49 Ferroelectric and Piezoelectric materials 49.1 Introduction 49.2 Mechanical Characteristics Applications. Structure of Ferroelectric and Piezoelectric Materials 49.3 Ferroelectric materials K. EEtzold Electrical Characteristics IBM T. I. Watson Research Center 49.4 Ferroelectric and High Epsilon Thin Films 49.1 Introduction Piezoelectric materials have been used extensively in actuator and ultrasonic receiver applications, while ferroelectric materials have recently received much attention for their potential use in nonvolatile(Nv)memory applications. We will discuss the basic concepts in the use of these materials, highlight their applications, and describe the constraints limiting their uses. This chapter emphasizes properties which need to be understood for the effective use of these materials but are often very difficult to research. Among the properties which are discussed are hysteresis and domains. Ferroelectric and piezoelectric materials derive their properties from a combination of structural and elec trical properties. As the name implies, both types of materials have electric attributes. A large number of materials which are ferroelectric are also piezoelectric. However, the converse is not true. Pyroelectricity closely related to ferroelectric and piezoelectric properties via the symmetry properties of the crystals. Examples of the classes of materials that are technologically important are given in Table 49. 1. It is apparent that many materials exhibit electric phenomena which can be attributed to ferroelectric, piezoelectric, and electret materials. It is also clear that vastly different materials(organic and inorganic)can exhibit ferroelec tricity or piezoelectricity, and many have actually been commercially exploited for these properties As shown in Table 49.1, there are two dominant classes of ferroelectric materials, ceramics and organics. Both classes have important applications of their piezoelectric properties. To exploit the ferroelectric property, ently a large effort has been devoted to producing thin films of PzT (lead [Pb] zirconate titanate)on various lbstrates for silicon-based memory chips for nonvolatile storage. In these devices, data is retained in the absence of external power as positive and negative polarization. Organic materials have not been used for their ferroelectric properties. Liquid crystals in display applications are used for their ability to rotate the plane of polarization of light and not their ferroelectric attribute It should be noted that the prefix ferro refers to the permanent nature of the electric polarization in analog with the magnetization in the magnetic case. It does not imply the presence of iron, even though the root of the word means iron. The root of the word piezo means pressure; hence the original meaning of the word piezoelectric implied"pressure electricity-the generation of electric field from applied pressure. This defini tion ignores the fact that these materials are reversible, allowing the generation of mechanical motion by applying a field. c 2000 by CRC Press LLC© 2000 by CRC Press LLC 49 Ferroelectric and Piezoelectric Materials 49.1 Introduction 49.2 Mechanical Characteristics Applications • Structure of Ferroelectric and Piezoelectric Materials 49.3 Ferroelectric Materials Electrical Characteristics 49.4 Ferroelectric and High Epsilon Thin Films 49.1 Introduction Piezoelectric materials have been used extensively in actuator and ultrasonic receiver applications, while ferroelectric materials have recently received much attention for their potential use in nonvolatile (NV) memory applications. We will discuss the basic concepts in the use of these materials, highlight their applications, and describe the constraints limiting their uses. This chapter emphasizes properties which need to be understood for the effective use of these materials but are often very difficult to research. Among the properties which are discussed are hysteresis and domains. Ferroelectric and piezoelectric materials derive their properties from a combination of structural and elec￾trical properties. As the name implies, both types of materials have electric attributes. A large number of materials which are ferroelectric are also piezoelectric. However, the converse is not true. Pyroelectricity is closely related to ferroelectric and piezoelectric properties via the symmetry properties of the crystals. Examples of the classes of materials that are technologically important are given in Table 49.1. It is apparent that many materials exhibit electric phenomena which can be attributed to ferroelectric, piezoelectric, and electret materials. It is also clear that vastly different materials (organic and inorganic) can exhibit ferroelec￾tricity or piezoelectricity, and many have actually been commercially exploited for these properties. As shown in Table 49.1, there are two dominant classes of ferroelectric materials, ceramics and organics. Both classes have important applications of their piezoelectric properties. To exploit the ferroelectric property, recently a large effort has been devoted to producing thin films of PZT (lead [Pb] zirconate titanate) on various substrates for silicon-based memory chips for nonvolatile storage. In these devices, data is retained in the absence of external power as positive and negative polarization. Organic materials have not been used for their ferroelectric properties. Liquid crystals in display applications are used for their ability to rotate the plane of polarization of light and not their ferroelectric attribute. It should be noted that the prefix ferro refers to the permanent nature of the electric polarization in analogy with the magnetization in the magnetic case. It does not imply the presence of iron, even though the root of the word means iron. The root of the word piezo means pressure; hence the original meaning of the word piezoelectric implied “pressure electricity”—the generation of electric field from applied pressure. This defini￾tion ignores the fact that these materials are reversible, allowing the generation of mechanical motion by applying a field. K. F. Etzold IBM T. J. Watson Research Center