Positive Bias Illumination Stress Research Articles

Effects of Laser Treatment of Terbium-Doped Indium Oxide Thin Films and Transistors.

In this study, a KrF excimer laser with a high-absorption coefficient in metal oxide films and a wavelength of 248 nm was selected for the post-processing of a film and metal oxide thin film transistor (MOTFT). Due to the poor negative bias illumination stress (NBIS) stability of indium gallium zinc oxide thin film transistor (IGZO-TFT) devices, terbium-doped Tb:In2O3 material was selected as the target of this study. The XPS test revealed the presence of both Tb3+ and Tb4+ ions in the Tb:In2O3 film. It was hypothesized that the peak of the laser thermal effect was reduced and the action time was prolonged by the f-f jump of Tb3+ ions and the C-T jump of Tb4+ ions during the laser treatment. Studies related to the treatment of Tb:In2O3 films with different laser energy densities have been carried out. It is shown that as the laser energy density increases, the film density increases, the thickness decreases, the carrier concentration increases, and the optical band gap widens. Terbium has a low electronegativity (1.1 eV) and a high Tb-O dissociation energy (707 kJ/mol), which brings about a large lattice distortion. The Tb:In2O3 films did not show significant crystallization even under laser energy density treatment of up to 250 mJ/cm2. Compared with pure In2O3-TFT, the doping of Tb ions effectively reduces the off-state current (1.16 × 10-11 A vs. 1.66 × 10-12 A), improves the switching current ratio (1.63 × 106 vs. 1.34 × 107) and improves the NBIS stability (ΔVON = -10.4 V vs. 6.4 V) and positive bias illumination stress (PBIS) stability (ΔVON = 8 V vs. 1.6 V).

Electrical instabilities of a-IGZO TFTs under different conditions of bias and illumination stress

Amorphous In-Ga-Zn-O (a-IGZO) thin film transistors (TFTs) have been widely applied in display technologies. An important factor of these devices is the electrical stability to avoid misinterpretations of current or voltage values under different conditions such as: bias stress, recovery time, and illumination. This work presents the effects of ΔVT under positive bias stress, negative bias stress, positive bias illumination stress, negative bias illumination stress (PBS, NBS, PBIS, NBIS), stress recovery, cyclic bias stress, hysteresis, fixed bias, and aging effects. It was found that a full recovery was achieved only under illumination because of the de-trapping effect (PBS) and ionization of oxygen vacancies (NBS). Some tests showed a low ΔVT over time, however, some considerations must be taken to carry out this purpose. Finally, fixed polarization under illumination was shown to find a stable operating region over time showing negligible variations upon aging.

Fabrication and investigation of the electrical performance of nitrogenated bilayer ZnO:N/ZnO thin-film transistors

In this study, a bilayer ZnO:N/ZnO thin-film transistors (TFTs) was designed to improve both the performance and stability of single-layer ZnO TFTs, using the effects of N-treatment on oxygen vacancy (VO) and the interface trap density. Bilayer ZnO:N/ZnO films and related TFTs were fabricated via radiofrequency magnetron sputtering in a mixture of Ar and N2 gas at 150 °C. The electrical performance and bias-stress stability were systematically investigated. The bilayer ZnO:N/ZnO TFT exhibited a linear field-effect mobility of 13.6 cm2/Vs, high current on-to-off ratio (Ion/Ioff) of 1 × 107, small threshold voltage (Vth) of 2.6 V, and low subthreshold swing of 0.32 V/decade compared with single-layer undoped ZnO and ZnO:N TFTs. Moreover, ZnO:N/ZnO TFT exhibited small threshold voltage shifts (∆Vth) of 0.8 and –0.9 V according to positive bias illumination stress and negative bias illumination stress measurements, respectively. X-ray photoelectron spectroscopy analysis showed that the N-treatment passivated the VO defects, reduced the density of interface traps, and controlled the carrier concentration. Thus, the performance and stability of the ZnO:N/ZnO TFTs were improved. Therefore, ZnO:N/ZnO TFTs have good application prospects in transparent thin-film electronics and flat-panel displays.

