Anomalous C-V response correlated to relaxation processes in TiO2 thin film based-metal-insulator-metal capacitor: Effect of titanium and oxygen defects

Abstract

Capacitance-voltage (C V) and capacitance-frequency (C f) measurements are performed on atomic layer deposited TiO 2 thin films with top and bottom Au and Pt electrodes, respectively, over a large temperature and frequency range. A sharp capacitance peak/discontinuity (C V anomalous) is observed in the C V characteristics at various temperatures and voltages. It is demonstrated that this phenomenon is directly associated with oxygen vacancies. The C V peak irreversibility and dissymmetry at the reversal dc voltage are attributed to difference between the Schottky contacts at the metal/TiO 2 interfaces. Dielectric analyses reveal two relaxation processes with degeneration of the activation energy. The low trap level of 0.60 0.65 eV is associated with the first ionized oxygen vacancy at low temperature, while the deep trap level of 1.05 eV is associated to the second ionized oxygen vacancy at high temperature. The DC conductivity of the films exhibits a transition temperature at 200 C, suggesting a transition from a conduction regime governed by ionized oxygen vacancies to one governed by interstitial Ti 3þ ions. Both the C V anomalous and relaxation processes in TiO 2 arise from oxygen vacancies, while the conduction mechanism at high temperature is governed by interstitial titanium ions. V C 2015 AIP Publishing LLC.

Effects of oxygen pressure during deposition on the dielectric properties of amorphous titanium dioxide thin films

“…For the 0.005 mbar sample, κ shows a decrease of 70% going through the relaxation, reaching a value at 100 kHz of around 31. This latter value corresponds well to what is observed in other amorphous thin films [14]. The high κ observed in the samples grown at low oxygen pressure would therefore be generated directly by the accumulation of the mobile charges at the dielectric/electrode interface.…”

“…TiO 2 is a versatile material, useful for a large range of applications such as dye-sensitized solar cells [1,2], photocatalysis [3], resistive switching [4][5][6], field emission [7] and as transparent conductor [8] or diluted magnetic semiconductors if doped [9,10]. Notably, TiO 2 is also part of the so-called highk dielectrics, showing a strongly growth dependent dielectric constant of ≈80 [11], and was used therefore as a dielectric in capacitors [12][13][14] or as gate oxide in MOSFETs [15,16]. This high versatility of TiO 2 for application is primarily a consequence of the wide range of electronic properties which can be encountered in TiO 2 , ranging from an insulating character to a high mobility semi-conductor.…”

“…However, in applications such as capacitors, high-k oxides are often used in its amorphous phase in order to avoid the degradation of the properties due to the presence of grain boundaries. In spite of the technological interest, only very few studies on amorphous TiO 2 thin films exist [12,14,22]. All these studies were concentrated on the dielectric properties, showing lower dielectric constants than some of the crystalline films [12,22] and complex behavior in capacitance-voltage characteristics [12,24].…”

Structural and Dielectric Properties of Subnanometric Laminates of Binary Oxides

“…It was shown that a pure TiO 2 dielectric can reach such high values of κ in the rutile crystalline state, , but this phase is hard to access and the dielectric losses and leakage current are typically higher. Amorphous TiO 2 exhibits a κ of 20–40, , but the leakage current is still enhanced compared to the subnanometric laminates presented here. The leakage current of pure TiO 2 was shown to decrease with lamination of Al 2 O 3 , but so does κ. , Most of the values found for crystalline nanometric laminates are ranging from 10 to 40, ,, in the amorphous phase κ = 8 .…”

Titanium dioxide thin films by atomic layer deposition: a review

“…x [598]; [523,[598][599][600][601][602][603]; [604,605]; [576,606]; b Ti(OEt) 4 [37,54,63,91,[607][608][609][610][611][612][613][614][615][616][617]; [54,63,91] Note that a process (free from conventional oxygen sources) by combining TiCl 4 and Ti(O i Pr) 4 has also been demonstrated [798]. Note that in references [792][793][794][795][796][797] a process with molecular N 2 O has also been reported.…”