Query: Systematic Defect Manipulation in Metal Oxide Semiconductors towards High-Performance Thin-Film Transistors

Candidate papers:

abstract: The manipulation of donor like defects, including generation, suppression and diffusion, in metal oxide (MO) thin film transistors (TFTs) has been reviewed systematically. Based on this, the defect populated source/drain (S/D) regions and defect free channel region are realized for high performance TFTs, and even the location of self aligned (SA) homojunctions can be accurately controlled.
author_names: Yuqing Zhang

Zhihe Xia

Jiapeng Li

Yang Shao

Sisi Wang

Lei Lu

Shengdong Zhang

H S Kwok

Man Wong
title: Systematic Defect Manipulation in Metal Oxide Semiconductors towards High Performance Thin Film Transistors
venue: 2020 4th IEEE Electron Devices Technology Manufacturing Conference (EDTM)
year: 2020

abstract: Solution based metal oxide semiconductors (MOSs) have emerged, with their potential for low cost and low temperature processability preserving their intrinsic properties of high optical transparency and high carrier mobility. In particular, MOS field effect transistors (FETs) using the spray pyrolysis technique have drawn huge attention with the electrical performances compatible with those of vacuum based FETs. However, further intensive investigations are still desirable, associated with the processing optimization and operational instabilities when compared to other methodologies for depositing thin film semiconductors. Here, we demonstrate high performing transparent ZnO FETs using the spray pyrolysis technique, exhibiting a field effect mobility of ~14.7 cm2 V 1 s 1, an on/off ratio of ~109, and an SS of ~0.49 V/decade. We examine the optical and electrical characteristics of the prepared ZnO films formed by spray pyrolysis via various analysis techniques. The influence of spray process conditions was also studied for realizing high quality ZnO films. Furthermore, we measure and analyze time dependence of the threshold voltage (Vth) shifts and their recovery behaviors under prolonged positive and negative gate bias, which were expected to be attributed to defect creation and charge trapping at or near the interface between channel and insulator, respectively.
author_names: Junhee Cho

Seongkwon Hwang

Doo-Hyun Ko

Seungjun Chung
title: Transparent ZnO Thin Film Deposition by Spray Pyrolysis for High Performance Metal Oxide Field Effect Transistors
venue: Materials
year: 2019

abstract: The use of a semiconductor heterojunction channel layer has been explored as a method of improving the performance of metal oxide thin film transistors (TFTs) Construction of such a heterojunction bilayer is easy using a vacuum sputtering deposition process but difficult using inkjet printing deposition. Some attempts in this direction have not shown significant improvement compared to single channel layer TFTs, and the present work systematically studied inkjet printing of In2O3/IGZO heterojunction channel TFTs. It was found that the bilayer alignment is the most critical factor for obtaining high performance TFTs. A simple UV/ozone treatment on an inkjet printed In2O3 layer can be effective in achieving perfect alignment for IGZO printed on the In2O3 pattern area. The mechanism of alignment is not due to the difference in surface energy between the In2O3 layer and SiO2 dielectric layer, but due to the topography of the In2O3 layer sidewall. With well aligned heterojunction channels, the embedded In2O3 front channel layers transform the carrier transport from the main trap limited charge (TLC) transport process to the PC dominated process. Therefore, the maximum mobility of 14.5 cm2 V 1 s 1 was achieved for inkjet printed In2O3/IGZO TFTs, which is an unattainable result that only increases the proportion of In atoms in IGZO. The average mobility of the In2O3/IGZO TFTs is twice that of single layer In2O3 TFTs or IGZO TFTs. Furthermore, the In2O3/IGZO TFTs show superior bias stress stability.
author_names: Kun Liang

