in Wiley InterScience (www.interscience.wiley.com).Design methodology and flow characterization of a miniaturized trickle-bed system for singlet-oxygen production via exothermic reaction of chlorine gas and basic hydrogen peroxide aqueous solution are reported. Miniaturized singlet oxygen production is accomplished by integration of several components developed for microsystems (uniform phase distributors, integrated on-chip cooling, and capillary-based phase separation) within a single device. Macroscale design equations for pressure-drop and heattransfer rates are verified experimentally in the miniature trickle-bed reactor. Flow regime data from the present study are summarized with previous reports in microdevices and compared to conventional multiphase flow maps; these maps are found to be incapable of accurately predicting the flow regime trends within the miniaturized trickle-bed system. Operation of the silicon-based miniaturized trickle-bed reactor achieved estimated singlet-oxygen yields of 78%, comparing well with the reactor model predictions.

We present a way of predicting spatial nonuniformity in deep reactive ion etching ͑DRIE͒. In addition to well-known feature size or aspect-ratio-dependent etch ͑ARDE͒ nonuniformity, etch rate can vary between regions of the wafer, such that supposedly identical microelectromechanical systems ͑MEMS͒ fabricated on that wafer may vary in performance or fail in use. Wafer-and die-scale uniformity may be improved by changing conditions in the etching chamber, but this usually compromises etching speed and may accentuate ARDE. An alternative approach is to lay out the patterns being etched so that they compete for reactants in a controlled way. We demonstrate a way of precharacterizing any DRIE tool plus associated "recipes" of operating parameters. Several test wafers are etched and measured, and simple data-fitting algorithms are run. The model constructed captures etch nonuniformity occurring over the diameter of a wafer plus variations caused by the localization of patterns within the wafer. Our technique models etch rate variation across experimental wafers with fitting errors of between 0.8 and 4.5% root-mean-square per wafer. Our model can then predict etch rate on a 1 mm lateral grid for any etched pattern. We envisage this method being integrated into computer-aided MEMS design systems.

Wafer and die level uniformity effects in Deep Reactive Ion Etching (DRIE) are quantitatively modeled and characterized. A two-level etching model has been developed to predict non-uniformities in high-speed rotating microstructures. The separation of wafer level and die level effects is achieved by sequentially etching wafers with uniformly distributed holes. The wafer level loadings range from 0.06% to 17.6%. Resulting wafer maps reflect the transition from an ion-limited region to a neutral-transport limited region. Additionally, long-range die-level interactions are also evaluated. Resulting die-level etching non-uniformities have a comparable magnitude to wafer-level effects. A model taking into account both the diffusion and reaction rate of neutrals is applied to predict the etching of up to 21 dies. Agreement between measurement and prediction support the hypothesis that the depletion of radicals is the main cause of die-level etch variation. The characterization and prediction methods are applied to etching a micro-scale turbine engine.

The design, creation, and demonstration of a singlet oxygen generator (SOG) that operates on the microscale are presented. The micro singlet oxygen generator ( SOG) chip creates singlet delta oxygen (O 2 ( 1 )) in an array of packed bed reaction channels fed by inlets with pressure drop channels to equalize flow. An integrated capillary array separates the liquid and gas byproducts, and microscale cooling channels remove excess heat of reaction. The fabrication process and package are designed to minimize collisional and wall deactivation of O 2 ( 1 ). Flow behavior and capillary separation are characterized over a range of plenum (gas outlet) pressures and feed rates. The testing setup enables measurement of O 2 ( 1 ) via optical emission measurements and mass spectrometry. Spontaneous decay of the O 2 ( 1 ) molecule into its triplet state is observed, confirming the production of O 2 ( 1 ).

Travel support has been generously provided by the Transducers Research Foundation and by the DARPA MEMS and DARPA BioFlips programs.