Oxygen Pressure and Mn-Doping Effects on the Structure and Leakage Current of Bi[sub 6]Ti[sub 5]TeO[sub 22] Thin Film

Abstract

Te ions existed as Te 6+ in the Bi 6 Ti 5 TeO 22 ͑BTT͒ film grown at 300°C under a high oxygen pressure ͑OP͒ of 80.0 Pa and contributed to the formation of the crystalline BTT phase after subsequent annealing at 600°C. However, for the BTT film grown under a low OP of 53.3 Pa ͑or 9.33 Pa͒, Te 6+ ions, were converted to Te 4+ ions, which induced the phase transition of the BTT phase to the pseudo-Bi 4 Ti 3 O 12 and pseudo-Bi 2 Ti 2 O 7 phases after annealing at 600°C. The leakage current density decreased with increasing OP during the growth due to the decreased number of oxygen vacancies. The breakdown voltage also improved with increasing OP during the deposition. The Mn ions introduced in the BTT films by Mn doping existed as Mn 2+ or Mn 4+ and acted as the acceptors. This Mn doping to 10 mol % also reduced the leakage current density and increased the breakdown voltage by decreasing the number of intrinsic oxygen vacancies.Investigations on dielectric thin films with a high dielectric constant ͑k͒ which can be deposited at low temperatures ͑ഛ300°C͒ have multiplied for applications to the embedded decoupling capacitors for printed circuit board ͑PCB͒ and the gate insulators of ZnObased, thin-film transistors for organic light-emitting diodes ͑OLEDs͒ on plastic substrate. 1-3 The radio-frequency ͑rf͒ or analog/ mixed metal-insulator-metal ͑MIM͒ capacitors in semiconductor devices also require a dielectric thin film with low processing temperatures due to the limitation of the very large-scale integration back-end line integration temperature ͑Ͻ400°C͒. Previously, ͑Ba,Sr͒TiO 3 , Ta 2 O 5 , TaTiO, and BaSm 2 Ti 4 O 12 films grown at low temperatures were used as the gate insulators for OLEDs and rf MIM capacitors but suffered from a low-k value. 4-8 Ca-doped Pb͑Zr,Ti͒O 3 films were grown for use as the embedded capacitors for PCBs, but their growth temperature was too high for such application. 9 Recently, Bi-based, dielectric thin films such as Bi 6 Ti 5 TeO 22 ͑BTT͒, 10 Bi 5 Nb 3 O 15 , 11 and Bi 1.5 Zn 1.0 Nb 1.5 O 7 1,3,12 have been extensively studied because of their achievement of high-k value with low deposition temperatures. In particular, the high-k value of 69 with a low dissipation factor ͑Ͻ1.3%͒ 10 obtained by BTT films grown at 300°C using sputtering demonstrated their promise as a good candidate material for high-k dielectric films with low processing temperatures. However, their leakage current density was relatively high with a low breakdown voltage, 10 thereby necessitating the improvement of their electrical properties before the application of such BTT films. Furthermore, the structure of the BTT films was considerably influenced by the valence of the Te ions, which was determined by the oxygen pressure ͑OP͒ during the fabrication processes. 10 However, no detailed investigation on the variation of the crystal structure of the BTT film with OP has yet been conducted.In this work, BTT films were grown using pulsed laser deposition ͑PLD͒ and annealed under various OPs. The PLD method was selected...

Significantly reduced leakage currents in organic thin film transistors with Mn‐doped Bi2Ti2O7 high‐k gate dielectrics

“…Second, effective potential barriers are formed at grain boundaries and metal/dielectric interfaces by the addition of Mn dopant [10]. In this work, the Mn 2+ ion, acting as a B site acceptor in the A 2 B 2 O 7 structure [11] substitutes for the Ti 4+ ion in BTO [12]. The Mn″ Ti dopant ion carries two extra negative charges and compensates the positive charges of the oxygen vacancies, and thus the concentration of free electrons in the film is reduced as expressed in the following equations: As a result, the decrease in the carrier concentration enhances the dielectric properties of BTO films, such as the lower dielectric loss and lower leakage current density.…”

Investigation on the valence state of Te ions in the Bi6Ti5TeO22 thin film using X-ray photoelectron spectroscopy

“…1,2 Moreover, due to the low sintering temperatures of the BTT ceramics, the BTT films with a high ε r were easily grown at low temperatures (≤300 • C). [3][4][5] Therefore, their electrical properties have been studied for application to the embedded decoupling capacitors for printed circuit boards and the radio frequency (RF) metal-insulator-metal capacitors in semiconductor devices which require low processing temperatures. [3][4][5] It was reported that Te 4+ ions in the Bi 2 O 3 -TiO 2 -TeO 2 compounds were easily oxidized and transformed to Te 6+ ions when exposed to an oxidizing atmosphere and that this transition induced a phase change.…”

“…[3][4][5] Therefore, their electrical properties have been studied for application to the embedded decoupling capacitors for printed circuit boards and the radio frequency (RF) metal-insulator-metal capacitors in semiconductor devices which require low processing temperatures. [3][4][5] It was reported that Te 4+ ions in the Bi 2 O 3 -TiO 2 -TeO 2 compounds were easily oxidized and transformed to Te 6+ ions when exposed to an oxidizing atmosphere and that this transition induced a phase change. 1,2 The changes of the crystal structure and electrical properties were also observed for the BTT * Corresponding author.…”

“…[3][4][5] Therefore, it is important to investigate the valence state of the Te ions in order to understand the variations of the structural and electrical properties of the BTT films. For Te-based ceramics, the oxidation of the Te 4+ ions was indirectly identified by the mass gain resulting from the Te 4+ -Te 6+ oxidation.…”

“…2 However, for the BTT films, the valence state of the Te ion has not been investigated systematically despite its considerable influence on the type of phase formed in the BTT films and their electrical properties. 4,5 In this work, therefore, BTT films were grown under various process conditions using RF magnetron sputtering or pulsed laser deposition (PLD). The valence state of the Te ions in these films were investigated using X-ray photoelectron spectroscopy (XPS) and the relation between the crystal structure of the films and the valence of the Te ions was also studied.…”