Shuangshuang Shao

Manman Luo

Vincenzo Pecunia

Lin Shao

Jianwen Zhao

Zheng Chen

Lixin Mo

Zheng Cui
title: High performance metal oxide thin film transistors based on inkjet printed self confined bilayer heterojunction channels
year: 2019

abstract: Oxide semiconductors thin film transistors (OS TFTs) with good transparency and electrical performance have great potential for future display technology. In particular, solution processed OS TFTs have been attracted much attention due to many advantages such as continuous, large scale, and low cost processability. Recently, OS TFTs fabricated with a metal aqua complex have been focused because they have low temperature processability for deposition on flexible substrate as well as high field effect mobility for application of advanced display. However, despite some remarkable results, important factors to optimize their electrical performance with reproducibility and uniformity have not yet been achieved. Here, we newly introduce the strong effects of humidity to enhance the electrical performance of OS TFTs fabricated with the metal aqua complex. Through humidity control during the spin coating process and annealing process, we successfully demonstrate solution processed InOx/SiO2 TFTs with a good electrical uniformity of ~5% standard deviation, showing high average field effect mobility of 2.76 cm2V 1s 1 and 15.28 cm2V 1s 1 fabricated at 200 and 250 degC, respectively. Also, on the basis of the systematic analyses, we demonstrate the mechanism for the change in electrical properties of InOx TFTs depending on the humidity control. Finally, on the basis of the mechanism, we extended the humidity control to the fabrication of the AlOx insulator. Subsequently, we successfully achieved humidity controlled InOx/AlOx TFTs fabricated at 200 degC showing high average field effect mobility of 9.5 cm2V 1s 1.
author_names: Keon-Hee Lim

Jae-Eun Huh

Jinwon Lee

Nam-Kwang Cho

Jun-Woo Park

Bu-il Nam

Eungkyu Lee

Youn Sang Kim
title: Strong Influence of Humidity on Low Temperature Thin Film Fabrication via Metal Aqua Complex for High Performance Oxide Semiconductor Thin Film Transistors.
venue: ACS applied materials interfaces
year: 2017

abstract: We present high performance, low voltage 3 V) operation of thin film transistors (TFTs) with indium zinc tin oxide (IZTO: In4Sn4ZnO15) semiconductor. The film of IZTO was fabricated via low temperature (200 degC) solution combustion processing without incorporating an external fuel. As 2 methoxyethanol is a widely used organic solvent due to its high dissolution capability, serve the purpose of both the solvent and the fuel. On quantification from the balanced redox reaction, 0.3% of 2 methoxyethanol assisted for the action of fuel and helped in the formation of metal oxide, and the rest (99.7% served the purpose of being dissolution medium. The balanced redox chemistry yielded a significant fraction of (56.5% metal oxide at 200 degC confirmed via high resolution oxygen 1s spectrum. Further, the chemically derived thin film of sodium b alumina with a dielectric constant of 21, while annealing at 350 degC incorporated in the TFT for the realization of low voltage operation. The performance assessment is systematically carried out both silicon dioxide (SiO2) and sodium b alumina and found that the TFTs with SiO2 and IZTO exhibited a saturation mobility (usat) Ion/Ioff ratio and the threshold voltage (Vth) of 0.50 0.02 cm2 V 1 s 1, 1.25 x 104 and 6.6 0.79 V respectively. While changing the dielectric to sodium b alumina presented a usat, Ion/Ioff ratio and Vth of 4.21 0.18 cm2 V 1 s 1, 1.4 x 102 and 0.47 0.08 V respectively.
author_names: Pavan Pujar

