Mechanism of the performance improvement of TiO2-x-based field-effect transistor using SiO2 as gate insulator

Zhong, Ni; Shima, Hisashi; Akinaga, H.

doi:10.1063/1.3646525

Cited by 20 publications

(15 citation statements)

References 26 publications

(39 reference statements)

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“…On the other hand, TiO 2 has not seriously been considered as a transistor channel, although the TiO 2 channel carries a potential of modulating various surface properties by electrostatic back gating. It is partially because the previously fabricated TiO 2 ‐channel thin film transistors (TFTs) only showed a limited value of field effect mobility ( μ FE ) below 1 cm 2 V −1 s −1 in TFTs . This μ FE is one‐order lower than indium gallium zinc oxide (IGZO) channel, which is used in TFTs for displays due to its relatively high electron mobility >10 cm 2 V −1 s −1 and spatial uniformity .…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…In the past literature, TiO 2 ‐channel TFTs were fabricated with several different gate insulators: SiO 2 , LaAlO 3 , and Y 2 O 3 . The low μ FE in these devices was sometimes attributed to electronic traps or scattering centers at the gate‐channel interface . On the other hand, the low μ FE can also be attributed to the poor control of phases and defects in TiO 2 thin films, rather than the problems at the interface, considering TiO 2 often has mixed phases , and point defects .…”

Section: Introductionmentioning

confidence: 99%

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Independent control of phases and defects in TiO₂ thin films for functional transistor channels

Yajima

Oike

Nishimura

et al. 2016

Physica Status Solidi (a)

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TiO2 has various inherent advantages in practical devices: chemical stability, non‐toxicity, and abundance on earth, as highlighted in a range of applications of TiO2 surfaces in photocatalysis/optoelectronics. However, the application of TiO2 to three‐terminal devices has been limited; for example, TiO2‐channel transistors, which may potentially modulate the TiO2 surface properties by electrostatic back gating, has suffered from low field‐effect mobility (μFE < 1 cm2 V−1 s−1) irrespective of fabrication methods. The major challenge is to control phases (rutile/anatase) and defects (oxygen vacancy) simultaneously in TiO2 thin films. Here, we achieved μFE ∼ 10 cm2 V−1 s−1 in TiO2‐channel transistors, one order higher than before and even comparable to InGaZnO channels. The major improvement is the independent control of phases and defects in TiO2 thin films; we formed short‐range order of anatase phase in the amorphous deposition, and minimized the number of defects in the subsequent thermal treatment. Besides, we showed this independent control of phases and defects are underpinned by excellent thermal stability of TiO2/SiO2 interfaces. These results demonstrate TiO2 can be a transistor channel with a reasonable μFE and ON/OFF ratio (>6 orders), not only changing the conventional image of this material, but also promising new functionalities based on unique properties of TiO2.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Independent control of phases and defects in TiO₂ thin films for functional transistor channels

Yajima

Oike

Nishimura

et al. 2016

Physica Status Solidi (a)

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“…The typical μ FE in O 2 -PDA is around 10 cm 2 /Vsec, and the highest one in this work is approximately 19 cm 2 /Vsec as shown in Fig. 5, which is to our knowledge the highest in deposited-TiO 2 FETs on thermally grown SiO 2 1,2) . It has been expected that the reductive PDA may form donor-type defects, such as Ti interstitials and oxygen vacancies in TiO 2 , and that FETs should have lower V th .…”

Section: Record-high Electron Mobility In Tio 2 Fetmentioning

confidence: 89%

High electron mobility (>16 cm2/V<inf>sec</inf>) FETs with high on/off ratio (>106) and highly conductive films (σ>102 S/cm) by chemical doping in very thin (∼20 nm) TiO<inf>2</inf> films on thermally grown SiO<inf>2</inf>

