Metal multilayers are a unique way to manufacture reliable conductive members for MEMS devices. These members are particularly suited for electrostatic switches. Unlike elemental Al, which experiences curvature problems during processing, the residual stress in these beams can be controlled and calibrated during stress measurements to have repeatable shapes and stresses upon release. In this study, curvature experiments were performed to determine the optimal deposition parameters (pressure, thickness) to produce metal multilayer beams with zero average stress and zero bending moment, which can be obtained by alternating tensile and compressive layers within. Resistivity measurements were made to determine the effect of interfaces on resistivity.

Lead zirconate titanate (PZT) films are very attractive for microelectromechanical systems (MEMS) applications because of their high piezoelectric coefficients and good electromechanical coupling. In this work, wet-etch patterning of sol-gel PZT films for MEMS applications, typically with film thicknesses ranging from 2 to 10 microns, was studied. A two- step wet-etch process was developed. In the first step, 10:1 buffered HF is used to remove the majority of the film at room temperature. Then a solution of 2HCl:H2O at 45°C is used to remove metal-fluoride residues remaining from the first step. This enabled successful patterning of PZT films up to 8 microns thick. A high etch rate (0.13μm/min), high selectivity with respect to photoresist, and limited undercutting (2:1 lateral:thickness) were obtained. The processed PZT films have a relative permittivity of 1000, dielectric loss of 1.6%, remanent polarization (Pr) of 24μC/cm2, and coercive field (Ec) of 42.1kV/cm, all similar to those of unpatterned films of the same thickness.

Corrosion fatigue properties of micro-sized materials are extremely important to design MEMS devices and micro-machines used in corrosive environments. However, there have been few studies that investigate corrosion fatigue properties of micro-sized materials. Thus, it is necessary to develop a corrosion fatigue test method for micro-sized materials. However, there are several difficulties in corrosion fatigue tests on micro-sized specimens. It is also necessary to clarify the problems for the method and to find their solutions. In this investigation, a corrosion fatigue test method for micro-sized specimens has been developed and corrosion fatigue tests for micro-sized Ni-P amorphous alloy specimens have been carried out in a 0.9% NaCl solution. Specimens of cantilever-beam-type with dimensions of 10 × 12 × 50 μm3 were prepared from a Ni-P amorphous thin film by focused ion beam machining. Corrosion fatigue tests on the micro-sized specimens were succeeded, and environmental effects on fatigue properties of micro-sized specimens were clearly observed. Several problems and solutions for the method were described.

Amorphous diamond is a new material for surface-micromachined microelectromechanical systems (MEMS) that offers promise for reducing wear and stiction of MEMS components. The material is an amorphous mixture of 4-fold and 3-fold coordinated carbon with mechanical properties close to that of crystalline diamond. A unique form of structural relaxation permits the residual stress in the material to be reduced from an as-deposited value of 8 GPa compressive down to zero stress or even to slightly tensile values. Irreversible plastic deformation, achieved by heat treating elastically strained structures, is also possible in this material. Several types of amorphous diamond MEMS devices have been fabricated, including electrostatically-actuated comb drives, micro-tensile test structures, and cantilever beams. Measurements using these structures indicate the material has an elastic modulus close to 800 GPa, fracture toughness of 8 MPa.m½, an advancing H2O contact angle of 84° to 94°, and a surface roughness of 0.1 to 0.9 nm R.M.S. on Si and SiO2, respectively.

It is well recognized that controlling surface forces is one of the key issues in the design, fabrication, and operation of microelectromechanical systems (MEMS). In this report we present a novel strategy for the efficient assembly of organic monolayers onto silicon surfaces to control surface energy. This is achieved by the reaction between an alcohol functional group and a chlorinated Si surface. The resulting molecular monolayers are thermally and chemically stable. Surface adhesion energy on silicon is reduced by a factor of 40 by the monolayer coating and friction coefficient of the coated surface is only 0.013. The coatings are successfully demonstrated in adhesion reduction in a model MEMS structure: cantilever beam array (CBA). Polycrystalline beams with length up to 1.5 mm can be released.