Dipti Gupta

Saumen Mandal
title: High performance low voltage operation of indium zinc tin oxide thin film transistors using chemically derived sodium b alumina dielectric
venue: Journal of Materials Science: Materials in Electronics
year: 2019

abstract: Thin film transistors (TFTs) made of metal oxide semiconductors are now increasingly used in flat panel displays. Metal oxides are mainly fabricated via vacuum based technologies, but solution approaches are of great interest due to the advantages of low cost and high throughput manufacturing. Unfortunately, solution processed oxide TFTs suffer from relatively poor electrical performance, hindering further development. Recent studies suggest that this issue could be solved by introducing a novel heterojunction strategy. This article reviews the recent advances in solution processed heterojunction oxide TFTs, with a specific focus on the latest developments over the past five years. Two of the most prominent advantages of heterostructure oxide TFTs are discussed, namely electrical property modulation and mobility enhancement by forming 2D electron gas. It is expected that this review will manifest the strong potential of solution based heterojunction oxide TFTs towards high performance and large scale electronics.
author_names: Yanwei Li

Chun Zhao

Deliang Zhu

Peijiang Cao

Shun Yu Han

Youming Lu

Mingzhi Fang

Wenjun Liu

Wangying Xu
title: Recent Advances of Solution Processed Heterojunction Oxide Thin Film Transistors
venue: Nanomaterials
year: 2020

abstract: The recent development of high performance colloidal quantum dot (QD) thin film transistors (TFTs) has been achieved with removal of surface ligand, defect passivation, and facile electronic doping. Here, we report on high performance solution processed CdSe QD TFTs with an optimized surface functionalization and robust defect passivation via hydrazine free metal chalcogenide (MCC) ligands. The underlying mechanism of the ligand effects on CdSe QDs has been studied with hydrazine free ex situ reaction derived MCC ligands, such as Sn2S64 Sn2Se64 and In2Se42 to allow benign solution process available. Furthermore, the defect passivation and remote n type doping effects have been investigated by incorporating indium nanoparticles over the QD layer. Strong electronic coupling and solid defect passivation of QDs could be achieved by introducing electronically active MCC capping and thermal diffusion of the indium nanoparticles, respectively. It is also noteworthy that the diffused indium nanoparticles facilitate charge injection not only inter QDs but also between source/drain electrodes and the QD semiconductors, significantly reducing contact resistance. With benign organic solvents, the Sn2S64 Sn2Se64 and In2Se42 ligand based QD TFTs exhibited field effect mobilities exceeding 4.8, 12.0, and 44.2 cm2/(V s) respectively. The results reported here imply that the incorporation of MCC ligands and appropriate dopants provide a general route to high performance, extremely stable solution processed QD based electronic devices with marginal toxicity, offering compatibility with standard complementary metal oxide semiconductor processing and large scale on chip device applications.
author_names: Su Min Jung

Han Lim Kang

Jong Kook Won

Jae Hyun Kim

Chahwan Hwang

Kyunghan Ahn

In Chung

Byeong Kwon Ju

Myung-Gil Kim

Sung Kyu Park
title: High Performance Quantum Dot Thin Film Transistors with Environmentally Benign Surface Functionalization and Robust Defect Passivation.
venue: ACS applied materials interfaces
year: 2018

