File Name: an introduction to physics and technology of thin films .zip
Download PDF Flyer. DOI: Recommend this Book to your Library. This well organized reference book covers the newest and most important practically applicable results in thin film-based semiconductor A2B6-A4B6 and chalcogenide sensors, heterojunction-based active elements and other devices. This book is written for researchers, material scientists and advanced students who wish to increase their familiarity with different topics of novel semiconductor material science related to production of thin film-based sensors and active elements for micro- and nanoelectronics.
Ultrathin ferroelectric films are of increasing interests these years, owing to the need of device miniaturization and their wide spectrum of appealing properties. Recent advanced deposition methods and characterization techniques have largely broadened the scope of experimental researches of ultrathin ferroelectric films, pushing intensive property study and promising device applications.
This review aims to cover state-of-the-art experimental works of ultrathin ferroelectric films, with a comprehensive survey of growth methods, characterization techniques, important phenomena and properties, as well as device applications. The strongest emphasis is on those aspects intimately related to the unique phenomena and physics of ultrathin ferroelectric films. Prospects and challenges of this field also have been highlighted.
Ferroelectrics are defined as polar materials that possess at least two equilibrium orientations of the spontaneous polarization vector in absence of an external electric field, and can be switched between those orientations by an electric field [ 1 ]. Its investigation can date back to s when Valasek made researches on Rochelle salt [ 2 ].
Typically, ferroelectric materials undergo a structural phase transition at Curie point T c , transforming from a nonpolar high-temperature paraelectric phase into a polar low-temperature ferroelectric phase accompanied with a lowering of symmetry.
A fundamental issue in ferroelectrics is the scaling of ferroelectric properties with size, namely ferroelectric size effects. Among various ferroelectric systems, thin film ferroelectrics have been the objectives of great interests for decades; a very large number of works has been established. Driven by the trend of device miniaturization and the fast developments achieved in film deposition methods and characterization techniques, ultrathin ferroelectric films typically, with thickness smaller than nm have been successfully grown.
Owing to their striking properties and application potential, they have drawn increasingly interests and have become the most popular research branch in the field of ferroelectrics. Recently, a variety of works both theoretical and experimental have been carried out on ultrathin ferroelectric films with remarkable progresses being made in many aspects, including film deposition, characterization, property research, and device design, etc.
Although there have been some reviews on the topic of ferroelectric thin films, an up-to-date review specially focusing on ultrathin ferroelectric films and the recent progresses in this field is in demand. Based on a comprehensive survey of excellent experimental works on ultrathin ferroelectric films, we set the target of this review paper as providing an extensive insight on state-of-the-art researches in the field.
In the first part, the common deposition methods of ferroelectric ultrathin films have been introduced with thin film growth physics, also with special attention to the choice of substrates and the growth of heterostructures. For a deep understanding and for investigation of the behaviors of ultrathin films with thickness at nanometer magnitude, it is necessary to establish the analysis both at the level of macroscale and nanoscale.
Thus, characterization methods for ultrathin ferroelectric films have been summarized in the second part, focusing on film property characterization, particularly on those unique properties in ultrathin ferroelectric films such as nanoscale domain structure and tunneling property. It will be emphasized that when the film thickness shrinks to a great extent, many intriguing phenomena can be observed and controlled.
In the next part, significant developments of researches on important phenomena and properties in ultrathin ferroelectric films are thoroughly reviewed and discussed, aiming at providing readers snapshots on physics in ultrathin ferroelectric films.
Associated with the fast development of integrated circuit technology, the advantages to be gained from the availability of ferroelectric thin films have been widely appreciated and significant efforts have been directed towards researches on exploitation of ferroelectric thin films in devices and multifunctional integrated MEMS [ 3 ].
In the final part of this review, an overview of the current state of ferroelectric thin film devices is introduced followed by identification and discussion of the key physics issues that determine device performance. In particular, the promising applications of ultrathin ferroelectric films, such as newly nonvolatile memory devices based on ferroelectric tunnel junctions, are highlighted with the prospects and current challenges being pointed out.