Optimizing Photonic Annealing Technique for High-k Dielectric of Full-Solution-Processed Oxide Thin Film Transistor

In this article, it is demonstrated that the photonic annealing process of ultraviolet (UV) irradiation or rapid thermal annealing (RTA)-assisted LA technique can effectively enhance the bias and illumination stability of full-solution-processed oxide thin film transistor (TFT). Although both post-annealing treatments have comparable effects, UV irradiation has relatively less heat loss and time consumption of only 3 min, compared to the RTA process that heats at a temperature of 400 °C and holds 10 min. Depending on the laser annealing (LA)/UV technique, the amorphous hafnium-aluminum oxide (HAO) dielectric thin film exhibits a smooth surface with an rms value of 0.293 nm, a high optical bandgap of 6.19 eV, and good dielectric performance with high dielectric constants of 12.9, low leakage current densities, and high breakdown field of about 4 MV/cm. Moreover, full-solution-processed indium-tin-oxide (ITO)–HAO–tungsten-zinc-tin-oxide (WZTO) TFT shows excellent overall properties with the mobility ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> ) of 10.65 cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{{2}}\cdot \text{V}^{-{1}}\cdot \text{s}^{-{1}}$ </tex-math></inline-formula> , subthreshold swing (SS) of 198 mV/dec. And the device has good bias and illumination stability, especially the threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{T}$ </tex-math></inline-formula> ) shifts are all less than 3 V under positive bias illumination stress (PBIS) and negative bias illumination stress (NBIS) testing for 10000 s. These indicate the potential for the photonic annealing process of the UV-assisted LA technique on improving the stability of the full-solution-processed TFTs, which is attributed to high-throughput fabrication for large-area, transparent, and flexible electronics.

Turn-around of threshold voltage shift in amorphous InGaZnO TFT under positive bias illumination stress

Amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) have attracted significant attention in display devices and 3D-stacked dynamic random-access memory (DRAM) devices. They have superior advantages, while they have much remained to be studied such as threshold voltage (VT) instability. We investigated the transfer characteristics of a-IGZO TFTs under positive bias stress (PBS) and positive bias illumination stress (PBIS). The behaviors of VT shift under PBS and PBIS differed due to illumination. The direction of the VT shift depended on the illumination condition (on or off), including the turn-around of the VT shift under PBIS. The two mechanisms of ionized oxygen vacancies and trapped electrons competed, and one mechanism became dominant under PBS and PBIS. The dominant mechanism determined the direction of the VT shift; turn-around occurred if the dominant mechanism changed. In addition, the subthreshold swing and field-effect mobility consistently described the mechanisms using the corresponding energy band diagrams. Understanding the behavior of the VT shift under various stress conditions provides insights into the instability of a-IGZO TFTs.

P‐4.4: Multifunctional Laminated Organic Passivation Layer on InSnZnO Thin‐Film Transistors for Enhanced Reliability

To improve the stability of the ZnO‐based thin‐film transistors (TFTs) in multiple environments, we propose a new multifunctional laminated organic passivation layer (MLO PVL) structure for ITZO TFTs. This MLO PVL structure is composed of a self‐assembled monolayer (SAM) and an ultraviolet (UV) absorber‐modified polydimethylsiloxane (PDMS) layer, which provides the functionality of both passivation layers at the same time. The SAM film could be prepared by vapor‐phase treatment, while the UV‐absorber‐modified PDMS layer could be fabricated using the spin‐coating method. Thus, the MLO PVL could be manufactured through a low‐temperature and low‐cost process. Compared to the unpassivated devices, the MLO‐passivated ITZO TFTs exhibit better properties, such as an on‐off current ratio (Ion/Ioff) of up to 8.99×109, a field‐effect mobility of 19.55 cm2V−1s−1, and a subthreshold swing (SS) down to 100 mV/dec. Furthermore, the MLO‐passivated ITZO TFTs showed an outstanding improvement in the bias stress stability and UV light illumination stress stability with negligible threshold voltage shifts in both positive bias stress (PBS) and positive bias illumination stress (PBIS) tests. This new passivation structure provides a potential strategy for improving the stability of ZnO‐based TFTs.

