Investigation and modeling of the electrical properties of metal–oxide–metal structures formed from chemical vapor deposited Ta2O5 films

Abstract

Amorphous Ta2O5 films were deposited by low pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD) at temperatures below 450 °C. These films were used to fabricate metal–oxide–metal (MOM) structures with titanium nitride (TiN) electrodes. The electrical properties of the MOM capacitance were investigated by the means of current–voltage and capacitance–voltage characteristics in the 100 Hz–1 MHz frequency range. It is shown that the conduction mechanism changed from Schottky emission, for the LPCVD material, to Poole–Frenkel current for the PECVD material. The roughness of the bottom electrode, as determined by atomic force microscopy measurements, is found to impact the leakage current. For the LPCVD material the capacitance exhibits a strong dependency on the applied bias and the frequency. For the PECVD material, only a small variation of the capacitance is observed when the bias is increased, with almost no frequency dependency. A clear correlation between the capacitance variation and the current density is demonstrated. As far as the current density is lower than 0.1 A/cm2, the capacitance is almost constant. For a higher current density the capacitance increases exponentially. Transmission electron microscope observations have shown that the Ta2O5 films are homogeneous in-depth. Consequently, the capacitance variations could not be explained by interfacial polarization (Maxwell–Wagner mechanism). We suggest a model that well explains the observed capacitance variations. This model is based on the relaxation of the free carriers and the nonlinear Kerr effect (dipolar relaxation). A good fit of the experimental results is obtained by summing both contributions (free carrier relaxation and Kerr effect). For the LPCVD material, the carrier relaxation is found to be the predominant process. For the PECVD material, which exhibits lower leakage current than the LPCVD material, the Kerr effect is the predominant mechanism.

$hboxBaSm_2hboxTi_4hboxO_12$Thin Film for High-Performance Metal–Insulator–Metal Capacitors

“…The quadratic VCC is slightly larger than the required value but the linear VCC is sufficiently lower than the required value (α < 100 ppm/V 2 , β < 1000 ppm/V) for the precision analog capacitor. Since the variation of the capacitance with the voltage is assumed to be related to the leakage current [8], an improved value of α might be obtained by optimizing the growth conditions. On the other hand, the α and β values of the amorphous BST film were 48.6 ppm/V 2 and −738 ppm/V, respectively, [see Fig.…”

High permittivity Bi24Fe2O39 thin films prepared by a low temperature process

“…Combining the aforementioned C-V variation and the temperature dependence of capacitance ͑C-T͒ presented here, one can find that the Bi 24 Fe 2 O 39 film exhibits positive variations both with dc bias field and temperature ͑i.e., both ␣ and ␣ T positive͒. There are various explanations reported in literature for the observed C-V and C-T variations, such as enhanced electron injection, 18 logarithmic temperature-dependent mobility, 19 electrode coupling and "hopping" conduction between vacancy sites, 20 thermal expansion leading to an entropy increase, 9 ionic motion, 9,21 and so on. In particular, the model based on the ionic motion of Al 3+ between two different sites has been used for the interpretation of both positive ␣ and ␣ T coefficients observed in Al 2 O 3 .…”

Metal gates and gate-deposition-induced defects in Ta2O5 stack capacitors

“…An important characteristic of a potential electrode material is its chemical compatibility with Ta 2 O 5 , and a requirement of this compatibility is the metal's inability to reduce Ta 2 O 5 . Many materials (including double-gate, alloys) are under investigation to meet metal electrode requirements [1,[3][4][5][6][7][8]. Compatible metal (or metal system) has not been, however, selected yet for Ta 2 O 5 -based capacitors.…”