Random access memories, ferroelectric

Kim K (2004) High density integration. In Ishiwara H, Okuyama M, Arimoto Y (eds) Ferroelectric random access memories. Top Appl Phys 93 165-176... 

A Comparison of Magnetic Random Access Memories (MRAMs) and Ferroelectric Random Access Memories (FRAMs)... 

Funakubo H (2004) Recent development in the preparation of ferroelectric thin films by MOCVD. Ferroelectric Random Access Memories Fundamentals and Applications 93,95-103... 

Figure 5.53(a) indicates the situation for a passive FeRAM (ferroelectric random access memory). If the capacitor is in the +P state (say a T) and the application of two V/2 voltages is sufficient to switch the polarization to the —P state, there is a resulting large current pulse. However were the cell in the —P state (a 0 ) then the current pulse would be very much smaller. If the state of the cell is such that the polarization is switched then a follow-on pulse must be applied to return it to its original state. 

Dynamic Random Access Memory FeRAM = Ferroelectric Random Access Memory HCP = Hexagonal close packed HREM = High-resolution electron microscopy HTB = Hexagonal tungsten bronze MPTBh = Monophosphate tungsten bronzes with hexagonal tunnels MPTBp =... 

Ferroelectrics are high dielectric materials that are easily polarized in an electric field and can remain polarized to some degree after the field is removed. Such properties make them ideal candidates for computer memory applications and they have been used in the form of thin films as ferroelectric random access memories (FeRAMs) and as high permittivity dielectrics for Dynamic Random Access Memory DRAMs. They have also been looked at as a replacement for silicon dioxide in certain MOS applications. 

The ferroelectric effect is an electrical phenomenon. Parhcular materials, including the ternary oxides (Ba,Sr)Ti03, Pb(Zr,Ti)03 and (Bi,La)Ti03, exhibit a spontaneous dipole moment which can be switched between equivalent states by an external electric held. Ferroelectric thin hlms are of importance for the production of nonvolahle ferroelectric random access memory devices (FeRAM) °. Two possibilities to synthesize such mixed metal oxides are given by the CVD and ALD methods. Table 10 shows the preparation methods of such materials synthesized from metal enolates recently. 

Schulz S (2002) Synthesis, Structure and Reactivity of Group 13/15 Compounds Containing the Heavier Elements of Group 15, Sb and Bi 103 117-166 Scott JF (2007) A Comparison of Magnetic Random Access Memories (MRAMs) and Ferroelectric Random Access Memories (FRAMs). 124 199-207 Seeler F, see Braunschweig H (2008) 130 1-27... 

Ishiwara, H., Okuyama, M., Arimoto, Y. Ferroelectric Random Access Memories Fundamentals and Applications. Springer, Berlin (2004). 291 p... 

Nonvolatile ferroelectric random access memory (FRAM) devices Dynamic random access memory (DRAM) and static random access memory (SRAM) devices based on semiconductor technology are volatile that is, they wiU lose stored information when the power fails. Nonvolatile devices such as CMOS (complementary metal oxide semiconductors) and EEPROMs (electrically erasable read-only memories) are forbiddingly expensive for mass-produced electronic devices. As described above (see Section 8.3), the magnitude and direction of polarization of a ferroelectric ceramics can be reversed by applying an external electric field, and this method is used by FRAMs to store (or erase) data. As the materials have a nonlinear hysteresis curve, the polarization remains in the same state when the voltage is switched off (i.e., the information originally stored is maintained). In addition, FRAMs may be radiation-hardened for use in harsh environments such as outer space (Scott and Paz de Araujo, 1989). 

Ferroelectrics and related materials are applied to elements of capacitor, piezoelectric transducer, pyroelectric temperature sensor, surface acoustic wave device and other devices. The recent important application is for non-volatile ferroelectric random access memories (NVFRAM). Many ferroelectric materials are used in the form of thin films. So far, most of the thin films of ferroelectric materials have been produced via gas phase. However, a great many number of works on sol-gel derived thin films of ferroelectrics have appeared since 15 years ago. 

Another technique whereby the two possible electrical polarization states can be recorded as well as read by means of a transistor was described recently (145). A nonvolatile 64K ferroelectric random-access memory (RAM) based on PZT as ferroelectric storage medium in combination with the common semiconductor dreuils was developed... 

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