Lithography-free fabrication of low operating voltage and large channel length graphene transistor with current saturation by utilizing Li+ of ion-conducting-oxide gate dielectric

Nitesh K Chourasia,Vijay K Singh,Anchal Srivastava,Anand Sharma,Bhola N Pal

doi:10.1063/5.0016466

Abstract

The large channel length graphene field-effect transistor (GFET) can outperform its competitors due to its larger active area and lower noise. Such long channel length devices have numerous applications, e.g., in photodetectors, biosensors, etc. However, long channel length graphene devices are not common due to their semi-metallic nature. Here, we fabricate large channel length (up to 5.7 mm) GFETs through a simple, cost-effective method that requires thermally evaporated source-drain electrode deposition, which is less cumbersome than the conventional wet-chemistry based photolithography. The semiconducting nature of graphene has been achieved by utilizing the Li+ ion of the Li5AlO4 gate dielectric, which shows current saturation at a low operating voltage (∼2 V). The length scaling of these GFETs has been studied with respect to channel length variation within a range from 0.2 mm to 5.7 mm. It is observed that a GFET of 1.65 mm channel length shows optimum device performance with good current saturation. This particular GFET shows a “hole” mobility of 312 cm2 V−1 s−1 with an on/off ratio of 3. For comparison, another GFET has been fabricated in the same geometry by using a conventional SiO2 dielectric that does not show any gate-dependent transport property, which indicates the superior effect of Li+ of the ionic gate dielectric on current saturation.

Highlights

A number of theoretical10,11 and experimental studies12,13 suggest that lithium-ion (Li+) intercalation can open a bandgap of ∼0.85 eV in single-layer graphene (SLG), which is very encouraging for graphene logic circuits in the future
A single layer of graphene has been was grown on a Cu substrate by the chemical vapor deposition (CVD) method and has been transferred on the Li5AlO5 gate dielectric by the standard graphene transfer method
The CVD that grew large-area graphene film was characterized by an optical microscope [Fig. S1(a)], scanning electron microscope [SEM, Fig. S1(b)], transmission electron microscope [TEM, Fig. S1(c)], and Raman spectrum [Fig. S1(d)], which are discussed in Sec. 3 of the supplementary material

Summary

Introduction

In the twenty-first century, graphene, a single layer two dimensional (2D) allotrope of carbon atoms, has attracted immense attention in the electronics world due to its unusually high carrier mobility.1 Along with this, its chemical stability, lightweight, and excellent optoelectronic properties have added more flavor to the exploration of this material in different areas of electronics.2 unlike conventional semiconductors, large-area single-layer graphene (SLG) is semimetal in nature with zero bandgap.2 The valence and conduction bands of SLG meet to form a cone shape at the K points (named Dirac points) of the Brillouin zone.3 Because of having zero bandgap, field-effect transistors (FETs) made with a larger channel length cannot be switched off, which makes them unsuitable for logic applications.2 Large channel length devices can be used in power handling owing to their efficient operation at higher voltages without breaking down the junction and have low noise, which is very beneficial for analog devices. We have developed a simple, cost-effective method to fabricate large channel length SLG thin-film transistors that show a good current saturation with low operating voltage.

Results

Conclusion