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Review

Recent Advances of Solution-Processed Heterojunction Oxide Thin-Film Transistors

by
Yanwei Li
1,
Chun Zhao
2,
Deliang Zhu
1,
Peijiang Cao
1,
Shun Han
1,
Youming Lu
1,
Ming Fang
1,
Wenjun Liu
1 and
Wangying Xu
1,*
1
Shenzhen Key Laboratory of Special Functional Materials, College of Materials Science and Engineering, Guangdong Research Center for Interfacial Engineering of Functional Materials, Shenzhen University, Shenzhen 518060, China
2
Department of Electrical and Electronic Engineering, Xi’an Jiaotong-Liverpool University, Suzhou 215123, China
*
Author to whom correspondence should be addressed.
Nanomaterials 2020, 10(5), 965; https://doi.org/10.3390/nano10050965
Submission received: 19 April 2020 / Revised: 13 May 2020 / Accepted: 13 May 2020 / Published: 18 May 2020
(This article belongs to the Special Issue Wet Chemical Synthesis of Functional Nanomaterials)
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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.

1. Introduction

Today, there is a growing demand for flat-panel displays with higher resolution, larger screen sizes, better viewing, and lower power consumption, pushing traditional amorphous silicon thin-film transistor (TFT) technology to its limits [1,2,3]. TFTs made of metal oxide semiconductors hold great promise in future display technology, owing to their high mobility, good transparency, and scalability [4,5,6,7]. Commercial metal oxides are grown via physical vapor deposition technologies, but solution-based approaches have been attracting particular attention recently [5,8,9,10,11]. Compared with conventional vacuum-based technologies, the solution approaches have additional advantages, including cost effectiveness, atmospheric fabrication, higher throughput, and material composition that is easy to tune [12,13,14,15]. Ways to reduce defect states and improve electrical performance and stability are an urgent challenge for solution-based metal oxide TFTs [16,17]. Various approaches have been taken to solve the above challenge, such as doping, modification of components, addition of additives, and novel post-treatments [9,18,19,20]. However, electron transport properties are still hindered by these defect-prone oxides [21,22,23,24,25].
A notable strategy has been recently developed to enhance the electrical performance of solution-derived oxide TFTs by utilizing heterojunction channels [26]. The schematic of the heterojunction oxide TFTs is demonstrated in Figure 1. It is revealed that heterostructures could modulate electrical performance by taking advantage of both the front channel (providing high mobility) and the back channel (maintaining low off current) [27,28]. More importantly, some recent studies argue that the presence of a 2D electron gas system formed at the carefully engineered oxide heterointerface can greatly improve device mobility [24,29,30,31,32,33]. In this review, we summarize the recent progress of solution-processed heterostructure oxide TFTs. The heterojunction channel strategy could address the shortcomings of single-layer devices, providing a new route for future TFT technology development [34,35,36].

2. Heterojunction Oxide TFTs

2.1. Vacuum-Processed Heterojunction Oxide TFTs

Before reviewing solution-processed heterojunction oxide TFTs, we would like to make a short introduction on vacuum-based heterojunction oxide devices. In 2008, Kim et al. produced InSnO/GaInZnO (ITO/GIZO) heterojunction TFTs by magnetron sputtering, with a high mobility of 104 cm2/Vs, a suitable threshold voltage (Vth) of 0.5 V, and a low Vth shift of 0.75 V for 4 h under 10 V bias voltage [37]. They found that the lower layer of highly conductive oxides could provide high mobility for the TFTs, while the upper layer of oxides with lower carrier concentration could adjust the threshold voltage. This new structure provides a new way to adjust the performance of TFTs. Subsequently, a number of scientists have studied and produced various excellent heterojunction oxide TFTs. In 2014, Chen et al. prepared InSnO/SnZnO (ITO/TZO) TFT on a glass substrate by taking advantage of ITO’s higher carrier concentration and TZO’s ability to control the charge conductance, and they obtained a high mobility of 105 cm2/Vs [38]. In 2016, Cong et al. built quasi-double-channel (QDC) AlSnZnO (ATZO) TFTs with a superior mobility of 108 cm2/Vs and an on/off ratio of 109 [36]. In 2019, He et al. prepared InGaZnO/In2O3 (IGZO/In2O3) TFTs by magnetron sputtering at room temperature, exhibiting high mobility (64.4 cm2/Vs) and high on/off ratio (107), with large enhancement compared with single-layer IGZO and In2O3 TFTs [39]. They attributed this improvement to the defect self-compensation mechanism between the two layers. In 2019, Furuta et al. prepared IGZO/IGZO TFTs with a mobility of 24.7 cm2/Vs and an on/off ratio of 107 [40]. Table 1 summarizes the recent progress in vacuum-processed heterojunction oxide TFTs. It can be observed that heterojunction oxide TFTs show excellent electrical properties, which are much better than those of the traditional single-layer device.

