Memristive FG-PVA Structures Fabricated with the Use of High Energy Xe Ion Irradiation

Abstract

A new approach based on the irradiation by heavy high energy ions (Xe ions with 26 and 167 MeV) was used for the creation of graphene quantum dots in the fluorinated matrix and the formation of the memristors in double-layer structures consisting of fluorinated graphene (FG) on polyvinyl alcohol (PVA). As a result, memristive switchings with an ON/OFF current relation ~2-4 orders of magnitude were observed in 2D printed crossbar structures with the active layer consisting of dielectric FG films on PVA after ion irradiation. All used ion energies and fluences (3 × 10¹⁰ and 3 × 10¹¹ cm^-2) led to the appearance of memristive switchings. Pockets with 10³ pulses through each sample were passed for testing, and any changes in the ON/OFF current ratio were not observed. Pulse measurements allowed us to determine the time of crossbar structures opening of about 30-40 ns for the opening voltage of 2.5 V. Thus, the graphene quantum dots created in the fluorinated matrix by the high energy ions are a perspective approach for the development of flexible memristors and signal processing.

Keywords: FG–PVA active layer; flexible memristors; fluorinated graphene; graphene quantum dots; high energy ion irradiation; pulse measurements; switching parameters.

Figure 1

(a) SEM images of the two crossbar memristor structure variants and, in the insert, the sketch of the crossbar memristor structures. (b) Optical photo of the 2D printed crossbar memristor structures array on PET without top Ag contact to the active FG–PVA layer of one of the structures. The insert shows the SEM image of the one structure with a colored active FG–PVA layer. The active layer size is 900 × 900 μm, and the Ag contact size is 300 × 300 μm. The crossbar memristor structures are given in the inserts.

Figure 2

(a) AFM image of active FG–PVA layer of the crossbar structures on the Si substrate before irradiation. (b) SEM image of active FG–PVA layer of the crossbar structures on the Ag printed layer before irradiation (c) Sketch of the active FG–PVA layer in the crossbar structures and the formation of the GQD after high energy ion irradiation. (d) SEM image of active FG–PVA layer of the crossbar structures on the Ag printed layer after irradiation (167 MeV, 3 × 10¹¹ cm⁻²).

Figure 3

AFM images of the active layer of the Ag–FG–PVA–Si crossbar structures irradiated by Xe ions with the fluence of 3 × 10¹¹ cm⁻² and the energy of 26 MeV (a) and 167 MeV (b). The FG layer thickness is 7–10 (a) and 17–20 nm (b).

Figure 4

(a–c) AFM images of the pristine (a) and 167 MeV ion irradiated active FG–PVA layers. The ion fluence was equal to 3 × 10¹⁰ (b) and 3 × 10¹¹ cm⁻² (c). An enlarged surface fragment (c) is shown in (d). (d–f) The FG–PVA film irradiated with 167 MeV Xe ions (fluence was 3 × 10¹¹ cm⁻²) was recorded in different regimes (height, MagSin, and Mag).

Figure 5

Current-voltage characteristics for the printed Ag–FG–PVA–Si crossbar structures with different thicknesses (5 L corresponds to 4 nm, 15 L to 13 nm, and 25 L to 20 nm) measured before and after the irradiation by Xe ions with the fluence of 3 × 10¹¹ cm⁻². (a,b) I–V curves before (a) and after (b) the irradiation by ions with energy 26 MeV and the fluence 3 × 10¹¹ cm⁻². (c,d) I–V curves measured before (1) and after (2) the irradiation: (c) FG thickness is 15 L (12 nm) and Xe ions with the energy of 26 MeV, (d) FG thickness is 25 L (20 nm) and Xe ions with the energy of 167 MeV. The contact area is 300 × 300 µm².

Figure 6

(a) Current-voltage characteristics for the printed Ag–FG–PVA–Ag crossbar structure measured after the irradiation by Xe ions with the energy of 167 MeV and the fluence 3 × 10¹⁰ cm⁻². (b) The ON-state current in the coordinate of the space charge limited conduction (SCLC) ln(I) versus ln(V) for a few measurements given in (a).

Figure 7

Current switchings for the structure irradiated with Xe ions (167 MeV, 3 × 10¹¹ cm⁻²) with the FG thickness of 17–20 nm: (a) Circuit for measuring the pulse characteristics; (b) The I_ON and I_OFF currents as a function of pulse number. The sketches of the measured structures and the tested voltage pulses are given in the insets of (a) and (b), respectively. The second inset in (b) presents the Set-read-Reset-read cycle for the tested structure.

Figure 8

(a,b) Current in the memristive structures in the open state as a function of the FG layer thickness for irradiation with different Xe ion energies: (c,d) Open-state current versus opening pulse duration for the structures with the FG thickness of (c) 10–12 nm and (d) 17–20 nm. The irradiation regimes are as follows: the energies were (a,c) 26 MeV and (b,d) 167 MeV, the fluences were: 1–3 × 10¹⁰ cm⁻², 2–3 × 10¹¹ cm⁻². The voltage pulse is 2.5 V.