Ferroelectric RAM presentation

Detailed information about ferroelectric RAM

1. seminar on FERROELECTRIC RAM(Fe-ram ) Presented by: NITHEESH KUMAR

2. CONTENTS: Introduction Basic Memory Cell Structure Ferro Electric Crystal FRAM Technology FRAM Read Operation FRAM Write Operation Advantages Disadvantages Future Applications Conclusion References

3. INTRODUCTION Ferroelectric RAM, is a form of random access memory that combines speed and Non-Volatility. A Ferroelectric memory cell consists of a ferroelectric capacitor and a MOS transistor. The most well-known ferroelectric substance is PZT(Lead Zirconate Titanate ) . Data is read by applying an electric field to the capacitor. The memory is non-volatile. FRAM allows systems to retain information even when power is lost.

4. BASIC MEMORY CELL STRUCTURE Bitline (BL ) Plateline (PL ) WORDLINE(WL)

5. A ferroelectric memory cell, known as 1T- 1C (one transistor, one capacitor) structure which is similar to that of DRAM. The difference is that ferroelectric film is used as its storage capacitor rather than para electric material as in DRAM. Figure above shows memory cell structure, consists of a single ferroelectric capacitor that is connected to a Plate line(PL) at one end and, via an access transistor, to a Bit line(BL) at the other end. Raising the word line (WL) and hence turning ON the access transistor accesses the cell.

6. FERRO ELECTRIC CRYSTAL Ferroelectric Crystal: The center atom moves to store ones and zeros Consist of 8 atom of lead at corners 6 atom of oxygen at face centers 1 atom of titanium at cube centers

7. FE-RAM TECHNOLOGY When an electric field is applied to a ferroelectric crystal, the central atom moves in the direction of the field. As the atom moves within the crystal, it passes through an energy barrier causing a charge spike. Internal circuits sense the charge spike and set the memory. If the electric field is removed from the crystal, the central atom stays in position, preserving the state of the memory. This makes FE-RAM non-volatile, without any periodic refresh.

8. FE-RAM READ OPERATION An electric field is applied. If the atoms are near the cube "floors" and the electric field pushes them to the top, the cell gives off a current pulse. This pulse, representing a stored 1 or 0, is detected by a sense amplifier. If the atoms are already near their cubes' "ceilings," they don't budge when the field is applied and the cell gives off a smaller pulse. Reading an FRAM cell destroys the data stored in its capacitor. So after the bit is read, the sense amplifier writes the data back into the cell, just as in a DRAM.

9. FE-RAM WRITE OPERATION To write a "1" into the memory cell , The BL is raised to V DD Then the WL is raised to V DD + Vt. This allows a full V DD to appear across the ferroelectric capacitor At this time the state of ferroelectric is independent of its initial state. Next, the PL is pulsed, WL stays activated until the PL is pulled down completely and the BL is driven back to zero. The final state of the capacitor is a negative charge state S1.

10. To write a "0" into the cell The BL is driven to 0V prior to activating the WL. The rest of the operation is similar to that of writing a "1“ The written data is held in the cell even though the selection of the word line is changed to non selected state (i.e. transistor is OFF), so it is nonvolatile.

11. ADVANTAGES FRAM allows systems to retain information even when power is lost, without resorting to batteries, EEPROM, or flash. Access times are the same as for standard SRAM, so there's no delay-at-write access as there is for EEPROM or flash. Low power consumption, low voltage operation and high write endurance make it superior than other non-volatile memories like EEPROM & FLASH. It is less expensive than magnetic memories.

12. FRAM AS RAM & ROM The key advantage to FRAM over DRAM is what happens between the read and write cycles. In DRAM, every cell must be periodically read and then re-written, a process known as refresh. In contrast, FRAM only requires power when actually reading or writing a cell. The vast majority of power used in DRAM is used for refresh power usage about 99% lower than DRAM. FRAM memory fills the RAM and ROM performance gap

13. COMPARISON

14. DISADVANTAGES Present high cost when compared with FLASH,EEPROM. Low density compared to DRAM & SRAM. FUTURE OF FRAM Increased memory capacity High density, to operate under very high temperatures. Combine FRAM with other logic technologies to offer more enhanced devices.

15. CONCLUSION Ferroelectric memories are superior to EPROM’s & Flash memories in terms of write access time & overall power consumption too. eg : of such applications are contactless smart cards & digital cameras. Future personal wireless connectivity applications that are battery driven will demand large amounts of non volatile storage to retain accessed internet web pages, contain compressed video, voice and data. The density and energy efficiency of writing data to memory would seem to indicate that ferroelectric memory will play a major role in these types of consumer products.

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