Oike

Yajima

Nishimura

et al. 2013

2013 IEEE International Electron Devices Meeting

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We have investigated electrical conduction of TiO 2 films by both field-effect and chemical doping. We report that FET characteristics of TiO 2 are affected very much by PDA condition and that its conductivity is also significantly increased by chemical doping. The results are quite promising for both TFT and transparent electrode applications of TiO 2 . Background and ObjectiveTiO 2 is quite an interesting material in terms of versatile functionality as well as various applications such as photo-catalyst, transparent semiconductor, and resistive memory without using rare metals. To put TiO 2 to practical use in electronics, both high carrier mobility as well as high on/off ratio for large area TFTs in driving OLEDs and highly conductive sheets for transparent electrodes are required. Thus, the objective of this work is to experimentally demonstrate promising feasibility and potentiality of TiO 2 films from above viewpoints. Results and Discussion3.1 Device fabrication TiO 2 films were prepared by the pulsed laser deposition on SiO 2 /n + -Si, under O 2 pressure of 1 Pa at room temperature. TiO 2 film thickness was varied by the laser pulse count ranging from 20 to 80 nm, which was estimated by grazing incident X-ray reflectivity (GIXR) measurement. The post deposition annealing (PDA) was performed at 500˚C for 30 min in various ambient conditions. TiO 2 films in the present PDA were crystallized to anatase, identified by Raman spectroscopy. The gate electrode was n + Si substrate (back-gate), and source and drain electrodes were prepared by vacuum evaporation of Al. The FET structure is schematically shown in Fig. 1. Moreover, the chemical doping was performed by immersing TiO 2 surface in several solutions (N(CH 3 ) 4 OH, NH 4 OH, HCl, NaCl, and H 2 O). The cross-sectional TEM is shown in Fig. 2, in which well-crystallized TiO 2 film is clearly seen. Record-high electron mobility in TiO 2 FETFirst, the transfer characteristics of 20-nm-thick TiO 2 FETs on 120-nm-thick SiO 2 /Si annealed in O 2 and (H 2 +He) are shown in Fig. 3. It is obviously seen that O 2 -PDA provides much better I-V characteristics than (He+H 2 )-PDA. The highest on/off ratio of ~10 6 , and typically 10 5 were obtained experimentally in O 2 -PDA. The operation mode of TiO 2 FETs was the surface channel type, which was suggested by the fact that thick TiO 2 FETs was well cut-off, and µ FE was very slightly dependent on SiO 2 thickness.Next, effects of PDA condition on TFT performance are discussed. Both V th and μ FE of TiO 2 FETs annealed in O 2 , O 2 +N 2 and He+H 2 are shown in Fig. 4. The O 2 or O 2 +N 2 -PDA enables to lower V th and higher μ FE . Considering that the ideal value of V th is around 0 V in terms of the band alignment of the present gate stack, V th value in O 2 -PDA FETs is quite reasonable. The typical μ FE in O 2 -PDA is around 10 cm 2 /Vsec, and the highest one in this work is approximately 19 cm 2 /Vsec as shown in Fig. 5, which is to our knowledge the highest in deposited-TiO 2 FETs on thermally grown SiO 2 ...

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“…These properties include high conductivity, high refractive index, and high transparency in the visible region. Thus TiO 2 is useful in applications such as photocatalyst [1], dye sensitized solar cells [2], chemical sensors [3][4][5], electrochromics [6], and electronic devices [7].…”

Section: Introductionmentioning

confidence: 99%

Influence of Pore Size on the Optical and Electrical Properties of Screen PrintedTiO2Thin Films

Domtau

Simiyu

Ayieta

et al. 2016

Advances in Materials Science and Engineering

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Influence of pore size on the optical and electrical properties of TiO2thin films was studied. TiO2thin films with different weight percentages (wt%) of carbon black were deposited by screen printing method on fluorine doped tin oxide (FTO) coated on glass substrate. Carbon black decomposed on annealing and artificial pores were created in the films. All the films were 3.2 µm thick as measured by a surface profiler. UV-VIS-NIR spectrophotometer was used to study transmittance and reflectance spectra of the films in the photon wavelength of 300–900 nm while absorbance was studied in the range of 350–900 nm. Band gaps and refractive index of the films were studied using the spectra. Reflectance, absorbance, and refractive index were found to increase with concentrations of carbon black. There was no significant variation in band gaps of films with change in carbon black concentrations. Transmittance reduced as the concentration of carbon black in TiO2increased (i.e., increase in pore size). Currents and voltages (I-V) characteristics of the films were measured by a 4-point probe. Resistivity (ρ) and conductivity (σ) of the films were computed from theI-Vvalues. It was observed that resistivity increased with carbon black concentrations while conductivity decreased as the pore size of the films increased.

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Mechanism of the performance improvement of TiO2-x-based field-effect transistor using SiO2 as gate insulator

Cited by 20 publications

References 26 publications

Independent control of phases and defects in TiO₂ thin films for functional transistor channels

Independent control of phases and defects in TiO₂ thin films for functional transistor channels

High electron mobility (>16 cm<sup>2</sup>/V<inf>sec</inf>) FETs with high on/off ratio (>10<sup>6</sup>) and highly conductive films (σ>10<sup>2</sup> S/cm) by chemical doping in very thin (∼20 nm) TiO<inf>2</inf> films on thermally grown SiO<inf>2</inf>

Influence of Pore Size on the Optical and Electrical Properties of Screen PrintedTiO2Thin Films

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Mechanism of the performance improvement of TiO2-x-based field-effect transistor using SiO2 as gate insulator

Cited by 20 publications

References 26 publications

Independent control of phases and defects in TiO2 thin films for functional transistor channels

Independent control of phases and defects in TiO2 thin films for functional transistor channels

High electron mobility (&#x003E;16 cm<sup>2</sup>/V<inf>sec</inf>) FETs with high on/off ratio (&#x003E;10<sup>6</sup>) and highly conductive films (&#x03C3;&#x003E;10<sup>2</sup> S/cm) by chemical doping in very thin (&#x223C;20 nm) TiO<inf>2</inf> films on thermally grown SiO<inf>2</inf>

Influence of Pore Size on the Optical and Electrical Properties of Screen PrintedTiO2Thin Films

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About

Independent control of phases and defects in TiO₂ thin films for functional transistor channels

Independent control of phases and defects in TiO₂ thin films for functional transistor channels

High electron mobility (>16 cm<sup>2</sup>/V<inf>sec</inf>) FETs with high on/off ratio (>10<sup>6</sup>) and highly conductive films (σ>10<sup>2</sup> S/cm) by chemical doping in very thin (∼20 nm) TiO<inf>2</inf> films on thermally grown SiO<inf>2</inf>