View source for Projects:2021s1-13482 Nanoscale Devices for 6G Technologies

[[Category:Projects]]
[[Category:Final Year Projects]]
[[Category:2021s1|13482]]
In telecommunications, 6G is the 6th generation standard for telecommunication that is currently under research and development for wireless communication technologies for supporting cellular data networks. It is the successor of the 5G network and will be significantly faster. The development of 6G communication technologies requires new devices that will access into Terahertz spectral range. 

== Introduction ==
Compared to 5G, the most outstanding difference between 5G and 6G is that 6G communication technology will access into Terahertz(THz) spectral range. To access the terahertz frequency spectral, we need electronic devices that can operate in the terahertz frequency environment. Some high-speed electronic devices such as High Electron Mobility Transistor (HEMT) has already been used at the top edge of the communication devices, and the result is successful. However, other high-speed electronic devices such as Heterogeneous Bipolar Transistors (HBTs), Resonance Tunneling Diodes (RTDs) have even better high-frequency performance.

=== Project team ===
==== Project students ====
* Zicong Wen
* Jiayue Liang
==== Supervisors ====
* Professor Nelson Tansu

=== Objectives ===
This project aims to research electronic devices that can support the 6G wireless telecommunication technology standard and analyse the frequency performance of the researched devices. Two devices were researched in this project, Heterogeneous Bipolar Transistor and Resonance Tunnelling Diode

== Background ==
=== 6G Requirements ===
As 5G initiated, many organizations have already defined the 6G system in various ways. A difference that distinguishes 6G telecommunication technology from its predecessors is that 6G technology can access into Terahertz frequency range. The development of 6G technology does not only mean the revolution of telecommunication technology, it also means the speed of wireless data transmission technology will be progressed significantly. The following table shows the comparison of 4G, 5G and 6G network systems [1].
{| class="wikitable"
|+ Key requirements of 5G, beyond 5G and 6G network systems 
|-
! '''KPI''' !! 5G !! Beyond 5G !! 6G
|-
| Operating frequency bandwidth || Sub-6 GHz Mm-Wave for fixed access  || Sub-6 GHz Mm-Wave for fixed access || Sub-6 GHz Mm-Wave for mobile access
Exploration for higher frequency and THz bands
|-
| Rate requirements || 1Gb/s || 100Gb/s || 1Tb/s
|}

== Method ==
===Resonant Tunneling Diode (RTD)===
RTD is one type of diode based on the quantum mechanical phenomenon, resonant tunnelling. The electrons can flow through the energy barriers with some probability, which is impossible in classical physics. And the tunnelling can happen in an instant. Its IV graph also indicates its negative resistance characteristic. Due to these features, RTD can operate over the THz theoretically.

===Heterogeneous Bipolar Transistors (HBT)===
Bipolar Junction Transistor (BJT) has dominated the electronic world for a very long time. It is a good, effective semiconductor that is widely used in many applications. However, with the rapid development of the 6G technology, BJT is no longer fulfilling the demand for extremely high transmitting speed. Hence, introducing HBT can enable devices to work in the terahertz environment so that the speed of the device is improved.
====Material used====
The following table shows the key material parameters for the heterojunction in the project.

====Current Components====
[[File:Current component of an NPN transistor.jpg|thumb|Figure 1: Current components of an NPN transistor]]
Figure 1 [1] is a model of the current components of an NPN transistor, it is applicable for either BJT and HBT. The description of these components is given as the following:
* I<sub>nE</sub>: Electron diffusion current injected at the EB junction
* I<sub>pE</sub>: Hole diffusion current injected at the EB junction
* I<sub>B</sub>: Base current
* I<sub>C</sub>: Collector current
* I<sub>E</sub> = I<sub>nE</sub> + I<sub>pE</sub>
* I<sub>E</sub> = I<sub>B</sub> + I<sub>C</sub>
<br>
Therefore, the DC parameters of HBT can be calculated using these relationships.<br>

