Postfabrication rapid thermal annealing ͑RTA͒ and subsequent nitrous oxide ͑N 2 O͒ plasma treatment improved the performance of zinc oxide ͑ZnO͒ thin-film transistors ͑TFTs͒ in terms of off current and on/off current ratio by almost 2 orders of magnitude. The off current of 2 ϫ 10 −8 A and on/off current ratio of 3 ϫ 10 3 obtained after RTA were improved to 10 −10 A and 10 5 , respectively, by the subsequent N 2 O plasma treatment. X-ray photoelectron spectroscopy analysis of the TFT samples showed that the RTAtreated ZnO surface had more oxygen vacancies as compared to as-deposited samples, and the oxygen vacancies at the surface of RTA-treated ZnO were reduced by subsequent N 2 O plasma treatment. The reduction of oxygen vacancies at the top region of the ZnO channel is the cause of better off current and on/off current ratio of the TFTs.Zinc oxide ͑ZnO͒, with a direct bandgap energy of 3.37 eV, is one of the semiconductor materials well suited for transparent thinfilm transistors ͑TFTs͒ in the application areas of active matrix liquid crystal displays ͑AMLCDs͒ and electronic papers. 1-10 However, there are some technical challenges to overcome to achieve manufacturability of ZnO-based TFTs. One of the problems facing ZnObased TFTs is high off current ͑leakage current͒ and hence low on/off current ratio. 5-9 Low off current as well as on/off current ratio higher than 10 6 are required for the ZnO TFTs to function as select transistors in AMLCDs. 10 In TFTs with bottom-gate configuration, the drain-to-source current flow through the undepleted channel region as well as the gate-leakage current contribute to the off current. To eliminate the undesired drain-to-source current under the off condition, thinner channel layers have been employed in TFTs. 2,4 However, the crystalline quality of the ZnO materials improves with thickness, so the thinner ZnO channel tends to have more defects, which affects the carrier mobility and subthreshold slope of devices. 1,6 In this work, we studied the effect of postfabrication rapid thermal annealing ͑RTA͒ and subsequent nitrous oxide ͑N 2 O͒ plasma treatment on the off current and on/off current ratio of the fabricated bottom-gated ZnO TFTs. We found that the TFTs subjected to N 2 O plasma treatment exhibit better off current and on/off current ratio. X-ray photoelectron spectroscopy ͑XPS͒ analysis was performed to examine the surface modification of ZnO channel layer due to RTA and N 2 O plasma treatment.Corning 1737 glass coated with 200 nm thick indium tin oxide ͑ITO͒ was used as starting substrates ͑sheet resistance = 4-8 ⍀/Ǣ, Delta Technologies limited, USA͒ for fabricating TFTs with bottomgate configuration, and the ITO acted as the gate electrode. The substrates were ultrasonically cleaned with acetone, methanol, and deionized water. ITO gate electrodes were defined by standard photolithography and wet-etching process using LCE-12k ͑ITO etchant, Cyantek Corporation͒ at 45°C. Next, a 200 nm thick silicon nitride gate-dielectric layer was deposited by plasma-enhanced chemi...

Thin-film transistors ͑TFTs͒ on glass substrates were fabricated using ZnO, grown by a metallorganic chemical vapor deposition ͑MOCVD͒ technique, with N-and Si-rich silicon nitrides as gate dielectrics. This is a report on MOCVD-grown ZnO TFTs that use silicon nitride as gate dielectrics. The ZnO TFTs using N-rich silicon nitride exhibited a field-effect mobility of 6.5 cm 2 /V s, a subthreshold slope of 0.8 V/decade, an on/off current ratio of 10 8 , and a threshold voltage of 2.05 V. The performance of these TFTs is better than that of TFTs employing Si-rich silicon nitride. This enhanced device performance can be attributed to a larger average grain size of 126 nm observed in the ZnO film grown on the N-rich silicon nitride compared to an average grain size of 69 nm for the ZnO film grown on Si-rich silicon nitride.

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ZnO thin-film transistors (TFTs) with and without a thin MgZnO layer at the channel/gate insulator interface were fabricated using glass substrates. Both ZnO and MgZnO films were grown by metal organic chemical vapor deposition (MOCVD). The ZnO TFTs employing the MgZnO layer exhibit high performance with a field-effect mobility (μFE) of 9.1cm2∕Vs , a subthreshold slope (S) of 0.38V∕dec , an on/off current ratio of 2.3×108 , and a turn-on voltage of −2.75V . This is the best performance reported to date for ZnO TFTs that are realized on glass substrates with MOCVD-grown channel layers. The ZnO TFTs without the MgZnO layer, on the other hand, exhibit poor performance, and the μFE , S , on/off current ratio, and turn-on voltage of these devices are 2.3cm2∕Vs , 0.78V∕dec , 6.4×107 , and −6.75V , respectively. The superior performance of ZnO TFTs with the MgZnO layer is attributed to the larger grains in the ZnO film.

Thin-film transistors (TFTs) with a bottom-gate configuration were fabricated with an RF magnetron sputtered undoped zinc oxide (ZnO) channel layer and plasma-enhanced chemical vapor deposition (PECVD) grown silicon nitride as a gate dielectric. Postfabrication rapid thermal annealing (RTA) and subsequent nitrous oxide (N 2 O) plasma treatment were employed to improve the performance of ZnO TFTs in terms of on-current and on/off current ratio. The RTA treatment increases the on-current of the TFT significantly, but it also increases its off-current. The off-current of 2 Â 10 À8 A and on/off current ratio of 3 Â 10 3 obtained after the RTA treatment were improved to 10 À10 A and 10 5 , respectively, by the subsequent N 2 O plasma treatment. The better device performance can be attributed to the reduction of oxygen vacancies at the top region of the channel due to oxygen incorporation from the N 2 O plasma. X-ray photoelectron spectroscopy (XPS) analysis of the TFT samples showed that the RTA-treated ZnO surface has more oxygen vacancies than as-deposited samples, which results in the increased drain current. The XPS study also showed that the subsequent N 2 O plasma treatment reduces oxygen vacancies only at the surface of ZnO so that the better off-current and on/off current ratio can be obtained.