Positive Bias Stress Stability Research Articles

Thermal Dehydrogenation Impact on Positive Bias Stability of Amorphous InSnZnO Thin-Film Transistors.

Recently, the growing demand for amorphous oxide semiconductor thin-film transistors (AOS TFTs) with high mobility and good stability to implement ultrahigh-resolution displays has made tracking the role of hydrogen in oxide semiconductor films increasingly important. Hydrogen is an essential element that contributes significantly to the field effect mobility and bias stability characteristics of AOS TFTs. However, because hydrogen is the lightest atom and has high reactivity to metal and oxide materials, elucidating its impact on AOS thin films has been challenging. Therefore, in this study, we propose controlling the hydrogen quantities in amorphous InSnZnO (a-ITZO) thin films through thermal dehydrogenation to precisely reveal the hydrogen influences on the electrical characteristics of a-ITZO TFTs. The as-deposited device containing 15.69 × 1015 atoms/cm2 of hydrogen exhibited a relatively low saturation mobility of 18.1 cm2/V·s and poor positive bias stress stability. However, depending on the extent of thermal dehydrogenation, not only did the hydrogen quantity and interface defect density (DIT) decrease but also the conductivity and surface energy increased due to the rise in oxygen vacancies and hydroxyl groups in a-ITZO thin films. As a result, the a-ITZO TFT with a hydrogen amount of 4.828 × 1015 atoms/cm2 showed that the saturation mobility improved up to 36.8 cm2/V·s, and positive bias stress stability was remarkably enhanced. Hence, we report the ability to manage the hydrogen quantity with thermal dehydrogenation and demonstrate that high-performance a-ITZO TFTs can be realized when an appropriate hydrogen concentration is achieved.

Mechanically Durable Organic/High-k Inorganic Hybrid Gate Dielectrics Enabled by Plasma-Polymerization of PTFE for Flexible Electronics.

To achieve both the synergistic advantages of outstanding flexibility in organic dielectrics and remarkable dielectric/insulating properties in inorganic dielectrics, a plasma-polymerized hafnium oxide (HfOx) hybrid (PPH-hybrid) dielectric is proposed. Using a radio-frequency magnetron cosputtering process, the high-k HfOx dielectric is plasma-polymerized with polytetrafluoroethylene (PTFE), which is a flexible, thermally stable, and hydrophobic fluoropolymer dielectric. The PPH-hybrid dielectric with a high dielectric constant of 14.17 exhibits excellent flexibility, maintaining a leakage current density of ∼10-8 A/cm2 even after repetitive bending stress (up to 10000 bending cycles with a radius of 2 mm), whereas the HfOx dielectric degrades to be leaky. To evaluate its practical applicability to flexible thin-film transistors (TFTs), the PPH-hybrid dielectric is applied to amorphous indium-gallium-zinc oxide (IGZO) TFTs as a gate dielectric. Consequently, the PPH-hybrid dielectric-based IGZO TFTs exhibit stable electrical performance under the same harsh bending cycles: a field-effect mobility of 16.99 cm2/(V s), an on/off current ratio of 1.15 × 108, a subthreshold swing of 0.35 V/dec, and a threshold voltage of 0.96 V (averaged in nine devices). Moreover, the PPH-hybrid dielectric-based IGZO TFTs exhibit a reduced I-V hysteresis and an enhanced positive bias stress stability, with the threshold voltage shift decreasing from 4.99 to 1.74 V, due to fluorine incorporation. These results demonstrate that PTFE improves both the mechanical durability and electrical stability, indicating that the PPH-hybrid dielectric is a promising candidate for high-performance and low-power flexible electronics.

