Electron irradiation-induced defects for reliability improvement in monolayer MoS2-based conductive-point memory devices

Abstract

Monolayer molybdenum disulfide has been previously discovered to exhibit non-volatile resistive switching behavior in a vertical metal-insulator-metal structure, featuring ultra-thin sub-nanometer active layer thickness. However, the reliability of these nascent 2D-based memory devices was not previously investigated for practical applications. Here, we employ an electron irradiation treatment on monolayer MoS2 film to modify the defect properties. Raman, photoluminescence, and X-ray photoelectron spectroscopy measurements have been performed to confirm the increasing amount of sulfur vacancies introduced by the e-beam irradiation process. The statistical electrical studies reveal the reliability can be improved by up to 1.5× for yield and 11× for average DC cycling endurance in the devices with a moderate radiation dose compared to unirradiated devices. Based on our previously proposed virtual conductive-point model with the metal ion substitution into sulfur vacancy, Monte Carlo simulations have been performed to illustrate the irradiation effect on device reliability, elucidating a clustering failure mechanism. This work provides an approach by electron irradiation to enhance the reliability of 2D memory devices and inspires further research in defect engineering to precisely control the switching properties for a wide range of applications from memory computing to radio-frequency switches.

Electron Irradiation Effects on Single‐Layer MoS2 Obtained by Gold‐Assisted Exfoliation

“…Regarding the origin of the induced defects, it can be guessed that they could be S vacancies because we have found a red shift of the PL in agreement with previous reports. [ 28 ] On increasing the dose, also the Raman spectrum is somehow changed and the emission of the exciton is strongly reduced suggesting that larger modifications probably involving also the structure have been induced. It is worth noting that the irradiation up to the highest dose is not able to induce extended defects as testified by the comparison of the AFM measurements of the irradiated and not irradiated samples reported in Figure 2b–d.…”

“…In addition, the quenching of the exciton emission has been highlighted as a consequence of ionizing radiation exposure and attributed to the presence of point defects. [ 25,28 ] In this context, somehow contrasting results have been found with an emission reduction or enhancement depending on the irradiation type. [ 25,26 ] In these and other literature articles semiconducting and insulating substrates have been employed.…”

“…[25,26] The presence of defects has been also connected to Raman feature changes. [27][28][29] In particular, the generation of sulfur vacancies in 1L MoS 2 by electron beams has been suggested and connected to quite clear spectroscopic changes induced at about 10 5 e nm À2 . [27,28] These studies have shown that a vacancy content of 5% gives rise to a Raman shift of E 2g up to 8 cm À1 .…”

“…[27][28][29] In particular, the generation of sulfur vacancies in 1L MoS 2 by electron beams has been suggested and connected to quite clear spectroscopic changes induced at about 10 5 e nm À2 . [27,28] These studies have shown that a vacancy content of 5% gives rise to a Raman shift of E 2g up to 8 cm À1 . In addition, the quenching of the exciton emission has been highlighted as a consequence of ionizing radiation exposure and attributed to the presence of point defects.…”

“…[25,26] In these and other literature articles semiconducting and insulating substrates have been employed. [27,28,30] These aspects have been poorly investigated for conductive substrates and need further deepening both for device performance and endurance but also in view of materials defect engineering. To further contribute to these studies, we have carried out an experimental investigation of the room temperature irradiation effects by 2.5 MeV electrons up to 4.0 Â 10 17 e cm À2 on goldassisted exfoliated 1L MoS 2 evidencing that in the used dose range strong effects can be induced in the exciton emission whereas structural modifications by Raman spectroscopy are minor suggesting a prominent role of point defects.…”