Optimization of Subthreshold Swing and Hysteresis in Hf_0.5Zr_0.5O₂-Based MoS₂ Negative Capacitance Field-Effect Transistors by Modulating Capacitance Matching

Abstract

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.

High-Detectivity and Broadband MoS2 Phototransistor Array by Coupling Negative Capacitance and Local Surface Plasmon Resonance Effects

“…Furthermore, Figure c shows the I d - SS scatter plot extracted from Figure b for the pure MoS 2 , AuNPs/MoS 2 , and AuNPs/Al 2 O 3 /MoS 2 phototransistors, with the lowest SS ’s of 69.1, 213.3, and 28.2 mV/dec, respectively. The involved mechanisms for the improved SS of the AuNPs/Al 2 O 3 /MoS 2 device compared to other two devices lie in (1) the enhancement of the ferroelectric polarization of the HZO film by in situ prepared AuNPs and (2) the stabilized NC effect and effectively improved interface qualities by the insertion of the Al 2 O 3 layer.…”

“…On the other hand, the tensile strain caused by the AuNPs in MoS 2 narrows its bandgap, facilitating the broadband photodetection. Moreover, Al 2 O 3 as a capacitance-matching layer (CML) for the HZO film can further suppress the I off , reduce the SS , and enhance the detectivity by utilizing NC effect of the HZO film. , For the first time, a NC-LSPR-coupled phototransistor is fabricated, demonstrating a remarkable responsivity ( R ) and a detectivity ( D* ) at 528 nm (122.5 A/W, 3.23 × 10 14 Jones) and 740 nm (28.3 A/W, 9.14 × 10 13 Jones), respectively, i.e., high detectivity and broadband detection are concurrently achieved. Additionally, the good stability and uniformity of the photodetectors with a stack of HZO/AuNPs/Al 2 O 3 /MoS 2 are demonstrated through a statistic analysis of 30 phototransistors.…”

An Ultralow Subthreshold Swing of 28 mV dec–1 in Negative-Capacitance Thin-Film Transistors with Ferroelectric Zirconium–Aluminum Oxide Gate Oxide

“…2 Recently, Guo et al also reported MoS 2 /HZO NC-FE-FET, exhibiting a steep SS of 27.9 mV dec −1 and a high I ON /I OFF ratio of 1.5 × 10 7 . 10 An ultralow SS of 11 mV dec −1 was reported by Daw et al for a NC-Dirac source−drain FET with 2D CuInP 2 S 6 (CIPS) flakes/MoS 2 /graphene structure. 11 Although 2D materials are emerging for next-generation quantum computing and nanoscale integration, oxide semiconductors could be suitable candidates for low-cost and largescale integration (LSI) of energy-efficient high-speed electronics.…”

“…Note that the steep SS below 60 mV dec −1 could have originated from the NC effect in FE-ZAO TFTs. 3,6,8,10,11 To investigate the needle-like hump phenomena at ultralow V DS during the forward sweep, the I DS −V GS hysteresis characteristics were measured at V DS = 0.1−0.9 mV with 0.2 mV steps, as depicted in Figure 4a. Figure 4b exhibits the zoomed-in view of the needle-like hump for the forward sweep, demonstrating the gradual decrease of hump behavior near V GS = 0 V with increasing V DS .…”

“…Recently, Guo et al. also reported MoS 2 /HZO NC-FE-FET, exhibiting a steep SS of 27.9 mV dec –1 and a high I ON / I OFF ratio of 1.5 × 10 7 . An ultralow SS of 11 mV dec –1 was reported by Daw et al for a NC-Dirac source–drain FET with 2D CuInP 2 S 6 (CIPS) flakes/MoS 2 /graphene structure .…”