Mg-doped InSnO nanofiber field-effect transistor for methanol gas detection at room temperature

Research on high-performance gas sensors for detecting toxic and harmful methanol gas is still a very important issue. For gas sensors, it is very important to be able to achieve low concentration detection at room temperature. In this work, we used the electrospinning method to prepare Mg-doped InSnO nanofiber field-effect transistors (FETs) methanol gas sensor. When the Mg element doping concentration is 2.3 mol.%, InSnO nanofiber FET exhibits excellent electrical properties, including higher mobility of 3.17 cm2 V−1 s−1, threshold voltage of 1.51 V, subthreshold swing of 0.42 V/decade, the excellent on/off current ratio is about 108 and the positive bias stress stability of the InSnO nanofiber FET through Mg doping has been greatly improved. In addition, the InSnMgO nanofiber FET gas sensor exhibits acceptable gas selectivity and sensitivity to methanol gas at room temperature. In the methanol gas sensor test at room temperature, when the methanol gas concentration is 60 ppm at room temperature, the response value of the InSnMgO nanofiber FET gas sensor is 81.92; and when the methanol concentration is 5 ppm, the response value is still 1.21. This work provides an effective and novel way to build a gas sensor at room temperature and use it to detect methanol gas at room temperature.

Atmosphere Effect in Post-Annealing Treatments for Amorphous InGaZnO Thin-Film Transistors with SiOx Passivation Layers.

We investigated the electrical performance and positive bias stress (PBS) stability of the amorphous InGaZnO thin-film transistors (a-IGZO TFTs) with SiOx passivation layers after the post-annealing treatments in different atmospheres (air, N2, O2 and vacuum). Both the chamber atmospheres and the device passivation layers proved important for the post-annealing effects on a-IGZO TFTs. For the heat treatments in O2 or air, the larger threshold voltage (VTH) and off current (IOFF), smaller field-effect mobility (μFE), and slightly better PBS stability of a-IGZO TFTs were obtained. The X-ray photoemission spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) measurement results indicated that the oxygen atoms from the ambience led to less oxygen vacancies (VO) and more oxygen-related defects in a-IGZO after the heat treatments in O2 or air. For the annealing processes in vacuum or N2, the electrical performance of the a-IGZO TFTs showed nearly no change, but their PBS stability evidently improved. After 4500 seconds’ stressing at 40 V, the VTH shift decreased to nearly 1 V. In this situation, the SiOx passivation layers were assumed to effectively prevent the oxygen diffusion, keep the VO concentration unchanged and refuse the oxygen-related defects into the a-IGZO films.

Effects of Channel Thickness on Electrical Performance and Stability of High-Performance InSnO Thin-Film Transistors

InSnO (ITO) thin-film transistors (TFTs) attract much attention in fields of displays and low-cost integrated circuits (IC). In the present work, we demonstrate the high-performance, robust ITO TFTs that fabricated at process temperature no higher than 100 °C. The influences of channel thickness (tITO, respectively, 6, 9, 12, and 15 nm) on device performance and positive bias stress (PBS) stability of the ITO TFTs are examined. We found that content of oxygen defects positively correlates with tITO, leading to increases of both trap states as well as carrier concentration and synthetically determining electrical properties of the ITO TFTs. Interestingly, the ITO TFTs with a tITO of 9 nm exhibit the best performance and PBS stability, and typical electrical properties include a field-effect mobility (µFE) of 37.69 cm2/Vs, a Von of −2.3 V, a SS of 167.49 mV/decade, and an on–off current ratio over 107. This work paves the way for practical application of the ITO TFTs.

Effects of Oxygen Content on Operational Characteristics and Stability of High-Mobility IGTO Thin-Film Transistors during Channel Layer Deposition

In this study, we investigated the effects of oxygen content on the transfer characteristics and stability of high-mobility indium-gallium-tin oxide (IGTO) thin-film transistors (TFTs) during channel layer deposition. The IGTO thin films were deposited through direct current sputtering at different ambient oxygen percentages of 10%, 20%, 30%, 40%, and 50%. The experimental results indicate that the drain currents were hardly modulated by the gate-to-source voltage in the IGTO TFT prepared at 10% ambient oxygen. However, as the oxygen content increased from 20% to 50%, the transfer curves shifted to the positive direction with a decrease in field-effect mobility (μFE). The IGTO TFTs exhibited deteriorated positive bias stress (PBS) stability as the oxygen content increased. However, the stabilities of the IGTO TFTs under negative bias illumination stress (NBIS) improved with an increase in the ambient oxygen percentage during the channel layer deposition. Furthermore, to understand the mechanism of the observed phenomena, we performed X-ray photoelectron spectroscopy (XPS) analysis of the IGTO thin films prepared at different oxygen percentages. The XPS results demonstrate that the deteriorated PBS stability and enhanced NBIS stability of the IGTO TFTs prepared at higher oxygen percentages were mainly ascribed to the larger amount of oxygen interstitials resulting from the excess oxygen and the smaller number of oxygen vacancies within the IGTO, respectively. The obtained results suggest that the oxygen percentages of 30% in the sputtering ambient is the most suitable oxygen percentage for optimizing the electrical properties (μFE = 24.2 cm2/V·s, subthreshold swing = 0.43 V/dec, and threshold voltage = −2.2 V) and adequate PBS and NBIS stabilities of IGTO TFTs.

