Recent Advances of Solution-Processed Metal Oxide Thin-Film

Subscriber access provided by Kaohsiung Medical University

Recent Advances of Solution-Processed Metal Oxide Thin-Film Transistors Wangying Xu, Hao Li, Jian-Bin Xu, and Lei Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b16010 • Publication Date (Web): 06 Mar 2018 Downloaded from http://pubs.acs.org on March 7, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Recent Advances of Solution-Processed Metal Oxide Thin-Film Transistors Wangying Xu,1#* Hao Li,2# Jian-Bin Xu,2* Lei Wang2,3 1 College of Materials Science and Engineering, Guangdong Research Center for Interfacial Engineering of Functional Materials, Shenzhen Key Laboratory of Special Functional Materials, Shenzhen University, Shenzhen, 518060, China 2 Department of Electronic Engineering, Materials Science and Technology Research Center, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, 999077, China 3 Department of Applied Physics, School of Physical and Mathematical Sciences, Nanjing Tech University, Nanjing, 211816, China #These authors contributed equally *Corresponding authors: [email protected]; [email protected]

Abstract Solution-processed metal oxide thin-film transistors (TFTs) are considered as one of the most promising transistor technologies for future large-area flexible electronics. This paper surveys the recent advances in solution-processed metal oxide TFTs, including n-type oxide semiconductors, oxide dielectrics and p-type oxide semiconductors. We first deliver a review on the history and present status of metal oxide TFTs. Then, we present the recent progress in solution-processed n-type oxide semiconductors, with a special focus on low-temperature and large-area solution-based approaches as well as emerging non-display applications. Next, we give a detailed analysis of the state-of-the-art solution-processed oxide dielectrics for low power electronics. We further discuss the recent advances in solution-based p-type oxide semiconductors, which will enable the highly desirable future low-cost large-area complementary circuits. Finally, we draw the conclusions and outline the perspectives over the research field.

Keywords:

solution-processed,

metal

oxide

TFTs,

low-temperature,

semiconductors, oxide dielectrics, p-type oxide semiconductors

1

ACS Paragon Plus Environment

n-type

oxide

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1. Introduction Thin-film transistors (TFTs) are the key elements for flat-panel displays (FPDs) applications, including both active matrix liquid crystal displays (AMLCD) and active matrix organic light emitting diode (AMOLED) displays. In recent years, there is a great demand for higher resolution, larger screen size, and lower power consumption in the FPDs, which has pushed the traditional amorphous Si (a-Si) TFTs technology to its limits. Metal oxide TFTs are now expected to be one of the most promising technologies for next generation display technologies, because of their high carrier mobility, good transparency, excellent uniformity, and reasonable electrical reliability/stability.1-18 Compared with the traditional a-Si, metal oxide TFTs show much higher carrier mobility and better long-term stability. In comparison with low temperature poly-Si (LTPS) TFTs, oxide TFTs present a better large-area uniformity and much lower manufacturing cost. The advantages of oxide TFTs are summarized as follows: (1) Low processing temperature, even at room temperature; (2) Large electron mobility (10 ~ 50 cm2V-1s-1); (3) Good transparency, due to the wide bandgap of oxide semiconductor (~ 3.5 eV); (4) Excellent uniformity and surface flatness, owning to the amorphous structure.5 Some initial attempts on metal oxide TFTs started in 1960s, using SnO2 semiconductor,19 but had almost faded in the accessible literature. In the 2000s, oxide TFTs research became active based on polycrystalline metal oxide materials such as ZnO, In2O3 or SnO220-22. However, these materials usually exhibit high carrier concentrations (typically >> 1018 cm-3), which results in the difficulty in control of the channel conductance for TFT applications. Besides, polycrystalline oxide TFTs usually suffer from the non-uniformity issue due to the polycrystalline nature similar to that of LTPS TFTs.23 In 2004, Hosono made a breakthrough by introducing multicomponent amorphous oxide semiconductors such as In-Ga-Zn-O (IGZO). This attracted the worldwide attention, both in academia and industry.24 Due to the amorphous nature, IGZO TFTs show excellent uniformity similar to that of conventional a-Si TFTs, but much higher mobility. Besides, the production line of oxide TFTs is very similar to that of the current a-Si TFTs, showing a great advantage for industrialization. In addition to IGZO, other multi-component amorphous oxide semiconductors have been developed, including In-Zn-O (IZO), Zn-Sn-O (ZTO), Hf-In-Zn-O 2


