David L. Wilcox

Microplasma devices fabricated in silicon, ceramic, and metal/polymer structures: arrays, emitters and photodetectors

Recent advances in the development of microplasma devices fabricated in a variety of materials systems (Si, ceramic multilayers, and metal/polymer structures) and configurations are reviewed. Arrays of microplasma emitters, having inverted pyramidal Si electrodes or produced in ceramic multilayer sandwiches with integrated ballasting for each pixel, have been demonstrated and arrays as large as 30 ? 30 pixels are described. A new class of photodetectors, hybrid semiconductor/microplasma devices, is shown to exhibit photoresponsivities in the visible and near-infrared that are more than an order of magnitude larger than those typical of semiconductor avalanche photodiodes. Microdischarge devices having refractory or piezoelectric dielectric films such as Al2O3 or BN have extended lifetimes (~86% of initial radiant output after 100?h with an Al2O3 dielectric) and controllable electrical characteristics. A segmented, linear array of microdischarges, fabricated in a ceramic multilayer structure and having an active length of ~1?cm and a clear aperture of 80 ? 360??m2, exhibits evidence of gain on the 460.3 nm transition of Xe+, making it the first example of a microdischarge-driven optical amplifier.

Multistage, monolithic ceramic microdischarge device having an active length of ∼0.27 mm

A three-stage, multilayer ceramic microdischarge device, having an active length of ∼267 μm and a cylindrical discharge channel 140–150 μm in diameter, has been developed and operated continuously in Ne gas. Stable glow discharges are produced for pressures above 1 atm, operating voltages as low as 137 V (at 800 Torr), and specific power loadings of ∼40 kW cm−3. The V–I characteristics for a fired ceramic structure exhibit a negative resistance, whereas the resistance is positive prior to firing. The manufacturability of the fabrication process as well as the “flow-through” and multistage design of this device make it well suited for the excitation of gas microlasers or the dissociation of toxic or environmentally hazardous gases and vapors.

Effects of alumina on devitrification kinetics and mechanism of K2O-CaO-SrO-BaO-B2O3-SiO2 glass

Effects of alumina on the devitrification kinetics and mechanism of a low-dielectric K2O–CaO–SrO–BaO–B2O3–SiO2 glass powder have been investigated. Crystalline phases including cristobalite (SiO2) and pseudowollastonite [(Ca, Ba, Sr)SiO3] are formed during the firing of the pure glass. With added alumina content greater than a critical value, e.g., 10–20 vol% at 900–1000°C, the above crystalline phases are completely prevented but anorthite [(Ca, Sr, Ba)Al2Si2O8] is formed. This result is attributed to the dissolution of alumina into the glass. The dissolution changes the composition of the glass to become aluminum-rich, and the dissolution kinetics of alumina into the glass is far too rapid compared with the formation of cristobalite and pseudowollastonite. The crystallization kinetics of anorthite follows the analysis of the Avrami equations, and the results show an apparent activation energy close to that of the Al–O bond strength, suggesting a reaction-controlled kinetics.

Add Ceramic “MEMS” to the Pallet of MicroSystems Technologies

Just as the 40+ years of technology developments associated with the electronic application of semiconductor fabrication processes is “morphing” into a micro-electro- mechanical systems (MEMS) technology in the past dozen years or so, so it seems may the “mature” multilayer ceramic fabrication technology associated with capacitor components and interconnect substrates for the integrated circuit industry, be morphed into MEMS – microsystems technology applications. This paper highlights work underway in Motorola Labs aimed at exploring the potential to develop 3D multilayer ceramic structures to integrate (monolithic and hybrid) multiple functions to create microsystems for wireless, energy and life science applications. By multiple functions, we refer to the ability for a microsystem to perform electronic, fluidic, thermonic, photonic and mechatronic (or actuator) based functions. Current capabilities of the multilayer ceramic materials and processes to achieve integrated functionalities for wireless applications will be described including the development of a new dielectric enabling increased performance for wireless applications. Also to be highlighted will be exploratory microscale fuel cell prototypes exploiting advances in the multilayer ceramic lamination and feature forming technologies enabling the insertion of 3D microchannels for microfluidic functions. These prototypes also feature the ability of the technology to provide thermonic functionality for microreactor devices. Feasibility of a light source that can be integrated into the technology platform hinting at photonic applications will be described. Many materials science and engineering advancements are needed to achieve the potential of this “old” but newly “morphing” technology and some of these will be noted.

Sintering of a crystallizable K2O-CaO-SrO-BaO-B2O3-SiO2 glass with titania present

Crystallization and reaction kinetics of a crystallizable K 2 O-CaO-SrO-BaO-B 2 O 3 -SiO 2 glass powder with 1-40 vol% titania powder were investigated. The initially amorphous K 2 O-CaO-SrO-BaO-B 2 O 3 -SiO 2 glass powder formed cristobalite (SiO 2 ) and pseudowollastonite [(Ca, Ba, Sr)SiO 3 ] during firing. The above crystalline phases were completely replaced by a crystalline phase of titanite [(Ca,Sr,Ba)TiSiO 5 ] when the amount of added titania was greater than a critical value, e.g., 10 vol%, at 99-1100 °C. A chemical reaction taking place at the interface between titania and the glass was attributed to the above observation. The dissolved titania changed the composition of the glass, and the dissolution kinetics was much faster than the formation of cristobalite and pseudowollastonite. Activation energy analysis showed that the crystallization of titanite [(Ca,Sr,Ba)TiSiO 5 ] was controlled by a reaction-limiting kinetics of formation for the Ti-O bond.