More parking... from 2004 status report on FeRAM:
Introduction
Ferroelectric random-access memory
(FeRAM) is a type of nonvolatile randomaccess memory that uses a ferroelectric film as a capacitor for storing data. FeRAM can achieve high-speed read/write operations comparable to that of dynamic RAM (DRAM), without losing data when the power is turned off (unlike DRAM). In addition to nonvolatility and high-speed operation, FeRAM cells offer the advantages of easy embedding into LSI logic circuits (LSI large-scale integration, the technology that allows thousands of transistors per chip) and low power consumption, perhaps their greatest advantage for many applications.
The market for FeRAM has expanded rapidly; FeRAM-embedded LSI circuits have been used in smart cards, radiofrequency
identification (RFID) tags, and as a replacement for BBSRAM (batterybacked-up static RAM), which is used in various devices to protect data from an unexpected power failure, as well as in many other SoC (system on a chip) applications.
FeRAM cells have been extensively developed to improve their density, speed, read/write endurance, and reliability. A memory cell, where one bit of data is stored, is composed of a cell-selection transistor and a capacitor for 1T1C (one transistor, one capacitor)-type FeRAM. A major problem encountered when reducing the size of the memory cell is preventing reliability degradation. The reliability of FeRAM cells is dependent on the materials used (for the ferroelectric film, electrode, interlayer dielectric, etc.), the fabrication process, the device structure, the memory cell circuit, and the operation sequence. Various types of FeRAM are compared in Table I. By optimizing these parameters, new types of FeRAM, designated by the number of transistors (T) and capacitors (C) per cell, have been commercialized: 1T1C-type FeRAM and 6T4C-type FeRAM (Table I) were shipped to customers starting last year.
Mass production of FeRAM cells started in the latter half of the 1990s. FeRAM cells with a planar capacitor, a 2T2C memory cell architecture, and a design rule of 0.5 m or larger (meaning a minimum feature width of 0.5 m) were the first type of FeRAM manufactured on a large scale. Now, FeRAM with 0.18m 1T1C memory cells and a memory density of 1 Mbit or
more are being mass-produced. The application fields of FeRAM are growing rapidly as well.
The performance of FeRAM has also greatly improved. The readout operation in a conventional FeRAM is destructive (i.e., reading the data destroys it), and thus there are limitations in the read/write cycles and the access time (the time required to read one bit of data). Recently, Masui et al. developed a 6T4C-type FeRAM with a nondestructive readout, unlimited read/write cycles, and an access time of less than 10 ns.1 This type of FeRAM is currently in use in RFID tags and other applications.
Field-effect-transistor (FET)-type FeRAMis also being actively developed to achieve a small-geometry cell and a long data retention time when the system is turned off. Recently, a data retention time of more than a month was achieved by using a
HfO2 buffer layer with low leakage current in which no Hf diffused into the Si.2
FET-type FeRAM is one of the most promising candidates for high-capacity nonvolatile RAM (NVRAM) because the memory cell can be scaled down to a size smaller than DRAM. FET-type FeRAM cells are comparable in size to those of flash memory. With improved data retention characteristics, FET-type FeRAM could enable high-speed (sub-100-ns access; comparable to DRAM), high-capacity (1 Gbit; comparable to flash), nonvolatile memory with low power consumption.
It is certain that the capacity and performance of FeRAM will be enhanced by the continuing improvements that are being made in the materials (including parameters such as switching charge, coercive field, fatigue, stability, leakage current, etc.), the processing steps (temperature control, uniformity, limiting damage due to processing, etc.), the device (scaling, improved processing steps, reliability, etc.), and the circuits (margin of operation, power consumption, access speed, reliability, etc.). Moreover, it is expected that increased activity in the market will further accelerate the development of FeRAM. In this short article, we review the current status of FeRAM technology, and then focus, in turn, on conventional (capacitor-type) FeRAM (2T2C and 1T1C), 6T4C-type FeRAM, and FET-type FeRAM.
mrs.org
The 6T4C FeRAM design (remember the DPGA chip from 2002? same memory cell) is Fujitsu's. They call it NVSRAM for obvious reasons. I found evidence that it is used in a SX300 RAID Server they produced in 2005 if not earlier... but can't verify its use in RFID apps. If it is in fact used commercially there, I would assume its in industrial/medical systems. I see no indication at all that they want to sell it externally.
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