Page 2 of 59

Page 3 of 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(HIZO), In-Sn-Zn-O (ITZO) and so on.2, 5-6, 11 The good electrical properties of these oxide semiconductors are due to the strong iconicity of oxides, which results in small effective masses and hence high carrier mobilities even in amorphous state.2, 5-6, 11, 25 Metal oxide TFTs by conventional vacuum-based technologies have been well established and gone to commercialization in a short period of time.6 However, the high cost of necessary equipment and restriction of deposition on a relatively small area have limited their potential applications in large-area electronics. In contrast, the solution process has many advantages including large-area fabrication, equipment simplicity, roll-to-roll capability, atmospheric processing, and low cost.2, 12, 14 The development of solution-processed oxide TFTs is first focused on n-type oxide semiconductors, and later extends to high-k oxide dielectrics and p-type oxide semiconductors. It is surprising that the TFT performance achieved by the simple solution process could approach those fabricated by traditional vacuum-based technologies. For industrial applications, Evonik Resource Efficiency GmbH has demonstrated the large-area processing of solution-processed metal oxide TFT backplanes and the integration in highly stable OLED displays.26 Besides, emerging non-display applications (e.g. photodetectors, biosensors, and memories) based on solution-processed metal oxides are rapidly advancing.10-11 Although there are a large number of reviews on metal oxide TFTs,1-14, 18 the focus of the current review is to provide a thorough examination of the recent advances in solution-processed oxide TFTs, especially the latest development in the past five years. We first briefly introduce the history and the current status of metal oxide TFTs. We then survey the latest development on solution-processed n-type oxide semiconductors, and in particular, highlight the low temperature large-area processing methods and novel non-display applications. Afterwards, we focus on a variety of solution-processed oxide dielectrics for fully-solution-processed oxide TFTs. We further discuss the latest advances in solution-processed p-type oxide semiconductors, which will enable the highly desired complementary circuits. We finally give a brief summary and outlook of solution-based oxide TFTs.

3



2. Vacuum-based Metal Oxide TFTs and Performance Estimation Metal oxide TFTs fabricated by vacuum-based technologies are now widely used as the backplane to drive high resolution LCD panels and large-sized OLED-TVs. After the discovery of IGZO in 2004, oxide TFTs have commercialized within a very short period of time. The first commercialization of oxide (IGZO) TFTs was achieved by Sharp in March 2012 for TFT backplane in retina LCD in Apple’s new iPad. In early 2013, LG Display commercialized its 55-inch OLED TV using oxide TFTs backplane.6 Other companies such as Samsung, AUO, and BOE are following up. The global market for oxide TFTs backplane display is expected to grow to 87.2 billion USD by 2025.2 Before discussing solution-based oxide TFTs, we would like to introduce the basis of vacuum-based oxide TFTs since this subject is well established and will help readers to better understand the solution-based oxide devices. Among the metal oxide TFTs, IGZO is the most studied and currently commercialized for FPD backplane applications. The IGZO TFT is usually fabricated by magnetron sputtering using a ceramic IGZO target. The IGZO composition greatly affects the device performance. It is found that the In ions contribute to a large mobility, while the Ga ions suppress the generation of conduction electrons due to the stronger chemical bond with oxygen. IGZO with atomic ration of In:Ga:Zn=1:1:1 or 2:2:1 have been widely adopted due to the balance of mobility and reliability.5-6 Another key process is that post thermal annealing is followed after the deposition of oxide semiconductor. Although oxide TFT with good mobility could be achieved without thermal annealing, these devices often show poor hysteresis and stability. Post annealing at about 400 oC improves these issues due to elimination of subgap density of states. 5-6 The most important TFT device parameters could be extracted from the output (Figure 1(a)) and transfer (Figure 1(b)) curves. These parameters include carrier mobility (µ), threshold voltage (VT), subthreshold swing (S), and on/off current ratio (Ion/Ioff). Each of the characteristics is well described in previous review paper.2 In this section, we would like to discuss the TFT mobility assessment, which is often overestimated in the literature.

