Ferroelectric Random Access Memory

Ferroelectric Random Access Memory Before the 1950s, ferromagnetic cores were the only type of random-access, nonvolatile memories available. A core memory is a regular array of tiny magnetic cores that can be magnetized in one of two opposite directions, making it possible to store binary data in the form of a magnetic field. The success of the core memory was due to a simple architecture that resulted in a relatively dense array of cells. This approach was emulated in the semiconductor memories of today (DRAMs, EPROMs, and FRAMs). Ferromagnetic cores, however, were too bulky and expensive compared to the smaller, low-power semiconductor memories. In place of ferromagnetic cores ferroelectric memories are a good substitute. The term ferroelectric indicates the similarity, despite the lack of iron in the materials themselves. Ferroelectric memory is a new type of semiconductor memory, which exhibit short programming time, low power consumption and nonvolatile memory, making highly suitable for application like contact less smart card, digital cameras which demands many memory write operations. A ferroelectric memory technology consists of a complementary metal-oxide-semiconductor (CMOS) technology with added layers on top for ferroelectric capacitors. A ferroelectric memory cell has at least one ferroelectric capacitor to store the binary data, and one transistor that provide access to the capacitor or amplify its content for a read operation. Once a cell is accessed for a read operation, its data are presented in the form of an analog signal to a sense amplifier, where they are compared against a reference voltage to determine their logic level. Ferroelectric memories have borrowed many circuit techniques (such as folded-bit line architecture) from DRAMs due to similarities of their cells and DRAMs maturity. Some architectures are reviewed here