Advanced

Fabrication of Tunneling Field Effect Transistors (TFETs) and the study of graphene

Nunez Lobato, Carlos LU (2018) FYSK02 20172
Solid State Physics
Department of Physics
Abstract
After the discovery of graphene in 2004, a single layer of graphite, the assembly of 2D materials became a promising research area in solid state Physics. This thesis explores fabrication of 2D-heterostructures that aim to probe into graphene’s electronic structure with the Tunneling Field Effect Transistor (TFET).

In the fabrication process, we used mechanical exfoliation to obtain monolayer graphene and Si-SiO2 as the substrate and back gate of the device. Then, atomically thin hexagonal boron nitride (hBN) was used as the tunneling barrier because of its insulating properties and smooth surface. Gold (Au) leads were evaporated on the devices so that a tunneling current could be extracted from the sample.

In this thesis, TFETs are... (More)
After the discovery of graphene in 2004, a single layer of graphite, the assembly of 2D materials became a promising research area in solid state Physics. This thesis explores fabrication of 2D-heterostructures that aim to probe into graphene’s electronic structure with the Tunneling Field Effect Transistor (TFET).

In the fabrication process, we used mechanical exfoliation to obtain monolayer graphene and Si-SiO2 as the substrate and back gate of the device. Then, atomically thin hexagonal boron nitride (hBN) was used as the tunneling barrier because of its insulating properties and smooth surface. Gold (Au) leads were evaporated on the devices so that a tunneling current could be extracted from the sample.

In this thesis, TFETs are suggested as a complementary alternative to Scanning Tunneling Microscopy (STM) in order to study the electronic properties of 2D materials. Our results showed several spectroscopic features of graphene, some of which could be tuned by an applied gate voltage while others could not . Analysis of the gate tunable spectroscopic feature suggests it may be the Dirac point (E_D), a signature of graphene’s unique band structure. On the other hand, the spectroscopic feature that is insensitive to gate voltage could be attributed to inelastic tunneling processes i.e. a phonon excitation.

Future research will be able to use these devices under high magnetic fields (∼ 45T) and low temperatures (∼ 25mK). TFET’s also open the door to an alternative probing method to study the electronic properties of any 2D-material by simply replacing graphene by the desired sample to be studied. (Less)
Popular Abstract
The wonder material, as some like to address graphene, has drawn an extensive interest for being the strongest, most flexible and first one-atom-thick structure to be found. The unexpected discovery in 2004 of this structure, made of carbon atoms, laid the groundwork for the broad spectrum of new slim materials yet to come. The combination of graphene with these highly thin materials (2D-materials) allows not only to study graphene’s re- markable properties, but also to create novel microscopic devices out of it. Because of its unique nature, graphene is steadily working its way into today’s silicon dominated elec- tronic industry.

It was not long ago when transistors made of silicon revolutionized our computers and phones. These small... (More)
The wonder material, as some like to address graphene, has drawn an extensive interest for being the strongest, most flexible and first one-atom-thick structure to be found. The unexpected discovery in 2004 of this structure, made of carbon atoms, laid the groundwork for the broad spectrum of new slim materials yet to come. The combination of graphene with these highly thin materials (2D-materials) allows not only to study graphene’s re- markable properties, but also to create novel microscopic devices out of it. Because of its unique nature, graphene is steadily working its way into today’s silicon dominated elec- tronic industry.

It was not long ago when transistors made of silicon revolutionized our computers and phones. These small devices, presently of the size of ten to a few nanometers (1 nm = 0.0000000001 meters), are able to act as a switch when a voltage is applied. The larger the number of “electrical switches” the faster our computers or phones will work. The discov- ery of graphene and its great conducting properties has led scientists to try and integrate it in silicon-based transistors by combining it with other new 2D-materials.

It seems rather fictional to be dealing with atomically thin layers of materials. However, graphene is a material that comes from the very same graphite that our pencils are made of. Imagine a stack of post-its representing bulk graphite; then, each post-it would correspond to precisely one graphene layer. Surprisingly, isolating a thin layer of graphene is as simple as placing scotch tape on top of bulk graphite and peeling away graphene layers as the tape is lifted. In the same way a post-it is placed onto a paper, once isolated, graphene can be placed onto a substrate and then observed through a microscope. This entire process is called exfoliation and it is an important part of this thesis, because it can be repeated with a plethora of other materials to create unique 2D-material devices.

The work in this project shows how one graphene layer, sandwiched between a silicon sub- strate and a thin insulating material (e.g. boron nitride), can be a prototype for a transistor if a bias is applied. For this purpose, a very thin film of metal (gold) must be evaporated onto the device, to function as an electrical contact. Theoretically, current should not be able to flow due to the insulating material. However, in the realm of quantum mechanics (i.e. at the atomic scale), some of the current is able to tunnel through the insulator. Thus, this special type of transistors bears the name of ‘tunneling field effect transistor’ and the current extracted through it will give intrinsic information about graphene, such as its conductive properties. Before tunneling transistors are realizable in the market, the properties of graphene can be studied with these actual devices. Understanding them is of utter importance for future applications of graphene in not just electronics, but also areas like solar cells technology or even medicine. (Less)
Please use this url to cite or link to this publication:
author
Nunez Lobato, Carlos LU
supervisor
organization
course
FYSK02 20172
year
type
M2 - Bachelor Degree
subject
keywords
graphene, semiconductor, exfoliation, boron nitride
language
English
id
8935790
date added to LUP
2018-02-15 09:30:46
date last changed
2018-02-15 09:30:46
@misc{8935790,
  abstract     = {After the discovery of graphene in 2004, a single layer of graphite, the assembly of 2D materials became a promising research area in solid state Physics. This thesis explores fabrication of 2D-heterostructures that aim to probe into graphene’s electronic structure with the Tunneling Field Effect Transistor (TFET).

In the fabrication process, we used mechanical exfoliation to obtain monolayer graphene and Si-SiO2 as the substrate and back gate of the device. Then, atomically thin hexagonal boron nitride (hBN) was used as the tunneling barrier because of its insulating properties and smooth surface. Gold (Au) leads were evaporated on the devices so that a tunneling current could be extracted from the sample.

In this thesis, TFETs are suggested as a complementary alternative to Scanning Tunneling Microscopy (STM) in order to study the electronic properties of 2D materials. Our results showed several spectroscopic features of graphene, some of which could be tuned by an applied gate voltage while others could not . Analysis of the gate tunable spectroscopic feature suggests it may be the Dirac point (E_D), a signature of graphene’s unique band structure. On the other hand, the spectroscopic feature that is insensitive to gate voltage could be attributed to inelastic tunneling processes i.e. a phonon excitation.

Future research will be able to use these devices under high magnetic fields (∼ 45T) and low temperatures (∼ 25mK). TFET’s also open the door to an alternative probing method to study the electronic properties of any 2D-material by simply replacing graphene by the desired sample to be studied.},
  author       = {Nunez Lobato, Carlos},
  keyword      = {graphene,semiconductor,exfoliation,boron nitride},
  language     = {eng},
  note         = {Student Paper},
  title        = {Fabrication of Tunneling Field Effect Transistors (TFETs) and the study of graphene},
  year         = {2018},
}