InGaZnO Thin-film Transistors Research Articles

Rational Design of Different Ga Content Bilayer InGaZnO Thin-Film Transistors With Al₂O₃/HfO₂ Passivation Layer

Rational Design of Different Ga Content Bilayer InGaZnO Thin-Film Transistors With Al₂O₃/HfO₂ Passivation Layer

Enhancing Reliability of Short-Channel Dual Gate InGaZnO Thin Film Transistors by Bottom-Gate Oxide Engineering

Enhancing Reliability of Short-Channel Dual Gate InGaZnO Thin Film Transistors by Bottom-Gate Oxide Engineering

Influence of RF power in the sputter deposition of amorphous InGaZnO film on the transient drain current of amorphous InGaZnO thin-film transistors

The device electrical and transient current characteristics of the amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) are comprehensively investigated according to the radio-frequency (RF) power during the sputter-deposition of IGZO active film. The RF power dependencies of the oxygen vacancy (VO) concentration in IGZO and the surface morphology of IGZO film are analyzed through X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). According to the RF power change in the range of 100 ∼ 250 W, the optimal point in terms of threshold voltage (VT), ON current (Ion), field-effect mobility in the linear region (μFE_lin), hysteresis voltage (VHys), and the VT shift under current stress (ΔVT) is found to be 200 W. The existence of the optimal power condition originates from the RF-power dependencies of the electron carrier concentration, the density of electron traps in gate insulator (GI), and the interface trap density related to surface roughness.Furthermore, compared to the direct current (DC) current stress (CS) condition, it is found that when VGS rises rapidly, a total transient current ΔID can be decomposed into three components, i.e., ΔIOS, ΔIBOOST, ΔIDEG. While ΔIOS is attributed to the non-quasi static Fermi-level rising, ΔIBOOST and ΔIDEG result from the donor creation in IGZO and the electron trapping into GI and interface. Noticeably, the occurrence level of each component changes sensitively according to RF power.Our result suggests that the 200 W device has the least overshoot of transient current and shows the best reliability in terms of deterioration due to transient current characteristics.

Output breakdown characteristics of amorphous InGaZnO thin-film transistors at high gate voltage

Output characteristics of top-gate amorphous InGaZnO thin-film transistors are investigated at high gate voltage. With the increasing drain voltage, an output breakdown crops up closely following a drastic uprush of drain current. Such dramatically elevated drain current derives from the self-heating (SH) effect-generated channel donors. Measured at different high gate voltages, the output breakdown occurs in either linear or saturation regime, respectively, corresponding to normally-on and normally-off transfer curve, while the SH-triggering powers are almost identical. The conductor-like channel originates from the SH-induced high donor population, while the disconnection between channel and drain is caused by a highly defective region near drain, where the hot-carrier damage is violently activated by the SH-induced high temperature and the high drain electric field in saturation regime.

Control of Interfacial Defect States in the Flexible InGaZnO Thin Film Transistor with a 6FDA-MDA Gate Insulator by Using an Al2O3 Interlayer

Control of Interfacial Defect States in the Flexible InGaZnO Thin Film Transistor with a 6FDA-MDA Gate Insulator by Using an Al₂O₃ Interlayer

Bi-directional threshold voltage shift of amorphous InGaZnO thin film transistors under alternating bias stress

Amorphous InGaZnO (a-IGZO) has attracted a lot of attention as a high-mobility channel material for thin film transistors (TFTs). However, the instability mechanism involving threshold voltage and subthreshold swing (SS) in a-IGZO TFTs still requires further investigation. In this study, we investigated the electrical instability of amorphous InGaZnO TFTs subjected to alternating positive and negative bias stresses. Based on the respective mechanisms under positive and negative bias stresses, including ionization and spatial movement of oxygen vacancies, bi-directional threshold voltage shifts were observed under alternating bias stress. The SS values vary with the bias stress polarity, reflecting the presence and distribution of oxygen vacancies. Our findings reveal a complementary mechanism based on oxygen vacancies, elucidating the behavior under complex bias stress schemes and extending our understanding of instability mechanisms beyond monotonous bias stress.

Reduction of internal stress in InGaZnO (IGZO) thin film transistors by ultra-thin metal oxide layer

In this study, the modification of indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) with an ultrathin metal oxide layer successfully reduces internal film stress. The introduction of an Al2O3 metal oxide layer effectively diminishes defects within the film and minimizes distortion in the film densification process. A low-temperature annealing process at 200 °C was employed to mitigate thermal expansion differences between the film and the substrate, thus reducing internal stress within the device. Furthermore, we have discovered that this structural modification holds the potential to enhance mechanical stress resistance. This paper offers a novel perspective and an experimental foundation for the stress analysis of flexible TFTs.

