Photolithographic techniques

By photolithographic techniques, we most specifically mean multi-color photolithography where spatially controlled index of refraction variations are created by photo-initiation of physical and chemical changes in the material. Again, this topic has been reviewed in considerable depth elsewhere so we will only briefly review the central concept here [2,3,5,63,64]. 

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This type of coil was prepared from copper cladded printed circuit board material by applying photolithographic techniques. The p.c. board material is available with difierent copper thicknesses and with either a stiff or a flexible carrier. The flexible material offers the opportunity to adapt the planar coil to a curved three dimensional test object. In our turbine blade application this is a major advantage. The thickness of the copper layer was chosen to be 17 pm The period of the coil was 100 pm The coils were patterned by wet etching, A major advantage of this approach is the parallel processing with narrow tolerances, resulting in many identical Eddy current probes. An example of such a probe is shown in fig. 10. 

As the complexity of integrated circuits increases and the dimensions of each circuit element decrease, greater demands are placed on the lithographic process, particularly with respect to resolution. Indeed, we are rapidly approaching the limits of photolithographic techniques for reproduc-... 

Many of the variations developed to make pressure sensors and accelerometers for a wide variety of applications have been reviewed (5). These sensors can be made in very laige batches using photolithographic techniques that keep unit manufacturing costs low and ensure part-to-part uniformity. A pressure differential across these thin diaphragms causes mechanical deformation that can be monitored in several ways piezoresistors implanted on the diaphragm are one way changes in electrical capacitance are another. 

II), effective at 193 nm were prepared by the authors (1,2), respectively, and used in the fabrication of semiconductor devices by photolithographic techniques. 

An alternative to DNA chips is to miniaturize DNA sequencing and analysis machinery. Using nanoliter droplets of fluid passing through microchannels built by photolithographic techniques of computer chip construction, these nanolaboratories may be the size of a credit card but able to cleave DNA and conduct PCR reactions, gel electrophoresis, and sequence determinations.435 436... 

A two-dimensional array was patterned by standard photolithographic techniques on a substrate [99], An open fluid reservoir was achieved simply by sealing the internal part of the device, including the array, with an O-ring. This open-face arrangement was for laboratory experiments, while the device has to be sealed for later practical uses. A hydrophobic coating served for electrical insulation. The device was connected to a computer-controlled switching circuit. 

Amlani et al. [49] combined conventional photolithographic techniques with self-assembly aspects to form a metal-SAM-metal-SAM-metal junction. Au-covered electrodes with a separation of 40-100 nm were covered with SAMs of OPEs or alkanethiols and an Au nanoparticle (d = 40-100 nm) was trapped in the gap between the electrodes by applying an alternating-current bias. An illustration of the system is shown in Fig. 10.13. 

Two important points were established at an early stage of the present development. The first is that conventional photolithographic techniques, widely used in the semiconductor industry, can be applied successfully to a-Si H thin-film devices. The second equally relevant point is that the a-Si H FETs perform adequately at voltages below 15 V, so that they are compatible with modern integrated-circuit vol tage levels. 

Then the surface of the undoped layer must be oxidized. This can be done in two ways (1) The sample can be exposed to air at room temperature for several days to permit the growth of a thin oxide layer and then the oxide thickness can be evaluated according to available data on the oxidation of a-Si H as a function of time, already examined by Ponpon and Bourdon (1982). (2) The oxidation could be obtained by leaving the sample (Abeles et al., 1981 Wronski et al., 1981), at a given temperature (100- 200°C) in a cleaned chamber, in the presence of pure Oz. Finally, a Pd film, whose thickness can range between 80 and 500 A, can be thermally evaporated to complete the procedure. Photolithographic techniques and lift-off procedures can be used to define the catalytic area. Figure 6 shows a schematic of a typical MIS structure with the overall dimensions. 

FIG. 6.1. Schematic diagram of the thin film transistor using an -6T polymer for the active layer [155]. Gold source and drain pads are fabricated using the photolithographic technique. The gate length varied between 2.5 and 150 nm and the width was 250 pm. The polymer (from 2.5 to 150 nm thick) is sublimed over the contacts. 

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