Ferroelectric non-volatile memories for low-voltage, low-power applications

Non-volatile ferroelectric random access memories (FERAM) offer substantial advantages over conventional floating-gate electrically erasable programmable read only memory (EEPROM) and flash EEPROM devices. FERAMS can be written at high speeds (≈100 ns) and at standard supply voltages 95 V or less) without the use of charge pumps. Switching of ferroelectric capacitors at voltages of 1.5 V or below has been demonstrated. FERAMS also have a high endurance for writes (>10 12 cycles demonstrated). The combination of high-speed and low-voltage writing means a FERAM requires far less energy to program than a EEPROM. However, FERAMs use a destructive read followed by a rewrite so that endurance limits also apply to reading. Other reliability concerns include retention (loss of data with time) and imprint (loss of ability to write into the opposite state). We discuss the present ability of ferroelectric materials (lead zirconate titanate and Bi layered perovskites) to meet the electrical requirements and reliability requirements of practical non-volatile memory applications. We also review some of the process challenges in integrating ferroelectrics into typical complementary metal oxide semiconductor (CMOS) integrated circuit fabrication.