2.2. Solution-Processed Heterojunction Oxide TFTs

Compared with conventional vapor-based techniques, solution processing (such as spin-coating, spraying, and printing) allows for the design and fabrication of novel oxide TFTs in a low-cost and straightforward fashion [43,44,45]. Many researchers have begun to study solution-grown heterojunction oxide TFTs. Table 2 and Figure 2 summarize the recent advances in solution-processed heterojunction oxide TFTs. For heterojunction oxide TFTs, we discuss two of the most prominent advantages, namely electrical-property modulation and mobility enhancement by forming 2D electron gas.

2.2.1. Electrical-Property Modulation

As a product of structural engineering technology, heterojunction oxide TFTs can take advantage of the excellent electrical properties of each layer [30,37]. As the front-channel layer has good conductivity, it can provide higher carrier concentration, thus forming maximum charge accumulation and finally achieving high mobility [10,41,42]. The carrier concentration in the back-channel layer is much lower than that of the front-channel layer, which leads to the difference in electron activation energy between the conduction band minimum and the Fermi energy level, forming an energy barrier at the interface [51]. Due to the existence of an energy barrier, the back-channel layer can effectively control the electron flow, thus reducing off current (Ioff) and adjusting threshold voltage (Vth) [46]. A series of representative papers show that heterojunction TFTs can achieve both high mobility and Ioff by selecting suitable front- and back-channel materials.
In 2012, Jeong et al. adjusted the carrier concentration of the AlInZnO/InZnO (AIZO/IZO) interface and barrier height by changing the ratio of In/Zn in the IZO layer and the thickness of the IZO layer. The IZO layer could provide an enhanced mobility for the device due to its high electron concentration. Compared with the IZO layer, the AIZO layer had a larger EC–EF due to its lower carrier concentration, forming an energy barrier at the interface and reducing Ioff. As the thickness of the conductive IZO layer decreased, the AIZO/IZO TFTs Vth shifted positive, and Ioff decreased from 10−8 to 10−11 A. With a 12-nm-thick IZO layer, they obtained a device mobility of 5.63 cm2/Vs and an on/off ratio of 106 [46]. For similar reports, refer to Kim et al. ZnSnO/InGaZnO (ZTO/IGZO), Yu et al. In2O3/InGaO (In2O3/IGO), Kim et al. InGaZnO/InGaZnO (IGZO/IGZO), Seo et al. AIZO/IZO, and Lee et al. In2O3/In2O3 (amorphous In2O3 and polycrystalline In2O3) [47,48,49,50].
Rim et al. boosted up the mobility of solution-processed oxide TFTs using an extremely thin layer of conductive InSnZnO (ITZO) inserted between the dielectric layer and the InGaZnO (IGZO) active layer [51]. The ITZO/IGZO TFTs have a high mobility (22.16 cm2/Vs) and an excellent on/off current ratio (107). As shown in Figure 3a, the mobility of ITZO/IGZO is over ten times higher than that of single-layer IGZO (from 1.56 to 22.16 cm2/Vs). At the front channel of ITZO, Sn4+ replaced In3+ to provide additional electrons to increase electron concentration, forming a highly conductive channel and providing high mobility for devices. Moreover, a barrier height (0.15 eV) between IGZO and ITZO (Figure 3b) could effectively modulate off current and threshold voltage. Nadarajah et al. (2015) also tried solution-processed ITZO/IGZO TFTs, showing a mobility of ~30 cm2/Vs and an Ion/Ioff of 106 [59].
Nam et al. prepared high-performance solution-processed indium-free ZnO/SnO2 TFTs at 300 °C by UV annealing [53]. The ZnO/SnO2 TFTs exhibited a mobility of 15.4 cm2/Vs, an outstanding on/off ratio of 108, and superior bias stability. As shown in Figure 4a, ZnO/SnO2 bilayers are composed of a Zn-rich layer, a Zn-Sn mixed zone, and an Sn-rich layer. The Sn-rich channel has high conductivity and provides a path for rapid electronic transport. Meanwhile, Zn atoms can diffuse into the Zn-Sn mixing zone to reduce Ioff by control carrier concentration. Furthermore, due to the suppression of oxygen vacancy (Vo) defects in the bilayer film, the ZnO/SnO2 TFTs exhibited remarkable bias-stress stability (Figure 4b).

