, the incorporation of organic ligands prevented formation of cracks. Nanoscale oxide particles were dispersed and incorporated into the gel network by surface condensation. The incorporation of solid nanoparticles into sols greatly reduced the shrinkage of gels and enhanced the mechanical strength of the components. In addition, silica sol was applied to coat metallic microcomponents and a thin uniform was formed.

Pressure transducers with promising characteristics at high pressure and temperatures have been developed using low temperature co-fired ceramic (LTCC) tape technology. All parts for the transducer were machined from DuPont 951 series LTCC tapes utilizing either a numerically controlled milling machine, or an isotropic etching technique involving the removal of the glassy binder of a partially sintered LTCC tape. Device dimensions are in the meso (intermediate) scale range, with the smallest device size of 8mm in diameter, and the cavity of 2 mm. Utilizing the anisotropy induced during the casting process a chemical exfoliation technique was developed. This technique allowed us to separate the original tape in three layers, the middle one being highly elastic, isotropic and homogeneous. The middle layer can be chemically thinned to achieve membrane like behavior, with thickness of the order of 50 µm. The pressure is measured as a function of the membrane deformation where two piezo-resistors are screen printed. Two piezo-resistors were used to achieve temperature compensation. Using shrinkage matched paste, nominal thick film technology was used in the screen printing of the piezoresistors. The rest of the transducer was fabricated using several layers of LTCC tapes, which were laminated and fired. Devices of different sizes were fabricated and compared. Devices were characterized by comparing its dynamic response with a micro-fabricated silicon pressure transducer.

A study of the structure and thermodynamics of the densification process in a model alumina-based ceramic tape system during thermal processing is presented. DuPont's Green Tape™ 951, which is primarily composed of frit (>50% silica), alumina and an organic binder, is used as the model system. The microstructures of annealed specimens are characterized by scanning electron microscopy as a function of annealing time and temperature. The distribution and shape of pre-existent pores and frit particles are found to be strongly dependent on the processing conditions. With the processing temperatures significantly below conventional sintering temperature of alumina, the behavior of the frit is the critical determinant of the final microstructure and mechanical behavior.

A technology for the direct molding and release of silica micro-optical components in polymethyl methacrylate (PMMA) molds is developed. The objectives of this work are to bypass some of the usual steps in deep x-ray lithography (DXRL) and to determine the suitability of GR650 resin (methylpolysilsequioxane) for molding thick, high aspect ratio structures. The process is initiated by DXRL exposure of PMMA, followed by spin-on glass application, a cure at 85°C to set the shape of the resin, followed by demolding. The cure is below the glass transition temperature of PMMA and the demolding process allows re-use of the mold. There is no need for electroforming in the replication process. PMMA molds with thickness of 250, 350 and 500 um were fabricated by DXRL and standard resist development. A novel metal sacrificial layer technique is used in the release process with initial yield of about 50%. Microoptical elements that were fabricated include lenses, prisms, grating structures and transmission test structures. These components are cured above 400°C after release, to convert the organosilicon polymer to a silica-like material. Weight loss from the high temperature cure was in the range of 15 to 25%, while linear dimensions of the components decreased by about 1%. Composition of the molded, cured structures was measured by XPS depth profiles.

We have developed a variety of processes for fabricating components for micro devices based on deep x-ray lithography (DXRL). Although the techniques are applicable to many materials, we have demonstrated them using hard (Nd 2Fe14B) and soft (Ni-Zn ferrite) magnetic materials because of the importance of these materials in magnetic micro-actuators and other devices and because of the difficulty fabricating them by other means. The simplest technique involves pressing a mixture of magnetic powder and a binder into a DXRL-formed mold. In the second technique, powder is pressed into the mold and then sintered to densify. The other two processes involve pressing at high temperature either powder or a dense bulk material into a ceramic mold that was previously made using a DXRL mold. These techniques allow arbitrary 2-dimensional shapes to be made 10 to 1000 μm thick with in-plane dimensions as small as 50μm and dimensional tolerances in the micron range. Bonded isotropic Nd2Fe14B micro-magnets made by these processes had an energy product of 7 MGOe.

This work combines focused ion beam sputtering and ultra-precision machining for microfabrication of metal alloys and polymers. Specifically, micro-end mills are made by Ga ion beam sputtering of a cylindrical tool shank. Using an ion energy of 20keV, the focused beam defines the tool cutting edges that have submicrometer radii of curvature. We demonstrate 25μm diameter micromilling tools having 2, 4 and 5 cutting edges. These tools fabricate fine channels, 26–28 microns wide, in 6061 aluminum, brass, and polymethyl methacrylate. Micro-tools are structurally robust and operate for more than 5 hours without fracture.

