Journal
ACS APPLIED ELECTRONIC MATERIALS
Volume 4, Issue 3, Pages 1002-1009Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsaelm.1c01181
Keywords
hafnium oxide; tunneling electroresistance; ferroelectric tunnel junction; thin films; work function
Funding
- Swedish Research Council (VR) [2018-05379, 2016-6186, 2017-4108]
- NanoLund Centre for Nanoscience at Lund University
- Swedish Research Council [2018-05379] Funding Source: Swedish Research Council
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Ferroelectric tunnel junctions (FTJs) based on ultra-thin HfO2 have great potential for fast and energy-efficient memory technology, and the choice of device design and electrode materials can greatly affect their performance in terms of tunneling electroresistance (TER) and reliability.
Ferroelectric tunnel junctions (FTJs) based on ultra-thin HfO2 have great potential as a fast and energy-efficient memory technology compatible with complementary metal oxide semi-conductors. FTJs consist of a ferroelectric film sandwiched between two distinct electrodes, the properties of which are intricately linked to the electrical properties of the FTJs. Here we utilize a W crystallization electrode (CE) to achieve a high and reproducible remanent polarization, combined with a metal replacement process in which the W is carefully removed and replaced by another top electrode (TE). In this way we separate the ferroelectric film properties from the device design and can thereby evaluate the effect of the TE work function (WF) and conduction band electron density (n(e)) on the tunneling electroresistance (TER) and device reliability. We compare FTJs designed with a TiN bottom electrode and W, Cr, or Ni TE and find that the use of high electron density metals such as Ni or Cr as TE allows for an improved TER, albeit at the cost of reliability due to a large built-in electric field. To bypass this effect, a bilayer Cr/Ni TE is implemented, which allows for a high TER and minimal built-in field, leading to excellent retention and endurance beyond 10(8) cycles. The results presented here thus highlight a process flow for reliable design and implementation of FTJs.
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