Ferroelectric capacitors

Shebanovs L, Borman K, Lawless WN, Kalvane A Electrocaloric effect in some per-ovskite ferroelectric ceramics and multilayer capacitor. Ferroelectr., 2002 273 137-142. DOI 10.1080/00150190211761... 

Fig. 3. An overview of atomistic mechanisms involved in electroceramic components and the corresponding uses (a) ferroelectric domains capacitors and piezoelectrics, PTC thermistors (b) electronic conduction NTC thermistor (c) insulators and substrates (d) surface conduction humidity sensors (e) ferrimagnetic domains ferrite hard and soft magnets, magnetic tape (f) metal—semiconductor transition critical temperature NTC thermistor (g) ionic conduction gas sensors and batteries and (h) grain boundary phenomena varistors, boundary layer capacitors, PTC thermistors.

Multilayer Capacitors. Multilayer capacitors (MLC), at greater than 30 biUion units per year, outnumber any other ferroelectric device in production. Multilayer capacitors consist of alternating layers of dielectric material and metal electrodes, as shown in Figure 7. The reason for this configuration is miniaturization of the capacitor. Capacitance is given by... 

Ferroelectric—polymer composite devices have been developed for large-area transducers, active noise control, and medical imaging appHcations. North American Philips, Hewlett-Packard, and Toshiba make composite medical imaging probes for in-house use. Krautkramer Branson Co. produces the same purpose composite transducer for the open market. NTK Technical Ceramics and Mitsubishi Petrochemical market ferroelectric—polymer composite materials (108) for various device appHcations, such as a towed array hydrophone and robotic use. Whereas the composite market is growing with the invention of new devices, total unit volume and doUar amounts are small compared to the ferroelectric capacitor and ferroelectric—piezoelectric ceramic markets (see Medical imaging technology). 

Approximately 40% of the U.S. electronic ceramics industry is represented by ferroelectrics. Table 3 shows U.S. consumption of ceramic capacitors and piezoelectric materials (109). 

Japanese suppHers generally dominate the electronic ceramic business. Japanese production of ferroelectric devices in the first nine months of 1990 was valued at 711 x 10 for ceramic capacitors and 353 x 10 for piezoelectric devices, representing growths of 7 and 10.8%, respectively, over the previous year. 

Principal producers of ferroelectric capacitors are (110) Murata Manufacturing Co., Ltd., Kyoto, Japan Kyocera Corp., Kyoto, Japan Philips Electronics, N.V., Eindhoven, the Netherlands and NEC Corp., Tokyo, Japan. Principal piezoelectric ceramic component producers are (110) Murata Manufacturing Co., Ltd., Kyoto, Japan Motorola, Inc., Schaumburg, lU. EDO Corp., College Point, N.Y. Morgan Matroc, Inc., Bedford, Ohio Kyocera Corp., Kyoto, Japan and Philips Electronics, N.V., Eindhoven, the Netherlands. 

Because of very high dielectric constants k > 20, 000), lead-based relaxor ferroelectrics, Pb(B, B2)02, where B is typically a low valence cation and B2 is a high valence cation, have been iavestigated for multilayer capacitor appHcations. Relaxor ferroelectrics are dielectric materials that display frequency dependent dielectric constant versus temperature behavior near the Curie transition. Dielectric properties result from the compositional disorder ia the B and B2 cation distribution and the associated dipolar and ferroelectric polarization mechanisms. Close control of the processiag conditions is requited for property optimization. Capacitor compositions are often based on lead magnesium niobate (PMN), Pb(Mg2 3Nb2 3)02, and lead ziac niobate (PZN), Pb(Zn 3Nb2 3)03. 

Numerous uses for PZT/PLZT thin films are under investigation. The device that, as of this writing, is closest to commercialization is a nonvolatile memory. This device, which utilizes a ferroelectric thin-film capacitor integrated onto siUcon circuitry, provides memory retention when the power is off because of the polarization retention of the ferroelectric capacitor. One and zero memory states arise from the two polarization states, — and +F, of the ferroelectric. Because PZT is radiation-hard, the devices are also of interest for military and space appHcations. 

In addition to requiring high dielectric films for DRAM capacitors (dynamic random access memories) and for the active memory elements in FRAMs, the microelectronics industry has a stated demand for a replacement for Si02 gate oxides very soon. The leading candidate is hafnia (Hf02), and there are significant opportunities for the ferroelectrics community to contribute to the solution of this problem. 

Barium titanate has many important commercial apphcations. It has both ferroelectric and piezoelectric properties. Also, it has a very high dielectric constant (about 1,000 times that of water). The compound has five crystalline modifications, each of which is stable over a particular temperature range. Ceramic bodies of barium titanate find wide applications in dielectric amplifiers, magnetic amplifiers, and capacitors. These storage devices are used in digital calculators, radio and television sets, ultrasonic apparatus, crystal microphone and telephone, sonar equipment, and many other electronic devices. 

Hada H, Amanuma K, et al (2004) Capacitor-on-metal/via-stacked-plug (CMVP) memory cell technologies and application to a nonvolatile SRAM. Ferroelectric Random Access Memories Fundamentals and Applications 93, 215-232... 

Barium titanate, BaTiOs, is a ferroelectric material (see Chapter 9) widely used in capacitors because of its high dielectric constant. It was initially prepared by heating barium carbonate and titanium dioxide at high temperature. 

See Diestelhorst et al. [64]. In particular, multivalued conjugate reflectivities may become involved in some ferroelectric capacitors see also Itoh et al. [65]. 

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