Investigation on Stability in Solution-Processed In-Zn-Sn-O TFT Array Under Various Intensity of Illumination

The effect of light illumination intensity on the stability of In-Zn-Sn-O (IZTO) thin-film transistors (TFTs) array fabricated by solution processed is investigated. Comparison with positive bias stress, the light illumination suppresses the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> shift under positive bias illumination stress because of the increase in the free electrons induced by the ionized oxygen vacancies in the IZTO channel layer, but transfer characteristics show two-stage degradation under negative bias illumination stress (NBIS). The hump phenomenon is induced after NBIS, and the light illumination intensity is higher, the hump phenomenon becomes more serious. The hump phenomenon is relevant to ionized oxygen vacancies, which act as shallow donor-like states near the conduction-band minimum in IZTO.

Flexible Platform Oriented: Unipolar‐Type Hybrid Dual‐Channel Scalable Field‐Effect Phototransistors Array Based on Tellurium Nanowires and Tellurium‐Film with Highly Linear Photoresponsivity

AbstractHere, a novel method is introduced to synthesize the uniform hybrid structure of tellurium nanowires (TeNWs) and tellurium‐film (Te‐film) for flexible field‐effect transistor (FET) array device to exhibit excellent electrical, mechanical, and optical performance. To fabricate such a device, all the processes are performed at low temperatures (&lt; 100 °C) with easy processing methods. The uniformity of the hybrid structure of TeNWs/Te‐film is confirmed using scanning electron microscopy (SEM) and Raman spectroscopy with a comparison of the bare TeNWs‐film. Electrical properties of the TeNWs/Te‐based FET device exhibits high mobility of 5.35 cm2 V−1 s−1 and on/off ratio of &gt;104 along with stable and uniform results of the transistor array device, which consists of 50 devices. The optical properties show highly linear photodetection behavior in terms of threshold voltage shift, responsivity, sensitivity, photocurrent, detectivity, and time‐domain behavior. Also, the various stability tests are performed to confirm the consistency of the device in terms of positive bias stress, negative bias stress, positive bias illumination stress, long‐term stability response (up to 60 days), mechanical bending stress, and the results reveal a constant and consistent behavior of the device, which can be attributed to enable wide range applications in the field of electronics devices.

Degradation and its fast recovery in a-IGZO thin-film transistors under negative gate bias stress* *Project supported in part by the National Natural Science Foundation of China (Grant Nos. 61971299 and 61974101), the Natural Science Foundation of JiangsuProvince, China (Grant No. SBK2020021406), the Fund from the State Key Laboratory of ASIC and System, Fudan University (Grant No. 2019KF007), theFund from the

A new type of degradation phenomena featured with increased subthreshold swing and threshold voltage after negative gate bias stress (NBS) is observed for amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs), which can recover in a short time. After comparing with the degradation phenomena under negative bias illumination stress (NBIS), positive bias stress (PBS), and positive bias illumination stress (PBIS), degradation mechanisms under NBS is proposed to be the generation of singly charged oxygen vacancies () in addition to the commonly reported doubly charged oxygen vacancies (). Furthermore, the NBS degradation phenomena can only be observed when the transfer curves after NBS are measured from the negative gate bias to the positive gate bias direction due to the fast recovery of under positive gate bias. The proposed degradation mechanisms are verified by TCAD simulation.

