Lift-off method

A first ZnS film 2, an aluminium film and a second ZnS film 4 are formed on top of each other on an HgCdTe substrate. The second insulating film 4 is selectively removed by a photoetching method and first transfer electrodes 3 are formed by removing the exposed aluminium film. Subsequently, a film of aluminium is deposited and patterned into second transfer electrodes 5 by a lift-off method. 

Fig. 8. Flow diagram for constructing a photolithographic enzyme membrane by three methods (1) direct photolithographic patterning method (2) micropool injection method (3) lift-off method. UV, ultraviolet light M, photomasL (Reproduced by permission of CMC Press, Tokyo, Japan.)...

The micropool injection method was developed by Miyahara et al. (20), and independendy by Kimura and his collaborators (15,16, 43). It was successfully used for a monolithic enzymatically coupled FET, sensitive to urea and glucose, and for the urea-, glucose-, and potassium-sensitive trifunctional FET biosensor (see Section 2.3). The thickness of an enzyme membrane is about 10 pm, and the thickness of an enzyme-immobilized membrane prepared by the ink jet-micropool injection method is 0.1 -1 pm. The lift-off method was developed by Kimura and Kuriyama s group and used for the deposition of a urease- and a glucose oxidase-immobilized membrane (16, 17) (see Fig. 8(3)). The enzyme membrane thickness is similar to the thickness of the film resist layer, about 1 pm thick. 

Fig. 73. Schematic representation of the lift-off method for enzyme coating of FETs. (Redrawn from Nakamoto et al., 1987).

On the other hand, with a somewhat different approach, Dong, et al, showed that it is also possible to fabricate CPNWs using a lift-off method following CP layer deposition on patterns in a resist layer created by NIL (Figures 10.2 and 10.3) [8]. 

Figure 6.13. Experimental arrangement of the hot-explosive compaction method for the preparation of consolidated Ni-Al alloys (after Kecskes etal. 2004). (a) Precursor powder sample inside a steel-tube container placed in, (b) an asbestos thermal insulation sheet (c) a concentric card-box filled with the powdered explosive (80% NH4NO3 + 20% TNT) (d) threaded steel plugs serving as contacts for the preliminary heating and to be lifted off just before detonating the explosive (e) detonating cords.

Like almost any other technique, thermoelectric power, does however also have some of its own limitations. For example, thermoelectric power is a contact method, which means that if hydrogen content needed to be measured on the exterior of a coated pipeline, the coating would need to removed, however in-line pig inspection would allow for in-situ inspection of the pipeline inner wall. In these limited cases, alternative complimentary techniques can be utilized. Low frequency impedance measurements can provide an alternative non-destructive, non-contact method of measuring hydrogen through an entire specimen thickness, dependent upon lift-off. 

A jet flame in the presence of a crosswind has been addressed (Brzustowski et al., 1975a Gollahalli et al., 1975 Kalghatki, 1983). Generally, the flame can be considered as the frustum of a cone, with increasing flame diameters further from the nozzle. Calculation methods and the effects of wind on the jet flame diameter and lift-off distance are presented in the literature (Beyler, 2002 SINTEF, 1997). 

Theoretically, electrical patterning is one the simplest method to structure materials since they can be patterned directly on the surface of an electrode. Creating conducting microelectrodes is, nowadays, fast and simple using micro and nanotechnology tools. Deposition and etching, or deposition followed by lift-off, are the conventional methods [35], Other solutions based on electrodeposition of metals... 

The lift-off process is usually employed to fabricate metal electrodes. This method, as opposed to the wet-etch process, allows the dual-composition electrode to be patterned in a single step [747]. In order to achieve well-defined metal electrodes in a channel recess using the lift-off technique, the metal (Pt/Ta) will not be deposited onto the sidewalls of the photoresist structure (see Figure 2.32). This discontinuity of the deposited metal layer around the sidewalls allows metal on the resist to be removed cleanly from the surface without tearing away from the metal on the surface. Thus negative resists were used because they can be easily processed to produce negatively inclined sidewalls. To achieve this, the photoresist is subjected to underexposure, followed by overdevelopment [141]. 

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