Lift-off technology

In order to maintain the advantage of the microfabrication approach which is intended for a reproducible production of multiple devices, parallel development of membrane deposition technology is of importance. Using modified on-wafer membrane deposition techniques and commercially available compounds an improvement of the membrane thickness control as well as the membrane adhesion can be achieved. This has been presented here for three electrochemical sensors - an enzymatic glucose electrode, an amperometric free chlorine sensor and a potentiometric Ca + sensitive device based on a membrane modified ISFET. Unfortunately, the on-wafer membrane deposition technique could not yet be applied in the preparation of the glucose sensors for in vivo applications, since this particular application requires relatively thick enzymatic membranes, whilst the lift-off technique is usable only for the patterning of relatively thin membranes. 

A variation of the selective Cu deposition process, limited to electroless Cu deposition, is the lift-off process, known as a planarized metallization process [102]. Figure 39 shows a process sequence for this technology. 

Epitaxial lift-off (ELO) was a promising emerging technology for SPAs in the mid-1990s, and still may find a market niche in LED-based displays, but it now appears likely that ELO will be replaced by wafer fusion (refer to Section II.A.3), especially for thin-film VCSEL SPAs. Wafer-fused SPAs are not listed in Table II since the reported work to date has been only in realizing improved... 

Clearly, heat transfer, flammability and catalyst stability are the major concerns of fixed-bed technology. In the early 1990s, tests were conducted at a commercial plant to increase MA productivity by feeding butane concentrations beyond the flammability limit (which is nominally 1.8 vol% butane in air). Apparently, the butane feed concentration in the vessel approached 2.3 vol% before the reactor head lifted off the body of the vessel (the reactor was designed to allow for such an event). Many patents have been issued that claim the interior vessel walls can be passivated to reduce the frequency of free radical formation (or quench free radicals). Free radicals initiate thermal events that lead to combustion or deflagration and even to detonation when the flame front exceeds the speed of sound. 

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