Effects of Active Layer Thickness on the Electrical Characteristics and Stability of High-Mobility Amorphous Indium–Gallium–Tin Oxide Thin-Film Transistors

Herein, we investigated the effects of active layer thickness (tS) on the electrical characteristics and stability of high-mobility indium–gallium–tin oxide (IGTO) thin-film transistors (TFTs). IGTO TFTs, with tS values of 7 nm, 15 nm, 25 nm, 35 nm, and 50 nm, were prepared for this analysis. The drain current was only slightly modulated by the gate-to-source voltage, in the case of the IGTO TFT with tS = 50 nm. Under positive bias stress (PBS), the electrical stability of the IGTO TFTs with a tS less than 35 nm improved as the tS increased. However, the negative bias illumination stress (NBIS) stability of these IGTO TFTs deteriorated as the tS increased. To explain these phenomena, we compared the O1s spectra of IGTO thin films with different tS values, acquired using X-ray photoelectron spectroscopy. The characterization results revealed that the better PBS stability, and the low NBIS stability, of the IGTO TFTs with thicker active layers were mainly due to a decrease in the number of hydroxyl groups and an increase in the number of oxygen vacancies in the IGTO thin films with an increase in tS, respectively. Among the IGTO TFTs with different tS, the IGTO TFT with a 15-nm thick active layer exhibited the best electrical characteristics with a field-effect mobility (µFE) of 26.5 cm2/V·s, a subthreshold swing (SS) of 0.16 V/dec, and a threshold voltage (VTH) of 0.3 V. Moreover, the device exhibited robust stability under PBS (ΔVTH = 0.9 V) and NBIS (ΔVTH = −1.87 V).

The effect of the dielectric end groups on the positive bias stress stability of N2200 organic field effect transistors

Bias stress degradation in conjugated polymer field-effect transistors is a fundamental problem in these disordered materials and can be traced back to interactions of the material with environmental species,1,2,3 as well as fabrication-induced defects.4,5 However, the effect of the end groups of the polymer gate dielectric and the associated dipole-induced disorder on bias stress stability has not been studied so far in high-performing n-type materials, such as N2200.6,7 In this work, the performance metrics of N2200 transistors are examined with respect to dielectrics with different end groups (Cytop-M and Cytop-S8). We hypothesize that the polar end groups would lead to increased dipole-induced disorder, and worse performance.1,9,10 The long-time annealing scheme at lower temperatures used in the paper is assumed to lead to better crystallization by allowing the crystalline domains to reorganize in the presence of the solvent.11 It is hypothesized that the higher crystallinity could narrow down the range at which energy carriers are induced and thus decrease the gate dependence of the mobility. The results show that the dielectric end groups do not influence the bias stress stability of N2200 transistors. However, long annealing times result in a dramatic improvement in bias stress stability, with the most stable devices having a mobility that is only weakly dependent on or independent of gate voltage.

Effects of 5 MeV Proton Irradiation on Nitrided SiO2/4H-SiC MOS Capacitors and the Related Mechanisms.

