Dielectric response of sputtered transition metal oxides

Abstract

We have investigated the dielectric properties of thin layers of five oxides of transition metals (Ta 2 O 5 , HfO 2 , ZrO 2 , (ZrO 2 ) 0.91 (Y 2 O 3 ) 0.09 , and Sn 0.2 Zr 0.2 Ti 0.6 O 2 ) sputtered from ceramic targets at different pressures. We find that layers deposited at low pressure behave as expected from literature, whereas layers deposited at high pressure all exhibit an anomalous dielectric response similar to that reported for the so-called ''colossal'' dielectric constant materials. The characterization of the thickness, frequency, and temperature dependence of the capacitance, as well as the comparison of film properties before and after annealing show that the anomalous dielectric response is due to quenched-in vacancies that act as dopants and cause the insulating layers to behave as semiconductors. An increase in quenched-in vacancies concentration with sputtering pressure results in a transition from normal to anomalous dielectric response and gradual increase in layer conductivity. In contrast, the refractive index does not depend on sputtering pressure. This observation indicates the possible application of these materials as transparent coatings with a tunable electrical conductivity.

A study of thermally stimulated dielectric relaxation currents in Al/Lu2O3/Al thin-film sandwiches

“…Several transition metal oxides, such as ZrO 2 and HfO 2 have been studied as alternative high-dielectric constant thin-film materials for replacement of SiO 2 layers in thin-film microdevices [2,5,7]. Recently, thin films of rare earth oxides (REO) have also been investigated as a new, alternative and perspective group of materials for different thin-film applications [6,8,9].…”

“…In recent years various experimental studies in search of dielectric materials for integrated optoelectronic and electronic devices have been conducted [1][2][3][4][5][6][7][8]. These applications utilize dielectric materials mainly in thinfilm forms.…”

Electrical conductivity in oxygen-deficient phases of transition metal oxides from first-principles calculations.

“…At the low temperature reference of 10 K, E g is only about 3 eV for aTa48O120 with the PBE functional, while E g is nearly 4.5 eV with the HSE06 functional. Experimentally reported values for the Ta 2 O 5 E g range from 3.9 to 5.28 eV [18,19], but the average value is about 4 eV; this wide range is typical of many dielectrics and is a result of the variability in dielectric quality and sometimes band gap definition. As temperature increases, the E g for both functionals decreases and the corresponding step function in () softens.…”

“…Since high-k capacitor dielectrics are the most common application of Ta 2 O 5 to date, many studies in recent years focused on the breakdown and leakage characteristics of a-Ta 2 O 5 to assess the feasibility of incorporation in integrated circuit manufacturing. The work of Fleming et al [18] concluded that O vacancy (V O ) defect concentrations near metal-oxide interfaces are an essential contributor to spurious Ta 2 O 5 leakage currents, while Iosad et al [19] attributed the variability in dielectric response of several transition metal oxides (TMOs), including Ta 2 O 5 , to a dopant-like behavior that depends on the concentration of quenched-in vacancies. Nakamura et al [20] provided one of the first studies of V O aggregation, which is likely an essential mechanism of conductivity modulation.…”

“…We calculated 1  o values in the literature can be extracted from various studies of dielectric breakdown; as a result, reported values cover a wide range (1×10 -5 to 1×10 -11 (-m) -1 ) and are influenced by extreme current densities and electric field magnitudes, as well as the inherent quality of the deposited films [18,19,55]. The largest sources of error in our DFT calculations originate in the small supercell sizes used and are manifested in discretization of eigenvalues and inadequate sampling of ideally random networks in the amorphous structures.…”