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Wafer scale arrays of nanostructured titania ͑NST͒ sensing elements have been fabricated using standard microfabrication techniques. Sensing elements are 20 m on a side and formed by the oxidation of titanium thin films in aqueous hydrogen peroxide. NST elements are highly sensitive to oxygen, but only slightly sensitive to hydrogen. High sensitivity to hydrogen is achieved by modification of the sensors with platinum. A platinum salt solution is introduced to the NST sensor elements and subsequently thermally decomposed. When exposed to 10 mT of hydrogen at 250°C, the functionalized devices exhibit over a one-order-ofmagnitude resistance decrease with a response time of ϳ7 s; conversely, unmodified NST exhibit little, if any, response under the same conditions. Proposed sensing mechanisms of the NST elements are briefly discussed.An ongoing effort in chemical sensor research is the miniaturization of devices. One approach to achieving this goal is the use of nanostructured materials as the sensing element; their high surfaceto-volume ratio can yield very sensitive devices with micron-scale footprints. Metal oxides have proven to be a good candidate for this application due to their established functionality as a sensing platform and the numerous existing routes to their formation in a nanostructured configuration. With regard to titania, thin films of nanorods, nanotubes, and inverse opal structures have been formed by electrospinning, anodic oxidation, and templating methods, respectively. [1][2][3] Titania was first investigated as a chemical sensor for the monitoring of oxygen in automobile exhaust. Research on these lambda sensors focused on the rutile phase of titania due to the stability of this phase in the high-temperature operating environments of an exhaust sensor. 4 More recently, the anatase phase of titania has received considerable attention as a gas-sensing material. Anatase has a less dense crystal structure, and studies on both bulk single crystals and sputtered thin films have shown that the Hall mobility in the anatase phase is one to three orders of magnitude greater than in the rutile phase. Studies also found that the mobility was n-type and carriers are generated thermally from shallow donor sites arising from oxygen vacancies. 5,6 Anatase titania has been shown to be sensitive to O 2 , H 2 , and C 2 H 4 , in porous ceramic, thin-film, and nanostructured arrangements. 1,[7][8][9][10][11] One method of forming nanostructured titania ͑NST͒ is to oxidize metallic titanium in a hydrogen peroxide solution. 12 Recently, members of our group developed processes to integrate this method of NST formation with standard microfabrication techniques to create arrays of micron-scale, individually addressable nanostructured thin films. 13 These devices, which were annealed to form the anatase phase, exhibited a two-order-of-magnitude resistance increase when exposed to millitorr levels of oxygen at 200°C. 11 Because these thin films are microlithographically defined, large arrays of individually addressa...

A novel wicking material using nanostructured titania grown on high aspect ratio titanium micropillars is demonstrated. High aspect ratio titanium micropillars were micromachined from bulk titanium sheets. Nanostructured titania was then grown on the surface of titanium micropillars by oxidation in aqueous hydrogen peroxide solution followed by thermal annealing. The nanostructured titania formed has an open porous structure with a nanoscale pore diameter and wall thickness. X-ray diffraction and pole figure studies indicate the formation of anatase phase of titania and the absence of a preferred orientation in the porous film. The hybrid nanostructured titania on titanium micropillars has excellent hydrophilic properties with a water capillary speed comparable to or exceeding that of conventional wick materials commonly used in heat pipes for the thermal management of electronic devices.

Microstructured titanium (Ti) surfaces often suffer from poor hydrophilicity which makes the realization of open microfluidic devices difficult. Here, we investigate the effect of a superficial porous titania (TiO2) layer on the hydrophilicity of microstructured surfaces. High aspect ratio Ti micropillars were micromachined from bulk Ti sheets. Porous TiO2 was subsequently grown on Ti micropillars by a wet oxidation route followed by thermal annealing. Porous TiO2 was characterized using atomic force microscopy, x-ray diffraction and x-ray photoelectron spectroscopy. Detailed morphology study and pore size analysis were carried using focused ion beam machining coupled with scanning electron microscopy. Static contact angle and dynamic spreading studies clearly demonstrate enhanced hydrophilicity of microstructured Ti surfaces with a superficial porous TiO2 layer. Such enhancement promises interesting applications in the microfluidics and microsystems fields.

This paper presents a new type of control scheme and device for controlling gas flow into semiconductor process chambers. The key component of the Gas Flow Controller (GFC) is a high-precision valve with an integrated position sensor, which is used to maintain a constant flow rate. A map lookup scheme is employed to adjust the valve position to accommodate the upstream pressure, including any changes or disturbances. The layout of the flow controller also allows for the incorporation of a pressure-volume-time-temperature-based flow measurement, which is a primary standard flow measurement, to confirm and maintain flow accuracy throughout the device's lifetime. The fast response time of the sensors and the high sampling rate in the control loop enables the control of the gas flow within the order of tens of milliseconds.