A discrete ferroelectric memory

Abstract

Ferroelectric-based nonvolatile memory (FeRAM) is now a mainstream product category supported by Ramtron, Fujitsu, Texas Instruments, IBM, and Matsushita. The internal array of ferroelectric capacitors in FeRAMs consumes absolutely no energy when the chip is powered. This lack of energy consumption combined with SRAM-like operation at SRAM speeds constitutes a unique advantage for FeRAM memory in low-power embedded applications. Because the ferroelectric technology is buried deep inside the IC package surrounded by digital interface circuits, the true nature of ferroelectric memory capacitor operation is obscured from the user. It is possible to operate a simple ferroelectric nonvolatile memory from the I/O pins of a microprocessor using discrete ferroelectric capacitors in a Sawyer-Tower circuit configuration. Designing and operating a ferroelectric memory with discrete capacitors provides insight into the nature of FeRAMs, their internal operation, and their reliability. The read and write times of the discrete memory will be fast, limited only by the current capacity of the I/O pins. The discrete ferroelectric capacitors will retain their written state without concern for whether the microcontroller is powered or not. Unlike EEPROM or FLASH transistors, discrete ferroelectric capacitors can be physically handled during retention without corrupting their stored states.