FERROELECTRIC NONVOLATILE MEMORIES FOR LOW-VOLTAGE, LOW-POWER APPLICATIONS

Non-volatile ferroelectric random access memories (FERAM) offer substa ntial advantages over conventional floating-gate electrically erasable programmable read only memory (EEPROM) and Rash EEPROM devices. FERAM S can be written at high speeds (approximate to 100 ns) and at standar d supply voltages 95 V or less) without the use of charge pumps. Switc hing of ferroelectric capacitors at voltages of 1.5 V or below has bee n demonstrated. FERAMS also have a high endurance for writes (> 10(12) cycles demonstrated), The combination of high-speed and low-voltage w riting 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 i nclude 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 perovs kites) to meet the electrical requirements and reliability requirement s of practical non-volatile memory applications, We also review some o f the process challenges in integrating ferroelectrics into typical co mplementary metal oxide semiconductor (CMOS) integrated circuit fabric ation.