2.2.2. Mobility Enhancement by Forming 2D Electron Gas

In addition to electrical-performance modulation, some recent studies suggest that well-designed heterojunction oxides could greatly boost mobility by forming 2D electron gas at the interface [52]. Through careful interface engineering, electron transfer and confinement at the heterointerface can occur because of a large conduction band offset between the two layers, resulting in the formation of 2D electron gas in the interface [55]. The formation of 2D electron gas enables the realization of TFTs with mobilities close to the theoretical limit set by phonon scattering in the absence of impurity scattering [30]. In this situation, the mobility of the heterojunction device is often several times or even ten times higher than that of the single-layer device. Additionally, the enhanced electron mobility is accompanied by a marked change in the charge transport mechanism. Through fitting the transfer curves and analyzing the temperature dependence of mobility, it was revealed that heterojunction TFTs exhibited band-like electron transport, while the single-layer device showed trap-limited conduction [55]. It should be mentioned that the transfer curve of the heterojunction TFTs shifted to the negative direction compared with the single-layer device, due to the formation of 2D electron gas.
Faber et al. demonstrated In2O3/ZnO TFTs with unprecedented electron mobility grown from the solution [55]. The mobility of In2O3/ZnO TFTs (45 cm2/Vs) was 2 to 100 times greater than that of single-layer In2O3 and ZnO devices. According to X-ray photoelectron spectroscopy, optical absorption, and Kelvin probe measurements, the In2O3/ZnO interface has a large conduction band offset (0.36 eV), which makes the electron transfer from the ZnO layer to In2O3 and forms 2D electron gas. 2D electron gas greatly increases the concentration of free electrons in the In2O3 layer of the crystal. The electron transport mechanism of In2O3/ZnO TFTs was changed from trap-limited conduction to percolation conduction. This marked improvement originated from the presence of 2D electron gas formed at the atomically sharp heterointerface induced by the large conduction band offset between In2O3 and ZnO. The In2O3/ZnO TFTs developed in this work not only surpassed the performance of single-layer In2O3 and ZnO TFTs but also compared favorably to state-of-the-art vacuum-processed devices. Lin et al. used solution-grown In2O3, Ga2O3, and ZnO to construct heterojunction and quasi-superlattice (QSL) TFTs (Figure 5a) [52]. By carefully optimizing the structure, QSLs with smooth interfaces and surfaces could be realized (Figure 5b). As shown in Figure 5c, it was proved that single-layer metal oxide TFTs were dominated by trap-limited conduction (TLC), while QSL-I/III were dominated by percolation conduction (PC). The change of electron transport mode led to a great increase in electron mobility (from 4 to 30 cm2/Vs).
Later studies showed that layer configuration and annealing temperature greatly affect heterojunction device performance. Khim explored the effect of layer configuration on electron transport in heterojunction transistors composed of ZnO and In2O3 [57]. They found that depositing In2O3 first followed by ZnO resulted in a smooth interface, while reversing the layer order yielded poor interface roughness. Tetzner et al. studied the influence of annealing temperature on morphology, chemical state, and electrical performance of solution-based heterostructure In2O3/ZnO TFTs [54]. It was found that the annealing temperature changed surface roughness and atomic diffusion at the interface of In2O3/ZnO. At the annealing temperature of 400 °C, the In2O3/ZnO TFTs showed an optimized mobility of 48 cm2/Vs and an on/off current ratio of ~104.
The large conduction band offset between the two layers is one of the key points to induce 2D electron gas for mobility improvement. A doping strategy has been adopted to enlarge the conduction band offset between the two layers. Khim and co-workers reported the controlled growth of In2O3/Li-ZnO TFTs by modulation doping [29]. It was revealed that Li addition in ZnO led to n-type doping and allowed for the accurate tuning of its Fermi energy. Therefore, doping of Li could precisely regulate ΔEF between In2O3 and Li-ZnO and change the conduction band offset between the two layers (Figure 6). When the doping amount of Li was 20%, the mobility of In2O3/Li-ZnO heterojunction TFTs reached the maximum value of 11.4 cm2/Vs and the on/off current ratio of ~105. Chen et al. demonstrated high performance In2O3/In2O3:polyethylenimine (PEI) heterostructure TFTs [56]. The 2D electron gas was achieved by creating a band offset between In2O3 and In2O3:PEI via work function tuning of the PEI-doping ratio. The resulting device exhibited a mobility of 10 cm2/Vs on SiO2 gate dielectric. Similarly, Liu et al. took In2O3 as the front channel and combined it with the back-channel AlInO to construct heterojunction transistors. By adjusting the thickness of AlInO and the doping amount of Al, AlInO (30%)/In2O3 heterostructure TFTs with a high mobility of 40 cm2/Vs, a threshold slope of 0.7 V/dec, and an on/off ratio of 107 could be realized [58].

