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We studied hydrogen (H) behavior in amorphous In-Ga-Zn-O (a-IGZO) films under X-ray irradiation by evaluating the threshold voltage (VTH) shift in a-IGZO thin film transistors (TFTs) with different H concentrations in the active layers. We fabricated three types of a-IGZO TFTs: (i) one without a buffer layer and postannealed in N2, (ii) one with a H-resolved buffer layer and postannealed in N2, and (iii) one with a H-resolved buffer layer and postannealed in a mixture of N2 and H2. All three TFTs showed a negative VTH shift after 100 Gy of X-ray exposure. The degree of VTH shift correlated with an increase in conductivity, which, in turn, corresponds to the H concentration in the active layer of the as-fabricated TFTs. Based on spectroscopic ellipsometry analysis, we confirmed a large increase in the donorlike H related D1 state after X-ray irradiation in high-H concentration a-IGZO films. In addition, an increase in the number of H2 molecules in a-IGZO films after X-ray irradiation was observed via thermal desorption spectroscopy analysis. Therefore, we conclude that the increase in conductivity and/or the resulting negative VTH shift in a-IGZO TFTs during X-ray irradiation can be attributed not only to the state transition from acceptorlike to donorlike H in the as-prepared a-IGZO but also to the incorporation of additional H radicals generated by X-ray irradiation. [ABSTRACT FROM AUTHOR]

Self-aligned coplanar top gate indium–gallium–zinc-oxide thin-film transistors (TFTs), with source/drain (S/D) regions that were heavily doped by various deep-ultraviolet (DUV) irradiation energies at dual wavelengths of 185 and 254 nm, were investigated. The electrical performances of TFTs improved as the DUV irradiation energy increased. The proposed TFTs, with DUV irradiation of 20 J/cm2, have a field-effect mobility of 22.0 cm2/ \text V\cdot \text s , a threshold voltage of 2.2 V, a subthreshold swing value of 0.24 V/decade, and an on/off current ratio of 1.34 \times 10^6 . In addition, the channel length modulation ( \Delta L ) and the width-normalized contact resistance ( R_{\mathrm {SD}}W ) were 1.04 \mu \text{m} and 60.5 \Omega \cdot \text cm , respectively. Such short \Delta L and low R\mathrm {\mathbf {SD}}W values indicate that the S/D regions were properly formed by the DUV irradiation. This simple and cost-effective doping technique can be useful for the fabrication of self-aligned TFTs. [ABSTRACT FROM PUBLISHER]

In recent, research about the oxide semiconductor based photo sensor such as photosensitive oxide TFTs and diodes has been emphasized. In this study, we report a new photosensitive a‐IGZO diode for photo sensor in interactive display. The diode has high on/off ratio and low leakage current density of ~10‐9 A/cm2. Also, the diode has a great photosensitivity of ~107 and ~104 at reverse bias under ultra‐violet (UV) and visible light conditions, respectively. [ABSTRACT FROM AUTHOR]

The effect of an AlO/TiO stacked passivation layer on the performance of amorphous ZnSnO ( a-ZTO) thin-film transistors (TFTs) was investigated by comparing field-effect mobility ( μ) and subthreshold swing after passivation layer deposition. The values observed were 4.7 cm/Vs and 0.64 V/decade, respectively, for uncoated TFTs and 4.6 cm/Vs and 0.62 V/decade for passivated TFTs. In addition, excellent water vapor transmission was observed for electron beam-irradiated AlO/TiO-passivated poly(ether sulfone) substrates in a humidity test, because the AlO/TiO passivation layer can enhance the interface properties between AlO and TiO. To investigate the origin of this enhancement, we performed x-ray photoelectron spectroscopy of both unpassivated and AlO/TiO-passivated TFTs with a-ZTO back-channel layers after Ar annealing. [ABSTRACT FROM AUTHOR]

