Integrated 2D multi-fin field-effect transistors

Abstract

Vertical semiconducting fins integrated with high-κ oxide dielectrics have been at the centre of the key device architecture that has promoted advanced transistor scaling during the last decades. Single-fin channels based on two-dimensional (2D) semiconductors are expected to offer unique advantages in achieving sub-1 nm fin-width and atomically flat interfaces, resulting in superior performance and potentially high-density integration. However, multi-fin structures integrated with high-κ dielectrics are commonly required to achieve higher electrical performance and integration density. Here we report a ledge-guided epitaxy strategy for growing high-density, mono-oriented 2D Bi₂O₂Se fin arrays that can be used to fabricate integrated 2D multi-fin field-effect transistors. Aligned substrate steps enabled precise control of both nucleation sites and orientation of 2D fin arrays. Multi-channel 2D fin field-effect transistors based on epitaxially integrated 2D Bi₂O₂Se/Bi₂SeO₅ fin-oxide heterostructures were fabricated, exhibiting an on/off current ratio greater than 10⁶, high on-state current, low off-state current, and high durability. 2D multi-fin channel arrays integrated with high-κ oxide dielectrics offer a strategy to improve the device performance and integration density in ultrascaled 2D electronics.

Fig. 1. Ledge-guided epitaxy of mono-oriented vertical 2D fin arrays for 2D multi-fin field-effect transistors (FETs).

a Schematic illustration for 2D multi-fin FETs potentially applied in advanced integrated circuits. b–d Schematic (b) and corresponding scanning electron microscopy (SEM) images of 2D Bi₂O₂Se fins with two perpendicular orientations on pristine LaAlO₃ (100) surface, including top view (c) and tilted view (d). e–g Schematic (e) and corresponding SEM images of ledge-guided epitaxial mono-oriented 2D Bi₂O₂Se fins on pre-treated LaAlO₃ (100) surface, including top view (f) and tilted view (g).

Fig. 2. Structure characterization and nucleation mechanism of vertical 2D fin grown by ledge-guided epitaxy.

a Cross-sectional low-magnification transmission electron microscopy (TEM) image of a vertical Bi₂O₂Se fin grown by ledge-guided epitaxy. b Cross-sectional high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image showing clear steps on the surface of the substrate, where the fin nucleated. The dashed line means Bi₂O₂Se/LaAlO₃ interface. c Fast Fourier Transform (FFT) diffraction spots of (b). d Strain mapping (ɛ_xx) estimated from a filtered version of the panel (b). e High-magnification HAADF-STEM image with atomic resolution and corresponding schematic of Bi₂O₂Se/LaAlO₃ interface. The dashed line represents actual interface. f, g The binding energies and optimized structures of Bi/Se atoms (f) and Bi-O monomers (g) adsorbed at the step edge and the terrace of the LaAlO₃ substrate, respectively. h The binding energies and optimized structures of a 2D Bi₂O₂Se nucleus at the step edge and terrace, demonstrate that nucleation at the step edge is energetically favorable. ΔE is the energy difference between two nucleation sites.

Fig. 3. Guided-growth of mono-oriented high-density 2D fin arrays for 2D multi-fin FETs with the assistance of steps.

a Schematic and SEM images showing the effect of the step density on the orientation of 2D Bi₂O₂Se fin arrays. b Statistic for mono-oriented fin percentage of 2D Bi₂O₂Se fin arrays growth with miscut angle of the epitaxial substrate. Error bars indicate standard deviations of mono-oriented fin percentage for different miscut angle. c–e SEM images of high-density 2D Bi₂O₂Se fin arrays grown by ledge-guided epitaxy on LaAlO₃ (100) surface (c), MgO (110) surface (d) and CaF₂ (110) surface (e). Insets: corresponding tilted-view high-magnification SEM images. L_FS represents fin spacing. f Statistical minimum fin pitch and fin spacing of different vertical 2D Bi₂O₂Se fin arrays grown by ledge-guided epitaxy on various substrates. Error bars indicate standard deviations of minimum fin spacing and fin pitch for different 2D fin arrays.

Fig. 4. Electrical performance of 2D multi-fin FinFETs based on aligned 2D Bi₂O₂Se-Bi₂SeO₅ fin-oxide arrays.

a Schematic diagram of 2D Bi₂O₂Se/Bi₂SeO₅/HfO₂ FinFET with three fins. b Cross-sectional STEM image of fin arrays. c–e Low-magnification STEM image (c), Energy-dispersive X-ray spectroscopy (EDS) image (d), and high-magnification STEM image (e) of Bi₂O₂Se/Bi₂SeO₅ fin-oxide heterostructures covered with HfO₂ dielectric layer. f Tilted SEM image of a 3-fin FinFET. g Typical output curves of the 2D multi-fin FET in (f). I_DS is the source-drain current. V_DS is the source-drain voltage and V_G is the gate voltage. L_ch represents the channel length of the devices. h Transfer curves of the 2D multi-fin FET in (f) and the repeated transfer curve measurement results for 50 cycles of the 2D multi-fin FET. I_G is the gate leakage current, V_th is the threshold voltage and ΔV_th means the shift of threshold voltage. The intersection of the two dashed lines is the threshold voltage of the device, represented by a solid line. i Statistical on-state current (I_ON) and off-state current (I_OFF) measured over 50 cycles for different multiple-channel 2D FinFETs. j, k Transfer curves (j) and statistical I_ON and I_OFF (k) of the 2D multi-fin FET in (f) operated under different temperatures. l Comparison of normalized current of the fabricated 2D multi-fin FETs with 2D MoS₂ FET, 2D InSe FET, 2D MoS₂ FinFETs and Intel’s 14 nm-node Si FinFETs under low gate-voltage modulation. L is the channel length and W_eff is the effective width of device.

Fig. 5. Comparison of the electrical performances of 2D FinFETs with different number of fins.

a Top SEM image of FinFETs with single fin and two fins, respectively, which share one fin. b Transfer curves of 2D FinFETs with single fin and two fins. c Comparison of the transconductance of 2D FinFETs with single fin and two fins. The different data symbols were obtained from different devices. d Comparison of on-state current and transconductance of 2D FinFETs with different number of fins, demonstrating that multiple-channel FinFETs possess higher electrical performance. e Typical output curves of the 2D FinFETs with five fins. f Benchmarking of the gate delay of 2D multi-fin FETs versus the channel length (L_ch) with Si MOS, Ge MOS, MoS₂ FET^– and WS₂ FET (Part of data of MoS₂ and WS₂ are calculated from ref. ^,). IRDS 2017–2033 targets for high-performance (HP) transistors are also plotted.