In this paper the effects of 5 MeV proton irradiation on nitrided SiO2/4H-SiC metal–oxide–semiconductor (MOS) capacitors are studied in detail and the related mechanisms are revealed. The density of interface states (Dit) is increased with the irradiation doses, and the annealing response suggests that the worse of Dit is mainly caused by displacement effect of proton irradiation. However, the X-rays photoelectron spectroscopy (XPS) measurement shows that the quantity proportion of breaking of Si≡N induced by displacement is only 8%, which means that the numbers of near interface electron traps (NIETs) and near interface hole traps (NIHTs) are not significantly changed by the displacement effect. The measurements of bidirectional high frequency (HF) C-V characteristics and positive bias stress stability show that the number of un-trapped NIETs and oxide electron traps decreased with increasing irradiation doses because they are filled by electrons resulted from the ionization effect of proton irradiation, benefiting to the field effective mobility (μFE) and threshold voltage stability of metal–oxide–semiconductor field-effect transistors (MOSFETs). The obviously negative shift of flat-band voltage (VFB) resulted from the dominant NIHTs induced by nitrogen passivation capture more holes produced by ionization effect, which has been revealed by the experimental samples with different nitrogen content under same irradiation dose.

ZnO bilayer thin film transistors using H2O and O3 as oxidants by atomic layer deposition

This work demonstrates a novel design of thin film transistors composed of a bilayer structure of ZnO thin films (O3 as oxidant/H2O as oxidant) prepared by atomic layer deposition. Based on this structure, a large ION/IOFF ratio of 108 at VDS = 0.1 V, a high field-effect mobility of 31.1 ± 0.26 cm2 V−1 s−1, a low threshold voltage of 0.14 ± 0.07 V and a proper subthreshold swing of 0.21 ± 0.02 V/decade as well as an excellent positive bias stress stability have been obtained. The improved performance of the bilayer structured devices is attributed to the first channel layer of ZnO (H2O as oxidant) decreasing the interfacial trap density and providing high mobility, and the second channel layer of ZnO (O3 as oxidant) suppressing the off-state current as well as a newly formed sub-channel at the interface between the two channel layers.

Positive Bias-Stress Stability of Flexible Amorphous InGaZnO Thin Film Transistors with Double-Stacked Gate Insulators

Positive Bias-Stress Stability of Flexible Amorphous InGaZnO Thin Film Transistors with Double-Stacked Gate Insulators

Positive Bias-Stress Stability of Flexible Amorphous InGaZnO Thin Film Transistors with Double-Stacked Gate Insulators

Positive Bias-Stress Stability of Flexible Amorphous InGaZnO Thin Film Transistors with Double-Stacked Gate Insulators

Solution Processed AlInO/In2O3 Heterostructure Channel Thin Film Transistor with Enhanced Performance

AbstractThin film transistors (TFTs) with solution processed AlInO/In2O3 heterostructure channels are demonstrated with enhanced performance. TFTs with single AlInO channels with various Al concentrations are used for comparison. Appropriate concentrations of Al in AlInO single layer can slightly improve the TFT performance. For the AlInO layer with Al concentration higher than 20%, the resistance is so large that no typical transfer characteristics are observed. In contrast, the overall performances are greatly improved using the AlInO/In2O3 heterostructure channel. High field effect mobility is achieved greater than 40 cm2 V−1 s−1 with a sub threshold slope of 0.7 V decade−1 and on/off ratio of 107 from the heterostructure TFT with a AlInO (30%) top layer. The mobility is affected by the tunnel contact series resistance, which can be modulated by the thickness of the AlInO layer. The enhanced field effect mobility is attributed to the formation of 2D electron gas confined at the AlInO/In2O3 interface, which results in a bulk accumulation effect. Finally, improved positive bias stress stability is obtained by inducing the AlInO top layer with a strong AlO bond. The as investigated results show a very promising future for oxide thin film transistor performance enhancements via heterostructure engineering.

Collaborative optimization of thermal budget annealing and active layer defect content enhancing electrical characteristics and bias stress stability in InGaZnO thin-film transistors

The impact of thermal treatment temperature on the density of oxygen-related defects in the lattice of amorphous InGaZnO is investigated. X-ray photoelectron spectroscopy results state that the oxygen-deficient defects are remarkably reduced and the quality of a-IGZO film is effectively improved after annealing under the appropriate temperature of 350 °C. With the help of synergistic effect of proper treatment temperature and high quality IGZO layer, the IGZO thin-film transistor exhibits outstanding electrical properties, including a field effect mobility of 8.70 cm2 V−1 s−1, a threshold voltage of 1.81 V, a subthreshold swing of 307 mV/dec., and a small hysteresis of 0.32 V. Moreover, the transmission line model clarifies that the suitable heating temperature is beneficial to alleviate the source/drain contact resistance as well as the effective channel length loss. More notably, the positive bias stress stability of a-IGZO TFTs is simultaneously improved.