Performance Enhancement of Transparent Amorphous IGZO Thin-Film Transistor Realized by Sputtered Amorphous AlOx Passivation Layer

We report a high-mobility transparent Indium-Gallium-Zinc-Oxide (IGZO) thin-film transistor (TFT) with sputtered AlOx passivation layer. The interfacial region between the IGZO layer and the AlOx layer played a crucial role in improving the field-effect mobility (the maximum field-effect mobility increased from 6.292 cm2 Vs−1 for the TFT without the AlOx layer to 69.01 cm2 Vs−1 for the TFT with the passivation layer) and the on/off current ratio (from ∼107 without the layer to ∼108 with the layer). The driving current of IGZO TFT was also significantly enhanced. The formation of the interfacial layer has been investigated and verified. The ion bombardment during the AlOx deposition broke the In-O bond in IGZO, generating oxygen ions (O2−). The segregation of the O2− was facilitated by the sputtered amorphous AlOx. A metallic In-rich layer with high oxygen vacancy concentration was formed at the interface, leading to an increase in the carrier concentration in the interfacial layer. Besides the electrical performance, the reliability tests, including long-term exposure in the ambient environment and positive bias illumination stress (PBIS), showed improved results as well.

Conduction band offset-dependent induced threshold voltage shifts in a-InGaZnO TFTs under positive bias illumination stress

In this paper, the dependence of threshold voltage (Vth) changes to amorphous-indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) under positive bias light illumination (PBIS) on the height of the conduction band offset was studied. Using SiO2, HfO2, and Al2O3 as gate dielectrics, three different types of a-IGZO TFTs were used in the experiment. Electrical parameters and the density of states of each TFT were measured. Of the devices studied, the interface characteristics between the a-IGZO and the gate dielectric were the best using SiO2 and the worst using Al2O3. HfO2 had the smallest conduction band offsets (CBO) of 2.26 eV. We also performed PBS and PBIS evaluation to confirm the stability of TFTs. The Vth shift in the three samples was insignificant under PBS, but the Vth shifts occurred under PBIS in the order of HfO2, Al2O3, and SiO2. The interfacial characteristics of a-IGZO and the dielectric did not change after PBIS in all three devices; the lower the CBO height, the greater the Vth shift after PBIS. The predominant cause of the Vth shift under PBIS is the accumulation of injected photoelectrons that have sufficient energy to tunnel the CBO barrier into the gate dielectric by positive gate bias.

A Unified Degradation Model of Elevated-Metal Metal Oxide (EMMO) TFTs Under Positive Gate Bias With or Without an Illumination

Degradations of elevated-metal metal oxide (EMMO) thin-film transistors (TFTs) under positive bias stress (PBS) and positive bias illumination stress (PBIS) are systematically investigated and compared. An intrinsic correlation between PBS and PBIS degradation is demonstrated. Continuous negative threshold voltage ( ${V}_{\text {th}}$ ) shift is observed under both stresses, with similar time-dependent $V_{\text {th}}$ shift and recovery behavior. Characterization parameters for dependencies of ${V}_{\text {th}}$ shift on both stress ${V}_{G}$ and temperature are also very close for the two degradations. PBS and PBIS degradation of EMMO TFTs and their correlation can be consistently understood based on a unified model, which emphasizes stress-induced accumulation of doubly-ionized ${V}_{O}$ traps at the back-channel interface, and is verified with simulation.

Effective encapsulation of ZnO thin film transistors controlled by thermal energy

Passivation still remains a challenging issue for the oxide-based thin film transistors because it requires thermal treatments at elevated temperatures to recover the original transistor characteristics. Particularly, the threshold voltage encounters a strong reduction due to the extraction of oxygen from the channel layers. This work demonstrates an effective way to reduce the reaction between the metal-organic precursor and the oxygen from the channel layers based on the bond-energy of the Al-O (569 kJ/mol) that is higher than Zn-O (250 kJ/mol). Reducing the growth temperatures of the passivation layers (PVLs) in the conventional process of thermal atomic layer deposition (ALD) leaves the performance of the thin film transistors (TFTs) only slightly varied but within an acceptable range. Among all devices, the TFTs with Al2O3 PVLs deposited at 100 °C by using H2O as oxidant remain a high mobility of 31.2 ± 0.4 cm2 V−1 s−1, a proper threshold voltage of 1.05 ± 0.04 V, a low subthreshold swing 0.17 ± 0.03 V/dec as well as an excellent stability with a small threshold voltage shift of 0.19, −0.03 and −0.12 V under positive bias stress, illumination bias stress and positive bias illumination stress, respectively. This improved stabilities are attributed to the presence of the high-quality PVLs that protect the channels from environmental effects.

