Impact of ZrO₂ Dielectrics Thickness on Electrical Performance of TiO₂ Thin Film Transistors with Sub-2 V Operation

Abstract

In the present work, the impact of ZrO 2 gate dielectric thickness on the electrical performance of TiO 2 thin film transistors (TFTs) is systematically investigated. Exhaustive electrical measurements on TFTs, metal−insulator−metal, and metal−oxide−semiconductor capacitors are carried out with varying ZrO 2 dielectrics of different thicknesses. It is found that the ZrO 2 possesses an outstanding thickness scalability, providing reliable dielectric properties under an ultrathin physical thickness of 5 nm, while further reduction in ZrO 2 thickness would lead to a breakdown of the TFTs, indicating the physical limitations for the ultrathin ZrO 2 dielectrics. The TiO 2 TFTs with the 5 nm-thick ZrO 2 dielectric exhibit an enhanced electrical performance, including a high on/off current ratio (I on /I off ) of 7.7 × 10 8 , a nearly ideal subthreshold (SS) of 72 mV/dec, and a high electron mobility (μ eff ) of 5.74 cm 2 •V −1 •s −1 under an ultralow voltage of 2 V. Such prominent electrical characteristics with a battery-drivable low-voltage operation prove the suitability of the TiO 2 TFTs for Internet of Things applications. This comprehensive study, revealing the behaviors of leakage current, oxide capacitance, oxide charges, and interface traps with respect to the ZrO 2 thickness, sheds light on the quality and scalability of the ZrO 2 dielectrics that can be extended to other channel materials, and also offers a framework for evaluating the material quality of other dielectrics. Furthermore, from a material point of view, the underlying physical reasons for the excellent ZrO 2 thickness scalability are believed to be (1) the smooth surfaces of TiO 2 and ZrO 2 , (2) the well-structured ZrO 2 without detectable oxygen-related defects, and (3) the large conduction band offset between ZrO 2 and TiO 2 . Overall, this study not only shows that the TiO 2 TFTs hold great potential to empower future IoT applications, but also provides important guidance regarding dielectric scaling and quality evaluation in the nanometer scale.

Near-Ideal Top-Gate Controllability of InGaZnO Thin-Film Transistors by Suppressing Interface Defects with an Ultrathin Atomic Layer Deposited Gate Insulator

“…The leakage mechanism of the ultrathin insulator was further analyzed. In the low-voltage range from 2.70 to 3.45 V, J was found to follow the relation of the Poole−Frenkel (P−F) emission, 38,39…”

“…The leakage mechanism of the ultrathin insulator was further analyzed. In the low-voltage range from 2.70 to 3.45 V, J was found to follow the relation of the Poole–Frenkel (P–F) emission, , J = C 1 E exp { − q false[ ϕ normalT − false( q E / π ε normali false) 1 / 2 false] k T } where C 1 is a prefactor, k is the Boltzmann constant, T is the absolute temperature in Kelvin, q is the unit electron charge, E is the electric field across the dielectric layer, Φ T is the trap energy, and ε i is the dielectric constant of AlO x and extracted to be 6.5 from the capacitance–voltage ( C – V ) characteristics (Figure S1), close to the reported value . As shown in Figure b, ln( J / E ) increases linearly with E 1/2 , which is consistent with the P–F emission mechanism.…”

A Review on the Progress of Optoelectronic Devices Based on TiO2 Thin Films and Nanomaterials

“…For the solution-treated films, the presence of Li + in the selected-pass medium resulted in a significant increase in electron mobility. Zhang et al systematically investigated the effect of zirconia gate dielectric thickness on the electrical properties of TiO 2 thin-film transistors [ 59 ] ( Figure 9 a,b). Figure 9 c shows the equivalent parallel conductance ( Gm / ω ) of the samples measured at different frequencies versus the applied voltage.…”

Ultra-thin gate insulator of atomic-layer-deposited AlO x and HfO x for amorphous InGaZnO thin-film transistors

“…To further reduce the EOT of AOS TFTs, the atomiclayer-deposited (ALD) GIs of higher dielectric constant (k) were widely studied, such as AlO x [10,11], HfO x [12], and ZrO x [13]. However, high-k materials usually have some shortcomings that cannot be ignored, where the intrinsic defects and the narrow band gaps for high-k materials often lead to unexpected device performance [14,15], such as an uncontrollable I g , degraded SS, and serious insatiability under bias stresses.…”