High-performance organic thin-film transistor by using LaNbO as gate dielectric

Abstract

Pentacene organic thin-film transistors (OTFTs) using La x Nb (1Àx) O y as gate dielectric with different La contents (x ¼ 0.347, 0.648) have been fabricated and compared with those using Nb oxide or La oxide. The OTFT with La 0.648 Nb 0.352 O y as gate dielectric can achieve a high carrier mobility of 1.14 cm 2 V À1 s À1 (about 1000 times and 2 times those of the devices using Nb oxide and La oxide, respectively), and has negligible hysteresis of À0.130 V, small sub-threshold swing of 0.280 V/ dec, and low threshold voltage of À1.35 V. AFM and XPS reveal that La can suppress the formation of oxygen vacancies in Nb oxide while Nb can alleviate the hygroscopicity of La oxide, which results in a more passivated and smoother dielectric surface, leading to larger pentacene grains grown and thus higher carrier mobility. The OTFT with Nb oxide has an anticlockwise hysteresis but the device with La oxide shows an opposite direction. This can be explained in terms of donorlike traps due to oxygen vacancies and acceptor-like traps originated from hydroxyl ions formed after La 2 O 3 absorbing water moisture. V

High‐Performance Pentacene Organic Thin‐Film Transistor by Using Nd2O3 Gate Dielectric Doped with Nb

“…With increasing Nb content from sample A to sample C, the entire Nd 3 d curve firstly shifts to lower binding energy due to less Nd‐OH bonds (with higher binding energy than Nd‐O bond) in the dielectric, thus further supporting the hygroscopicity suppression by the Nb incorporation. On the other hand, Nb has higher electronegativity (1.59) than Nd (1.14) and so is more likely to generate oxygen vacancies, which, widely accepted as positively charged, can increase the binding energy of an electron in a nearby atom . This can be demonstrated by sample D with further increase in Nb content, whose curve moves back to higher binding energy.…”

“…The surface roughness of pure Nd 2 O 3 is the largest among the films. This is caused by the formation of hydroxide (‐OH) in the dielectric oxide due to the high hygroscopicity of Nd oxide, resulting in non‐uniform expansion of the oxide film . After the Nb incorporation, the dielectric roughness is greatly reduced for samples B–D as the hygroscopicity of Nd oxide is suppressed by the presence of Nb.…”

“…Although some OTFTs could achieve high performance including carrier mobility comparable to that of amorphous silicon devices, the use of battery‐powered electronic products is increasing, causing a great demand for gate insulator with high dielectric constant (k) to reduce the threshold voltage of the transistors. Pentacene OTFTs with various high‐k dielectric materials have been reported to achieve carrier mobility ranging from 0.03 to 1.4 cm 2 V −1 s −1 . Neodymium oxide (Nd 2 O 3 ) , one of the lanthanide oxides, has been found to be a promising high‐k material to replace SiO 2 to reduce the operating voltage of OTFTs, but like the much more expensive La 2 O 3 , it suffers from high hygroscopicity, easily forming hydroxide in the air .…”

“…On the other hand, niobium oxide (Nb 2 O 5 ) has a higher dielectric constant (≈29) than Nd 2 O 3 (≈20) . However, it has smaller band gap (≈4.4 eV) and suffers from a high density of defects/traps . By mixing these two oxides, it is expected that Nb could suppress the hygroscopicity of Nd 2 O 3 while Nd could passivate the defects/traps in Nb 2 O 5 (like La, but at lower cost), thus allowing the two oxides to complement each other.…”

“…However, it has smaller band gap (≈4.4 eV) and suffers from a high density of defects/traps . By mixing these two oxides, it is expected that Nb could suppress the hygroscopicity of Nd 2 O 3 while Nd could passivate the defects/traps in Nb 2 O 5 (like La, but at lower cost), thus allowing the two oxides to complement each other. Therefore, in this work, Nd x Nb (1− x ) O films with different Nb contents are prepared by co‐sputtering and used as the gate dielectric of pentacene OTFT.…”