Influence of Titanium Content on the Structural and Electrical Properties of Er[sub 1−x]Ti[sub x]O[sub y] Gate Dielectrics

Abstract

This paper describes the structural properties and electrical characteristics of thin erbium titanium oxide ͑Er 2 TiO 5 ͒ as gate dielectrics deposited on silicon substrates through reactive radio frequency sputtering. The structural and morphological features of these films were explored by X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy measurements. It is found that the Er 2 TiO 5 film prepared under a 4.5 nm Ti metal film and annealed at 700°C exhibited a thinner capacitance equivalent thickness and excellent electrical properties than other films, including the leakage current density, interface trap density, and hysteresis in the capacitance-voltage curves. We attribute this behavior to the optimum titanium content in the metal oxide film which helps to suppress the information of the interfacial SiO 2 and silicate at the Er 2 TiO 5 /Si interface. These materials also show negligible degrees of charge trapping at high electric field stress.High-k insulators are widely considered to replace the conventional SiO 2 gate oxides to suppress the gate leakage current with scaling of complementary metal-oxide semiconductor ͑CMOS͒ devices. 1 Among the various high-k materials, ZrO 2 , HfO 2 , and other Hf-based materials are the most promising candidates for the gate dielectrics in future CMOS devices. 2,3 The interface between HfO 2 and Si, however, is not as stable and perfect as the SiO 2 /Si interface. There are physical and electrical defects at the HfO 2 /Si interface, causing the degradation of device performance. 4 Lanthanide oxides are promising materials to substitute SiO 2 as the gate insulator because they possess a high permittivity and a large bandgap. 5,6 Thin lanthanide oxide films are thermodynamically stable in contact with silicon substrate, preventing the formation of silicide layers and rough surfaces. However, concerning the moisture absorption of the lanthanide oxides there is a thicker film thickness and a larger flatband voltage shift reported in the literature. 7 This is due to hygroscopic forming hydroxide, leading to charges in the gate dielectric. Zhao et al. 8 reported that the moisture absorption for La 2 O 3 films on silicon generates a large scattering of k-values due to the formation of hexagonal La͑OH͒ 3 with a low permittivity and the enhancement of surface roughness of La 2 O 3 film after the films were exposed to air. To solve the problem of moisture absorption of La 2 O 3 film, radio frequency ͑rf͒ cosputtering using Y 2 O 3 and La 2 O 3 targets can produce LaYO x films that exhibit high permittivities and good resistance to moisture due to the structural stability of Y-doped hexagonal phase La 2 O 3 . 9 It is well known that erbium oxide ͑Er 2 O 3 ͒ as an optical film is used in several optoelectronic devices. 10 Recently, it has been reported that Er 2 O 3 thin film was deposited on silicon substrate by molecular beam epitaxy or physical vapor deposition ͑PVD͒ as a promising gate dielectric material because of its high dielectric constant and ...

Structural and Sensing Characteristics of Dy2O3 and Dy2TiO5 Electrolyte−Insulator−Semiconductor pH Sensors

“…30 It is thought that the addition of Ti or TiO 2 into the Dy 2 O 3 can improve the hysteresis characteristic due to the reduction of the defect chemistry (oxygen vacancies) and the formation of a barrier of grain boundaries that suppresses electromigration of the defect chemistry. 31 Figure 7 shows the hysteresis phenomenon (gate voltage variation) of Dy 2 O 3 and Dy 2 TiO 5 sensing membranes subjected to RTA at different temperatures during the pH loop of 7 f 4 f 7 f 10 f 7 over a period of 1500 s. The hysteresis voltage here is defined as the gate voltage difference between the initial and terminal voltages measured in the above cycle. From the experimental results, the EIS device with a Dy 2 TiO 5 sensing film exhibits a lower gate voltage compared with the Dy 2 O 3 film.…”