Circuit patterned nucleation of copper atoms onto polyimide surface was demonstrated by using ArF excimer laser (λ =193nm) and copper sulfate aqueous solution at an atmospheric pressure. Photo-excited C-H bonds of the polyimide surface were effectively dehydrated with hydrogen atoms which were photodissociated from the water. The dangling bonds of the dehydrated hydrogen atoms were combined with the oxygen and the copper atoms which were photodissociated by copper-sulfate aqueous solution. Thus, C-O-Cu bonds were formed on the surface. After this copper substitution, it was carried out onto the nucleated parts by usual electroless plating at 70°C. In this process, the conductive circuit pattern Cu thin film was deposited on polyimide surface.

An existing test system for recording the stress-strain curves of metal microspecimens has been used to measure the strength of the ultrathick photoresist SU-8. The microspecimens are 3 mm long with a gage section 0.2 mm wide. The SU-8-25 specimens were 0.08 mm thick with an average strength of nearly 120 MPa, and the SU-8-50 specimens were 0.125 or 0.145 mm thick with an average strength of 130 MPa. Measurements of Young's modulus proved difficult, but a preliminary value of 3 GPa was obtained.

The fabrication of MEMS and electronic devices relies heavily on lithography. We have explored the application of derivatives of C60, as high resolution, high etch durability resists. Spin coating was used to produce films of various methanofullerenes on silicon substrates, with thickness ranging from 20 to 200 nm. These films behave as effective high resolution negative tone electron beam resists allowing sub 20 nm patterning of silicon which compares favorably with other negative tone resists. Organic solvents such as monochlorobenzene and chloroform can be used to develop the exposed films. The films have sensitivities of 4 × 10−3 to 8 × 10−4 C/cm2 for 20 keV electrons, more than an order of magnitude higher than the sensitivity of C60,. The dry etch durabilities of these compounds are considerably higher than those of conventional resists. A silicon grid with hole depth 160 nm and wall thickness 20 nm has been fabricated to demonstrate the high resolution and high etch durability of these resists.

The preparation a nd characterisationo f a novel organoplatinum fluoride is described. The physical vapour deposition (PVD) of the material was performed in the temperature range 160–170°C, and electron beam bombardment or uv irradiation, results in the degradation of the compound to give high quality metal features down to dimensions of ca 60 nm.

The synthesis and peirastic characterisation of two new organogold(III) complexes with a high molar ratio of gold content is described. The proposed formulae for the complexes in the present study are [C2H2Au4F8(PPh3)4]n and [C2H2Au4F8(NCCH3)4]n (Figure 1). These complexes were found to be stable to the atmosphere. The aim of this work was to demonstrate that such materials have a high metal to ligand ratio, suitable for physical vapour deposition process (PVD) and, hence, can be used as precursors for the deposition of pure metallic features. Physical and chemical characterisation methods were employed to obtain information about i) the structures, ii) the thermal and chemical stability, iii) the volatility and iv) the adhesion of these materials to specific substrates. These include n.m.r. (1H, 19F, 13C and 31P) IR spectroscopy, EDX (Energy Dispersive X-ray analysis), DSC ( Differential Scanning Calorimetry), TGA (Thermogravimetric Analysis), Powder X-ray Diffraction and Electron Microscopy (Scanning, Transmission and Atomic Force).

The correlation of differences in the wettabilities of partially fluorinated self-assembled monolayers (SAMs) to changes in the chemical structure and composition of the films was explored by contact angle goniometry and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). SAMs of simple alkanethiols (CH3(CH2)nSH with n = 9-15) and their CF3-terminated analogs (CF3(CH2)nSH with n = 9-15) were prepared by adsorption from solution onto evaporated gold. Advancing contact angles of hexadecane were measured on both the terminally fluorinated surfaces and the hydrocarbon surfaces. These data were compared to those obtained using a series of polar aprotic contacting liquids. As expected, the contact angles of hexadecane were higher on the CF3-terminated SAMs than on the CH3-terminated SAMs. The contact angles of the polar aprotic solvents, however, were measurably lower on the CF3- terminated SAMs than on the CH3-terminated SAMs. These observations were rationalized on the basis that the introduction of the CF3 terminal groups yields oriented surface dipoles that interact with the dipoles of the polar contacting liquids. Further support for this model was provided by the observation of an inverse parity (“odd-even”) effect in the wettabilities of the polar aprotic solvents on the CF3-terminated surfaces. Analysis by PM-IRRAS revealed that both types of films consist of predominately trans-extended alkyl chains with relatively few gauche defects in a densely packed arrangement. The high degree of order is consistent with the detection of the parity effect, where small changes in the orientation of the tail groups can be sensed by contact angle measurements only in highly ordered organic thin films. The significance of the dipole-oriented dipole interaction in describing interfacial wettabilities is discussed.