abstract: Metal oxide semiconductors are emerging class of semiconductors with tremendous potential to replace existing silicon based semiconductors in a wide variety of next generation electronic applications. Solution processing of metal oxide semiconductor offers a low cost fabrication of oxide thin film transistors for large area film coatings. Use of traditional metal oxide precursors such metal salts require the addition of several additives to optimize the formation of the desired multinary metal oxide semiconductors. Within this thesis, the use of well defined, specifically tailored molecular precursor compounds with desired properties such air stable complexes with solubility in desired aqueous or organic solvents, microwave synthesis of oxide nanoparticles, reduction of process temperature for the formation of metal oxides as well as direct photo patterning of the multinary oxides are demonstrated. Firstly, indium zinc oxide nanoparticles were synthesized by a rapid microwave assisted decomposition employing solutions of molecular air stable In and Zn Schiff base type oximato precursors with methoxyiminopropionato ligands which led to the stable suspensions of IZO nanoparticles with a consistent particle size of 5nm. The removal of adherent organic and hydroxy moieties by annealing at 450degC thus led to an excellent semiconducting behaviour of the finally resulting high quality IZO TFTs with a mobility of 8.7 cm2 /V.s, an Ion/off ratio of 2.8 x 105 and a threshold voltage Vth of +3.3 V. This strategy was also extended towards the synthesis of the a bio inorganinc ZnO/TMV hybrid semiconductor, where a slightly modified precursor formulation with optimal amount of the base (TEAOH) provides mild basic conditions to ensure an efficient microwave based decomposition of the zinc complex and the in situ formation of crystalline zinc oxide nanoparticles at a low temperature of 60degC The ZnO nanoparticles mineralize selectively onto the TMV scaffold with and any structural damage to the TMV. For an optimum number (6 cycles) of ZnO mineralization, a field effect mobility (usat) of 6.7 x 10 4 cm2/V.s, Vth of +4.7 V and an Ion/off of 9.0 x 105 without the need for any post process thermal annealing. Similarly, employemnt of a new Sn(II) oximato precursor in combination with the zinc oximato precursor was employed for the formation of ZTO thin fim semiconductors. XRD analysis shows that the decomposition the tin(II) precursor alone, at temperatures as low as 350degC. The EPR investigations revealed only surface defects and not bulk defect sites with a higher defect concentration observed for the SnO2 compared to the ZnO. Hence, the precursor chemical composition with higher tin content with a Sn:Zn ratio of 7:3 delivered the optimum performance of the of the ZTO TFTs with a usat of 5.18 cm2/V.s, Vth of 7.5 V and a high Ion/off of 6 x 108 when annealed at a moderate temperature of 350oC. The oximato precursors were also explored for their direct DUV based photo patterning of IZO and ZTO semiconductors. This is enabled by accessing the intrinsic ability of the precursor thin film to undergo selective decomposition under UV irradiation and generate site selective patterning of oxide semiconductors, thereby eliminating the need for the traditional photolithography process. At annealing temperatures of 350degC, high performance TFTs with a usat of 7.8 cm2/V.s, Vth of 0.3 and a high Ion/off of 3.5 x 108 for IZO and 3.6 cm2/V.s, Vth of 2.4 and a high Ion/off of 5.3 x 107 for ZTO TFTs was achieved. In order to achieve low temperature solution processing, tailored multimetallic zinc and indium coordination compounds, [Zn4O(dmm NO)6] and In3O3(dmm NO2)3*(toluene) with nitro and nitroso functionalized dimethylmalonato ligands were investigated for the combustion synthesis of semiconducting indium zinc oxide (IZO) thin films at low processing temperatures. Devices annealed only at 250degC show an active TFT performance and at 300degC already demonstrate a robust FET performance with a usat of 2.1 cm2/V.s, Vth of +11.5 V and an Ion/off of 3.3 x 107 greater than that of the conventional amorphous hydrogenated silicon and also displays its potential to use integrated with plastic compatible temperatures 300oC, towards flexible electronics. Another approach based on water soluble, well defined urea nitrate coordination compounds of indium(III) gallium(III) and zinc(II) for the formation of amorphous IGZO thin films was succefully demonstrated. DSC analysis confirms the exothermic decomposition of all three precursors arising from the urea nitrate (fuel oxidiser) combination. Interestingly, IGZO TFTs processed even at 200oC show active TFT perfortmance and TFTs annealed at 300degC and 350degC exhibit a good device performance with charge carrier mobilities msat of 1.7 cm2/Vs and 3.1 cm2/Vs, respectively as well as current on off ratios of >107 in both cases. Such precursors are highly suitable for use in aqueous (non toxic) solution processing of IGZO semiconductors. Lastly, an ALD based In2O3/ZnO heterostructure design delivering high performance TFTs was successfully demonstrated using trimethyl indium and diethyl zinc as molecular precursors. Generation of an optimised In2O3/ZnO heterostructure based on sequential deposition of the individual oxides, processed at a reasonably low temperature regime (250 300degC) deliver high performance TFTs by the likely formation of 2D electron gas transport at the heterostructure interface. Devices based on such a fabrication process demonstrated an average saturation field effect mobility msat of 6.5 cm2/V.s and a high current on/off ratio of 4.6 x 107 and a low subthreshold swing (SS) of 0.7 V/dec. respectively, at a reasonable processing temperature of 300degC with potential applications in the field of large area oxide electronics.
author_names: Shawn Sanctis
title: Multinary metal oxide semiconductors A study of different material systems and their application in thin film transistors
year: 2020

