Gold layer, thin film sensors

The thin film sensors were deposited on 20 mm right angle prisms for characterization. The test apparatus was sealed to protect the film from the surrounding air and to expose the films to predetermined gas mixtures, as shown in Figure 1. The sensors consisted of three layers 40 nm gold, 600 nm W03 and 3 nm palladium. Figure 2 shows a set of spectra... 

For thin-film metallization, a thin metallic film is first deposited onto the surface of the substrate. The deposition can be accomplished by thermal evaporation, electronic-beam- or plasma-assisted sputtering, or ion-beam coating techniques, all standard microelectronic processes. A silicon wafer is the most commonly used substrate for thin-film sensor fabrication. Other substrate materials such as glass, quartz, and alumina can also be used. The adhesion of the thin metallic film to the substrate can be enhanced by using a selected metallic film. For example, the formation of gold film on silicon can be enhanced by first depositing a thin layer of chromium onto the substrate. This procedure is also a common practice in microelectronic processing. However, as noted above, this thin chromium layer may unintentionally participate in the electrode reaction. 

Aluminum Oxide Moisture Sensor. This type of sensor is a capacitor, formed by depositing a layer of porous aluminum oxide onto a conductive substrate, and then coaling the oxide with a thin film of gold The conductive base and the gold layer become the capacitor s electrodes. Water vapor penetrates the gold layer and is absorbed by the porous oxidation layer The number of water molecules absorbed determines the electrical impedance of the capacity, which is. m turn, a measure of water vapor pressure. 

A miniaturized planar amperometric glucose sensor has been created on Sapphire substrates. Thin film titanium-gold electrodes are covered with an enzyme layer which is patterned by a lift-off technique [66]. This sensor exhibits a fast response time of 30 seconds but the linear measuring range is poor. 

Tungsten trioxide thin films activated by gold layers have also been used for NOj. detection.115 This material possesses excellent sensitivity towards nitric oxide and nitrogen dioxide. An automobile exhaust gas NO sensor that uses a gold-platinum alloy electrode has also been reported.116... 

WO3 thin films activated by An layers have been used [625]. This type of material possesses excellent sensitivity towards NO and NO2 gases. An exhaust gas NOj sensor that uses a platinum-gold alloy electrode to selectively remove oxygen but not NO was also reported [626]. 

Thicker platinum layers are used extensively for temperature sensors, for example, deposited on ceramic substrates. Compared to other thin film metals, such as gold, silver, or nickel, platinum has a low thermal expansion coefficient, thus minimizing stress problems due to the differential thermal expansions of the various membrane layers. 

The thin films or coatings can be studied nondestructively, with no sample preparation other than deposition on a polished metal surface if necessary. Specular reflectance has been used to study lubricant films on computer disks, oxide layers on metal surfaces, paint curing as a function of time, and molecules adsorbed on surfaces. For example, the IR absorption spectrum of proteins adsorbed onto a polished gold surface can be studied. This spectrum from an adsorbed layer can form the basis of sensors for compounds that will bind to the proteins and change the spectrum. Use of a polarizer in conjunction with grazing angle analysis can provide information about the orientation of molecules adsorbed onto surfaces. 

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