Highly improved negative bias illumination stress stability was achieved in a Zn-Sn-O field effect transistor after an ozone (O 3 ) treatment. The untreated ZTO FET exhibited a huge negative threshold voltage shift of 4.2 V but the O 3 treated device exhibited superior stability under NBIS conditions: the V th value of the O 3 treated ZTO FET for 600 s showed almost no change (DV th ¼ À0.07 V) under the same NBIS. The improvement in NBIS stability of the O 3 treated ZTO FETs was attributed to the lower oxygen vacancy concentration and retarded desorption of adsorbed oxygen under photon irradiation by the O 3 treatment.

The effects of the annealing temperature on the structural and chemical properties of soluble-processed zinc-tin-oxide (ZTO) films were examined by transmission electron microscopy, atomic force microscopy, high resolution X-ray reflectivity, and X-ray photoelectron spectroscopy. The density and purity of the resulting ZTO channel layer increased with increasing annealing temperature, whereas the oxygen vacancy defect density decreased. As a result, the device performance of soluble ZTO thin film transistors (TFTs) was improved at higher annealing temperature. Although the 300 °C-annealed ZTO TFT showed a marginal field-effect mobility (μFE) and high threshold voltage (Vth) of 0.1 cm(2)/(V s) and 7.3 V, respectively, the 500 °C-annealed device exhibited a reasonably high μFE, low subthreshold gate swing (SS), Vth, and Ion/off of 6.0 cm(2)/(V s), 0.28 V/decade, 0.58 V, and 4.0 × 10(7), respectively. The effects of dark negative bias stress (NBS) and negative bias illumination stress (NBIS) on the degradation of transfer characteristics of ZTO TFTs were also investigated. The instability of Vth values of the ZTO TFTs under NBS and NBIS conditions was suppressed with increasing annealing temperature. To better understand the charge trapping mechanism, the dynamics of Vth shift with NBS and NBIS time for all ZTO TFTs was analyzed on the basis of the stretched exponential relaxation. The negative Vth shift for each transistor was accelerated under NBIS conditions compared to NBS, which resulted in a higher dispersion parameter and smaller relaxation time for NBIS degradation. The relaxation time for NBS and NBIS instability increased with increasing annealing temperature, which is discussed on the basis of the transition mechanism of oxygen vacancy defects.

Thin film transistors (TFTs) with In and Ga-free multicomponent Zn–Sn–Zr–O (ZTZO) channel layers were fabricated using the cosputtering approach. The incorporation of ZrO2 into the Zn–Sn–O (ZTO) films increased the contact resistance, which led to the degradation of the transport properties. In contrast, the threshold voltage shift under negative bias illumination stress (NBIS) was largely improved from −12.5 V (ZTO device) to −4.2 V (ZTZO device). This improvement was attributed to the reduction in the oxygen vacancy defects in the ZTZO film, suggesting that the photoinduced transition from VO to VO2+ was responsible for the NBIS-induced instability.

No abstract

This study examined the structural, chemical, and electrical properties of solution-processed (Zn,Sn)O3 (ZTO) films with various Sn/[Zn+Sn] ratios for potential applications to large-area flat panel displays. ZTO films with a Zn-rich composition had a polycrystalline wurtzite structure. On the other hand, the Sn-rich ZTO films exhibited a rutile structure, where the Zn atom was speculated to replace the Sn site, thereby acting as an acceptor. In the intermediate composition regions (Sn/[Zn+Sn] ratio from 0.28 to 0.48), the ZTO films had an amorphous structure, even after annealing at 450 °C. The electrical transport properties and photobias stability of ZTO thin film transistors (TFTs) were also examined according to the Sn/[Zn+Sn] ratio. The optimal transport property of ZTO TFT was observed for the device with an amorphous structure at a Sn/[Zn+Sn] ratio of 0.48. The mobility, threshold voltage, subthreshold swing, and on/off current ratio were 4.3 cm(2)/(V s), 0 V, 0.4 V/decade, and 4.1 × 10(7), respectively. In contrast, the device performance for the ZTO TFTs with either a higher or lower Sn concentration suffered from low mobility and a high off-state current, respectively. The photoelectrical stress measurements showed that the photobias stability of the ZTO TFTs was improved substantially when the ZTO semiconducting films had a lower oxygen vacancy concentration and an amorphous structure. The relevant rationale is discussed based on the phototransition and subsequent migration mechanism from neutral to positively charged oxygen vacancies.

No abstract

In this work, we investigated the structural, electrical and optical properties of molybdenum oxide thin films deposited by the reactive dc magnetron sputtering method. The molybdenum oxide films were prepared at sputtering pressures ranging from 6.7 × 10−1 to 6.7 × 10−2 Pa. In order to promote their electrical conductivity, all the deposited MoOx films were annealed in Ar ambient at 450 °C for 8 h. The resistivity of the MoOx films varied from 10−4 to 10−2 Ω cm depending on the O2 content in the sputtering ambient. The lowering of the resistivity of the MoO2 films was mainly attributed to the formation of a monoclinic MoO2 polycrystalline phase. As the sputtering pressure decreased, the content of monoclinic polycrystalline MoO2 phase increased, resulting in low resistivity films. The formation of the dominant MoO2 phase at lower sputtering pressures was attributed to the stress induced crystallization. The post-deposition annealed (PDA) MoOx film, deposited at an ultralow sputtering pressure (6.7 × 10−2 Pa) and O2 content of 40%, had an atomic ratio of O to Mo ≈ 2.85 and was highly transparent and conductive: the transmittance in the visible wavelength range of 400–500 nm was about 73% and the resistivity was 1.05 × 10−3 Ω cm. This result is superior to those of MoOx films epitaxially grown by the pulse laser deposition method.

No abstract