InGaZnO Layer Research Articles

Impact of Charge-Trap Layer Conductivity Control on Device Performances of Top-Gate Memory Thin-Film Transistors Using IGZO Channel and ZnO Charge-Trap Layer

A top-gate-structured charge-trap-type memory thin-film transistors (CTM-TFTs) using In-Ga–Zn-O (IGZO) channel and ZnO charge-trap layers were proposed to investigate effects of conductivity modulation for charge-trap layers on the memory performances. The electrical conductivity of ZnO charge-trap layers were controlled by varying the deposition temperatures to 100 °C (CTM1), 150 °C (CTM2), and 200 °C (CTM3) during the atomic layer deposition process and this strategy was well confirmed in the controlled devices using the conductivity-modulated ZnO channel layers. The IGZO TFT without charge-trap layer was also evaluated to have excellent device characteristics thanks to the high-quality interface between IGZO and Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> tunneling layer. The CTM1 and CMT2 exhibited a wide memory window (MW), sufficiently high program speed, and strong endurance properties. However, these promising memory behaviors could not be obtained for the CTM3 owing to its highly conductive charge-trap layer. For the evaluation of retention properties, there were big difference between the CTM1 and CTM2. Consequently, the CTM1 exhibited best memory performances. The MW and the memory margin in programmed current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(I_{\mathrm{{\scriptstyle ON}}}/{\mathrm{{\scriptstyle OFF}}}\) </tex-math></inline-formula> ) were estimated to be 17.1 V, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(1.3\times 10^{8}\) </tex-math></inline-formula> , respectively. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(I_{\mathrm{{\scriptstyle ON}}}/{\mathrm{{\scriptstyle OFF}}}\) </tex-math></inline-formula> was obtained to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(2.6\times \) </tex-math></inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(10^{6}\) </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(1.8\times 10^{3}\) </tex-math></inline-formula> after the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(10^{4}\) </tex-math></inline-formula> times cyclic operations and after the retention test for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(10^{4}\) </tex-math></inline-formula> s, respectively.

Performance improvement of the resistive memory properties of InGaZnO thin films by using microwave irradiation

Microwave irradiation (MWI) at low temperature was employed in resistive random access memory (ReRAM) fabrication with InGaZnO (IGZO) thin-films as a switching medium, and the resistive switching behaviors were compared with conventional thermal annealing (CTA) process. A surface roughness of the MWI-treated IGZO layer is smoother than that of the CTA-treated layer. An electrical conduction mechanism of the MWI-treated device is similar to that of the pristine device, whereas the CTA device exhibits a different mechanism. After MWI treatment, the current ON/OFF ratio of IGZO ReRAMs significantly increased from 0.49 × 101 to 1.16 × 102, which was ascribed to the reduction in the OFF current. Further, the enlarged ON/OFF resistance window allowed sufficient data retention of >10 years at 85 °C. Owing to its smoother surface for stable resistive switching, low thermal budget, and process simplicity, MWI has great potential for metal-oxide ReRAMs in transparent and flexible system-on-panel applications.

Hydrogen ion sensing characteristics of IGZO/Si electrode in EGFET

In-Ga-Zn-O (IGZO) was widely applied in the substrate of TFT to replace α-Si in recent years. In this study, IGZO layer with thickness of 70 nm is firstly proposed as a pH-sensing membrane directly deposited on P-type Si substrate acting as an extended gate of conventional extended-gate field-effect transistor (EGFET). Post-deposition rapid thermal anneal (RTA) was performed to improve pH sensing performance of IGZO layer sputtered with Ar/O 2 flow rate of 20/5 in sccm. Sensitivity could be increased from 41.5 mV/pH to 53.3 mV/pH by RTA in N 2 ambience at 700 o C in pH application range between pH 2 and 10. XRD analysis supports the orientation changes of IGZO layer after RTA at different temperature. Ar/O 2 ratio was also modified in the RF sputtering. IGZO-EGFET prepared by Ar/O 2 ambience of 24/1 in sputtering can have the highest sensitivity and linearity of 59.5 mV/pH and 99.7%, respectively. After 7 months, sensitivity and linearity are 51.4 mV/pH and 92%, respectively. Etch rate and drift coefficient in standard buffer solution are higher than in other sensing material for EGFET and ISFET. More studies on enlargement of pH application range and minimisation of non-ideal effect still need to be investigated before real applications.

