Numerical Simulation and Modeling for Vacuum Channel Field Effect Transistor Using Graphene Emitter
- Title
- Numerical Simulation and Modeling for Vacuum Channel Field Effect Transistor Using Graphene Emitter
- Authors
- Yoon, Cheul-Hyun; Yoon, Seok Hyun; KONG, BYOUNG DON
- Date Issued
- 2023-07-03
- Publisher
- IEEE Nano Technology Council
- Abstract
- Recent studies have investigated the potential of utilizing semi-metallic materials, specifically Graphene, as an emission
source in vacuum devices [1]. Due to its distinctive two-dimensional structure, Graphene exhibits a field enhancement effect
that induces band bending near its edge, rendering it a highly promising candidate as an emitter [2]. Furthermore, its
controllability of the fermi level offers a prospect for electrical state modulation, thereby augmenting its potential for highspeed
switching and rectification devices when combined with a gate-like structure [3].
In this context, we have conducted a numerical semiconductor device modeling of a three-terminal vacuum channel field
effect transistor and developed a simulator for it. The device comprises two metallic electrodes that serve as the source and
drain, a metal-oxide-graphene structure for gate bias modulation, an emitter of Graphene monolayer, and the vacuum channel
(Fig. 1). The absence of scattering in the vacuum channel, apart from electron-electron scattering, facilitates high-speed
transport of emitted electrons without velocity saturation. Our simulations confirm that the emission current, primarily driven
by Fowler-Nordheim tunneling, can be modulated through gate voltage modulation. We have simulated that the cut-off
frequency is expected to fall within the range of 0.4 ~ 1.7 THz, while the maximum oscillation frequency is anticipated to be
within the range of 6.4 × 102 ~ 1.9 × 104 THz under high source-drain voltage for the given structure. Furthermore, we have
conducted an investigation on the screening effect within the graphene channel and explored the limits of effective emission
current controllability through the gate structure. Our findings suggest that the screening length plays a critical role in
determining the device characteristics like I-V curve and frequency response. The screening length is highly dependent on
external voltage conditions, more fundamentally the induced charge concentration in the graphene channel. We have also
confirmed that the emission current controllability decreases exponentially with increasing emitter length, consistent with
prior research on the screening effect of Graphene [4]. In addition, we successfully conducted a simulation on a similar
device structure utilizing a Graphene bilayer emitter. We observed that, even in the same device structure, the device
characteristics differed somewhat from those when using a Graphene monolayer emitter. In this case, the screening effect
between the two Graphene layers played a significant role in determining the device characteristics. As a result of this effect
the controllability of the emission current through gate bias modulation was weakened, and the emission current decreased
compared to when the Graphene monolayer emitter was used. Additionally, the field enhancement effect was also weakened
because the induced charge concentration compensating for the externally applied voltage was distributed to the two
Graphene layers respectively.
Consequently, we have successfully developed a numerical simulator for semiconductor device utilizing semi-metallic
emitters. With this simulator, we were able to simulate vacuum device structures employing both Graphene monolayer
emitter and Graphene bilayer emitter. Our simulations have conclusively demonstrated that the given device structure is
capable of operating under high-frequency conditions.
- URI
- https://oasis.postech.ac.kr/handle/2014.oak/121111
- Article Type
- Conference
- Citation
- IEEE NANO 2023, 2023-07-03
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