Solution-processed bilayer InGaZnO/In2O3 thin film transistors at low temperature by lightwave annealing

At low temperatures about 230 °C, bilayer InGaZnO/In2O3 thin film transistors (TFTs) were prepared by a solution process with lightwave annealing. The InGaZnO/In2O3 bilayer TFTs with SiO2 as dielectric layer show high electrical performances, such as a mobility of 7.63 cm2V−1s−1, a threshold voltage (V th) of 3.8 V, and an on/off ratio higher than 107, which are superior to single-layer InGaZnO TFTs or In2O3 TFTs. Moreover, bilayer InGaZnO/In2O3 TFTs demonstrated a great bias stability enhancement due to the introduction of top InGaZnO film act as a passivation layer, which could prevent the interaction of ambient air with the bottom In2O3 layer. By using high dielectric constant AlO x film, the InGaZnO/In2O3 TFTs exhibit an improved mobility of 47.7 cm2V−1s−1. The excellent electrical performance of the solution-based InGaZnO/In2O3 TFTs shows great application potential for low-cost flexible printed electronics.

Increased Threshold Voltage of Amorphous InGaZnO Thin-Film Transistors After Negative Bias Illumination Stress

Increased Threshold Voltage of Amorphous InGaZnO Thin-Film Transistors After Negative Bias Illumination Stress

Effect of Oxygen Plasma Treatment on the Performance of GQDs-Modulated InGaZnO Thin-Film Transistors

Effect of Oxygen Plasma Treatment on the Performance of GQDs-Modulated InGaZnO Thin-Film Transistors

Control of hydrogen concentration on InGaZnO thin film using cryopumping system

Amorphous InGaZnO thin film transistors (a-IGZO TFTs) have been extensively studied as driving transistors for large organic light emitting diode (OLED) displays due to its’ exceptional uniformity. However, the positive bias stability (PBS) of a-IGZO TFT is not sufficiently acceptable to endure the long on-stress time. Here, the effect of hydrogen impurities in a-IGZO channels on the stability and performance of TFTs used in OLED displays are investigated. The hydrogen content in the a-IGZO film is reduced to limit the formation of trapping sites for charge carriers and improve TFT stability. This study uses a cryogenic pumping system to reduce the hydrogen impurity density during the deposition process and examines the electrical characteristics of bottom-gate a-IGZO TFTs. The threshold voltage shift (ΔVth) of the a-IGZO TFT fabricated using the cryogenic pumping system was found to be reduced by 3.4–6.9 V, compared to the TFT fabricated using the turbo molecular pump system. The hydrogen and oxygen concentrations in the oxide thin films are quantitatively analyzed, and the mechanism of OH bonding acting as an electron trap during positive bias stress is explained. Overall, this study provides insights into the impact of hydrogen impurities in a-IGZO TFT stability and performance, as well as proposes a method using cryopump for reducing hydrogen impurities to improve OLED display reliability.

Low temperature plasma deposited SiO2/organosilicon stacked film for transparent gate dielectric of InGaZnO thin film transistor

In this article, a 5-pair SiO2/organosilicon stacked film fabricated by inductively coupled plasma-enhanced chemical vapor deposition from hexamethyldisiloxane /O2 at low temperature was introduced as InGaZnO thin film transistor (IGZO TFT) gate dielectric for transparent flexible displays. The dielectric film has the flexibility of organosilicon while maintaining the high dielectric strength of SiO2. Due to the introduction of organosilicon, which connects with the IGZO active layer, the deep-state electron traps formed by oxygen vacancies are reduced, and moderate hydrogen diffused into IGZO layer becomes a shallow donor. Under the premise of high transmittance of the dielectric film, a high-performance TFT with mobility of 15.60 cm2/Vs was obtained.

Solution-Processed Aluminum-Zirconium Oxide as a Gate Dielectric for InGaZnO Thin Film Transistors

Solution-Processed Aluminum-Zirconium Oxide as a Gate Dielectric for InGaZnO Thin Film Transistors

Improved reliability of a-IGZO thin-film transistor under positive gate bias stress by utilizing NH3 plasma treatment

In this paper, the degradation mechanisms of the bottom-gate amorphous InGaZnO thin film transistors (a-IGZO TFTs) under positive gate bias stress (PBS) are investigated. The PBS-induced degradation can be attributed to the electron capture at the interface of the gate insulator and a-IGZO and the generation of oxygen interstitial defects (Oi) in a-IGZO. The oxygen interstitial defect density (NOi) can be calculated by the degradation of SS during recovery after PBS. It is found that the proportion of degradation caused by Oi increases with the increased a-IGZO thickness. By utilizing NH3 plasma treatment, the threshold voltage shift was reduced by >40 % under PBS (@VG = 5 V, t = 1000s). Further analysis shows that NH3 plasma treatment can effectively suppress the electron capture at the interface and the generation of Oi during PBS. Thus, PBS reliability of a-IGZO TFTs is improved by the proposed method.