We notice that great advances have been achieved in growth of ferroelectric thin film structures during the past decades. Particularly, due to the development of epitaxial growth methods, it is now possible to prepare high quality and ultrathin ferroelectric films that are single crystal and defect free.
Compared with the synthesis of thin films made of simple substances e. Each method has its own strength and weakness. Thus the growth method has to be carefully selected to obtain a certain film with desired properties. In this section, growth methods of ferroelectric thin films will be discussed and some comparisons will be made among them, which should be relevant for readers who want information of thin film growth physics and suggestions on choice of growth methods.
At the primary stage of thin film growth, which is the so-called nucleation stage, abundant vapor atoms or molecules condense and undergo surface diffusion and migration under the drive of both their self-energy and substrate thermal energy, then move to a stable position on the substrate [ 4 , 5 ].
Subsequently the nucleus ceaselessly incorporates surrounding atoms or molecules and gradually grows to a bigger size, finally resulting in film formation. The film nucleation and forming process have been well observed through many techniques [ 6 , 7 , 8 ], such as transmission electron microscopy TEM and scanning electron microscopy SEM , scanning probe microscopy SPM and field-ion microscopy FIM , etc.
Thin film formation on clean crystal substrates can be classified into three basic growth mode, including: 1 layer-by-layer growth mode Frank—Van der Merwe mode ; 2 island growth mode Volmer—Weber mode ; 3 Stranski—Krastanov mode, which are illustrated in Figure 1. The smallest nucleuses will extent on the substrate in two dimensions, leading to the thin film growth mode of layer-by-layer Figure 1 a.
It is noteworthy that the bonding effect in each layer tends to be weaker than its precious layer. This growth mode usually happens when the substrate and film are homogeneous materials or some particular dissimilar materials such as the epitaxial growth of semiconductor and oxide materials. For this island growth mode, polycrystalline thin films with rough surface are usually obtained as the continual growth of the islands.
Island growth mode often happens when the substrate and film are heterogeneous. Stranski—Krastanov mode lies between the two above mentioned growth modes, i. The most attractive and popular film growth way is epitaxial growth, which refers to the formation of an extended single-crystal overlayer on a crystalline substrate, achieved through layer-by-layer growth mode. Introductions in details for epitaxial growth can be found in somewhere else [ 5 , 9 ]. Schematic diagram of three basic growth modes: a layer-by-layer growth mode; b island growth mode; and c Stranski—Krastanov mode.
Ferroelectric thin films are always deposited on substrates. A proper choice of substrates is important for growth of ferroelectric thin films. Effects such as substrate misfit strain can affect the film grow process and film properties, giving rise to the crucial points resting on the choice of appropriate substrates and methods to prepare highly chemically and structurally matched substrate surfaces for epitaxial growth.
Some commercially perovskite and perovskite-related substrates, and the pseudotetragonal or pseudocubic a -axis lattice constants of some frequently-used ferroelectric perovskites have been listed in Table 1 , providing an intuitive reference for substrates select in film fabrication of this category [ 23 ]. Due to the fact that most of the commercially available perovskite substrates typically have lattice constants in the 3.
In atomic-scale epitaxy, substrates with defects—free surfaces of specific chemical termination are necessary. Commercially involved perovskite and perovskite-related substrates and the pseudotetragonal or pseudocubic a-axis lattice constants of some frequently-used ferroelectric perovskites. Substrates and thin films which are in the same lines possess similar lattice constants.
In one vertical line, lattice constants of thin films or substrates are gradually increasing from top to bottom [ 23 ].
Recent advances in mechanics and material science provide routes to integrated circuits that can offer the electrical properties of conventional rigid wafer-based technologies and with the ability to be deformed arbitrarily e.
Flexible substrates, which are usually some plastic or elastomeric substrates, have extended the classes of substrates and attracted much attention for their applications in high-performance flexible electronics [ 29 , 30 , 31 ].
