Flexible and transparent ReRAM with GZO memory layer and GZO-electrodes on large PEN sheet
Research highlights
► Low temperature formation of GZO films with arbitrary resistivity. ► Fabrication of all-GZO-based flexible and transparent ReRAM on a large plastic film. ► High memory performance such as compatibility for multilevel application was confirmed.
Introduction
Flexible transparent resistive random access memory (FT-ReRAM) can be fabricated by sandwiching a wide band gap oxide such as ZnO between transparent electrodes such as tin-doped indium oxide (ITO) on polymer flexible sheets [1]. However, an alternative transparent conducting oxide (TCO) to ITO is desired because of the high cost and scarcity of the indium element. Although one of the best candidates is Ga doped ZnO (GZO) [2], low glass transition temperature, Tg, of flexible substrates prevents fabrication of GZO films with low resistivity ρ [2]. Moreover, bombardment by energetic oxygen to the position of the substrate facing the erosion area of the target introduces the nonuniformity of the sputtered film [2], [3]. On the other hand, large dispersion of the resistance in the high resistance state, RHRS, during cycling is a serious problem in ReRAMs which show steep and discontinuous reset switching, where reset means resistance switching from the low resistance state (LRS) to the high resistance state (HRS). This is due to the fact that limiting the rapidly increasing current is relatively easy, whereas limiting the rapidly decreasing current is difficult. That is, RLRS is controllable simply by limiting the current which flows at the moment of the set switching to a target value using, for example, a transistor as a current limiter [4], whereas there is no method to limit the rapidly decreasing current which flows at the moment of the reset switching. Therefore, RHRS is uncontrollable and dispersive in ReRAMs with steep and discontinuous reset switching.
In this paper, we have solved all the above mentioned issues by introducing RF plasma assist for DC magnetron sputtering, which has not been practically applied to GZO–TCO films, and fabrication of FT-ReRAM consisting of GZO memory layer and GZO-electrodes (all-GZO-FT-ReRAM) was attained. It has been elucidated that memory effect is enhanced in moderately oxygen deficient GZO films, which is consistent with a resistance switching mechanism based on a redox reaction [5], [6], [7], [8], [9], [10]. GZO films deposited in the atmosphere of Ar + H2 (H2 5%) showed smooth and continuous reset switching. Therefore, RHRS of these films is controllable, which enables verify operation [11], [12], [13] and the multilevel application.
Section snippets
Experimental
Fig. 1 shows schematic of RF plasma assist DC magnetron sputtering system. For the optimization of the deposition conditions for fabrication of electrodes with low ρ and a memory layer with high ρ, GZO films were sputtered onto glass (Corning Eagle2000) or Poly Ethylene Naphthalate (PEN; Teijin DuPont Films Q-65FA) substrates in either Ar, Ar + H2, or Ar + O2 atmosphere at room temperature, where the strain point of the glass substrates and Tg of the PEN substrates are 593 °C and 155 °C,
Optimization of sputtering conditions for fabrication of FT-ReRAM
Fig. 2a and b represent the dependence of ρ and carrier concentration, n, measured at the center (x = 0) of the substrate on the H2-ratio as a function of the dT−S. WRF’s were set to 200 W for dT−S = 70 and 120 nm, whereas 0 W for dT−S = 50 nm. This is due to the structural problem of our sputtering system that dT−S cannot be reduced to less than 50 mm because the target interferes with the coil unless the coil is removed. However, ρ in the center of the substrate (i.e. x = 0) is almost independent of WRF
Conclusions
Fabrication of flexible transparent ReRAM consisting of the GZO memory layer and GZO-electrodes on the PEN sheet with large area was attained by introducing the RF plasma assist DC magnetron sputtering method. Resistive switching mechanism of all-GZO-FT-ReRAM can be explained by redox model as well as that of conventional binary transition metal oxides. Reset switching of all-GZO-FT-ReRAM which memory layer is GZO(H2-ratio 5%) is smooth and continuous, which enables the verify operation and the
References (19)
- et al.
Thin Solid Films
(1988) - et al.
Appl Phys Lett
(2009) - et al.
Jpn J Appl Phys
(1985) - et al.
Appl Phys Lett
(2008) - et al.
Appl Phys Lett
(2006) - et al.
Nature
(2006) - et al.
Phys Rev Lett
(2007) - et al.
Nature
(2008) - et al.
Appl Phys Lett
(2005)
Cited by (39)
Realization of high transparent conductive vanadium-doped zinc oxide thin films onto flexible PEN substrates by RF-magnetron sputtering using nanopowders targets
2021, Ceramics InternationalCitation Excerpt :The development of polymer materials and significant combinatorial studies between chemistry, physics and materials sciences have revealed the possibility of using the thin flexible polymers substrates in flexible optoelectronic devices fabrication [1–6], in order to offer many advantageous characteristics such as lightness, flexibility, robustness, and can be manufactured in mass via roll-to-roll processes [7,8]. Several types of polymeric materials were used as substrates in flexible optoelectronics fabrication, including polytetrafluoroethylene (Teflon) [9], polycarbonate (PC) [10], polyethylene naphthalate (PEN) [11,12], polyethylene terephthalate (PET) [13], polyethersulfone (PES) [14] and polyimide (PI) [15]. On behalf of the optical and mechanical properties, polyethylene naphthalate (PEN) is the potential candidate among all other polymeric substrates [16].
Film Deposition Processes Based on Eco-Friendly, Flexible, and Transparent Materials for High-Performance Resistive Switching
2021, Encyclopedia of Smart MaterialsNegative differential resistance effect and dual bipolar resistive switching properties in a transparent Ce-based devices with opposite forming polarity
2020, Applied Surface ScienceCitation Excerpt :For advanced applications, transparent NVM, such as transparent ReRAM (T-ReRAM) devices, are of particular interest [12]. The compulsory part of a T-ReRAM device is a large bandgap insulator film sandwiched between two transparent conducting electrodes (TCEs) such as indium–tin oxide (ITO) [13,14], gallium-doped zinc oxide (GZO) [15], aluminum-doped zinc oxide (AZO) [16], and fluorine-doped tin oxide (FTO) [17]. In microelectronics, CeO2 has been considered as a high κ-gate oxide material with unique properties, including a moderate band gap (3–3.6 eV), high dielectric constant (κ: 23–26), high refractive index (n: 2.2–2.8) and high dielectric strength (~2.6 MV cm−1) [18].
High mobility hydrogenated zinc oxide thin films
2017, Solar Energy Materials and Solar Cells