The electrical reliability properties of PZT (54/46) thin films have been measured for the purpose of integrating this material with silicon-based microelectromechanical systems. Ferroelectric thin films of PZT were prepared by metal organic decomposition. The charge trapping and degradation properties of these thin films were studied through device characteristics such as hysteresis loop, leakage current, fatigue, dielectric constant, capacitancevoltage, and loss factor measurements. Several unique experimental results have been found. Different degradation processes were verified through fatigue (bipolar stress), low and high charge injection (unipolar stress), and high field stressing (unipolar stress).

In this work, we proposed a direct bonding method using interlayers for single crystalline silicon wafers and glass wafers. Various materials were used for interlayers of thermal oxide, sputtered nitride, electron-beam(E-beam) evaporated silicon oxide and molybdenum. After hydrophilization, samples were spin dried and mated together without external forces. Three types of solutions were used for hydrophilizing the samples. Changes of average surface roughness after hydrophilization of the single crystalline silicon wafer, thermal oxide and E-beam silicon-oxide were inspected using atomic force microscope(AFM). Bonding interfaces of the bonded pairs were observed by scanning electron microscope(SEM). Voids and non-contact areas of the bonding pairs were also inspected using infrared(IR) transmission microscope. Surface energy, tensile strength measurements and breaking tests were also done.

A silicon-to-silicon anodic bonding process using a glass layer deposited by electron beam evaporation will be described. Corning #7740 Pyrex glass was used the source material of electron evaporation. From Auger electron spectroscopy (AES), the composition of the deposited glass layer is nearly same as that of the bulk Pyrex glass plate. Wafers are bonded at a temperature as low as 135 °C with an applied voltage as small as 35Vdc, enabling of this technique to be applied to vacuum packaging of microelectronic devices. Experimental results reveal that an evaporated glass layer of more than 1 μ m thick is suitable for anodic bonding. Finally, The role of sodium ions in anodic bonding was also studied by investigating the theoretical bonding mechanism and examining the results of secondary ion mass spectroscopy (SIMS) analysis.

Composite SiO2/Si membranes are used in various type of sensors among them, resonant and pressure sensors. However due to a large thermal mismatch, residual induced stresses may affect the devices long term reliability especially for thin membranes (˜5 μm). In this study, we have characterized test structures consisting of SiO2/Si membranes with respective thickness ratio between 2 and 10. Micro-Raman Spectroscopy, well known to be an accurate, non destructive method to determine residual stresses in microelectronic devices, has shown to be a powerful testing technique to measure local stresses on micromachined structures such as membranes, with a high spatial (10 μm2 ) and stress resolution (8 MPa). At room temperature, Raman line (520 cm−1) shifts between 0.05 and 1 cm−1 are observed. Highest frequency shifts of 1cm−1 corresponds to a 230 MPa biaxial stress. Finite Element analysis (ANSYS) was used to model the thermal stress distribution over the micromachined bilayer membrane, yielding a satisfactorily agreement with the experimental results over a large membrane area. The Finite Element analysis was correlated with optical profilometer deflection measurements. Membrane deflections up to 48 μm (more than 10 times the membrane thickness) have been measured. Furthermore, Micro-Raman Spectroscopy results up to 300°C are shown and related to temperature dependent deflection measurements.

New techniques and procedures for measuring Poisson's ratio of MEMS materials are presented. Tensile specimens of polysilicon that are 3.5 μm thick are pulled in a small test machine that has a linear air bearing to eliminate friction. Biaxial strain is measured directly by laser-based interferometry from four gold lines deposited on the specimen surface. The value of Poisson's ratio for vapor-deposited polysilicon is 0.22 +/- 0.01 as determined from 19 tests..

Silicon-based polymers with σconjugated electrons have specific properties; photoreactivity for microlithography and photoconductivity for hole transport materials. To explore the possibility of combining these two properties to develop photoresists with electronic transport capability, photoconductivity of polysilanes is investigated in connection with their photoinduced chemical modification. Increase in photocurrent is observed accompanying photoreaction of poly(dimethylsilane) vacuum deposited films. This increase is found to be greatly enhanced in oxygen atmosphere. Such changes of photocurrent can be explained by charge transfer to electron acceptors from Si dangling bonds postulated to be formed during photoreaction.