3. Conclusions and Outlooks

Great progress has been made in the past few years in solution-processed heterojunction oxide TFTs. A detailed review of this topic has been presented, with special attention on the latest developments over the past 5 years. It was revealed that heterojunction channels could overcome the disadvantages of single-layer structures. By using this novel strategy, solution-based oxide transistors with high mobility (~50 cm2/Vs) and operational stability could be realized, competing with or even surpassing vacuum-grown counterparts.
In terms of future research directions, several key issues need to be addressed. First, the reported high mobility heterojunction oxide TFTs often suffered from negative threshold voltages, high off-state currents, or poor stability, which have a negative impact on commercial applications. The negative threshold voltage and high off-state current of heterojunction oxide TFTs are closely related to the formation of 2D electron gas. Lee et al. constructed corrugated structure ITZO/IGZO TFTs with both high mobility (51 cm2/Vs) and low off-state current [30]. The thin ITZO/IGZO portion increased the overall resistivity of the current path, effectively reducing the off-state current. The thick ITZO/IGZO could provide free electrons to form a high-speed electronic channel, highly improving the electron mobility. By using this new corrugated heterojunction, solution-based oxide TFTs with high mobility and low off current could be realized. Unfortunately, this could increase the complexity of the process. Lin et al. reported solution-processed ZnO/ZnO-NPs/PS/In2O3 multilayer TFTs with high electron mobility (50 cm2/Vs) and prolonged operational stability [31]. Insertion of the ozone-treated polystyrene interlayer could passivate electron traps in the channel, leading to high mobility and excellent operational stability. However, continued work should be carried out. It should be mentioned that well-optimized single-layer vacuum-based metal oxide TFTs show high performance and stability. Secondly, previous studies argued that the mobility enhancement is attributed to the 2D electron gas that formed at the heterogeneous interface. However, the traditional 2D electron gas usually exists in high-quality epitaxial heterojunction systems (such as AlGaAs/GaAs heterojunctions). The oxide thin films prepared by the solution method are usually polycrystalline or amorphous, and the 2D electron gas formation mechanism is still unclear. Thirdly, the carrier transport properties in heterojunction oxide need further investigation. A deep understanding of the heterojunction electron transport can promote better design of high-performance heterojunction oxide devices. Fourthly, the previous research mainly focused on the In2O3/ZnO system; it is necessary to extend this to other multicomponent oxide semiconductor heterostructures (such as the IGZO system) for further device performance improvement. We believe that by addressing the issues presented above, solution-processed heterojunction oxide TFTs will show great promise in future large-area and high-performance electronics.

Author Contributions

W.X. conceived and supervised the project. Y.L. (Yanwei Li) and W.X. wrote the manuscript. Y.L. (Yanwei Li), C.Z., D.Z., P.C., S.H., Y.L. (Youming Lu), M.F., W.L. and W.X. revised and commented on the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Natural Science Foundation of China (61704111, 51872187, 51371120 and 11774241), Natural Science Foundation of Guangdong Province (2017A030310524) and Science and Technology Foundation of Shenzhen (JCYJ20170817100611468 and JCYJ20170818143417082).

Conflicts of Interest

There are no conflicts to declare.