4


Page 4 of 59

Page 5 of 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. (a) Output and (b) transfer curves of a typical n-type metal oxide TFT.

The importance of mobility in TFT stems from the fact that the higher the mobility, the greater the source-drain current (ID), within a certain span of the gate voltage (VG), at a given source-drain voltage (VG). The values for the linear mobility µlin (also known as field-effect mobility µFE) and saturation mobility µsat can be obtained from the transfer curve and expressed as

µlin = µ FE =

dI D L WCoxVD dVG

(1)

and

µsat

2L  d I D =  WCox  dVG

   

2

(2)

where W is the channel width, L is the channel length, µ is the charge carrier mobility, and Cox is the gate dielectric capacitance per unit area. Intrinsic TFT mobility does not exceed the Hall mobility. This is a well-established science. However, some papers report unbelievably high TFT mobility. We suggest ones with chemical background to read the papers by Wager et al. and Choi et al. carefully for correct assessment of device performance.27-29 We summarize several key points in the following. Firstly, the TFT channel should be patterned. If an unpatterned device is measured, fringe current would lead to overestimate of the TFT mobility due to the underestimation of the

5



channel width. This can lead to a factor of 10 overestimation of the TFT mobility, if the width to length ratio (W/L) is small (70 %) is commonly adopted for solution-based IGZO films.47 This large difference may be related to the different processing techniques (sputtering versus solution). However, the complete understanding is still unavailable. Secondly, for vacuum-deposited oxide TFTs, the device stability has been widely examined, since it is essential for practical display applications. However, the device stability fabricated by solution process has not been intensively investigated, especially the device under negative bias illumination stress (NBIS) conditions. More fundamental research should be carried out to study the electronic structure and film formation mechanism of the solution-processed oxide semiconductors. This will greatly facilitate development of large-area flexible oxide electronics with excellent reliability for display and emerging non-display applications.

Table 1. Recent advances of low-temperature (20 V), which limits their use in low power electronic applications. To circumvent this bottleneck, various gate insulators with large areal capacitances, including organic dielectrics, electrolyte dielectrics, and high-k oxide dielectrics, have been explored. Among these, high-k oxide dielectrics have received the most attention because of their large permittivity and the excellent heterogeneous interface with oxide-semiconductor active layers. TFT is a capacitance-based device, where the TFT source-drain current depends on the gate capacitance. The capacitance per unit area (C) can be simply expressed as 26


Page 27 of 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


C=k

ε0

(6)

d

where k, ε 0 , d is the dielectric constant, vacuum permittivity, and film thickness, respectively. For conventional SiO2 dielectric, the dielectric constant k=3.9. According to Equation 6, in order to gain large capacitance density for low voltage operation, two options are available: (a) reduced dielectric thickness; or (b) enhanced dielectric constant of gate dielectric. The conventional silicon dioxide (SiO2) is universally considered a unique gift of the nature to the MOSFET technology, having nearly-perfect properties for a gate dielectric: high electrical resistivity, large bandgap, high crystallization temperature, low defect density in the bulk, excellent Si-SiO2 interface. However, the traditional SiO2 has one drawback, that is the very low dielectric constant (k=3.9). Severe gate leakage current is usually observed when SiO2 thickness scaled down for large capacitance and low operatiion voltage.9, 102-103 High-k metal oxide dielectrics have been under investigation since the late 1990s in the silicon industry to overcome the above mentioned limitation of conventional SiO2 as the gate dielectric in MOSFETs.9, 102-103 According to Equation 6, thicker high-k oxide with similar C values can be obtained without causing the leakage problem. A large number of high-k oxide dielectrics have been developed, including Al2O3, ZrO2, HfO2, Y2O3, La2O3 and others.9, 102-103

