Kuan-I Ho

Fluorinated Graphene as High Performance Dielectric Materials and the Applications for Graphene Nanoelectronics

There is broad interest in surface functionalization of 2D materials and its related applications. In this work, we present a novel graphene layer transistor fabricated by introducing fluorinated graphene (fluorographene), one of the thinnest 2D insulator, as the gate dielectric material. For the first time, the dielectric properties of fluorographene, including its dielectric constant, frequency dispersion, breakdown electric field and thermal stability, were comprehensively investigated. We found that fluorographene with extremely thin thickness (5 nm) can sustain high resistance at temperature up to 400°C. The measured breakdown electric field is higher than 10 MV cm−1, which is the heightest value for dielectric materials in this thickness. Moreover, a proof-of-concept methodology, one-step fluorination of 10-layered graphene, is readily to obtain the fluorographene/graphene heterostructures, where the top-gated transistor based on this structure exhibits an average carrier mobility above 760 cm2/Vs, higher than that obtained when SiO2 and GO were used as gate dielectric materials. The demonstrated fluorographene shows excellent dielectric properties with fast and scalable processing, providing a universal applications for the integration of versatile nano-electronic devices.

One-Step Formation of a Single Atomic-Layer Transistor by the Selective Fluorination of a Graphene Film

In this study, the scalable and one-step fabrication of single atomic-layer transistors is demonstrated by the selective fluorination of graphene using a low-damage CF4 plasma treatment, where the generated F-radicals preferentially fluorinated the graphene at low temperature (<200 °C) while defect formation was suppressed by screening out the effect of ion damage. The chemical structure of the C-F bonds is well correlated with their optical and electrical properties in fluorinated graphene, as determined by X-ray photoelectron spectroscopy, Raman spectroscopy, and optical and electrical characterizations. The electrical conductivity of the resultant fluorinated graphene (F-graphene) was demonstrated to be in the range between 1.6 kΩ/sq and 1 MΩ/sq by adjusting the stoichiometric ratio of C/F in the range between 27.4 and 5.6, respectively. Moreover, a unique heterojunction structure of semi-metal/semiconductor/insulator can be directly formed in a single layer of graphene using a one-step fluorination process by introducing a Au thin-film as a buffer layer. With this heterojunction structure, it would be possible to fabricate transistors in a single graphene film via a one-step fluorination process, in which pristine graphene, partial F-graphene, and highly F-graphene serve as the source/drain contacts, the channel, and the channel isolation in a transistor, respectively. The demonstrated graphene transistor exhibits an on-off ratio above 10, which is 3-fold higher than that of devices made from pristine graphene. This efficient transistor fabrication method produces electrical heterojunctions of graphene over a large area and with selective patterning, providing the potential for the integration of electronics down to the single atomic-layer scale.

A Self‐Aligned High‐Mobility Graphene Transistor: Decoupling the Channel with Fluorographene to Reduce Scattering

The conduction channel of a graphene field-effect transistor (FET) is decoupled from the parasitic charge impurities of the underlying substrate. Fluorographene as a passivation layer is fabricated between the oxide substrate and channel, and a self-aligned gate-terminated FET is also fabricated. This approach significantly reduces the scattering and, as a result, the mobility increases ten fold.

Atmospheric pressure route to epitaxial nitrogen-doped trilayer graphene on 4H-SiC (0001) substrate

Large-area graphene film doped with nitrogen is of great interest for a wide spectrum of nanoelectronics applications, such as field effect devices, super capacitors, and fuel cells among many others. Here, we report on the structural and electronic properties of nitrogen doped trilayer graphene on 4H-SiC (0001) grown under atmospheric pressure. The trilayer nature of the growth is evidenced by scanning transmission electron microscopy. X-ray photoelectron spectroscopy shows the incorporation of 1.2% of nitrogen distributed in pyrrolic-N, and pyridinic-N configurations as well as a graphitic-N contribution. This incorporation causes an increase in the D band on the Raman signature indicating that the nitrogen is creating defects. Ultraviolet photoelectron spectroscopy shows a decrease of the work function of 0.3 eV due to the N-type doping of the nitrogen atoms in the carbon lattice and the edge defects. A top gate field effect transistor device has been fabricated and exhibits carrier mobilities up to 13...

Electrical probing of multi-ions solution by using graphene-based sensor

The multi-ion sensing properties of graphene based field effect transistor were investigated in this paper. Hydrogen and potassium ion sensitivities were measured. The believable detection concentration region was also defined. Finally, the distribution of time-dependence drift coefficient was also discussed. (keywords: graphene, ion sensitive field effect transistor, drift coefficient, potassium, and ion).

Characterization of N-doped multilayer graphene grown on 4H-SiC (0001)

Large-area graphene film doped with hetero-atoms is of great interest for a wide spectrum of nanoelectronics applications, such as field effect devices, super capacitors, fuel cells among many others. Here, we report the structural and electronic properties of nitrogen doped multilayer graphene on 4H-SiC (0001). The incorporation of nitrogen during the growth causes an increase in the D band on the Raman signature indicating that the nitrogen is creating defects. The analysis of micro-Raman mapping of G, D, 2D bands shows a predominantly trilayer graphene with a D band inherent to doping and inhomogeneous dopant distribution at the step edges. Ultraviolet photoelectron spectroscopy (UPS) indicates an n type work function (WF) of 4.1 eV. In addition, a top gate FET device was fabricated showing n-type I-V characteristic after the desorption of oxygen with high electron and holes mobilities.

One-step formation of atomic-layered transistor by selective fluorination of graphene film

In this work, the wafer scale fabrication of atomic layered transistors are demonstrated by selective fluorination of graphene with a remote CF4 plasma, where the generated F-radicals preferentially fluorinated graphene surface at low temperature (<;200°C) while this technique suppress the defect formation by screening out the ion damage effect. The resultant grapehene shows electrical semiconducting and isolation after subjected to the fluorination for 5~20 min, respectively. A back-gate transistor is then fabricated with a one-step fluorination of graphene film on SiO2 substrate. The chemical structure, C-F bonds, is well correlated to the electrical properties in fluorinated graphene by XPS, Raman spectroscopy and electrical meter. This efficient method provide electrical semiconducting and insulator of graphene with a large area and selective pattering, where it turns out the potential for the integration of electronics down to atomic layered scale.

High sensing performance of fluorinated HfO 2 membrane by low damage CF 4 plasma treatment for K + detections

A low damage CF4 plasma with a filter in a PECVD system was proposed to incorporate fluorine atoms into an HfO2 sensing membrane in an EIS structure for K+ ion sensor application. The highest sensitivities of 82mV/pK was obtained when the low damage plasma treatment with RF power of 100W was used for 30min. Compared with the conventional CF4 plasma, the sensitivity significantly improved. The reasons were the high polarization induced by fluorine atoms and elimination of plasma damage.