For instance, PZT, BTO, and STO thin films, originally deposited on rigid substrates, have been successfully transferred onto flexible substrates by removing the sacrificial layers such as SiO 2 , MgO and TiO 2 , with the deformation mechanics and material properties being studied [ 32 , 33 , 34 , 35 ]. In spite of the widely used PDMS substrates, many flexible substrates have been employed into multifunctional flexible circuits based on ferroelectric thin films both organic like P VdF-TrFE [ 36 ] and inorganic.
Some typical examples include polyethylene naphthalate PEN [ 35 ], polyethylene terephthalate PET [ 37 ], polyimide PI substrates [ 38 ], flexible aluminum substrates [ 36 ], and thin glass substrates [ 39 ] etc. More recently, to solve this problem and simplify experiment process, polycrystalline metal sheet e.
In general, a buffer layer is usually needed to effectively connect flexible substrates with ferroelectric thin films [ 40 ]. It is also noteworthy that significant efforts have been devoted to low-temperature fabrication of promising inorganic ferroelectric thin films e.
On the basis of these flexible substrates, ultrathin ferroelectric films can be further studied, with some piezo-related properties such as the specially-focused flexoelectric properties as will be discussed in Section 4. Moreover, the application scope of ultrathin ferroelectric films can be largely broadened by the use of flexible substrates, with ferroelectric thin-film-based devices such as nanogenerators, sensors and memories systems presenting stretchable properties and working efficiently with proper flexible substrates [ 32 , 33 ].
There are a large variety of physical vapor deposition PVD methods widely used in thin film growth, mainly including vacuum evaporation VE , molecular beam epitaxy MBE , and pulsed laser deposition PLD. For this kind of methods, the film growth is dominated by a physical evaporation process. Thermal energy is provided from a power supply unit to heat the atoms of a liquid or solid source to reach evaporating point.
The vaporized atoms travel a distance usually in a vacuum chamber and deposit onto the heated substrate. Thin film is formed after a continuous evaporating process.
According to different methods, the power supply unit may be a heating wire, electron beam, molecule beam or pulsed laser, etc. Note that some evaporation deposition methods also engage in chemical reactions between deposition sources, so-called activated reactive evaporation.
The basic components of a modern PVD system are shown in Figure 3 [ 11 ]. Schematic diagram of a basic physical vapor deposition PVD system [ 11 ]. Ferroelectric thin films are usually deposited through the activated reactive evaporation with reactions between sources and oxygen gas happen on the substrate. For example, for a typical perovskite ferroelectric, ABO 3 , thin film can be prepared by evaporating sources of A and B to react with introduced oxygen gas [ 42 ].
The essential reaction equation is:. Technological problems in controlling film stoichiometry are often encountered in reactive evaporation method [ 43 ], which could be receded through individual evaporation of A and B sources to form multilayers on substrate with subsequent reactions in oxygen gas during the following thermal treatment [ 44 ].
Several factors have vital influence on the film growth speed. The distance between sources and substrate also influence the growth speed. According to kinetic theory, the number of molecules which change from gas phase to solid or liquid phase at unit time on unit area is represented by d Z.
There is an equation as follows:. Here, m refers to molecule mass; p refers to the pressure; and T refers to temperature. When an equilibrium state is reached, the molecule numbers evaporated from source to gas is equal to those freezing back to source.
At this moment, d Z is almost equivalently to the number of molecules evaporated out of source. Thus, the main affecting factors during evaporation process can be seen from the equation above. No chemical reactions happen during the whole deposition process, giving rise to the stoichiometry of prepared film similar to that of deposition source.
Through this method, a lot of ferroelectric thin films, e. The main superiorities of VE are as follows. Firstly, film thickness is controllable in a wide range from several nanometers to hundreds of nanometers. Secondly, uniform film growth can be achieved and optimized through continuous source feeding with flash evaporation. Thirdly, the compatibility between thin film and substrate is good, thus there is little limit on choice of substrate.
Finally, none complicated reactions are engaged in the whole procedure, resulting in easy operation of the evaporating equipment. However, there are some drawbacks of VE.
Firstly, source materials with low vapor pressure are refractory, making them difficult to be evaporated and deposited onto substrate. Secondly, some source materials may react with source container, resulting in impurity of the thin film.
