Photolithography, water-based

The patterning steps are based on photolithography (Figure 4.26). In this procedure, a photosensitive compound known as a photoresist is first spin-coated onto the surface of the wafer. Frequently, the wafer is pretreated by a dehydration bake (to remove adsorbed water) and application of an adhesion promotor e.g., hexamethyl disilazane, HMDS - used to maintain a strong interaction between the photoresist and Si02 surface - Figure 4.27). 

The solution to photolithographically patterning the active layer of OFETs is to protect the semiconductor from materials it is not compatible with (i.e. organic solvents and water). One approach is to use water soluble resists which do not induce the phase transformation [57]. Another is to encapsulate the transistors using parylene first, and then proceed with normal photolithography and patterning [58]. A third approach is to use fluorinated or supercritical C02"based resist materials which also do not interact with pentacene or other organic semiconductors [59]. 

There has been a spate of recent activity associated with the formation and flow of aqueous droplets in channels surrounded by immiscible oil [10]. The typical configuration is similar to that used for flow cytometry in which a sample flow is injected into a co-fiowing sheath flow. In this chip-based manifestation, however, photolithography is used to fabricate a four-way intersection of channels and the sheath fluid is immiscible. Therefore, the water-oil interfacial tension results in the formation of droplets. Typically, the aqueous sample flow enters the intersection head-on and the two side channels... 

The reproducible drug loading of microcontainers for oral delivery of a poorly water-soluble compound has been detailed (40). A protot5rpe of such a device is made from an epoxy resin using a two-step photolithography process. The microcontainers are designed with a circular base, cylindrical walls, and an open top side with a cylindrical cavity of 50-300 pm in diameter. 

Recently, an anisotropic surface has been fabricated by micropatterned organic monolayers, which were prepared by the chemical vapor adsorption (CVA) method [17]. The CVA is one of the excellent and suitable processes for microfabrication based on photolithography of nanofihns because it produces a remarkably uniform surface without defects or aggregates [18,19]. We reported previously that the line-patterned fluoroalkylsilane monolayers with l-20- jm width showed an anisotropic wetting by a macroscopic water droplet with a 0.5-5-mm diameter [20]. Using this method, an anisotropic friction surface without microtrough or step structure can be... 

Furthermore, devices have been developed demonstrating reactions and passive valves with self assembled mono-layers of OTS via either multi-stream laminar flow or photolithography [9, 10]. The pressure sensitive valves were demonstrated with silane solutions and water with trace amounts rhodamine-B for visualization purposes. The maximum pressure experienced based on capillarity... 

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