Thin film insulator

The essential principle of an active matrix display is that each pixel has associated with it a semiconductor device that is used to control the operation of that pixel. It is this rectangular array of semiconductor devices (the active matrix) that is addressed by the drive circuitry. The devices, which are fabricated by thin-film techniques on the inner surface of a substrate (usually glass) forming one wall of the LCD cell, may be either two-terminal devices (Fig. 6) or three terminal devices (Fig. 7). Various two-terminal devices have been proposed ZnO varistors, MIM devices, and several structures involving one or more a-Si diodes. Much of the research effort, however, has concentrated on the three-terminal devices, namely thin-film, insulated-gate, field-effect transistors. The subject of thin-film transistors (TFTs) is considered elsewhere in this volume suffice it to say that of the various materials that have been suggested for the semiconductor, only a-Si and poly-Si appear to have serious prospects of commercial exploitation. 

Lindsay, A. E., O Hare, D. A comparative study of thin film insulation techniques for gold electrodes, Electrochim. Acta 2006, 51, 6572-6579. 

Polymers. The Tt-conjugated polymers used in semiconducting appHcations are usually insulating, with semiconducting or metallic properties induced by doping (see Flectrically conductive polymers). Most of the polymers of this type can be prepared by standard methods. The increasing use of polymers in devices in the last decade has led to a great deal of study to improve the processabiUty of thin films of commonly used polymers. 

PPQs possess a stepladder stmcture that combines good thermal stabiUty, electrical insulation, and chemical resistance with good processing characteristics (81). These properties allow unique appHcations in the aerospace and electronics industries (82,83). PPQ can be made conductive by the use of an electrochemical oxidation method (84). The conductivities of these films vary from 10 to 10 S/cm depending on the dopant anions, thus finding appHcations in electronics industry. Similarly, some thermally stable PQs with low dielectric constants have been produced for microelectronic appHcations (85). Thin films of PQs have been used in nonlinear optical appHcations (86,87). 

Deposition of Thin Films. Laser photochemical deposition has been extensively studied, especially with respect to fabrication of microelectronic stmctures (see Integrated circuits). This procedure could be used in integrated circuit fabrication for the direct generation of patterns. Laser-aided chemical vapor deposition, which can be used to deposit layers of semiconductors, metals, and insulators, could define the circuit features. The deposits can have dimensions in the micrometer regime and they can be produced in specific patterns. Laser chemical vapor deposition can use either of two approaches. 

Anodic Oxidation. The abiUty of tantalum to support a stable, insulating anodic oxide film accounts for the majority of tantalum powder usage (see Thin films). The film is produced or formed by making the metal, usually as a sintered porous pellet, the anode in an electrochemical cell. The electrolyte is most often a dilute aqueous solution of phosphoric acid, although high voltage appHcations often require substitution of some of the water with more aprotic solvents like ethylene glycol or Carbowax (49). The electrolyte temperature is between 60 and 90°C. 

Sample requirements Solid conductors and insulators typically, <2.5 cm in diameter, and < 1 cm thick, polished flat particles, rough surfaces, and thin films... 

In quadrupole-based SIMS instruments, mass separation is achieved by passing the secondary ions down a path surrounded by four rods excited with various AC and DC voltages. Different sets of AC and DC conditions are used to direct the flight path of the selected secondary ions into the detector. The primary advantage of this kind of spectrometer is the high speed at which they can switch from peak to peak and their ability to perform analysis of dielectric thin films and bulk insulators. The ability of the quadrupole to switch rapidly between mass peaks enables acquisition of depth profiles with more data points per depth, which improves depth resolution. Additionally, most quadrupole-based SIMS instruments are equipped with enhanced vacuum systems, reducing the detrimental contribution of residual atmospheric species to the mass spectrum. 

GDMS cannot be used instead of SSMS. As GDMS source designs are developed to allow clean, thin-film analyses, and some limitations are accepted for the analysis of insulators, GDMS instrumentation will replace more and more of the older SSMS installations. For the present, however, there are exceUent laboratories having SSMS instrumentation and services, and SSMS should be used when it proves to be the technique of choice. 

Polyethylene is a wax-like thermoplastic softening at about 80-130°C with a density less than that of water. It is tough but has moderate tensile strength, is an excellent electrical insulator and has very good chemical resistance. In the mass it is translucent or opaque but thin films may be transparent. 

Applications Although a wide range of metals can be sputtered, the method is often commercially restricted by the low rate of deposition. Applications include the coating of insulating surfaces, e.g. of crystal vibrators, to render them electrically conducting, and the manufacture of some selenium rectifiers. The micro-electronics industry now makes considerable use of sputtering in the production of thin-film resistors and capacitors . ... 

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