In this study, InGaZnO (IGZO) thin film transistors (TFTs) with a dual active layer (DAL) structure are fabricated by inserting a homogeneous embedded conductive layer (HECL) in an amorphous IGZO (a-IGZO) channel with the aim of enhancing the electrical characteristics of conventional bottom-gate-structure TFTs. A highly conductive HECL (carrier concentration at 1.6 × 10 cm, resistivity at 4.6 × 10 Ω∙cm, and Hall mobility at 14.6 cm/Vs at room temperature) is fabricated using photochemical H-doping by irradiating UV light on an a-IGZO film. The electrical properties of the fabricated DAL TFTs are evaluated by varying the HECL length. The results reveal that carrier mobility increased proportionally with the HECL length. Further, a DAL TFT with a 60-μm-long HECL embedded in an 80-μm-long channel exhibits comprehensive and outstanding improvements in its electrical properties: a saturation mobility of 60.2 cm/Vs, threshold voltage of 2.7 V, and subthreshold slope of 0.25 V/decade against the initial values of 19.9 cm/Vs, 4.7 V, and 0.45 V/decade, respectively, for a TFT without HECL. This result confirms that the photochemically H-doped HECL significantly improves the electrical properties of DAL IGZO TFTs. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the mobility enhancement in an Amorphous Oxide Semiconductor Thin Film Transistor (AOS TFT), particularly the effect of enhanced-mobility current path was investigated. In the TFT structure, the a-IGZO single active channel layer was replaced by double layers. Indium Tin Oxide (ITO) was employed as an enhanced-mobility current path material and was embedded in an amorphous Indium Gallium Zinc Oxide (a-IGZO) channel layer of a conventional bottom gate structure TFT. To analyze the effect of the length of an additional current path, the a-IGZO channel length was fixed at 80μm, and the length of the ITO enhanced-mobility current path was increased to 20, 40, and 60μm. As a result, the mobility increased monotonically with the length of the enhanced-mobility current path and was predictable from the rule of mixture. The maximum saturation mobility of 28.3cm2/Vs resulted when the length of the enhanced-mobility current path was 60μm. This value is more than double that of a single path TFT. Such enhancement in mobility is attributed to the high conductivity of ITO and a good conduction band match between a-IGZO and ITO. [Copyright &y& Elsevier]

In this study, a 2 in. Ni field aided lateral crystallization (FALC) polySi thinfilm transistor (TFT) (120 x 240) array was fabricated at the maximum process temperature of 500°C using an optimized current density distribution design. We investigated the correlation between crystallization and transistor characteristics in terms of transistor position in the array. Because an identical current density in the channel region of each pixel transistor was favorable to achieve uniform crystallization, an optimal common electrode design was chosen via Mathcad simulation. After the crystallization process, it was confirmed that the crystallinity variation in the transistor channels agreed well with the predicted simulation results. Furthermore, the positional variation in important transistor parameters in the array showed a good match with that of crystallization. The mean threshold voltage was 5.9 V (ΔVth = ± 0.2 V) while the mean mobility was 92.5 cm2 V1 s1 with a variation of 9.8%. These values suggested that the uniform NiFALC polySi TET arrays fabricated by the optimal design of the electrode were applicable to the active matrix organic light emitting display backplane. [ABSTRACT FROM AUTHOR]

The effects of hydrogen incorporation in the active layer of amorphous InGaZnO (a‐IGZO) thin‐film transistors (TFTs) on device characteristics and instability under positive bias stress (PBS) and positive bias temperature stress (PBTS) are studied. To control the amount of incorporated hydrogen, rapid thermal annealing (RTA) treatment is conducted on the gate insulator layer before active layer deposition. It is confirmed that the amount of residual hydrogen in the gate insulator layer decreases with increasing RTA treatment time. Device stability is examined with RTA treatment times of 1 and 3 min under PBS. The device fabricated with a shorter RTA treatment time shows relatively better stability. This result is attributed to defect passivation by hydrogen that diffuses to the active layer from the gate insulator during the post‐annealing process. Additionally, TFT shows the negative shift of Vth under a high‐temperature PBTS condition. This result is due to the additional diffusion of residual hydrogen from the gate insulator into the active layer and hydrogen‐related deep state transition in the active layer by external thermal energy and a PBS condition. [ABSTRACT FROM AUTHOR]

In recent years, many researchers have attempted to improve the bias stability of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs). In this study, the hydrogen cyanide (HCN) treatment was carried out to improve the positive bias stability of bottom-gate a-IGZO TFTs. The HCN treatment was performed using a 0.1 M HCN solution with a pH of 10 at room temperature. Before applying the positive bias stress, there were no differences in the major electrical properties, including the saturation mobility ( μ sat ), threshold voltage (V th ), and subthreshold swing (S/S), between HCN-treated and non-HCN-treated devices. However, after applying the positive bias stress, the HCN-treated device showed superior bias stability compared to the non-HCN-treated device. This difference is associated with the passivation of the defect states and the surface of the back-channel layer of the HCN-treated device by cyanide ions. [ABSTRACT FROM AUTHOR]