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Figure 1. Cross-sectional view of the heterojunction oxide thin-film transistors (TFTs).
Figure 1. Cross-sectional view of the heterojunction oxide thin-film transistors (TFTs).
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Figure 2. Mobility vs. processing temperature for solution-processed heterojunction oxide TFTs from Table 2 or high-k dielectrics. (QSL-III denotes In2O3/Ga2O3/ZnO/Ga2O3/In2O3; PEI-In2O3 denotes polyethylenimine-doped In2O3; IZIZ denotes In2O3/ZnO/In2O3/ZnO; Li-IZIZ denotes In2O3/ZnO-Li/In2O3/ZnO-Li.)
Figure 2. Mobility vs. processing temperature for solution-processed heterojunction oxide TFTs from Table 2 or high-k dielectrics. (QSL-III denotes In2O3/Ga2O3/ZnO/Ga2O3/In2O3; PEI-In2O3 denotes polyethylenimine-doped In2O3; IZIZ denotes In2O3/ZnO/In2O3/ZnO; Li-IZIZ denotes In2O3/ZnO-Li/In2O3/ZnO-Li.)
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Figure 3. (a) Transfer characteristics of InGaZnO (IGZO), InSnZnO (ITZO), and ITZO/IGZO TFTs. (b) Energy band diagram of ITZO/IGZO. Reproduced with permission [51]. Copyright 2014, Wiley-VCH.
Figure 3. (a) Transfer characteristics of InGaZnO (IGZO), InSnZnO (ITZO), and ITZO/IGZO TFTs. (b) Energy band diagram of ITZO/IGZO. Reproduced with permission [51]. Copyright 2014, Wiley-VCH.
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Figure 4. (a) Transmission electron microscope (TEM) of ZnO/SnO2 heterojunction thin film. (b) Transfer curve evolutions for ZnO/SnO2 heterojunction TFTs against a variety of bias stresses. Reproduced with permission [53]. Copyright 2016, Royal Society of Chemistry.
Figure 4. (a) Transmission electron microscope (TEM) of ZnO/SnO2 heterojunction thin film. (b) Transfer curve evolutions for ZnO/SnO2 heterojunction TFTs against a variety of bias stresses. Reproduced with permission [53]. Copyright 2016, Royal Society of Chemistry.
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Figure 5. (a) Thin-film schematics of heterojunction quasi-superlattices (QSLs) consisting of In2O3/ZnO/In2O3 (QSL-I), In2O3/Ga2O3/ZnO (QSL-II), and In2O3/Ga2O3/ZnO/Ga2O3/In2O3 (QSL-III). (b) Atomic force microscope (AFM) surface phase images of the different layered structures. (c) Arrhenius plots of the temperature dependence of the electron mobility for different layered structures. Reproduced with permission [52]. Copyright 2015, Wiley-VCH.
Figure 5. (a) Thin-film schematics of heterojunction quasi-superlattices (QSLs) consisting of In2O3/ZnO/In2O3 (QSL-I), In2O3/Ga2O3/ZnO (QSL-II), and In2O3/Ga2O3/ZnO/Ga2O3/In2O3 (QSL-III). (b) Atomic force microscope (AFM) surface phase images of the different layered structures. (c) Arrhenius plots of the temperature dependence of the electron mobility for different layered structures. Reproduced with permission [52]. Copyright 2015, Wiley-VCH.
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Figure 6. (a) Evolution of the Fermi energy level in In2O3 and ZnO layers as a function of Li concentration. (b) Schematic energy band diagram illustrating the shift of EF(Zn) to higher energies with increasing Li concentration in relation to EF(In). Reproduced with permission [29]. Copyright 2017, Wiley-VCH.
Figure 6. (a) Evolution of the Fermi energy level in In2O3 and ZnO layers as a function of Li concentration. (b) Schematic energy band diagram illustrating the shift of EF(Zn) to higher energies with increasing Li concentration in relation to EF(In). Reproduced with permission [29]. Copyright 2017, Wiley-VCH.
