Simulations of current transport phenomena in ferroelectric tunnel junctions
(2022) EITM01 20221Department of Electrical and Information Technology
- Abstract
- Ferroelectric memories pose as a potential candidate as resistive memory devices that could be used for in-memory computing and artificial synapses. One promising type of ferroelectric memory device is the ferroelectric tunnel junction (FTJ). The basic functionality of a FTJ device is based upon the fact that ferroelectric materials display two distinct polarisation states which could be switched in order to achieve two resistance states in the device.
There are several current pathways contributing to the current in a FTJ and the exact mechanisms are not entirely understood. There is a need for a numerical model, where electronic band structure and defect current pathways are considered, that includes physically well grounded fitting... (More) - Ferroelectric memories pose as a potential candidate as resistive memory devices that could be used for in-memory computing and artificial synapses. One promising type of ferroelectric memory device is the ferroelectric tunnel junction (FTJ). The basic functionality of a FTJ device is based upon the fact that ferroelectric materials display two distinct polarisation states which could be switched in order to achieve two resistance states in the device.
There are several current pathways contributing to the current in a FTJ and the exact mechanisms are not entirely understood. There is a need for a numerical model, where electronic band structure and defect current pathways are considered, that includes physically well grounded fitting parameters. In this thesis two such models for the trap-assisted tunnelling (TAT) current are investigated and fitted to experimental data. The first model is based upon occupational probability in the metal electrodes and transmission probabilities given by the WKB approximation. The second model utilises Fermi's golden rule in order to estimate transition rate.
Both models in general display unsatisfactory results in terms of reproducing and fitting to experimental data. The second model displays some promising results once empirical constants are introduced which indicate towards a certain accuracy in the parameters and models used. The main deviations are believed to stem from an overly simplified band structure model and normalisation problems. (Less) - Popular Abstract
- In modern day technologies the demand for high performance memory solutions increases rapidly as modern technologies and applications are data driven. The ever-increasing need for larger amounts of data and processing speeds has led to technological bottlenecks. The computational speed today is limited by the speed at which data could be fetched from memory. The solution? Perform computations in the memory directly and, thus reduce the time needed to transfer the memory to the processors. This is known as in-memory computation, and it probably partly will serve as the solution for the worlds data processing problems. The performance of modern-day memory devices is lacking for them to be utilized for in-memory computation. This opens up a... (More)
- In modern day technologies the demand for high performance memory solutions increases rapidly as modern technologies and applications are data driven. The ever-increasing need for larger amounts of data and processing speeds has led to technological bottlenecks. The computational speed today is limited by the speed at which data could be fetched from memory. The solution? Perform computations in the memory directly and, thus reduce the time needed to transfer the memory to the processors. This is known as in-memory computation, and it probably partly will serve as the solution for the worlds data processing problems. The performance of modern-day memory devices is lacking for them to be utilized for in-memory computation. This opens up a whole new field in search of better, faster and more advanced memory devices.
One promising type of future memory device is the ferroelectric tunnel junction (FTJ). The FTJ consists of two metal electrodes with a ferroelectric material sandwiched in between them. The basic functionality of an FTJ device is based upon the fact that ferroelectric materials display two distinct polarization states, that could be switched in order to achieve two different resistance states in the device which are needed in memory applications. The two resistance states are the binary, 1 and 0, used in computers. Polarization could in simple terms be explained as the separation of charge carriers in a certain direction. The phenomena behind the current transport in an FTJ is quantum mechanical tunnelling. Quantum mechanical tunnelling is a phenomenon where a particle can travel through an energy barrier even though it does not possess the sufficient energy to do so, an impossibility in classical physics! It might sound like the mechanics behind the current in FTJs are entirely understood, but this is not the case. There is in fact a need for good models describing the physics in an FTJ in order to aid our understanding of the device and how to optimize it for suitable applications. The idea of finding good model was the purpose of this project. The focus has been on trying to implement such a model for specific the dominating current mechanism in the FTJ and get it to match data from real devices. However, the task proved difficult and the model that was used was too simple in order to give represent the physics of the device accurately. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9090611
- author
- Lubar, Ivan ^{LU}
- supervisor
- organization
- course
- EITM01 20221
- year
- 2022
- type
- H2 - Master's Degree (Two Years)
- subject
- report number
- LU/LTH-EIT 2022-874
- language
- English
- id
- 9090611
- date added to LUP
- 2022-06-21 10:40:05
- date last changed
- 2022-06-21 10:40:05
@misc{9090611, abstract = {{Ferroelectric memories pose as a potential candidate as resistive memory devices that could be used for in-memory computing and artificial synapses. One promising type of ferroelectric memory device is the ferroelectric tunnel junction (FTJ). The basic functionality of a FTJ device is based upon the fact that ferroelectric materials display two distinct polarisation states which could be switched in order to achieve two resistance states in the device. There are several current pathways contributing to the current in a FTJ and the exact mechanisms are not entirely understood. There is a need for a numerical model, where electronic band structure and defect current pathways are considered, that includes physically well grounded fitting parameters. In this thesis two such models for the trap-assisted tunnelling (TAT) current are investigated and fitted to experimental data. The first model is based upon occupational probability in the metal electrodes and transmission probabilities given by the WKB approximation. The second model utilises Fermi's golden rule in order to estimate transition rate. Both models in general display unsatisfactory results in terms of reproducing and fitting to experimental data. The second model displays some promising results once empirical constants are introduced which indicate towards a certain accuracy in the parameters and models used. The main deviations are believed to stem from an overly simplified band structure model and normalisation problems.}}, author = {{Lubar, Ivan}}, language = {{eng}}, note = {{Student Paper}}, title = {{Simulations of current transport phenomena in ferroelectric tunnel junctions}}, year = {{2022}}, }