Bilayer Graphene Transistor

Features of Bilayer Graphene Transistor

Graphene is a thin crystalline film formed by the sp2 carbon atoms. Better structure is the main feature of graphene. Graphene is a semi-metal with zero band overlap, linear density and linear energy dispersion.  In the low energy range w.r.t the Fermi level, valence and conduction bands they form conic shapes and meet at Dirac points. Apart from having a better structure, graphene has a strong electric field in the range of n<1014 cm^-2.

Construction & Features of Bilayer Graphene Transistor

Bilayer Graphene is a simple material that consists of two layers of graphene. At first, the report of bilayer graphene came in the seminar of 2004 science paper by Geim and their colleagues. This bilayer graphene exist in the AB or Bernal stacked form. In this structure, the atoms lie directly to the center of hexagon in the lower part of the graphene sheet, while half of the other atoms lie on the atom.  In the AA form, the layers will be aligned and in Bernal stacked graphene two boundaries will be there which are common. Twisted arrangement of the layers are also seen where one layer is rotated with relative to the other.

Bilayer Graphene transistor can be made by using two methods. One is through the exfoliation from graphite while the other is by the chemical vapor deposition method. In bilayer graphene, it has zero bandgap and this property helps it good to behave like a metal. Many experiments have been done using bilayer graphene. One of the experiments was 1D ballistic electron conducting channels at bilayer graphene domain walls. Today many studies on bilayer graphene have been conducted to realize the Bose-Einstein condensate of excitons. Today, bilayer graphene is there to construct the FET transistors.

Bilayer graphene is basically difficult to produce. It uses a technique known as Hyperspectral global Raman Imaging an accurate and rapid technique to characterize the quality of growth.  Three dimensional bilayer graphene is a new type of carbon which can be produced by the passage of the electric current through graphite. This type of graphite consists of three dimensional shells which are bounded by bilayer graphene and nanotubes.

Researchers were able to make a graphene based transistor by using the band gap in graphene. A vertical electric field has been applied to the bilayer graphene which break the symmetry between the graphene layers. This modification helps to create the atomic sites with different electric potentials. When strong electric field is applied, a large band gap will be produced thereby damaging the graphene normal structure.

The dual gated FET is a transistor type which helps in controlling the electron flow from the source to the drain with the electric fields shaped out by the electrode gates. This FET uses silicon as the bottom gate and silicon dioxide is insulated between the graphene layers. Over the bilayer graphene a transparent layer of aluminum oxide lay over. On top of this layer, a top gate is made of platinum. This type of transistor helps in the control of flow of electrons from source to the drain with electric fields shaped by the gate electrodes.

Results from ALS measurements showed that by changing the voltage of two gates, two parameters can be controlled. Here, the size and the doping degree of the bilayer graphene are controlled.

With the precision control of bandgap over a wide range and independent manipulation of electronic states through doping, bilayer graphene becomes a flexible tool for nanoscale electronic devices.