The dielectric constant should be as high as possible, however, there is a trade-off

between the dielectric constant and the bandgap, as shown in Figure 13. The narrow band gap of the dielectric usually results in the small band offset with the oxide semiconductor, and hence large leakage current due to the Schottky emission. Basic requirements of oxide dielectrics for oxide TFTs are:9, 102-103 (1) robust insulating properties to maintain the low leakage current and high breakdown voltage; (2) high dielectric constant to increase the areal capacitance; (3) low defect densities; (4) excellent dielectric/semiconductor interface for carrier transport.

27



Figure 13.

Band gap versus static dielectric constant for different gate oxide materials.

(reprinted with permission from ref 80. Copyright 2015 John Wiley and Sons)

Regarding the film deposition technique, high-k metal oxide dielectrics have been conventionally fabricated by vacuum-based techniques, including pulsed laser deposition (PLD), atomic layer deposition (ALD), magnetron sputtering, e-beam evaporation etc. However, these methods require high equipment setup cost and are unsuitable for their future development in large-area flexible oxide electronics. Therefore, for the full realization of large-area low power metal oxide TFTs, the development of solution-based oxide dielectrics is a key issue in this emerging field. In this section, we will discuss the recent development in solution-processed high-k oxide dielectrics that can be combined with the solution-based oxide semiconductor for high performance oxide TFTs, which is summarized in Table 2. 4.2 Solution-Processed Binary Metal Oxide Dielectrics In the past 5 years or so, much effort has been devoted to develop solution-processed high-k dielectrics, including Al2O3, ZrO2, HfO2, Y2O3, Ga2O3, Sc2O3, MgO, Li2O, Nd2O3, Gd2O3, Yb2O3 etc. and their compounds.38, 45-47, 55, 61-63, 72, 76-78, 82, 104-118 The sol-gel chemistry of oxide dielectrics is similar to the n-type oxides (See to Section 3.1). Besides, the previous studies on low-temperature approaches (e.g., combustion chemistry, aqueous route, DUV activation) have been applied to producing high-k oxide dielectrics for flexible electronics. In

