Characterization of Al2O3 gate dielectric for graphene electronics on flexible substrates

Abstract

Abstract-To ensure the high performance of graphene-based field effect transistors (GFETs) on flexible substrates, an uniform and manufacturable dielectric film with good electrical properties is needed. Thus, electrical characterization of the dielectric film on graphene on flexible substrates is very important for the development of flexible electronics based on GFETs. Here, we have fabricated and characterized parallel-plate capacitor test structures consisting of 35 nm thick Al2O3 dielectric film and with graphene as bottom electrode on polyethylene terephthalate (PET). It was found that the leakage current density in the Al2O3 film is less than 100 μA/cm 2 at 5 V, which allows for applying it as a gate dielectric in GFETs on flexible substrates. The extracted dielectric constant of the Al2O3 film is approx. 7.6, which is close to the bulk value and confirms the good quality of the Al2O3 film. Analysis indicates that the measured loss tangent, which is up to 0.2, is governed mainly by the dielectric loss in the Al2O3 and can be associated with defects from the Al 2 O 3 film and the Al2O3/graphene interface. Our results will be used in further development of GFETs on flexible substrates.

Test structures for evaluating Al<inf>2</inf>O<inf>3</inf> dielectrics for graphene field effect transistors on flexible substrates

“…Therefore, most of the applied dc voltage appears across the dielectric between the inner electrode and the graphene film. As previously reported in [5], leakage currents were found to be less than 1 μA/cm 2 for most non-defect capacitors in a voltage range from -2 to 2 V. In the voltage range from -5 to 5V the leakage current density was found to be less than 100 μA/cm 2 -a level considered negligible compared to drain and photo currents typical for terahertz detectors based on GFETs [6].…”

“…The hysteresis effect is clearly visible in the graph shown in Fig. 3 where experimental data from [5] has been replotted on a semilogarithmic scale. GFET hysteresis effects are well known, and are generally believed to be due to the charging and discharging of dielectric interface states [7][8][9][10].…”

“…In the model, a capacitance per unit area of 200 nF/cm 2 was used. An area dependent series resistance on the order of 1000 Ω was estimated from measurements forcing the probes in direct contact with the graphene as described in [5] for structures 30 μm in diameter. While the loss tangents of both the parallel resistance RP and the PET substrate were found negligible, the loss tangent of the series resistance was found to dominate.…”

“…Characteristics obtained for increasing voltages are shown with circles (model: solid lines), while those obtained for the downwards voltage sweep are shown with crosses (model: dashed lines). Data replotted from[5].…”