In this investigation, the carrier concentration gradient between channel and contact region is achieved to improve the Thin film Transistors (TFT) performance by employing annealing at 350 °C in forming gas (N 2 + 5% H 2 ). The contact region is covered with Mo metal and the channel region is only exposed to forming gas to facilitate the diffusion controlled reaction. The TFT using a-IGZO active layer is fabricated in ambient of Ar:O 2 in ratio 60:40 and the conductivity of the order of 10 −3 S/cm is measured for as-deposited sample. The electrical conductivity of an annealed sample is of the order of 10 2 S/cm. The device performance is determined by measuring merit factors of TFT. The saturation mobility of magnitude 18.5 cm 2 V −1 s −1 has been determined for W/L (20/10) device at 15 V drain bias. The extrapolated field effect mobility for a device with channel width (W) 10 μm is 19.3 cm 2 V −1 s −1 . The on/off current ratio is 10 9 and threshold voltage is in the range between 2 and 3 V. The role of annealing on the electronic property of a-IGZO is carried out using X-ray photoelectron spectroscopy (XPS). The valance band cut-off has been approximately shifted to higher binding energy by 1 eV relative to as-deposited sample. [ABSTRACT FROM AUTHOR]

Abstract: In this work, Y2O3 was evaluated as a gate insulator for thin film transistors fabricated using an amorphous InGaZnO4 (a-IGZO) active layer. The properties of Y2O3 were examined as a function of various processing parameters including plasma power, chamber gas conditions, and working pressure. The leakage current density for the Y2O3 film prepared under the optimum conditions was observed to be ~3.5×10−9 A/cm2 at an electric field of 1 MV/cm. The RMS roughness of the Y2O3 film was improved from 1.6 nm to 0.8 nm by employing an ALD (Atomic Layer Deposition) HfO2 underlayer. Using the optimized Y2O3 deposition conditions, thin film transistors (TFTs) were fabricated on a glass substrate. The important TFT device parameters of the on/off current ratio, sub-threshold swing, threshold voltage, and electric field mobility were measured to be 7.0×107, 0.18 V/dec, 1.1 V, and 3.3 cm2/Vs, respectively. The stacked insulator consisting of Y2O3/HfO2 was highly effective in enhancing the device properties. [Copyright &y& Elsevier]

Abstract: In this investigation, an operating voltage as low as 5V has been achieved for Oxide TFT with Y2O3 as a gate oxide and a-IGZO as an active layer. The OTFT has been fabricated at room temperature using RF sputter. The mobility and threshold voltages are 11.3cm2/Vs and 3.4V for the device with W/L =0.8, respectively. The annealing at 400°C in N2 containing 5% H2 ambient has been utilized to improve the electrical performance of TFT. The on–off current which is determined by gate dielectric has been observed to be 104. It has also been observed that the dielectric properties of gate oxide deteriorate on annealing. The dielectric constant of Y2O3 is observed in the range between 5.1 and 5.4 measured on various devices. [Copyright &y& Elsevier]

Abstract: In this study, the characteristics of positive bias temperature instability (PBTI) and cyclic constant voltage stress (CVS) in thin film transistors (TFTs) incorporating Ni-FALC poly-Si film were investigated under various stress conditions. In PBTI, the threshold voltage (V TH) was degraded by a vertical electric field on the gate stack, and an abrupt variation of V TH was attributed to the creation of defects in the gate oxide and the increase of the effective interface trap state. In contrast to the formation of defects, the poly-Si film was not sensitive to PBTI stress (the fluctuation in the grain boundary trap density was just 5.6%). In two-cycle CVS of devices before and after O2 plasma treatment, the direction of the V TH shift and polarity of bias showed good correlation. In particular, the O2 plasma-treated device demonstrated low Subthreshold swing (S.S) and low minimum drain current compared to the untreated one. The improvement of device performance seemed to originate from the reduction of effective interface trap sites and leakage current paths. [Copyright &y& Elsevier]