Device Substrates

A thin film ( 100 nm) of a PPV derivative is sandwiched between two electrodes supported on a solid substrate, such as glass, a flexible plastic substrate, such as poly(propylene), or even a thin film of aluminium, see Figure 6.1. The device substrate provides the mechanical support to the anode, electroluminescent polymer layer and the cathode. The anode is transparent in... 

Figure 4.6 Schomatic representation of a diin polymer film formed on an impermeable AW device substrate. The SAW device probes the ctmcentration profile C( r,0 integrated over the film thickness. (Reprimed with pentiiasion. See Ref. 86J.)...

Note that the acoustic wavelength in the film depends on the velocity of sound in that material and can therefore be very different (often much smaller) than the wavelength in the AW device substrate, Consequently, the 1% rule" is an approximation, at best, unless correction is made for the acoustic wavelength in the film. 

The first practical problem to be addressed is the fabrication of acoustic-wave sensor devices. While some devices are commercially available (see Appendix D), a researcher may need a unique device in order to investigate some previously unexplored aspect of AW sensors and their interactions with their environment. It is therefore quite valuable to understand basic device configurations, fundamental design principles, the different properties of the range of materials that can serve as device substrates, fabrication practices, and coating technologies. These issues are addressed in Section 6.2. 

The two metallizations most commonly used to fabricate transducers on AW devices are gold-on-chromium and aluminum. Au is often chosen for chemical detection applications because of its inertness and resistance to corrosion a layer 100-200 nm diick is necessary to provide adequate electrical conductivity. Unfortunately, the inertness of Au also prevents its adhesion to quartz and other oxides utilized for AW device substrates. Therefore, an underlayer of Cr (2-10 nm thick) is utilized to promote the adhesion of Au to the substrate the electropositive (reactive) nature of Cr allows it to form strcxig bonds with oxide surfaces, while alloying between the Cr and Au chemically binds the two metal layers... 

Nanofibers can also be deposited directly on device substrates. Polyaniline being soluble, the electrospinning process has been successfully utilized for the production of polyaniline nanofibers [48]. However, this process cannot be directly employed for producing PPy nanofiber due to the intractability of PPy. 

Delamination may be complete or partial. Complete delamination results in gross separation of the device, substrate, or other adherend. Partial debonding can result in device or substrate cracking with complete detachment occurring in time. Numerous factors and mechanisms contribute to delamination, some of which are as follows ... 

Many sputtered metals do not adhere particularly well to typical device substrate materials such as silicon, glass, and polymers. For example, noble metals such as Au can only rely on van der Waals forces for adhesion, and these forces are relatively weak. Metals such as Cr, Al, and Ti readily form a suboxide interface layer on glass and so they are often used as adhesion layers. 

DI Adhesion to Device substrate Contrast enhancement Loading capacity Solubility Dark Erosion Resistanc e... 

We also evaluated contact an es on various device substrates (Si02, Al, poly Si, TiN) and measured minimum dot i-line resist pattern size fabricated on each substrate using each adhesion promoter. 

T. Urushidani, S. Ogino, Surface PoUshing of Silicon Carbide Electronic Device Substrate Using Ce02, US 5750434, 1998. 

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