====Transistor parameters====
The following parameters are essential to study and evaluate the characteristics of a transistor. 
# Emitter Injection Efficiency: Emitter injection efficiency defines the efficiency of the majority carrier injects from base to emitter. It is the quotient of the I<sub>C</sub> and I<sub>nE</sub>.
# Base transpose factor: The base transpose factor is defined as the base current that requires transferring the emitter current to the collector current. It is the quotient of the I<sub>nE</sub> and I<sub>E</sub>.
# Current transpose factor: Current transpose factor represents the emitter-to-collector current amplification, it is also known as the common-base current gain. It is the product of the emitter injection efficiency and the base transpose factor.
# Amplification factor: The Amplification factor is defined as the ratio of the collector current to the base current. It is also known as common-emitter current gain. It is the quotient of the I<sub>C</sub> and I<sub>B</sub>.

====Frequency Response====
Frequency response is an important parameter that demonstrates the performance of the device in the frequency environment. The cut-off frequency is an indicator in a frequency response diagram at which the power of the system begins to be reduced. It usually corresponds to the frequency that is 3 dB less than the initial gain, which is -3 dB in this case. The reason why choosing -3 dB as the standard for cut-off frequency is that reaching 3 dB means the output current is two times less than the input current.

== Results & Discussion ==

===Resonance Tunneling Diode===

===Heterogeneous Bipolar Transistor===
The result of the HBT simulation will be demonstrated in two parts. The first part demonstrates the DC characteristics and frequency performance of BJT and HBTs. The second part demonstrates how the size of the base width of the devices affects the frequency performance. 

====DC characteristics and frequency performance of BJT and HBTs====

{| class="wikitable"
|+ style="text-align: center;" | Simulation results of the BJT and HBT (Base Width = 1 micormetre)
|-
! '''Device''' !! '''Emitter injection efficiency''' !! '''Base transpose factor''' !! '''Current transpose factor''' !! '''Amplification factor''' !! '''Cut-off frequency'''
|-
| '''BJT''' || 0.99123 || 0.9958 || 0.99119|| 112.48|| 248.75 MHz
|-
| '''Si/SiGe HBT''' || 1|| 0.99307|| 0.99307|| 142.32|| 437.33 MHz
|-
| '''AlGaAs/GaAs HBT''' || 1|| 0.99984 || 0.99984 || 6209.1|| 2.3471 GHz
|-
| '''InGaAs/InP HBT''' || 1|| 0.99995|| 0.99995|| 19989|| 3.2977 GHz
|-
| '''InGaAs/InSb HBT''' || 1|| 0.99998|| 0.99998|| 44025|| 10.582 GHz
|-
|}
<br>
It is obvious that introducing the heterojunction to transistors improves the emitter injection efficiency and the base transpose factor. Moreover, when the energy bandgap between the two semiconductors is getting bigger, the base transpose factor is getting closer to 1. This also leads to the current transpose factor equal to the base transpose factor due to the current transpose factor being the product of the emitter injection efficiency and the base transpose factor. The current amplification factors of the HBT simulations are generally higher than BJT

====Size of the base region====
{| class="wikitable"
|+ style="text-align: center;" | Frequency performance of the HBT with different base width
|-
! '''Device''' !! '''1 micrometre base width''' !! 45 nanometre base width
|-
| '''Si/SiGe HBT''' || 437.33 MHz|| 67.532 GHz
|-
|  '''AlGaAs/GaAs HBT'''  || 2.3471 GHz|| 1.1535 THz
|-
| '''InGaAs/InP HBT'''  || 3.2977 GHz|| 1.6285 THz
|-
| '''InGaAs/InSb HBT'''|| 10.582 GHz|| 5.2247 THz
|-
|}

== Conclusion ==

== References ==
[1] W. Saad, M. Bennis and M. Chen, "A Vision of 6G Wireless Systems: Applications, Trends, Technologies, and Open Research Problems," in IEEE Network, vol. 34, no. 3, pp. 134-142, May/June 2020, doi: 10.1109/MNET.001.190028

[2] ...