Improving the Stability of High-Performance Multilayer MoS2 Field-Effect Transistors.

In this study, we propose a method for improving the stability of multilayer MoS2 field-effect transistors (FETs) by O2 plasma treatment and Al2O3 passivation while sustaining the high performance of bulk MoS2 FET. The MoS2 FETs were exposed to O2 plasma for 30 s before Al2O3 encapsulation to achieve a relatively small hysteresis and high electrical performance. A MoOx layer formed during the plasma treatment was found between MoS2 and the top passivation layer. The MoOx interlayer prevents the generation of excess electron carriers in the channel, owing to Al2O3 passivation, thereby minimizing the shift in the threshold voltage (Vth) and increase of the off-current leakage. However, prolonged exposure of the MoS2 surface to O2 plasma (90 and 120 s) was found to introduce excess oxygen into the MoOx interlayer, leading to more pronounced hysteresis and a high off-current. The stable MoS2 FETs were also subjected to gate-bias stress tests under different conditions. The MoS2 transistors exhibited negligible decline in performance under positive bias stress, positive bias illumination stress, and negative bias stress, but large negative shifts in Vth were observed under negative bias illumination stress, which is attributed to the presence of sulfur vacancies. This simple approach can be applied to other transition metal dichalcogenide materials to understand their FET properties and reliability, and the resulting high-performance hysteresis-free MoS2 transistors are expected to open up new opportunities for the development of sophisticated electronic applications.

Bias and illumination instability analysis of solution-processed a-InGaZnO thin-film transistors with different component ratios

We investigated the effect of In and Zn component ratios on an amorphous indium‑gallium‑zinc-oxide (a-IGZO) layer in oxide thin-film transistors (TFTs). Different types of stress including negative bias, positive bias, negative bias illumination stress, positive bias illumination stress, and instability of a-IGZO TFTs were compared. Owing to the difference in the composition ratio of In:Ga:Zn (5:1:4, 6:1:3, 7:1:2), the respective devices had threshold voltages of 7, 5, and 4.5V. The high content of In in a-IGZO leads to a higher concentration of oxygen vacancy, which results in sensitivity toward illumination stress. The above results indicate that the threshold voltage shift is primarily due to the trapping of electrons in the traps located in the interfaces or dielectric layers. We analyzed the IGZO thin film properties using UV–visible, X-ray diffraction, and X-ray photoelectron spectroscopy measurements.

Effect of Al2O3 passivation layer on the stability of aluminum-indium-zinc oxide thin film transistors

This study investigated the effect of an Al2O3 passivation layer on the stability of radio-frequency magnetron cosputtered aluminum-indium-zinc oxide (Al-IZO) thin-film transistors (TFTs) under positive bias stress, positive bias illumination stress, negative bias illumination stress, and constant current stress. In current devices, threshold-voltage (Vth) instability is dominated by the photo-generated hole/electron trapping at a back-channel surface and/or interface between an insulator and a channel, and the deep defects (subgap states) located near the valence band can easily cause a subgap photoexcitation, resulting in a large Vth shift. In this study, experimental results show that Al2O3-passivated Al-IZO TFTs exhibit stable electrical behaviors under each stress condition (ΔVth &amp;lt; 1.7 V), whereas the unpassivated Al-IZO TFTs exhibit obvious shifts in threshold voltage (ΔVth &amp;lt; 10.50 V). In this study, the authors demonstrated that Al2O3 could be an effective passivation layer to suppress O2 absorption/desorption on the Al-IZO back-channel and decrease photo-excitation on Al-IZO films.

Analysis of the Short-Term Response in the Drain Current of a-IGZO TFT to Light Pulses

In this letter, the response in the drain current ( $\text{I}_\text{D})$ of the amorphous indium–gallium–zinc oxide thin-film transistors under positive-bias illumination stress is measured with respect to time in less than 5 s under light pulses with altering frequencies and duty ratios. The curves of $\text{I}_\text{D}$ under the light pulses are affected by the different defect-reacting rates under illumination and in the dark. By taking the derivative of $\text{I}_\text{D}$ , the trend of the change in the number of defects becomes clear. The total behavior of $\text{I}_\text{D}$ in response to light pulses can be fairly predicted by the integral of the derivative terms with a correction factor of charge trapping.