A study on the microstructural and chemical evolution of In–Ga–Zn–O sol–gel films and the effects on the electrical properties

This study examines the chemical and microstructural evolution of In–Ga–Zn–O (IGZO) sol–gel films during post-annealing. Thorough material characterization discloses that the film annealed at 300°C is in an intermixed state of metallorganics and IGZO compound, and that the film annealed at 400°C or higher is a fully transformed IGZO layer with many pores produced by the evaporation of residual organics. Device characterization of transistors fabricated from the films reveals that the electrical characteristics also change sharply over the same temperature range (300–400°C): the 300°C sample exhibits a smooth transfer curve with a very low current while the samples annealed at 350°C or higher display a clear transistor behavior, reflecting the sensitive dependence of the device performance on the chemical state of IGZO sol–gel films.

Systematic Investigations on Self-Heating-Effect-Induced Degradation Behavior in a-InGaZnO Thin-Film Transistors

This paper investigates degradation behavior induced by the self-heating effect for InGaZnO (IGZO) thin-film transistors (TFTs). Both the surrounding oxide and other thermal insulating materials, as well as the low thermal conductivity of the InGaZnO layer itself, cause the self-heating effect in InGaZnO TFTs. The heated channel layer enhances the threshold voltage shift, and the evolution of threshold voltage shift is found to be dominated by charge-trapping effects. Moreover, a nonuniform distribution of channel carrier concentration leads to an uneven temperature distribution throughout the IGZO active layer, which results in the asymmetrical degradation behavior after the self-heating operation. Further verifications indicate that the degree of the threshold voltage shift is only dependent on stress power, regardless of stress <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Vg</i> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Vd</i> , and channel length. Further, two-stage dependence of the threshold voltage shift on dynamic stress frequency is found.

Origin of self-heating effect induced asymmetrical degradation behavior in InGaZnO thin-film transistors

This letter investigates asymmetrical degradation behavior induced by the self-heating effect in InGaZnO thin-film transistors. Both the surrounding oxide and other thermal insulating material, as well as the low thermal conductivity of the InGaZnO layer itself, cause the self-heating effect in InGaZnO thin-film transistors. The heated channel layer enhances threshold voltage shift, and the evolution of threshold voltage shift is found to be dominated by charge-trapping effect. Moreover, a non-uniform distribution of channel carrier concentration leads to an uneven temperature distribution through the InGaZnO active layer and results in the asymmetrical degradation behavior after self-heating operation.

Resistive Switching in $\hbox{TiO}_{2}$ Thin Films Using the Semiconducting In-Ga-Zn-O Electrode

Resistance switching behaviors in a Pt/In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ZnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> (IGZO)/TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Pt sample were examined for their potential use in diode-free memory integration. The In-Ga-Zn-O (IGZO) layer worked as the semiconductor layer, exhibiting accumulation or depletion of carriers depending on the polarity of the bias. Electroforming was possible only under the IGZO depletion condition due to the limited background leakage current flow. The repeated set/reset operation was also observed under the depletion condition. While the reset was possible, set was impeded by the high background current flow of the IGZO layer under the accumulation condition.

Planar ZnO ultraviolet modulator

A planar electroabsorption modulator suitable for spatial light modulation has been constructed. The device operates near the band edge of zinc oxide at 3.3eV and is based on broadening and shifting of the unconfined exciton with an externally applied electric field. The ZnO active layer was deposited on an aluminum/titanium oxide dielectric on an indium tin oxide conducting layer on glass. A transparent conductive InGaZnO layer on a spin on glass insulator served as the top contact, allowing high electric fields to be applied transverse to the ZnO layer. The modulator operates at room temperature in transmission mode with +45% modulation at 373nm and −18% modulation at 380nm at 140V applied bias, corresponding to ∼450kV∕cm electric field across the ZnO active layer.