Thirdly, non-stoichiometric films are likely to be found in multi-sources reactive evaporation. The last, evaporation happens in the whole vacuum chamber and causes large waste of sources. The research of pulse laser deposition PLD can be dated back to the s with the invention of high-power pulsed laser sources.
In late s, PLD was reinvented after the discovery of high-temperature superconductors. Now PLD has become an important material growth method capable of a wide range of materials and structures from single atomic layers to quasi-bulk crystalline materials [ 47 , 48 , 49 ]. Importantly, PLD provides the possibility of growing ultrathin epitaxial films, leading to enormous influence on modern film research. In typical PLD equipment, when a focused laser pulse projects on a solid target, the target ablation will happen with the ablated materials transferring in a preferential direction along with the surface normal of the target, resulting in the formation of the plume a feather-like luminophor.
Different deposition techniques based on vacuum and plasma processes are presented. Methods of surface and thin film analysis including coating thickness, structural, optical, electrical, mechanical and magnetic properties of films are detailed described. The several applications of thin coatings and a special chapter focusing on nanoparticle-based films can be found in this handbook. A complete reference for students and professionals interested in the science and technology of thin films. Skip to main content Skip to table of contents.
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Ultrathin ferroelectric films are of increasing interests these years, owing to the need of device miniaturization and their wide spectrum of appealing properties. Recent advanced deposition methods and characterization techniques have largely broadened the scope of experimental researches of ultrathin ferroelectric films, pushing intensive property study and promising device applications. This review aims to cover state-of-the-art experimental works of ultrathin ferroelectric films, with a comprehensive survey of growth methods, characterization techniques, important phenomena and properties, as well as device applications. The strongest emphasis is on those aspects intimately related to the unique phenomena and physics of ultrathin ferroelectric films. Prospects and challenges of this field also have been highlighted. Ferroelectrics are defined as polar materials that possess at least two equilibrium orientations of the spontaneous polarization vector in absence of an external electric field, and can be switched between those orientations by an electric field [ 1 ].
Part I: Thin Film Deposition Methods; Theories of Nucleation and Film Growth; Control and Measurement of Film Thickness; Electrical Conduction in Thin Films.
A thin-film transistor TFT is a special type of metal—oxide—semiconductor field-effect transistor MOSFET  made by depositing thin films of an active semiconductor layer as well as the dielectric layer and metallic contacts over a supporting but non-conducting substrate. This differs from the conventional bulk MOSFET transistor ,  where the semiconductor material typically is the substrate, such as a silicon wafer. TFTs can be made using a wide variety of semiconductor materials.
Thin-film science and technology play a crucial role in the high-tech industries that will bear the main burden of future American competitiveness. While the major exploitation of thin films has been in microelectronics, there are numerous and growing applications in communications, optical electronics, coatings of all kinds, and in energy generation and conservation strategies. A great many sophisticated analytical instruments and techniques, largely developed to characterize thin films and surfaces, have already become indispensable in virtually every scientific endeavor irrespective of discipline. When I was called upon to offer a course on thin films, it became a genuine source of concern to me that there were no suitable textbooks available on this unquestionably important topic. This book, written with a materials science flavor, is a response to this need. It is intended for.
It seems that you're in Germany. We have a dedicated site for Germany. Introduction to Thin Film Transistors reviews the operation, application and technology of the main classes of thin film transistor TFT of current interest for large area electronics. The TFT materials covered include hydrogenated amorphous silicon a-Si:H , poly-crystalline silicon poly-Si , transparent amorphous oxide semiconductors AOS , and organic semiconductors. Poly-Si TFTs facilitate the integration of electronic circuits into portable active matrix liquid crystal displays, and are increasingly used in active matrix organic light emitting diode AMOLED displays for smart phones. The organic TFTs are regarded as a cost effective route into flexible electronics. As well as treating the highly divergent preparation and properties of these materials, the physics of the devices fabricated from them is also covered, with emphasis on performance features such as carrier mobility limitations, leakage currents and instability mechanisms.
book. Some of the topics covered are intro-. ductions to methodology of self-assembly. in 3-D, massive.
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