Electrical Characterization of InGaZnO-Based Thin Film Transistor fabricated by Three-mask Process

Indium Gallium Zinc Oxide (InGaZnO) has gained increasing attention as a replacement for amorphous silicon in thin-film transistors (TFTs) owing to its excellent electrical and optoelectronic properties, chemical stability, and potential for low-temperature processing.
 However, efforts are being made to optimize the design to improve the performance and reduce costs.
 In this study, a top-contact top-gate (TCTG) structure of InGaZnO TFTs was fabricated using three lithography steps. The electrical current–voltage characteristics of the device were measured and used to extract the device parameters.
 The result shows transistor parameters with threshold voltage of –9 V, ON-OFF ratio of in the range of 103, maximum mobility of 1.15 cm2V-1 s-1, subthreshold slope of in the range of 103  mV/dec, and maximum interface trap density of 1.53x103  (cm-2eV-1) at maximum applied voltage of 5 V.  

Low-Cost and High-Performance, Back-Channel Etched InGaZnO Thin Film Transistors by Spray Pyrolysis

Low-Cost and High-Performance, Back-Channel Etched InGaZnO Thin Film Transistors by Spray Pyrolysis

Room-temperature-processed synaptic a-IGZO TFT with high-k HfLaO gate dielectric as neuromodulator

In this work, room-temperature-processed amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) have been fabricated with high-k HfLaO as gate dielectric for synaptic devices. By raising the indium content in the a-IGZO film via co-sputtering and treating the HfLaO gate dielectric in an Ar plasma, the TFT with In1.0Ga3.0Zn0.4O2.1 presents excellent electrical characteristics: a high intrinsic carrier mobility of 45.8 cm2 V−1·s−1, a small threshold voltage of 1.93 V, a small hysteresis of −0.015 V, and a small subthreshold swing (SS) of 0.21 V dec−1. Although the oxygen vacancies in the In1.0Ga3.0Zn0.4O2.1 TFT are increased to produce a high carrier mobility, memristive behaviors are hardly observed under zero gate bias due to their occupied states. Various conductance modulations and synaptic plasticities are achieved under a 2-V drain spiking voltage and a small gate bias of 1 V due to migration of oxygen ions and emptying/detrapping of oxygen vacancies in the In1.0Ga3.0Zn0.4O2.1 film, resulting in a concurrent emulation of neurotransmitter and neuromodulator through exploiting the native three-terminal structure of the TFT.

Remote Phonon Scattering in InGaZnO Thin-Film Transistor with Double-Layered High-κ Gate Dielectric

Remote Phonon Scattering in InGaZnO Thin-Film Transistor with Double-Layered High-κ Gate Dielectric

Influence of Channel Surface with Ozone Annealing and UV Treatment on the Electrical Characteristics of Top-Gate InGaZnO Thin-Film Transistors.

The effect of the channel interface of top-gate InGaZnO (IGZO) thin film transistors (TFTs) on the electrical properties caused by exposure to various wet chemicals such as deionized water, photoresist (PR), and strippers during the photolithography process was studied. Contrary to the good electrical characteristics of TFTs including a protective layer (PL) to avoid interface damage by wet chemical processes, TFTs without PL showed a conductive behavior with a negative threshold voltage shift, in which the ratio of Ga and Zn on the IGZO top surface reduced due to exposure to a stripper. In addition, the wet process in photolithography increased oxygen vacancy and oxygen impurity on the IGZO surface. The photo-patterning process increased donor-like defects in IGZO due to organic contamination on the IGZO surface by PR, making the TFT characteristics more conductive. The introduction of ozone (O3) annealing after photo-patterning and stripping of IGZO reduced the increased defect states on the surface of IGZO due to the wet process and effectively eliminated organic contamination by PR. In particular, by controlling surface oxygens on top of the IGZO surface excessively generated with O3 annealing using UV irradiation of 185 and 254 nm, IGZO TFTs with excellent current-voltage characteristics and reliability could be realized comparable to IGZO TFTs containing PL.

Fluorination-mitigated high-current degradation of amorphous InGaZnO thin-film transistors

As growing applications demand higher driving currents of oxide semiconductor thin-film transistors (TFTs), severe instabilities and even hard breakdown under high-current stress (HCS) become critical challenges. In this work, the triggering voltage of HCS-induced self-heating (SH) degradation is defined in the output characteristics of amorphous indium-gallium-zinc oxide (a-IGZO) TFTs, and used to quantitatively evaluate the thermal generation process of channel donor defects. The fluorinated a-IGZO (a-IGZO:F) was adopted to effectively retard the triggering of the self-heating (SH) effect, and was supposed to originate from the less population of initial deep-state defects and a slower rate of thermal defect transition in a-IGZO:F. The proposed scheme noticeably enhances the high-current applications of oxide TFTs.