Electronic devices- thin film

Thin films (qv) of vitreous silica have been used extensively in semiconductor technology. These serve as insulating layers between conductor stripes and a semiconductor surface in integrated circuits, and as a surface passivation material in planar diodes, transistors, and injection lasers. They are also used for diffusion masking, as etchant surfaces, and for encapsulation and protection of completed electronic devices. Thin films serve an important function in multilayer conductor insulation technology where a variety of conducting paths are deposited in overlay patterns and insulating layers are required for separation. 

Diamond Hints, although not approaching bulk diamond, are harder than most refractory nitride and carbide thin films, which makes them attractive for tribological coatings. Transparency in the visible and infrared regions of the optical spectrum can be maintained and index-of-refraction values approaching that of bulk diamond have been measured. Electrical resistivities of diamond films have been produced within the full range of bulk diamond, and thermal conductivities equivalent to those of bulk diamond also have been achieved. As substrates for semiconductor electronic devices, diamond films can be produced by both the PACVD and IBRD techniques. 

Deposition or formation of a metallic film is an important aspect in microfabrication. For traditional IC and electronic devices, metal films such as aluminum or copper film provide the electrical contact and connection from the device to external circuitry or equipment. In this circumstance, the line width and its electrical continuity are of interest. With the advancement of using microfabricated devices in chemical and biological application, formation of metallic films, such as gold, platinum, and others, becomes necessary. The formation of this metal film can be accomplished by thick or thin film techniques. 

Furukawa, S. 1998. Structure and orientation control of organopolysilanes and their application to electronic devices. Thin Solid Films 331 222. 

Atto-engineering for more than a whole century is in permanent and almost infinite development. Theoretical background is related to the surface physics and chemistry, quantum and wave mechanics, and quantum electrodynamics. Discrete and constrained discrete models are convenient for describing related events. Tools and equipment are nano- and atto-dispersions and beams (demons, ions, phonons, infons, photons, electrons), ultra-thin films and membranes, fullerenes and bucky tubules, Langmuir-Blodgett systems, molecular machines, nano-electronic devices, and various beam generators. Output is, generally, demonstrated as finely dispersed particles (plasma, fluosol-fog, fluosol-smoke, foam, emulsion, suspension, metal, vesicle, dispersoid). 

The focus of this chapter is therefore two-fold. First, the defining characteristics of electronic ceramics used for various applications are discussed and related to the underlying physical, chemical, and structural features of the material. Second, this chapter selectively describes the use of various analytical techniques for characterizing the properties of electronic ceramics that make them suitable for a given application. Since a growing area of research is the development of ceramic thin film devices, particular emphasis is placed on the applicability of various characterization techniques for analysis of electronic ceramic thin films. 

Thin films are integral parts of many micro-electro-mechanical systems designed to serve as sensors or actuators. For example, a piezoelectric or piezoresistive thin film deposited on a silicon membrane can be used to detect electronically a deflection of the membrane in response to a pressure applied on its surface or by an acceleration of its supports. Devices based on thin film technology are used as microphones in hearing aids, monitors of blood pressure during exercise, electronically positioned thin film mirrors on flexible supports in optical display systems, and probes for detecting the degree of ripeness of fruits. 

Transparent electronic conductor thin films of Sn02 Sb (ATO) and In203 Sn (ITO) are very important as transparent electrodes for liquid crystal display devices, plasma display devices and solar cells. These films have been prepared mainly by gas phase deposition such as sputtering and CVD. Sol-gel method can be also applied to fabrication of such films. Coating of large areas as well as small areas is possible in sol-gel coatings. 

The requirements of thin-film ferroelectrics are stoichiometry, phase formation, crystallization, and microstmctural development for the various device appHcations. As of this writing multimagnetron sputtering (MMS) (56), multiion beam-reactive sputter (MIBERS) deposition (57), uv-excimer laser ablation (58), and electron cyclotron resonance (ECR) plasma-assisted growth (59) are the latest ferroelectric thin-film growth processes to satisfy the requirements. 

Amorphous Silicon. Amorphous alloys made of thin films of hydrogenated siUcon (a-Si H) are an alternative to crystalline siUcon devices. Amorphous siUcon ahoy devices have demonstrated smah-area laboratory device efficiencies above 13%, but a-Si H materials exhibit an inherent dynamic effect cahed the Staebler-Wronski effect in which electron—hole recombination, via photogeneration or junction currents, creates electricahy active defects that reduce the light-to-electricity efficiency of a-Si H devices. Quasi-steady-state efficiencies are typicahy reached outdoors after a few weeks of exposure as photoinduced defect generation is balanced by thermally activated defect annihilation. Commercial single-junction devices have initial efficiencies of ca 7.5%, photoinduced losses of ca 20 rel %, and stabilized efficiencies of ca 6%. These stabilized efficiencies are approximately half those of commercial crystalline shicon PV modules. In the future, initial module efficiencies up to 12.5% and photoinduced losses of ca 10 rel % are projected, suggesting stabilized module aperture-area efficiencies above 11%. 

Fig. 4. Some electronic device applications using amorphous silicon (a) solar cell, (b) thin-fiLm transistor, (c) image sensor, and (d) nuclear particle detector.

Diamond and Refractory Ceramic Semiconductors. Ceramic thin films of diamond, sihcon carbide, and other refractory semiconductors (qv), eg, cubic BN and BP and GaN and GaAlN, are of interest because of the special combination of thermal, mechanical, and electronic properties (see Refractories). The majority of the research effort has focused on SiC and diamond, because these materials have much greater figures of merit for transistor power and frequency performance than Si, GaAs, and InP (13). Compared to typical semiconductors such as Si and GaAs, these materials also offer the possibiUty of device operation at considerably higher temperatures. For example, operation of a siUcon carbide MOSFET at temperatures above 900 K has been demonstrated. These devices have not yet been commercialized, however. 

Polymer LEDs are similar to thin film organic molecular LEDs first reported in 1987 17). Organic molecular LEDs utilize thin films of small organic molecules rather than polymer films as the light-emitting layer. The films of small organic molecules are undoped and have electronic properties comparable to the polymer films used in polymer LEDs. In general, the device physics of polymer LEDs is... 

Conventional electronic devices are made on silicon wafers. The fabrication of a silicon MISFET starts with the diffusion (or implantation) of the source and drain, followed by the growing of the insulating layer, usually thermally grown silicon oxide, and ends with the deposition of the metal electrodes. In TFTs, the semiconductor is not a bulk material, but a thin film, so that the device presents an inverted architecture. It is built on an appropriate substrate and the deposition of the semiconductor constitutes the last step of the process. TFT structures can be divided into two families (Fig. 14-12). In coplanar devices, all layers are on the same side of the semiconductor. Conversely, in staggered structures gate and source-drain stand on opposing sides of the semiconductor layer. 

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