Device fabrication, consideration

An important consideration in the sequence of semiconductor devices fabrication is the so-called thermal budget, a measure of both the CVD temperature and the time at that temperature for any given CVD operation. As a rule, the thermal budget becomes lower the farther away a given step is from the original surface of the silicon wafer. This restriction is the result of the temperature limitations of the already deposited materials. 

Unlike silicon-based materials where selective reactants are of ultimate importance, and III-V and metallic materials where product volatility dominates etching considerations, selective etching of organic films is driven by incorporating the desired reactivity (or lack of it) into the film itself. In device fabrication all types of materials are present simultaneously and the process engineer must be aware of the important aspects of the chemistry of each material in addition to the gas phase reactions that produce chemically active species. It is hoped that the discussions presented here provide a basis for approaching such a complex chemical system and for critically evaluating studies which appear in the literature. 

Donor adducts of aluminum and gallium trihydride were the subject of considerable interest in the late 1960s and early 1970s.1 Thin-film deposition and microelectronic device fabrication has been the driving force for the recent resurgence of synthetic and theoretical interest in these adducts of alane and gallane.24 This is directly attributable to their utility as low-temperature, relatively stable precursors for both conventional and laser-assisted CVD,59 and has resulted in the commercial availability of at least one adduct of alane. The absence of direct metal-carbon bonds in adducts of metal hydrides can minimize the formation of deleterious carbonaceous material during applications of CVD techniques, in contrast to some metal alkyl species.10, 11... 

Phthalocyanines were chosen for these experiments because they are electronic semiconductors and because they are quite stable materials — an important consideration in fabricating any practical gas-detecting device. A considerable body of literature exists describing the physical and chemical properties of the phthalocyanines. A review of the work prior to 1965 is contained in the chapter by A. B. P. Lever in Volume 7 of Advances in Inorganic Chemistry and Radiochemistry (2). Electrical properties of phthalocyanines have been receiving increased attention in recent years. The photoconductivity of metal-free phthalocyanine has been studied in detail (3,4). Electrical properties of lead phthalocyanine have been studied extensively, especially by Japanese workers (5, ,7,8i). They have also studied the alteration of the conductivity of this material upon exposure to oxygen ( ,10.). The effects of a series of adsorbed gases (0, , CO, and NO) on the conductivity of iron phthalo-... 

Lee and Hwang synthesized a PF with aryl side chains 6 via the Yamamoto coupling reaction [20]. The device fabricated therewith (ITO/PEDOT PSS/6/ Ca/Al) emits blue light with suppressed long tail emission but gives low performance with maximum efficiency of 0.03 cd A-1 and maximum luminance of 820 cd nr2. Note that the device could bear considerably high current density (>1.5 A cm-2). 

Specifically for the passivation of temperature sensitive bubble memory devices,these ultrapure materials proved to be of great value. A cure process was optimized to obtain a reliable low temperature cure without affecting the magnetic coercivities of the bubble memory devices. A positive resist process, using a simple development step to pattern via holes in devices has been optimized and successfully used to fabricate devices. The devices fabricated using the the polyimide process have been compared with conventional SiC offers reliable passivations with thinner stress free films for passivations. The fabrications involve simple inexpensive process steps and are compatible with conventional resist processes. The reliability of the imide passivated devices can be considerably enhanced by the use of ultrapure starting materials to preclude harmful ionic mobilities through passivated layers. 

Practical device fabrication is an important consideration. The planar nature of LB films and their precisely controllable thickness and composition make them compatible with existing electro-optic technology, and provide the opportunity to construct novel active optical structures. 

In conclusion, recent materials developments have tried to answer the needs of current electro-optical effects used in display devices. By concentrating more on desirable physical properties rather than just synthesizing new liquid crystals, considerable progress has been made. However, the materials cannot stand alone and must be linked to device fabrication and addressing to take full advantage of their properties. 

How much do the results we have obtained here tell us about the fundamental limits to the mobilities of carriers in devices fabricated with polymer that is very much better ordered than the polyacetylene that we have used here There are recent reports of very much improved mobilities for devices based on sexithiophene (the six repeat unit oligomer of polythiophene), with a value of 0.4 cm /Vsec now reported [73], and there is now considerable interest in the development of polymer FETs as large area thin film transistors, with interest in polythiophene derivatives [74] and in poly(arylenevinylenes) such as poly(2,5-thienylene vinylene) [75]. We can see from the optical characterisations of the MIS devices that the surface layer of polyacetylene formed on SiC>2 is very much more disordered than the bulk material, but we have not made FET devices with the polymer insulator layers which give better ordered structures as characterised optically. 

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