F-RAM (ferroelectric random access memory), pioneered by Ramtron International Corp., offers a unique set of features relative to other semiconductor technologies. Established semiconductor memories can be divided into two categories: volatile and nonvolatile. Volatile memory includes SRAM (static random access memory) and DRAM (dynamic random access memory), among others. RAM type devices are easy to use, offer high performance, but they share a common vulnerability: stored memory is lost when the power supply is removed。
The F-RAM chip contains a thin ferroelectric film of lead zirconate titanate [Pb(Zr,Ti)O3], commonly referred to as PZT (Figure 1). The Zr/Ti atoms in the PZT change polarity in an electric field, thereby producing a binary switch. Unlike RAM devices, F-RAM retains its data memory when power is shut off or interrupted, due to the PZT crystal maintaining polarity. This unique property makes F-RAM a low power, nonvolatile memory。
FRAM technology is compatible to standard CMOS manufacturing process: ferroelectric thin film was put on the base of CMOS and between positive and negative electrode, then connected with metal, the manufacturing process could be finished after passivation.
RAM technology of Ramtron has developed quite mature up to now. At the very start, FRAM adopted the structure of two transistors/ two capacitors(2T/2C) which resulting in large size. With the development of Ramtron material and manufacturing process, no unit of FRAM has to allocate standard capacitor and new structure of one transistor and one capacitor could run like DRAM, providing reference for every single memory array by using one capacitor. Compared with 2T/2C, new structure effectively reduced half of the size needed by internal memory. New design improved the efficiency of FARM to a large extent and cut down its cost.
Meanwhile, Ramtron improved cost and efficiency of every unit of FRAM by turning to smaller design rule. Compared with the manufacturing process (0.35/0.5um) of last generation, 0.13um adopted recently largely reduced power consumption and increased the utilization rate of every single wafer.
All these exciting development of ferroelectric memory have been widely applied in every field of people’s daily life which ranges from office duplicator, high-grade server to auto airbag and entertainment facilities. Ferroelectric memory will continuously improve its performance so as to be widely applied in the world.