28


Page 28 of 59

Page 29 of 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the following, we will introduce the common solution-processed binary high-k dielectric in detail. Al2O3: Al2O3 is one of the most widely studied oxide dielectrics for oxide TFTs, which has a very large bandgap of 9.0 eV and a relatively low dielectric constant of 9. Al2O3 has attracted much attention due to its abundance in the earth, good chemical stability, high breakdown field, and especially the excellent interface with oxide semiconductors. Solution-processed Al2O3 for oxide TFTs has been prepared by various aluminum sources, including aluminum nitrate, aluminum acetylacetonate, aluminum chloride, and aluminum alkoxide in combination with various solvent such as 2-ME, ethanol, acetonitrile and ethyleneglycol, and even DI water. 38, 45-47, 55, 72, 77, 82, 104-110, 119-120 In 2011, Jang and co-workers reported the fabrication of solution-processed Al2O3 gate dielectric for ZTO TFTs.104 The Al2O3 layer was achieved by spin-coating a solution of aluminum chloride (AlCl3) mixed into a solvent of acetonitrile and ethyleneglycol, and then annealed at 300 oC. The breakdown electrical field and dielectric constant were 4 MVcm-1 and 6.3, respectively. The solution-processed ZTO/Al2O3 TFTs exhibited an excellent field-effect mobility of 33 cm2V-1s-1 and an on/off current ratio of 108. In 2013, Alshareef and co-workers reported the solution-deposited Al2O3 for high performance In2O3 TFTs with a mobility of 127 cm2V-1s-1 and an on/off current ratio of 106.105 In early 2015, Xu, et al. demonstrated a facile and environmentally friendly solution-processed method for Al2O3 dielectrics.109 The Al2O3 film was used as gate dielectric for solution-processed oxide TFTs. Above all, the In2O3 and IZO TFTs exhibited high mobilities of 57.2 cm2V-1s-1 and 10.1 cm2V-1s-1 with low operation voltages of 4 V at processing temperature of 300 °C (Figure 14), respectively. In 2017, Xu and co-workers developed a low-temperature aqueous route for the fabrication of Al2O3 in combination with the aqueous In2O3 and IZO semiconductors for oxide TFTs.55 The Al2O3 dielectric showed a low leakage current (2.9×10-7 A cm-2 at 1 MV cm-1) and a dielectric constant of 8.6 at processing temperature of 250 oC. The In2O3/Al2O3 TFTs annealed at 200 °C and 250 °C showed good mobilities of 2.04 and 30.88 cm2V-1s-1 at low operation voltage of 4 V, respectively. In 2017, Park, et al. reported an innovative route to form highly reliable aluminum-oxide dielectric films using an ultralow temperature (< 60 29



˚C) solution process with a class of oxide nanocluster precursors.111 The extremely low-temperature synthesis of oxide dielectric films was achieved by using low-impurity bulky metal-oxo-hydroxy nanoclusters in combination with highly energetic light activation process, resulting in Al2O3 dielectric with high breakdown field (>6 MV cm-1) and low leakage current (10-8 A cm-2 at 2 MV cm-1).

Figure 14. Leakage currents of Al2O3 under different post-annealing temperature and the transfer curves for In2O3/Al2O3 TFTs and IZO/Al2O3 TFTs at maximum temperature of 300 o

C. (reprinted with permission from Ref 109. Copyright 2015 ACS Publishing)

ZrO2: ZrO2 constitutes another class of most-studied solution-processed high-k oxide dielectrics, which has a large dielectric constant of 25 and a wide bandgap of 5.8 eV. In 2011, Adamopoulos and co-workers demonstrated ZrO2 dielectric by spray coating method using precursor solution of zirconium acetylacetonate and methanol.76 Optimized Li-ZnO/ZrO2 TFTs demonstrated an operation voltage below 6 V, an on/off current ratio of 106, negligible hysteresis, and a mobility up to 85 cm2V-1s-1, produced at maximum temperature of 400 oC (Figure 15). In 2016, Marks, et al. demonstrated the fabrication of ZrO2 dielectric using spray-combustion synthesis (See Section 3.2.1 for details about combustion process).46 The ZrO2 dielectric showed a low leakage current (10-7 A cm-2 at 2 MV cm-1) and high areal capacitance (> 600 nF cm-2). The solution-processed IZO/ZrO2 TFTs annealed at 250 °C and 300 °C exhibited mobilities of 12.1 and 45.5 cm2V-1s-1, respectively. In 2016, Shan and co-workers demonstrated the low-temperature fabrication of high-quality ZrO2 dielectrics via an aqueous route using zirconium nitrate and DI-water solution.63 The In2O3/ZrO2 TFTs annealed at 250 oC exhibited a high mobility of 10.8 cm2V-1s-1, a small subthreshold swing of 75 mV dec-1, and an on/off current ratio of 106, respectively. The p-type NiO/ZrO2 TFTs 30


Page 30 of 59

Page 31 of 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


produced at 250 oC exhibited an on/off current ratio of 105 and a hole mobility of 4.8 cm2V-1s-1.

