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- Electronic thin film reliability | Materials science | Cambridge University Press
- Materials Science of Thin Films
- Mechanical Properties of Thin Films
When the laser beam strikes the target material, it produces the plume which could deposit on the various substrates. The created plume may contain neural- and ground-state atoms and ionized species. In the case of metal oxide thin films, oxygen is used to deposit the oxides of metals [ 18 ].
The thin-film quality from the PLD depends on the various parameters such as wavelength of the laser, energy, ambient gas pressure, pulsed duration, and the distance of the target to the substrate [ 19 ].
The ablation process during the deposition may control and monitor by using laser-induced fluorescence [ 20 ], laser ablation molecular isotopic spectroscopy [ 21 ], and optical emission spectroscopy [ 22 ]. The morphology of the deposited thin films is also affected by the substrate temperature. PLD has some advantages over other physical deposition systems because of its fast deposition time and its compatibility to oxygen and other inert gases. Sputtering technique is mostly used for depositing metal and oxide films by controlling the crystalline structure and surface roughness [ 11 , 25 ].
The simple form of the sputtering system consists of an evacuated chamber containing metallic anode and cathode [ 25 ] in order to obtain a glow discharge in the residual gas in the chamber. Also, an applied voltage in the order of several KeV with pressure more than 0. The sputtering process depends on the bombardment of the ions released from the discharge to the molecules in the cathode leading to the liberation of the molecules from the cathode with higher kinetic energy.
The atomic weight of the bombarding ions should be nearly to that of the target material in order to maximize the momentum transfer.
These molecules move in straight lines and strike on the anode or on the substrate to form a dense thin film [ 25 ]. The process of sputtering has several advantages. High-melting point materials can be easily formed by sputtering. The deposited films have composition similar to the composition of the starting materials.
Sputtering technique is available to use for ultrahigh vacuum applications. The sputtering sources are compatible with reactive gases such as oxygen. There are two common types of sputtering process: direct current DC and radio frequency RF sputtering. The first one depends on DC power, which is generally used with electrically conductive target materials. It is easy to control with low-cost option. The RF sputtering uses RF power for most dielectric materials. A common example for sputtered films is aluminum nitride films.
These films were prepared by both DC- and RF-sputtering technique, and their structure and optical properties were compared [ 26 , 27 ]. Although the production of thin films via physical methods as previously described gives good quality and functionalizes properties, it is highly expensive and perhaps requires a large amount of material target. Since the need to produce good-quality thin films with low economical cost is necessary, chemical deposition techniques are widely used globally. These techniques are cheap producing good-quality films.
Most of them do not require expensive equipment. The chemical deposition is strongly dependent on the chemistry of solutions, pH value, viscosity, and so on. The most common chemical deposition has been obtained via sol-gel route, chemical bath deposition, electrodeposition, chemical vapor deposition CVD , and spray pyrolysis technique. This section is concerned only on sol-gel and chemical bath deposition techniques because they can form good film quality with low equipment requirement. The sol-gel technique is broadly used for the synthesis of oxide materials [ 28 ].
Sol-gel process is one of the famous wet-chemical methods. It works under lower-temperature processing and gives better homogeneity for multicomponent materials. Two routes are used to prepare transition metal oxides TMOs as follows:. It can be synthesized via the reaction of metal salt chloride, acetate, nitrate, etc. Hydrolysis: this step is aimed to form reactive M-OH groups [ 30 ]:. Condensation : condensation is the second step after hydrolysis leading to the departure of a water molecule. The process of condensation can be either olation process or oxolation process.
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Oxolation: oxolation is a reaction in which an oxo bridge —O— is created between two metal centers. The previous description provides the preparation of the precursor solution. In order to make thin film from the precursor solution, there are two processes for the production of the films, that is, dip-coating and spin-coating techniques. Dip-coating technique is almost used to fabricate transparent layers of oxides on a transparent substrate with a high degree of planarity and surface quality [ 32 ]. Other substrates are also possible to use. Several additive layers can be superimposed.
Scriven [ 33 ] described the dip-coating process in five stages: immersion, start-up, deposition, drainage, and evaporation.
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Another technique is also available for usage after the precursor solution is prepared known as spin coating or spinning. The solution is dripped onto a spinning substrate and spreads evenly.
The spinning process is most suitable for the coating of small disks or lenses but is not very economical. Chemical bath deposition method is also known as solution growth technique or controlled precipitations [ 34 ]. It is the oldest method to deposit films on a substrate. Solution growth technique is mostly used to prepare chalcogenide films as well as metal oxide films.
Also, the deposition can be performed at lower temperatures.click
Electronic thin film reliability | Materials science | Cambridge University Press
In the solution growth method, the precursor solution of metal ions must be complexed by ligands. The complex solution is almost obtained with ammonia solution, triethanol amine, ethylene-diamine-tetraacetic acid EDTA , citric acid, and so on. When the complexation is completed, the addition of the anions should take place. These anions come from the thiourea, thioacetamide, thiosulfate, and sodium Sulfide solutions [ 34 ] as sources of sulfur anions or selenourea and sodium selenosalfate for selenium anions to deposit the chalcogenides.
Substrates are put in vertical, horizontal, or specific position inside the solution and left until the desired film thickness is obtained.
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The deposition of oxide films is quite different than chalcogenides. The hydroxide film can then be transferred to oxide by the annealing process. Indeed, much reviews and literature, which describes the chemical bath deposition for both chalcogenide and oxide films, are found elsewhere [ 34 — 36 ]. Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3.
Materials Science of Thin Films
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Mechanical Properties of Thin Films
Blamire Corresponding Author E-mail address: mb52 cam. Search for more papers by this author. Judith L. Neil D. Zoe H. Tools Request permission Export citation Add to favorites Track citation. Share Give access Share full text access. Share full text access. Please review our Terms and Conditions of Use and check box below to share full-text version of article. Abstract Research in the area of functional oxides has progressed from study of their basic chemistry and structure to the point at which an enormous range of desirable properties are being explored for potential applications.
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