Chi-Hsien Huang

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 (5u2005nm) can sustain high resistance at temperature up to 400°C. The measured breakdown electric field is higher than 10u2005MV 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 760u2005cm2/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.

pH sensing reliability of flexible ITO/PET electrodes on EGFETs prepared by a roll-to-roll process

Abstract In this work, indium tin oxide (ITO) layers were deposited by radio frequency sputtering using a roll-to-roll process on flexible polyethylene terephthalate substrates as pH-sensing electrodes of extended gate field effect transistors (EGFETs). When the pH sensitivity of EGFETs for ITO layers with different sheet resistances was compared, a higher sensitivity was found for samples with a lower sheet resistance (100xa0Ω/□), and a reliability evaluation was carried out for this condition. The average sensitivity was 50.1xa0mV/pH, as measured from pH 2 to pH 12. Over three additional runs, the standard variation of the average sensitivity was found to be ±1.7xa0mV/pH. The tolerance to light is high; the samples were measured in dark and light conditions, and a difference of only 0.6xa0mV was observed. The temperatures available for measurement are 25–40xa0°C. Up to this point, the behavior of samples stored in dry conditions has been found to persist for more than 55xa0days.

Immobilization of enzyme and antibody on ALD-HfO2-EIS structure by NH3 plasma treatment

Thin hafnium oxide layers deposited by an atomic layer deposition system were investigated as the sensing membrane of the electrolyte-insulator-semiconductor structure. Moreover, a post-remote NH3 plasma treatment was proposed to replace the complicated silanization procedure for enzyme immobilization. Compared to conventional methods using chemical procedures, remote NH3 plasma treatment reduces the processing steps and time. The results exhibited that urea and antigen can be successfully detected, which indicated that the immobilization process is correct.

Tunable bandgap energy of fluorinated nanocrystals for flash memory applications produced by low-damage plasma treatment

A plasma system with a complementary filter to shield samples from damage during tetrafluoromethane (CF(4)) plasma treatment was proposed in order to incorporate fluorine atoms into gadolinium oxide nanocrystals (Gd(2)O(3)-NCs) for flash memory applications. X-ray photoelectron spectroscopy confirmed that fluorine atoms were successfully introduced into the Gd(2)O(3)-NCs despite the use of a filter in the plasma-enhanced chemical vapour deposition system to shield against several potentially damaging species. The number of incorporated fluorine atoms can be controlled by varying the treatment time. The optimized memory window of the resulting flash memory devices was twice that of devices treated by a filterless system because more fluorine atoms were incorporated into the Gd(2)O(3)-NCs film with very little damage. This enlarged the bandgap energy from 5.48 to 6.83 eV, as observed by ultraviolet absorption measurements. This bandgap expansion can provide a large built-in electric field that allows more charges to be stored in the Gd(2)O(3)-NCs. The maximum improvement in the retention characteristic was >60%. Because plasma damage during treatment is minimal, maximum fluorination can be achieved. The concept of simply adding a filter to a plasma system to prevent plasma damage exhibits great promise for functionalization or modification of nanomaterials for advanced nanoelectronics while introducing minimal defects.

High Polarization and Low-Repulsion

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Thin Film for Alkali Metal Ion Detections by Plasma System With a Complementary Filter

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

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Charge storage and data retention characteristics of forming gas-annealed Gd2O3-nanocrystal nonvolatile memory cell

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