Temperature-Dependent Materials Research with Micromachined Array Platforms
This chapter describes the efficiency of studying temperature-dependent materials processing/property/performance relationships with MEMS-based microarrays. Varied types of microsamples (~ 100 m x 100 m in lateral dimension, and of thicknesses between ~ 10 nm and ~ 1000 nm or more) have been deposited on microhotplate elements that were replicated to produce the arrays. Each array element is individually addressable through integrated electronic leads, so that heating and temperature measurement can be performed on selected elements, and localized microsamples can also be electrically characterized. The microarray studies used in the illustrations of the approach were conducted to develop improved sensing films for solid state gas microsensors, and benefited greatly from the ability to use localized temperature control in depositing multiple samples and evaluating their performance. This application is an obvious one for MEMS microarrays, as the 16-element and 36-element arrays used in the example studies are essentially larger versions of the 4-element arrays we are using to fabricate chemical microsensor prototypes. However, the potential value of the methodology for other technological areas, such as in developing catalysts, photovoltaics or electronic materials, should also be clear from the presented work. As for the sensor materials case studies, other technical areas will have application-specific hurdles relating to design and fabrication of the most appropriate microarray platforms, localization of the library materials, characterization of microsample properties, and assessment of application-defined performance. In certain instances the rapid heating and cooling characteristics of the microhotplates will be especially important in providing novel thermal programs for depositing and testing films.There appear to be two critical points that must be focused on to carry micromachined array methods forward, more generally, as an important tool in the area of combinatorial materials science. The first is a challenge to develop external probes that can provide, on an acceptably fast time scale, viable signals for characterizing and evaluating large numbers of samples with very small areas and total volumes. The second is a challenge of sorts, as well, for researchers to use the tremendous flexibility offered by evolving microfabrication technology (Si micromachining, as emphasized here, but also micromachining of other materials, and a broad range of new techniques for constructing microdevices, nanodevices, and microanalytical systems) to tailor arrays with the specialized functionality necessary for a specific multielement materials study.