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oxygen vacancies is responsible for such a phenomenon because

it is hard to detect a switchable PV effect under such a low

electric field in BLFTO thin films with a low oxygen vacancy

concentration.We

demonstrated that the sign of the photocurrent

is independent of the direction of polarisation when the

modulation of the energy band induced by oxygen vacancies is

large enough to offset that induced by

polarisation.We

also found

that the PV effect induced by the electromigration of oxygen

vacancies is unstable due to the diffusion of oxygen vacancies

and the recombination of oxygen vacancies with hopping

electrons. Our results have provided deep insights into how oxygen

vacancies and polarisation flipping affect the diode and PV effect

in ferroelectric

films.We

are now expanding this investigation by

performing bandgap engineering with suitable substitution of

transition cations to cover a good range of the solar spectrum.

Collaborations are sought for the fabrication multi-bandgap

layered structures of BFO-based ferroelectric materials and study

of their PV characteristics.

Contact: Dr Ram S Katiyar,

rkatiyar@hpcf.upr.edu,

+1 787 751 4210

D) Unipolar resistive switching non-volatile

memory

The resistive random access memory (ReRAM), with its simple

design, excellent scalability, high speed storage capacity, low

power consumption, and semiconductor process flow

compatibility, has been identified by the International Technology

Roadmap for Semiconductors as a potential memory technology.

The memory effect in ReRAM is realised through reversible

switching of the resistance of a material between two conductive

states, high resistance state (HRS = off) and low resistance state

(LRS = on), when an adequate electrical signal (voltage or

current) is applied across it.

Initially, the application of a high voltage (known as forming

voltage) switches the resistance of the device from HRS to LRS by

the controlled breakdown at a limited current compliance. After

the forming process is complete, the memory cell is switched

back to HRS by applying a threshold voltage (Reset). Once in

HRS, the memory cell can again be switched to LRS simply by a

voltage sweep keeping the current compliance constant. Thus, the

resistance of the memory cell can be switched repeatedly

between the two states of low and high resistance provided the

current compliance is correctly

set.We

demonstrated unipolar

resistive switching suitable for non-volatile memory applications in

polycrystalline BiFeO3 (BFO) thin films in planar electrode

configuration with non-overlapping Set and Reset voltages and

on/off resistance ratio of ~10

4

, and good data retention (verified

for up to 3,000s). The resistive switching mechanism in this

planar device can be explained by two resistance states using the

conduction filament (thermochemical) model. Collaborations are

sought to move this technology forward and fabricate BFO-based

prototype resistive switching memory devices.

Contact: Dr Ram S Katiyar,

rkatiyar@hpcf.upr.edu,

+1 787 751 4210

Dr Gerardo Morell

Professor of Physics

University of Puerto Rico

tel :

+1 787 282 7047

gerardo.morell@upr.edu http://speclab.upr.edu/ http://www.uprnano.com/ www.horizon2020projects.com

H O R I Z O N 2 0 2 0 P R O J E C T S : P O R TA L

I S S U E S E V E N

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P R O F I L E

S P E C I A L F E AT U R E : M AT E R I A L S