The effect of ITO and Mo electrodes on the properties and stability of In-Ga-Zn-O thin film transistors

The effect of ITO and Mo electrodes on the electrical properties and stability of In-Ga-Zn-O (IGZO) thin film transistors (TFTs) are investigated. While the field effect mobility values of the devices employing ITO and Mo electrodes are similar, the former exhibit smaller threshold voltage (Vth) and subthreshold swing (SS). It is suggested that the relatively large workfunction of Mo (4.7 eV) compared to that of ITO (4.4 ~ 4.5 eV) induces a large Schottky barrier at the Mo/IGZO junction, which prohibits the effective injection of electrons from the metal into the IGZO semiconductor. The workfunction of IGZO is usually reported to be approximately 4.5 eV. The device stability of the two types of TFTs under negative bias stress (NBS) and positive bias stress (PBS) is similar, which implies that the degradation of the devices under bias stress is mainly affected by the trapping of carriers at the IGZO/gate insulator interface. In the presence of illumination, the devices using optically transparent ITO electrodes allow the penetration of a more abundant concentration of photons into the IGZO active layer, and thus undergo larger Vth shifts under negative bias illumination stress (NBIS). However, under positive bias illumination stress (PBIS), the TFTs using ITO exhibit smaller positive Vth shifts. The latter phenomenon is suggested to result from the excess photo-induced electrons in the bulk that counter the effect of electron trapping near the IGZO/gate insulator boundary.

Role of oxygen vacancies on the bias illumination stress stability of solution-processed zinc tin oxide thin film transistors

Solution-processed ultra-thin (∼3 nm) zinc tin oxide (ZTO) thin film transistors (TFTs) with a mobility of 8 cm2/Vs are obtained with post spin-coating annealing at only 350 °C. The effect of light illumination (at wavelengths of 405 nm or 532 nm) on the stability of TFT transfer characteristics under various gate bias stress conditions (zero, positive, and negative) is investigated. It is found that the ΔVth (Vthstress 3400 s − stress 0 s) window is significantly positive when ZTO TFTs are under positive bias stress (PBS, ΔVth = 9.98 V) and positive bias illumination stress (λ = 405 nm and ΔVth = 6.96 V), but ΔVth is slightly negative under only light illumination stress (λ = 405 nm and ΔVth = −2.02 V) or negative bias stress (ΔVth = −2.27 V). However, the ΔVth of ZTO TFT under negative bias illumination stress is substantial, and it will efficiently recover the ΔVth caused by PBS. The result is attributed to the photo-ionization and subsequent transition of electronic states of oxygen vacancies (i.e., Vo, Vo+, and Vo++) in ZTO. A detailed mechanism is discussed to better understand the bias stress stability of solution processed ZTO TFTs.

Improvements in the bias illumination stability of amorphous InGaZnO thin-film transistors by using thermal treatments

The a-IGZO deposited by using the rf sputtering method features a conductive or an insulator characteristic based on amount of oxygen. We demonstrated that a post-treatment affects the resistance patterns of particular-sized InGaZnO(IGZO) thin films in a-IGZO thin-film transistors (TFTs). Post-annealing shifted the driving voltage of a-IGZO TFT to positive or negative values, depending on the annealing temperatures. Post-annealing may introduce oxygen vacancies or desorbed oxygen in the IGZO thin film. The changed driving voltage of IGZO TFTs coincides with the shift of the resistance pattern of IGZO. The fabricated a-IGZO TFTs exhibited a field effect mobility of 6.2 cm2/Vs, an excellent subthreshold gate swing of 0.32 V/decade, and a high I on/off ratio of > 109. Under positive bias illumination stress (PBIS) and negative bias illumination stress (NBIS), after 3,600 seconds, the device threshold voltage shifted about 0.2 V and 0.3 V, respectively.