Nano-Memory Based on MoS2 Embedded in Al2O3 on Bulk Ge
Authors: Nayfeh Ammar , Rezk Ayman 
Published: September 2023

MoS2 captured a lot of attention in the past decade due to its intrinsic stability at nanoscale dimensions promising low power, high density, and CMOS-compatible devices [1-6]. The claimed improvements in MoS2-based devices can be related to their capacity to change the material interface properties and it’s not limited by the absence of a band gab. Despite this, such devices are still in the early stages of development due to several issues, including growth scalability, passivation, doping, and metal junctions [7, 8]. Almost no work conducted on MoS2/Ge-based systems which can be promising for various photonics applications, especially in the infrared regime.

Nanoscale resolution electrical characterizations utilizing conductive atomic force microscopy (cAFM) provide a useful method to study electronic transport and conduction in MoS2 structures. In this work, we demonstrate a nano-memory structure utilizing MoS2 flakes embedded in high-k ALD oxide on bulk Ge. The process of charge injection in the MoS2 flake was explored utilizing the fabricated structure along with a control structure with no embedded MoS2.

The cleaning and fabrication are conducted in a cleanroom of 100 level. A Ge bulk wafer is diced into 1×1 cm2 pieces and then ultrasonic cleaned in DI water, acetone, and IPA for native oxide removal and cleaning. The first 3 nm Al2O3 layer is grown using plasma-enhanced atomic layer deposition (PE-ALD) at 200⁰C. Immediately followed by spin coating 20µL of MoS2 solution on the Al2O3/Ge substrates at 1000 RPM for 30 seconds. The MoS2 solution concentration is 18 mg/L with flakes between 1-8 monolayers thick and 100-400 nm lateral size. The structure is finalized by depositing another 3 nm Al2O3 layer, capping the MoS2 flakes.

We performed the following 2.5×2.5 µm2 current scans using the cAFM, operating in contact mode, respectively: Read scan at 0.5 volts, write scan at 5 volts, read scan at 0.5 volts, erase scan -8 volts then read scan at 0.5 volts. Under the low read voltage (0.5V), no currents were observed in their pristine form. However, currents were spotted under higher write voltage (5V). The current readings, produced by the write scan, can also be seen under the following low read voltage scan (0.5V). The same currents are rarely visible after any erase scan (-8V) and during the subsequent read scan (0.5V). The results of cAFM demonstrate a MoS2-based structure that may be promising for future nano-memory applications.

References

[1] Rezk A, Alhammadi A, Alnaqbi W and Nayfeh A 2022 Utilizing trapped charge at Bilayer 2d MoS2/SiO2 interface for memory applications Nanotechnology
33 275201

[2] Si M, Liao P-Y, Qiu G, Duan Y and Ye P D 2018 Ferroelectric field-effect transistors based on MoS2 and cuinp2s6 two- dimensional van der waals heterostructure ACS Nano 12 6700–5

[3] Mukherjee B, Zulkefli A, Watanabe K, Taniguchi T, Wakayama Y and Nakaharai S 2020 Laser‐assisted multilevel non‐volatile memory device based on 2D van‐der‐waals few‐layer‐res 2 /h‐bn/graphene heterostructures Adv. Funct. Mater. 30 2001688

[4] Widiapradja L J, Nam T, Jeong Y, Jin H J, Lee Y, Kim K, Lee S, Kim H, Bae H and Im S 2021 2D MoS2 charge injection memory transistors utilizing hetero‐stack SIO2 /HFO2 dielectrics and oxide interface traps Adv. Electron. Mater. 7 2100074

[5] WooMH,JangBC,ChoiJ,LeeKJ,ShinGH,SeongH, Im S G and Choi S-Y 2017 Low-power nonvolatile charge storage memory based on MOS2 and an ultrathin polymer tunneling dielectric Adv. Funct. Mater. 27 1703545

[6] Radisavljevic B, Radenovic A, Brivio J, Giacometti V and Kis A 2011 Single-layer MOS2 transistors Nat. Nanotechnol. 6 147–50

[7] Das S, Chen H-Y, Penumatcha A V and Appenzeller J 2012 High performance multilayer MOS2 transistors with scandium contacts Nano Lett. 13 100–5

[8] Zhan Y, Liu Z, Najmaei S, Ajayan P M and Lou J 2012 Large- area vapor-phase growth and characterization of mos2atomic layers on a sio2 substrate Small 8 966–71

Figure 1