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Negative capacitance field effect transistors made of Hf0.5Zr0.5O2 (HZO) are one of the most promising candidates for low-power-density devices because of the extremely steep subthreshold swing and high open-state currents resulting from the addition of ferroelectric materials in the gate dielectric layer. In this paper, HZO thin films were prepared by magnetron sputtering combined with rapid thermal annealing. Their ferroelectric properties were adjusted by changing the annealing temperature and the thickness of HZO. Two-dimensional MoS2 back-gate negative capacitance field-effect transistors (NCFETs) based on HZO were prepared as well. Different annealing temperatures, thicknesses of HZO thin films, and Al2O3 thicknesses were studied to achieve optimal capacitance matching, aiming to reduce both the subthreshold swing of the transistor and the hysteresis of the NCFET. The NCFET exhibits a minimum subthreshold swing as low as 27.9 mV/decade, negligible hysteresis (∼20 mV), and the I ON/I OFF of up to 1.58 × 107. Moreover, a negative drain-induced barrier lowering effect and a negative differential resistance effect have been observed. This steep-slope transistor is compatible with standard CMOS manufacturing processes and attractive for 2D logic and sensor applications as well as future energy-efficient nanoelectronic devices with scaled power supplies.

Fe-oxide/Al2O3 samples (0.5-, 1.0-, 2.0-, and 4.0-Fe) containing various amounts of Fe-oxide on the porous Al2O3 were prepared by tr-CVD and subsequent annealing. The catalytic activities toward CO oxidation under a dry air atmosphere were examined in the temperature range of 30–350 °C. The activities varied upon the deposition amounts of Fe-oxide below 200 °C. At 50 °C, the activity order was 0.5-Fe, 1.0-Fe, 2.0-Fe, and 4.0-Fe, whereas it shifted to 2.0-Fe, 1.0-Fe, 0.5-Fe, and 4.0-Fe at a higher temperature region (100–150 °C). CO-TPD and -TPR results indicated that Fe-oxide structures were different qualitatively as well as quantitatively with respect to the deposition amounts of Fe-oxides. The surface analysis results of X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry revealed the formation of the interfacial Fe–C–Al species. The population of Fe–C–Al of each Fe-oxide nanoparticle decreased as the deposition amounts of Fe-oxide increased (0.5-Fe, 2.0-Fe, and 4.0-Fe) correlating to the activity order at ∼50 °C. It suggested that the Fe–C–Al species can facilitate the lower temperature CO oxidation (at ∼50 °C) on the surface of Fe-oxide nanoparticles by activating oxygen atoms. However, the surface of Fe-oxide nanoparticles can effectively catalyze CO oxidation at a higher temperature (>100 °C) without the aid of the Fe–C–Al species.

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