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Journal Paper review (MSE631A)
-By Priyanshu Jain (12518)
This paper is about the use of ferroelectric materials in memory devices (ferroelectric random
access memory-FRAM) where Secure, high speed, and low power consumption nonvolatile
memories are required. These devices are used with smart RFID tags and secure IC cards (i.e.
personal authentication e-services). In this review paper we will talk about the use of FRAM
over other conventional devices and we will introduce new ferroelectric material that will
enable us to fabricate FRAM in a 90‑nm technology node.
Because of ideal memory properties, such as very low power consumption and high‑speed
read/write performance, FRAM has been applied to LSIs (Large-Scale Integration) for IC cards,
RFID tags, smart cards, and for alternate memory addressing with battery backup. In order to
expand their applications some changes in the stoichiometry of these ceramics has been
made which increases memory capacity, reduces operating voltage, and increases the
read/write cycles.
PZT ( Pb(Zr,Ti)O
3
) is used in FRAMs but it has limited remnant polarization ie low storing
capacity. It does not have enough switching charge for 90-nm technology node because its
fabrication through semiconductor process restricts that. A method has been suggested to
overcome this problem by expanding the surface area by assembling a capacitor into a 3D
structure but that is also challenging because to get enough switching charge we have to
arrange the crystal orientation completely which is itself a difficult task.
A new ferroelectric material, BFO (BiFeO
3
) for a 90‑nm technology has replaced use of PZT.
In BFO some of the Fe ions are substituted with 5% Mn ions which decreases the leakage
current in the BFO film at room temperature and increases the withstand voltage. With the
use of BFO, 5 times larger switching charge is achieved and leakage current is also reduced
thus overall memory capacity of device increases. It has been shown that the relative
dielectric constant of BFO is one-fourth to that of PZT, and its Curie temperature is 800°C,
which is very higher than that of the conventional material. Thus, these properties makes BFO
work at high-speed read/write and high-temperature operations and makes them one of the
important material in this industry.
Some methods for further improvements in storing capacity of BFO has been discussed. These
mainly include reducing of operating voltage, low temperature deposition of BFO film and
selection of passivation film to prevent Fe diffusion. With implementation of these techniques
BFO has a great potential to serve this industry with much more higher storing capacity.