Application of porous silicon in thermal microsystem structures often requires the formation of deep localized porous silicon layers. The most commonly used method to prepare the porous layers is the dc anodic etching of monocrystalline silicon in a hydrofluoric acid (HF) based electrolyte. However inhomogeneity of the nanocrystallite size along the layer depth due to the decrease of HF concentration within the pores as well as the poor uniformity of the porous layer thickness limit the elaboration of deep porous layers. Thus we propose an original pulsed anodisation technique, using a double tank etching cell that allows localized porous silicon layers formation throughout the whole wafer thickness.

Furthermore a selective double sided pulsed anodisation of silicon was performed on patterned silicon substrates. Porous silicon is formed in pre-determined parts of the wafer using composite polysilicon-silicon nitride masking layers. Technological solutions to get rid of porous layer thickness inhomogeneity due to non uniform current density distribution are discussed. Finally a toric porous silicon layer, crossing the whole silicon wafer, surrounding a 20 mm diameter monocrystalline silicon cylinder was successfully achieved ensuring a new approach of thermal insulation for thermal effect microsystems.

Piezoelectric films for a MEMS microengine have been deposited using solution deposition routines onto platinized silicon wafers. These films are used as membranes above a bulk micromachined cavity. A dynamic bulge tester and interferometer were used to characterize the deformation of the films when pressurized. The mechanical strain at failure, as well as the fatigue behavior, have been characterized. Membranes between 300 and 500 nm thick have been shown to sustain mechanical fatigue damage over approximately 10 million cycles at strains of 30% of the monotonic failure strain. Defects in the films due to growth and thermal stresses during processing, and their role in membrane failure, are identified. Crack growth is demonstrated in these films by compliance measurements during fatigue testing, and interfacial failure is identified between the PZT and Pt layers.

Electrical charge transients have been measured during the nanoindentation of lanthanum modified lead titanate ferroelectric thin films. Using the spherical indenter as the top electrode, the films were locally poled. The films were then reindented at the exact same positions. The origin of the charge released is discussed in terms of piezoelectricity and depolarisation. The depolarisation must have been produced by a stress induced ferroelastic domain reorientation. Current intensity transients recorded during indentation showed a distinct maximum. This maximum corresponded to a force at which the depolarisation rate was a maximum. This provides the basis to define a coercive indentation force, and then a coercive indentation stress.

The mechanical properties of thin film materials are known to be different from those of bulk materials, which are generally overlooked in practice. The difference in mechanical properties can be misleading in the estimation of residual stress states in micro-gas sensors with multi-layer structures during manufacturing and in service.

In this study the residual stress of each film layer in a micro-gas sensor was measured according to the five difference sets of film stacking structure used for the sensor. The Pt thin film layer was found to have the highest tensile residual stress, which may affect the reliability of the micro-gas sensor. For the Pt layer the changes in residual stress were measured as a function of processing variables and thermal cycling.

We report here on the influence of the epitaxial growth conditions on the residual stress of heteroepitaxial 3C-SiC grown on silicon using atmospheric-pressure chemical vapour deposition (APCVD) and on the determination of its mechanical properties. 3C-SiC films were grown on (100) Si substrates in a vertical reactor by APCVD. SiH4 and C3H8 are used as precursor gases and H2 as carrier gas. The growth procedure involves the formation of a carburization buffer layer at 1150°C under a mixture of H 2 and C3H8. The epitaxial growth occurs then at 1350°C by adding SiH 4.

For as-deposited films the measurement techniques implemented are substrate curvature measurements, AFM, and nano-indentation. For micromachined self-suspended SiC membranes, load deflection measurements were used. The substrate curvature measurement leads to the determination of the residual stress in the deposited SiC film. We show that we can achieve 3C-SiC layers with a compressive or a tensile state having equivalent crystallinity. Whereas thermal mismatch just accounts for tensile stresses, we demonstrate that 3C-SiC thin films may have compressive stresses by using specific conditions for the formation of the buffer layer. The early stage of growth is indeed of major importance.

Regarding the mechanical properties, the 3C-SiC Young's modulus was determined using nano-indentation. Its mean value reaches 378 GPa comparable to the calculated value of 307 GPa. As test structures, we have processed self-suspended SiC membranes. Load deflection measurements enable the determination of the Young's modulus and the residual stress of the self-suspended films. For self-suspended SiC membranes, the absolute value of the residual stress in the SiC thin films decreases compared to the as-deposited films and takes a mean value of 170 MPa in a tensile state.