title: Thickness scaling of atomic-layer-deposited HfO2 films and their application to wafer-scale graphene tunnelling transistors.
abstract: The downscaling of the capacitance equivalent oxide thickness (CET) of a gate dielectric film with a high dielectric constant, such as atomic layer deposited (ALD) HfO2, is a fundamental challenge in achieving high-performance graphene-based transistors with a low gate leakage current. Here, we assess the application of various surface modification methods on monolayer graphene sheets grown by chemical vapour deposition to obtain a uniform and pinhole-free ALD HfO2 film with a substantially small CET at a wafer scale. The effects of various surface modifications, such as N-methyl-2-pyrrolidone treatment and introduction of sputtered ZnO and e-beam-evaporated Hf seed layers on monolayer graphene, and the subsequent HfO2 film formation under identical ALD process parameters were systematically evaluated. The nucleation layer provided by the Hf seed layer (which transforms to the HfO2 layer during ALD) resulted in the uniform and conformal deposition of the HfO2 film without damaging the graphene, which is suitable for downscaling the CET. After verifying the feasibility of scaling down the HfO2 thickness to achieve a CET of ~1.5 nm from an array of top-gated metal-oxide-graphene field-effect transistors, we fabricated graphene heterojunction tunnelling transistors with a record-low subthreshold swing value of <60 mV/dec on an 8" glass wafer.
authors: Device Laboratory, Device and System Research Center, Samsung Advanced Institute of Technology, Suwon 443-803, Korea.
authors: Seong-Jun
authors: SJ
authors: Jeong
authors: School of Advanced Materials Science and Engineering, Samsung-SKKU Graphene/2D Center, Sungkyunkwan University, Suwon 440-746, Korea.
authors: Yeahyun
authors: Y
authors: Gu
authors: Device Laboratory, Device and System Research Center, Samsung Advanced Institute of Technology, Suwon 443-803, Korea.
authors: Jinseong
authors: J
authors: Heo
authors: School of Advanced Materials Science and Engineering, Samsung-SKKU Graphene/2D Center, Sungkyunkwan University, Suwon 440-746, Korea.
authors: Jaehyun
authors: J
authors: Yang
authors: Device Laboratory, Device and System Research Center, Samsung Advanced Institute of Technology, Suwon 443-803, Korea.
authors: Chang-Seok
authors: CS
authors: Lee
authors: Device Laboratory, Device and System Research Center, Samsung Advanced Institute of Technology, Suwon 443-803, Korea.
authors: Min-Hyun
authors: MH
authors: Lee
authors: Device Laboratory, Device and System Research Center, Samsung Advanced Institute of Technology, Suwon 443-803, Korea.
authors: Yunseong
authors: Y
authors: Lee
authors: School of Advanced Materials Science and Engineering, Samsung-SKKU Graphene/2D Center, Sungkyunkwan University, Suwon 440-746, Korea.
authors: Hyoungsub
authors: H
authors: Kim
authors: Device Laboratory, Device and System Research Center, Samsung Advanced Institute of Technology, Suwon 443-803, Korea.
authors: Seongjun
authors: S
authors: Park
authors: Device Laboratory, Device and System Research Center, Samsung Advanced Institute of Technology, Suwon 443-803, Korea.
authors: Sungwoo
authors: S
authors: Hwang