A range of techniques were used to characterize p++ silicon layers created by boron diffusion into (001) silicon wafers. These films were characterized by TEM, EBIC/ SEM, triple-axis XRD, SIMS, and modified Schimmel etching. Boron profiles predicted by SUPREM-3 process simulation software were compared to SIMS data. The results revealed gradients in boron and lattice constant, as well as a graded three-dimensional dislocation array from lattice-mismatch stress. Boron precipitation, induced by lattice-mismatch stress and concentrations above the solubility limit, was found to occur preferentially on dislocations. Additionally, the presence of dislocations was shown to affect the boron diffusion profile as well as etch morphology.

The elastic modulus and hardness of materials used in a MEMS acoustic emission sensor were determined using nanoindentation techniques. In addition to testing each individual material, the behavior of four candidate bottom electrode structures, two based on nitride layers and two based on oxide layers, have been evaluated. The multilayer nitride bottom electrode is relatively unaffected by a 950 °C annealing step; however, some evidence of second phase formation in the polycrystalline silicon layer has been observed. Increasing the thickness of the thermally grown silicon dioxide in the oxide based electrodes lowers the measured hardness of the top layer of platinum while increasing the measured modulus of the entire electrode at depths corresponding to the oxide film. Errors of up to 25% in the calculated area of indentation based on the indenter shape function occur for indentations which penetrate both the platinum and oxide films.

Aluminum nitride is a promising material for use in thin-film bulk acoustic wave resonators for applications in RF bandpass filters. This paper discusses the requirements needed for a dc magnetron sputtering system to grow piezoelectrically active films with x-ray diffraction rocking curves of 3.3° on silicon substrates, 5° on aluminum substrates and oxygen concentrations of l at.%. For applications in integrated resonators, a materials characterization is insufficient in predicting the subsequent device performance. A simple acoustic device structure which allows a quick measurement of the device performance is used to extract maximum effective coupling coefficients keff2 of 0.009% at 3.4GHz and 0.002% at 2.4GHz for two different films with rocking curves of 5.7° and 9.0° respectively. This parameter extraction technique may be used to make relative comparisons between films grown under different deposition conditions.

Silicon bulk micromachined piezoresistive pressure sensors are sensitive to stresses caused by the application of inorganic thin films typically used for passivation purposes, and the change in stress that is caused by temperature changes in the operating environment of the sensor. Stress behavior over temperature is characterized for both thermal oxides grown on silicon at thicknesses from 0.18 μm to 0.36 μm, and PECVD silicon nitride films at thicknesses from 0.40 μm to 0.80 μn. Electrical parametric behavior is characterized for typical piezoresistive pressure sensors with these thin films deposited and patterned in several proposed passivation schemes. A finite element analysis is performed to predict how device parameters vary as a function of thin film patterning and properties. Correlations are drawn between model predictions, independent thin film behavior, and device performance.

Microelectromechanical valves have been fabricated from silicon wafers using standard bulk micromachining techniques, which utilize thin (2 μm) films of sputter-deposited titaniumnickel as the actuators. The TiNi shape memory alloy actuators are thermally driven by resistive heating, through the passage of an electric current. TiNi diaphragms (8.4 mm wide) are fabricated and tested in a pressure-temperature controlled fixture in order to determine the mechanical properties of the shape memory film. If a silicon island is left attached to the center of the diaphragm, this can act as a “boss” whose movement against an orifice will open and close the valve. The orifice can be etched into a second silicon wafer or machined from another rigid material. Use of mechanical spacers and external bias springs result in a normally-closed or normally-open configuration. Modulations of up to 90 percent have been observed in gas flows of up to 0.6 liter/min. Water flows as high as 5 ml/min. have been modulated by 60 percent.

The design and fabrication process of a micro-mirror device is presented. The device is driven by sol-gel deposited PZT-layer actuators. The mirror is designed to be able to carry out scanning in two lateral directions, and additionally movement in vertical direction using a FEMsimulation tool. The established fabrication process is described.