Patricia A. Beck

Fracture testing of bulk silicon microcantilever beams subjected to a side load

A custom experimental system was developed to fracture silicon microcantilever beams in side loading (i.e., the load was applied in the noncompliant direction), and the resulting force/deflection (stiffness) characteristics were obtained. A finite element model of these structures was analyzed using ABAQUS, and the resulting model stiffness correlated well with the experimental data. Fracture types were divided into two categories, {111} and {110}, according to the type of silicon crystalline plane along which fracture occurred. The initiation location of each fracture type was identified. The fracture stress (strength) in the beam was obtained from the stress produced in the model at the fracture initiation site for a load equivalent to the experimental fracture force. Numerous beams were tested, and the statistical results were compiled. The distributions and statistical data from each of the fracture types were compared to each other and to previously acquired results from front/back loading (i.e., loading in the compliant direction) of these same structures. Side-loading results indicated that the {110} fracture type had a greater fracture strength than the {111} type. Based on a comparison of the side loading data with the front/back loading data, it was concluded that side wall roughness and especially the edge roughness greatly affected the fracture strength of the silicon micromechanical structures.

Surface properties of platinum thin films as a function of plasma treatment conditions

We examined the surface properties of platinum (Pt) thin films exposed to oxygen and argon plasma treatments and compared them to as-deposited Pt films. The surface wetting properties, refractive index and extinction coefficient of the Pt films were monitored as a function of time after different plasma treatments. Surfaces treated with an oxygen plasma were dramatically different from as-deposited Pt, whereas argon plasma treated surfaces were similar to as-deposited films. X-ray photoelectron spectroscopy confirmed the formation of platinum oxide on films treated with an oxygen plasma, while such oxide diminished after argon plasma treatment. Surface morphology studied with atomic force microscopy indicated a strong dependence of the surface roughness of the Pt films on the power and duration of the argon plasma used for the treatment. Based on these studies, an oxygen plasma treatment followed by a brief low-power argon plasma etch was developed for the purpose of regenerating clean and metallic Pt surfaces, and at the same time providing the smoothest possible surface morphology.

Transient-current characteristics of dispersed charges in a non-polar medium

— Transient currents of reverse micelles in a non-polar solvent from voltage step stimuli were studied to investigate the electrophoretic behavior of the charges. The current showed a sharp peak directly after the voltage application and decayed afterward while it exhibited various time-dependent transients depending on the applied voltage and the charge content after the bias was removed. A one-dimensional drift-diffusion model could reproduce the behaviors for various conditions. The forward transient could be well-explained by a simple capacitor-charging model with a limited charge. It turned out that the broad peak in the reverse transient current is formed by a competition between an increasing number of charges available for drift and a decreasing electric field resulting from mixing of opposite charges and that the full development of the peak is a good indication of complete polarization of the charges. The slow initial release of charges from the electrodes is due to the electric field developed by accumulated charges that decreases as the charges are released by diffusion. The high density compaction of charges against the electrodes reduces electric-field screening by the accumulated charges and enables more accumulation, but individual charge-to-charge interaction limits the density.

High Current Density in m c-Si PECVD Diodes for Low Temperature Applications

The development of microcrystalline diodes grown at low temperature by PECVD techniques is reported. Current densities near 200 A/cm 2 at + 2 V, and rectification ratios on the order of 10 5 at +/- 1V and 10 7 at +/- 2V were obtained. The reverse currents were in the nano-ampere range. Correlations between deposition conditions and film quality are presented. The effects of mesa formation and subsequent treatments designed to reduce process damage are discussed: annealing conditions yield an increase in forward current, and a decrease in reverse current. Fabrication conditions are compatible with applications requiring low temperature processes (e. g., multi-layer structures, molecular layers, or plastic substrates and coatings).

Effects of hydrogen on InP light-emitting devices etched in a methane-hydrogen environment

Research has been conducted on the physical damage and hydrogenation effects during RF plasma exposure and epitaxial growth in the III-V material system. Device consequences of this damage or chemical alteration have received less attention, particularly in active light emitting devices. This paper discusses these effects for lasers and edge emitting light-emitting diodes (EELEDs) which use a ridge waveguide structure. By using analysis techniques such as SIMS we have concluded that methane-hydrogen reactive ion etching of InP induces hydrogen levels in an active device which are high enough to significantly alter the device properties. The decrease in light output is substantial, but subsequent annealing times as short as 1 min. at 430/spl deg/C can restore power dramatically.