Figure 15. (a) Transfer and (b) output curves of Li-ZnO/ZrO2 TFTs. (Reprinted with permission from Ref 76. Copyright 2011 John Wiley and Sons) HfO2: The commercially used high-k gate dielectric in conventional Si microelectronics is the HfO2-based material, due to its high dielectric constant (25), wide bandgap (5.7 eV), high resistance to impurity diffusion, and thermal stability up to 700 oC. In 2012, Jang, et al. reported a solution-processed high-k HfO2 dielectric with processing temperature of 300 °C.121 The ZTO/HfO2 TFTs showed a subthreshold swing of 105 mV dec-1 and a ﬁeld-effect mobility of 1.1 cm2V-1s-1. In 2015, Anthopoulos and co-workers demonstrated solution-processed HfO2 dielectrics under ambient conditions at 400 oC, by employing spray coating approach.78 Analyses reveal polycrystalline HfO2 with monoclinic structure, exhibiting a wide bandgap of 5.7 eV, a high dielectric constant of 18.8, and a high breakdown voltage of 2.7 MV cm-1. The solution-processed ZnO/HfO2 showed an excellent device performance with a low operation voltage of 6 V, a high on/off current ratio of 107 and electron mobility of 40 cm2V-1s-1. Y2O3: Y2O3 is an excellent candidate oxide dielectric because of its wide bandgap of 5.6 eV and relatively high dielectric constant of 15. In 2012, Moon, et al. studied high-k solution-processed

Y2O3

dielectrics

for

high

performance

oxide

TFTs.112

The

solution-processed Y2O3 dielectric showed a leakage current density less than 106 A cm-2 at 2 MV cm-1 and a high dielectric constant of nearly 16. All solution-processed fully transparent 31



ZnO TFTs based on Y2O3 gate dielectric were demonstrated, exhibiting a mobility of 135 cm2V-1s-1, an on/off current ratio of 107 as well as low-voltage operation. In 2015, Shan and co-workers also reported the fabrication of Y2O3 dielectric via an aqueous route, using precursor solution of Y(NO3)3·H2O and DI-water. 47 The Y2O3 dielectric produced at 300 oC showed a low leakage current (10-9 A cm-2 at 1 MV cm-1) and a dielectric constant of 14.8. The IZO/Y2O3 TFTs exhibited an excellent performance with a low operation voltage (≈1.5 V), a small subthreshold swing of 65 mV dec-1 and a high mobility of 25 cm2 V-1 s-1. Ga2O3: In 2015, Xu, et al. reported a novel aqueous route to fabricate Ga2O3 dielectric at low temperature.62 The Ga2O3 films produced at 200 oC exhibited a low leakage current of 10-6 A cm-2 at 2 MV cm-2 and a dielectric constant of 10.1. Furthermore, all aqueous solution-processed In2O3/Ga2O3 TFTs fabricated at 200 °C and 250 °C showed mobilities of 1.0 and 4.1 cm2V-1s-1, on/off current ratio of 105, low operation voltages of 4 V, and negligible hysteresis, respectively. Sc2O3: In 2015, Shan and co-workers reported the solution-processed Sc2O3 thin film via an aqueous route.61 The optimized Sc2O3 dielectric exhibited a low leakage of 0.2 nA cm-2 at 2 MVcm-1, a large areal capacitance of 460 nF cm-2, and a permittivity of 12.1. The solution-processed IZO/Sc2O3 TFTs showed an excellent performance, including a high electron mobility of 27.7 cm2V-1s-1, a large current ratio of 107 and high stability. The solution-processed p-type CuO/Sc2O3 TFTs exhibited a large current ratio of 105 and a hole mobility of 0.8 cm2V-1s-1 at low operation voltage of 3 V. MgO: In 2016, Shan, et al. reported the solution-processed MgO dielectrics, using precursor solution of magnesium nitrate hydrate (Mg(NO3)2·6H2O) in 2-ME.114 The MgO thin film annealed at 500 oC showed a smooth surface (

Recent Advances of Solution-Processed Metal Oxide Thin-Film

Recommend Documents