Ferroelectric optical memory

The scattering effects observed during the deformation of the ferroelectric helix have not yet been satisfactorily investigated [115]. For instance, one should explain the correlation between temperature dependence of the helix pitch and intensity of the scattered light [113], as well as the effect of FLC physical parameters on the response times and hysteresis behavior of transmission-voltage characteristics. Moreover, these effects have not been studied in commercial FLC mixtures operating at room temperature. Nevertheless, these electrooptical modes might be useful for applications in nonpolaroid FLC displays for realization of the optical memory, etc. 

Ferroelectric thin films may replace PLZT bulk ceramics for optical memory and display applications. The advantages offered by thin films for display applications include a simplification of the display device design and lower operating voltages compared to PLZT ceramic devices. Optical memories using PLZT thin films will also need lower operating voltages. 

Soon after the initial discovery of ferro-electricity in chiral smectic LCs it was predicted that, if the helix of an SmC phase were suppressed by surface forces in very thin layers between two glass electrodes, then this would pin the molecules in their positions and allow switching between two energetically equivalent polarization directions, thereby giving rise to an electro-optic memory effect [22]. This is the basis of the electro-optic display device called the surface stabilized ferroelectric liquid crystal... 

In addition to reflective, colored, and AR coatings, more recent optical applications include contrast enhancement filters [15,21], cold mirrors [15-21], patternable thick films for diffraction gratings [41] and optical memory disks [41,42], and ferroelectric films [38-40,58-67] (PLZT, KNbOj, or LiNbOs) for optoelectronic and integrated optics applications [38-40],... 

In this review, only results relative to co-crystalline materials exhibiting fluorescent guests, photoreactive guests (possibly suitable for optical memories), and polar guest (possibly suitable for nonlinear optics and ferroelectric-ity) will be briefly reviewed. 

Thin ferroelectric films are finding applications as optical waveguides to carry light along a substrate. PLZT is particularly interesting because it is transparent and has a high electro-optical coefficient which makes it a candidate for applications for optical switching, optical memories, and display devices. 

The electrical characterization of polar media is crucial to investigate their suitability for ferroelectric memories, piezo- or pyroelectric devices and many other ferroelectric applications (see Chapter 3). Optical characterization of polar media is fundamental to investigate their ser-vicability for electro-optic devices or applications in the field of nonlinear optics (see Chapter 4). Additionally there are intentions to characterize polar media with a combination of both, electrical and optical methods, such as to understand ferroelectric phenomena that are influenced by the action of light. 

Ferroelectric ceramics (such as barium titanate, lead zircanate titanate) Sensors and actuators, electronic memory, optical applications Tape casting, sputtering, pressing, templated grain growth Improved dielectric and piezoelectric properties... 

Chemical and physical processing techniques for ferroelectric thin films have undergone explosive advancement in the past few years (see Ref. 1, for example). The use of PZT (PbZri- cTi c03) family ferroelectrics in the nonvolatile and dynamic random access memory applications present potentially large markets [2]. Other thin-film devices based on a wide variety of ferroelectrics have also been explored. These include multilayer thin-film capacitors [3], piezoelectric or electroacoustic transducer and piezoelectric actuators [4-6], piezoelectric ultrasonic micromotors [7], high-frequency surface acoustic devices [8,9], pyroelectric intrared (IR) detectors [10-12], ferroelectric/photoconduc-tive displays [13], electrooptic waveguide devices or optical modulators [14], and ferroelectric gate and metal/insulator/semiconductor transistor (MIST) devices [15,16]. 

In the attempt to achieve optical signal processing, modulation, amplification, and memory functions in integrated circuits similar to those on electrical signals by semiconductor devices, integration of ferroelectric devices is the ultimate goal. However, to achieve integration of microscopic devices based on materials as complex as oxide ferroelectrics, which are predominantly multi-component metal oxide compounds, reliable thin-film deposition techniques are critically needed. One of the most important aspects of multicomponent oxide thin-film deposition is the control of stoichiometry. 

Much of this early effort dealt with modulator technology that is considered too slow (1-100 kilohertz) for high-speed applications such as optical interconnection and memory read/write. This includes modulators based on electrooptic effects in ferroelectric liquid crystals (ELCs) and in a ceramic containing lead, lanthanum, zinc, and titanium (PLZT). These electrooptic materials are bonded in some fashion to Si circuits to create hybrid SPAs. 

The concept of defects came about from crystallography. Defects are dismptions of ideal crystal lattice such as vacancies (point defects) or dislocations (linear defects). In numerous liquid crystalline phases, there is variety of defects and many of them are not observed in the solid crystals. A study of defects in liquid crystals is very important from both the academic and practical points of view [7,8]. Defects in liquid crystals are very useful for (i) identification of different phases by microscopic observation of the characteristic defects (ii) study of the elastic properties by observation of defect interactions (iii) understanding of the three-dimensional periodic structures (e.g., the blue phase in cholesterics) using a new concept of lattices of defects (iv) modelling of fundamental physical phenomena such as magnetic monopoles, interaction of quarks, etc. In the optical technology, defects usually play the detrimental role examples are defect walls in the twist nematic cells, shock instability in ferroelectric smectics, Grandjean disclinations in cholesteric cells used in dye microlasers, etc. However, more recently, defect structures find their applications in three-dimensional photonic crystals (e.g. blue phases), the bistable displays and smart memory cards. 

Ferroelectric crystals (especially oxides in the form of ceramics) are important basic materials for technological applications in capacitors and in piezoelectric, pyroelectric, and optical devices. In many cases their nonlinear characteristics turn out to be very useful, for example in optical second-harmonic generators and other nonlinear optical devices. In recent decades, ceramic thin-film ferroelectrics have been utilized intensively as parts of memory devices. Liquid crystal and polymer ferroelectrics are utilized in the broad field of fast displays in electronic equipment. 

Ferroelectric liquid crystals (FLC) have attracted attention because of their high speed response and memory effect (7-5). The characteristics of fast response and memory effect make them suitable in electro-optical device applications, such as display, light valve and memory devices. Ferroelectric side chain liquid crystalline polymers (FLCPs) exhibit desirable mechanical properties of polymers and electro-optical properties of low molecular weight FLC, which have been investigated extensively Corresponding author. 

The present 10 volume handbook has a much broader scope. It includes semiconductor materials, quantum wells and quantum dots, liquid crystals, conducting polymers, laser materids, photoconductors, electroluminescent and photorefractive materials, nanostructured, supramolecular, and self-assembled materials, ferroelectrics, and superconductors. Applications of these materials in photoconductors, optical fibers, xerography, solar cells, dynamic random access memory, and sensors are described. The Handbook contains contributions by 180 leading experts from 25 different countries. It truly represents the worldwide research efforts and results that support the global market of optoelectronics. All scientific and technical workers in this broad field are indebted to the contributing authors, the editor and Academic Press for publishing this comprehensive handbook for the new millennium. It will support further growth in a field that already has surpassed my wildest expectations of 40 years ago. 

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