image: In the left two figures, the isolated band can be formed through increasing the orbital energy difference or decreasing the orbital overlap between M and X elements. In the right, according to this guide principle, a class of 2D isolated band semiconductors have been identified to achieve sub-60-mV/dec SS in MOSFETs by high-throughput calculations, which provides a novel opportunity for the next-generation energy-efficient 2D nanoelectronics.
Credit: ©Science China Press
This study is led by Prof. Shengli Zhang and Prof. Haibo Zeng (MIIT Key Laboratory of Advanced Display Materials and Devices, College of Material Science and Engineering, Nanjing University of Science and Technology). They found the sub-thermionic transport performances in the MOSFETs using two-dimensional channels with isolated band features, which have potential overcome the power consumption bottleneck in the field of integrated circuit. Researchers further explored the structure and physical origin of this unique electronic structure. They found that it can be attributed to the differences in atomic orbital energy levels and the weak coupling of atomic orbitals induced by two-dimensional microstructure. This leads to the appearance of the other sub band gap below the valence band edge or above the conduction band edge, thereby inducing isolated band structures.
Using this as a fundamental feature, a high-throughput calculation was performed to further identify many other candidates with sub-thermionic potentials. 192 two-dimensional channel materials with potential to break through the thermionic limit were selected from a database of 1608 materials. This contains 66 transition metal nitrogen/sulfur/halogen compounds and 126 main group metal nitrogen/sulfur/halogen compounds.
Furthermore, about 50 representative two-dimensional isolated band channels were selected for device simulation based on non-equilibrium Green function and density functional theory. Although the sub-60 mV/dec sub-threshold swing were found in the transfer characteristics for all of them, their device performance displays huge difference. To analyze this, a specific functional relationship was provided between the electronic structures (their band broadening, effective mass and density of states) and the device performances (on-state current Ion and the current current when SS becomes 60 mV/dec, I60). Based on this relationship, more than 10 two-dimensional systems with isolated band width below 1 eV which can realize high-performance sub-thermionic MOSFETs at supply voltage below 0.5 V.
This kind of novel steep-slope MOSFETs mainly relies on the unique isolated band around the Fermi level to cut off the carrier transport in high energy regions at off state, while the thermionic emission remains at the on state like that in conventional MOSFETs. Compared with the negative capacitance FETs and tunneling FETs, it requires no complex device structures, such as the tunneling heterostructure or ferroelectric gate dielectrics. Therefore, this unique electronic transport mechanism and simple device architecture make it possible to achieve excellent device performance in the field of low-power applications.
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See the article:
Identifying atomically thin isolated-band channels for intrinsic steep-slope transistors by high-throughput study
https://doi.org/10.1016/j.scib.2024.03.017
Journal
Science Bulletin