abstract: For practical solution processed oxide thin film transistors (TFTs) with cost efficiency, high performance, and long term environmental reliability, we suggested a novel sol gel processed rare metal free oxide based semiconductor/insulator [ZnSnO (ZTO)/Al2O3] heterostructure channel and chemically stable sol gel multi stacking method. In the rare metal free ZTO/Al2O3 heterostructure, an In and Ga free ZTO semiconductor with high chemical durability is employed as an effective electron transport layer. An earth abundant Al2O3 insulator is employed as both an ambient gas molecule barrier in the ZTO back channel region and a tunneling induced electron transport layer beneath the source/drain electrodes. In order to minimize inevitable chemical attack coming from acidic and basic precursor solutions during the sol gel based heterostructure construction, chemically stable sol gel ZTO/Al2O3 heterostructure stacking was successfully demonstrated with a chemically durable Sn modulated ZTO semiconductor and weakly corrosive pH engineered Al2O3 precursor solution. The proposed rare metal free ZTO/Al2O3 heterostructure and chemically stable stacking realized sol gel processed oxide TFT with excellent stability under humidity, temperature, bias voltage, and light exposure. We believe that our novel ZTO/Al2O3 heterostructure and chemically stable sol gel stacking method will provide an interesting route for the fabrication of practical solution based oxide TFTs with cost efficiency, high performance, and long term reliability, instead of conventional rare metal based oxide materials and channel structures with high environmental instability.
author_names: Sung Woon Cho

Da Eun Kim

Kyung Su Kim

Sung-Hyun Jung

Hyung Koun Cho
title: Towards environmentally stable solution processed oxide thin film transistors: a rare metal free oxide based semiconductor/insulator heterostructure and chemically stable multi stacking
year: 2017

abstract: We report the results of a study to enhance metal oxide (MO) thin film transistor (TFT) performance by doping both the semiconductor (In2O3) and gate dielectric (Al2O3) layers with boron (yielding IBO and ABO, respectively) and provide the first quantitative analysis of how B doping affects charge transport in these MO dielectric and semiconducting matrices. The impact of 1 9 atom B doping on MO microstructure, morphology, oxygen defects, charge transport, and dielectric properties is analyzed together, in detail, by complementary experimental (microstructural, electrical) and theoretical (ab initio MD, DFT) methods. The results indicate that B doping frustrates In2O3 crystallization while suppressing defects responsible for electron trapping and carrier generation. In the adjacent Al2O3 dielectric, B doping increases the dielectric constant and refractive index while reducing leakage currents. Furthermore, optimized solution processed TFTs combining IBO channels with 6 atom B and ABO dielectrics with 10 atom B exhibit field effect mobilities as high as 11 cm2 V 1 s 1, current on/off ratios >105, threshold voltages 0.6 V, and superior bias stress durability.
author_names: Xinan Zhang

Binghao Wang

Wei Huang

Yao Chen

Gang Wang

Li Zeng

Weigang Zhu

Michael J Bedzyk

Weifeng Zhang

Julia E Medvedeva

Antonio F Facchetti

Tobin J Marks
title: Synergistic Boron Doping of Semiconductor and Dielectric Layers for High Performance Metal Oxide Transistors: Interplay of Experiment and Theory.
venue: Journal of the American Chemical Society
year: 2018