ZnO Bilayer Thin Film Transistors Using H 2O and O 3 as Oxidants by Atomic Layer Deposition

This work demonstrates a novel design of thin film transistors composed of a bilayer structure of ZnO thin films (O3 as oxidant/H2O as oxidant) prepared by atomic layer deposition. Based on this structure, a large ION/IOFF ratio of 108 at VDS = 0.1 V, a high filed-effect mobility of 30.8 cm2 V-1s-1, a low threshold voltage of 0.05 V and a proper subthreshold swing of 0.24 V/decade as well as an excellent positive bias stress stability have been obtained. The improved performance of the bilayer structured devices is attributed to the first channel layer of ZnO (H2O as oxidant) decreasing the interfacial trap density and providing high mobility, and the second channel layer of ZnO (O3 as oxidant) suppressing the off-state current as well as a newly formed sub-channel at the interface between the the two channel layers.

Nb Doped TiO2Protected Back-Channel-Etched Amorphous InGaZnO Thin Film Transistors

A new back-channel-etched process for the fabrication of amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) is demonstrated, in which a conductive Nb doped TiO 2 (TNO) thin film is used to serve as protective layer for the a-IGZO active layer. It is shown that the TNO film provides the active layer with excellent protection even when the thickness is only 1 nm. With treatment by N 2 O plasma +200°C annealing, the conductive TNO can be converted into an insulator to serve as an in situ passivation layer. Besides, by the introduction of the TNO layer, the source-drain parasitic resistance of the BCE process fabricated TFTs is significantly reduced and the positive bias stress stability is improved as well.

Investigating Effect of Postannealing Time on Positive Bias Stress Stability of In–Ga–Zn–O TFT by Conductance Method

The conductance method was used to investigate the positive bias stress (PBS) degradation mechanism of In–Ga–Zn–O (IGZO) thin-film transistor (TFT). The effects of postannealing time on the PBS degradation mechanism were investigated. The stabilization of the donorlike interface defects was found to be the reason for the threshold voltage instability in the IGZO-TFT under the PBS test. The donorlike defects at the front channel interface and in the plasma-enhanced chemical vapor deposition (PE-CVD) SiO x acted as the electron trapping centers. The electron trapping resistance of the PE-CVD SiO x was improved by increasing the postannealing time, resulting in an improvement in the PBS stability. However, long-time postannealing-induced creation of the deep acceptorlike interface defects in the TFT under the PBS. The energy distribution of the created deep acceptorlike interface defects was revealed using the conductance measurement.

P‐153L: Late‐News Poster: Interface Location Controlled Dual Stacked Solution‐Processed In‐Ga‐Zn‐O Thin Film Transistors for Improved Electrical Performances

Indium gallium zinc oxide (IGZO) thin‐film transistors (TFTs) with dual stacked active layers of different molarities are fabricated to improve their electrical performances. By controlling the molarities, the IGZO TFTs exhibit an enhanced field‐effect mobility and positive bias stress stability.

P‐25: Enhancement in Positive Bias Stress Stability of In‐Ga‐Zn‐O Thin‐Film Transistors with Vertically Graded‐Oxygen‐Vacancy Active Layer

To enhance the bias stability of amorphous indium gallium zinc oxide (a‐IGZO) thin‐film transistors (TFTs), we proposed a simple method to deposit the vertically graded‐oxygen‐vacancy active layer (VGA). The oxygen partial pressure was varied during deposition in order to fabricate VGA TFTs using sputtering. By adopting this method, we could control the concentration of oxygen vacancy in active layer according to the depth. The threshold voltage shift of optimized VGA TFTs was drastically improved under positive bias stress (PBS) condition compared with conventional ones.

P‐155L: Late‐News Poster: Low Temperature Activation of In‐Ga‐Zn‐O Thin Film Transistor using High Pressure Annealing

We investigated the effects of high‐pressure annealing as a source of activation energy to form the amorphous indium gallium zinc oxide (a‐IGZO) channel layer at 100°C. Thermal activation under oxygen pressure was used to facilitate the formation of channel layer as well as to improve positive bias stress stability.