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Table
Table 1. Recent advances in vacuum-processed heterojunction oxide TFTs and representative single-layer devices.
Table 1. Recent advances in vacuum-processed heterojunction oxide TFTs and representative single-layer devices.
ChannelMobility (cm2·V−1·s−1)Ion/IoffSubthreshold Swing DielectricYearReference
ITO/GIZO1041080.25PECVD SiO22008[37]
ZTO/ITO52108-PECVD SiO22010[7]
IZO/IGZO30108-PECVD SiO22010[11]
HxIZO/HyIZO151010-Thermal SiO22010[3]
IGZO/GZO101070.93Thermal SiO22011[6]
IGZO/ZIO181010-PECVD SiO22011[10]
ZTO/ITO431070.18PECVD SiO22011[41]
HIZO/IZO41.41071.45Thermal SiO22011[42]
IZO/GIZO481010-PECVD SiO22012[27]
HIZO/IZO481070.28PECVD SiO22012[13]
IGZO/IGZO:Ti631060.73HfO22014[22]
ZTO/IZO321080.20PECVD SiO22014[23]
ITO/TZO1051070.33PECVD SiO22014[38]
In2O3/IZO381090.12ZrO22014[24]
High-O-IGZO/Low-O-IGZO601080.2Thermal SiO22014[34]
IZO/AZTO53.210100.15PECVD SiO22016[12]
ZnO-H/ZnO431080.13Thermal SiO22016[35]
L-AZTO/H-ATZO1081090.15PECVD SiO22016[36]
IGXO/IGYO53.21070.19PECVD SiO22017[25]
AIZTO/IZO5310100.15PECVD SiO22018[32]
In2O3/IGZO64.41070.20Thermal SiO22019[39]
In2O3/IGZO67.51070.08HfO22019[39]
In2O3/IGZO79.11070.09Si3N42019[39]
ZnO(DEZ+O3)/ZnO(DEZ+H2O)31.11070.21Al2O32019[33]
IGZO/IGZO24.71070.1Thermal SiO22019[40]
SnO235.4107-Thermal SiO22015[43]
ZnO201050.38TiO2/Al2O32015[44]
Table
Table 2. Recent advances in solution-processed heterojunction oxide TFTs and representative single-layer devices.
Table 2. Recent advances in solution-processed heterojunction oxide TFTs and representative single-layer devices.
ChannelProcessing Temperature (°C)Mobility (cm2·V−1·s−1)Ion/IoffSubthreshold SwingDielectricYearReference
AIZO/IZO3501.571070.59SiO22011[26]
AIZO/IZO3505.621060.53SiO22012[46]
IGZO/IGZO4502.41070.69SiO22013[47]
ZTO/IGZO4502.091070.49SiO22013[48]
In2O3/IGO2502.6108-SiO22013[49]
AIZO/IZO35023.41070.27SiO22014[50]
ITZO/IGZO45022.161070.51SiO22014[51]
ITZO/IGZO45040.031050.12ZrO22014[51]
QSL-III 1200401040.27AlOx/ZrOx2015[52]
ZnO/SnO230015.4107-SiO22016[53]
In2O3/ZnO40048104 SiO22016[54]
In2O3/ZnO25045107-SiO22017[55]
In2O3/Li-ZnO35011.4105-SiO22017[29]
ITZO/IGZO350381080.41SiO22018[30]
In2O3/PEI-In2O3 225010106-SiO22018[56]
In2O3/PEI-In2O3 225030106-ZrO22018[56]
In2O3/IGZO40014.5106-SiO22019[17]
In2O3/ZnO-NPS/PS/ZnO20050.71062.71SiO22019[31]
IZIZ 320011.4107-SiO22019[57]
Li-IZIZ 420025108-AlOx/ZrO22019[57]
AlInO/In2O3300401070.7SiO22019[58]
In2O3/In2O325050106-SiO22019[28]
IGZO150141080.17Al2O32012[14]
InSmO35021.51080.66SiO22020[15]
1 In2O3/Ga2O3/ZnO/Ga2O3/In2O3 (QSL-III). 2 Polyethylenimine-doped In2O3 (PEI-In2O3). 3 In2O3/ZnO/In2O3/ZnO (IZIZ). 4 In2O3/ZnO-Li/In2O3/ZnO-Li (Li-IZIZ).

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Li, Y.; Zhao, C.; Zhu, D.; Cao, P.; Han, S.; Lu, Y.; Fang, M.; Liu, W.; Xu, W. Recent Advances of Solution-Processed Heterojunction Oxide Thin-Film Transistors. Nanomaterials 2020, 10, 965. https://doi.org/10.3390/nano10050965

AMA Style

Li Y, Zhao C, Zhu D, Cao P, Han S, Lu Y, Fang M, Liu W, Xu W. Recent Advances of Solution-Processed Heterojunction Oxide Thin-Film Transistors. Nanomaterials. 2020; 10(5):965. https://doi.org/10.3390/nano10050965

Chicago/Turabian Style

Li, Yanwei, Chun Zhao, Deliang Zhu, Peijiang Cao, Shun Han, Youming Lu, Ming Fang, Wenjun Liu, and Wangying Xu. 2020. "Recent Advances of Solution-Processed Heterojunction Oxide Thin-Film Transistors" Nanomaterials 10, no. 5: 965. https://doi.org/10.3390/nano10050965

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