Transparent Electronic Devices Research Articles

Simple chemical solution deposition of Al2O3 dielectric layers for low-cost fabrication of transparent electronic devices

Simple chemical solution deposition of Al2O3 dielectric layers for low-cost fabrication of transparent electronic devices

Transparent ionic liquid antenna based on multi-modes using multiple feeding structures

With the rapid development of modern wireless communication technology, there is an increasing demand for the functionality of the communication system carried by a single platform. To improve the utilization of the antenna, a multimode liquid antenna is proposed in this paper. The antenna is fabricated using 3D printing technology and mainly consists of a cylindrical dielectric resonator, a coaxial feeding structure, and a slot-coupling feeding structure. By hollowing out the middle of a resin container and filling it with low-loss ionic liquid with stable dielectric properties, a liquid dielectric resonator antenna (DRA) is formed. The various resonant modes (slot mode, HEM11δ, TM11δ, TM21δ, and TM31δ modes) can be excited by introducing different feeding structures. The operating frequencies and radiation patterns can be modulated by mode switching. Simulated and measured results show that the antenna operates in the frequency bands of 2.25–2.76 GHz (20.4 %) and 4.82–5.73 GHz (17.3 %), and the maximum gain can be up to 10.3 dBi. The proposed antenna structure avoids the complex RF control circuit design, which has various applications including 5G/6G communications, transparent electronic devices, and Internet of Things.

Fast and Massive Pixel-Level Morphology Detection by Imaging Processing for Inkjet Printing.

With the rapid development of the emerging intelligent, flexible, transparent, and wearable electronic devices, such as quantum-dot-based micro light-emitting diodes (micro-LEDs), thin-film transistors (TFTs), and flexible sensors, numerous pixel-level printing technologies have emerged. Among them, inkjet printing has proven to be a useful and effective tool for consistently printing micron-level ink droplets, for instance, smaller than 50 µm, onto wearable electronic devices. However, quickly and accurately determining the printing quality, which is significant for the electronic device performance, is challenging due to the large quantity and micron size of ink droplets. Therefore, leveraging existing image processing algorithms, we have developed an effective method and software for quickly detecting the morphology of printed inks served in inkjet printing. This method is based on the edge detection technology. We believe this method can greatly meet the increasing demands for quick evaluation of print quality in inkjet printing.

Cs‐Doped and Cs‐S Co‐Doped CuI p‐Type Transparent Semiconductors with Enhanced Conductivity

AbstractOne hindrance in transparent electronics is the lack of high‐performance p‐type transparent conductors (TCs). The state‐of‐the‐art p‐type TC, CuI, has a conductivity two orders of magnitude lower than n‐type TCs like ITO. While doping strategies have shown promise in enhancing the hole carrier density in CuI, they often come at the expense of hole mobility. Therefore, understanding how extrinsic dopants affect the mobility of CuI is critical to further improve the performance of CuI‐based TCs. Here the structural and electronic properties of Cs‐doped CuI are investigated. It is demonstrated that ≈4 at.% Cs doping in CuI increases the carrier density from 2.1 × 1019 to 3.8 × 1020 cm−3 while preserving the film microstructure and local coordination of Cu, as confirmed by HRTEM and XAS analysis. Introducing S as a co‐dopant in Cs:CuI boosts the carrier density to 8.2 × 1020 cm−3, reaching a stable conductivity of ≈450 S cm−1. In all cases, the enhanced carrier density negatively affects the hole mobility with ionized impurity scattering and increased Seebeck hole effective mass as mobility limiting mechanisms. Nonetheless, the new Cs, S co‐doped CuI exhibits high p‐type conductivity, Vis–NIR transparency, and stability, presenting an attractive candidate for future transparent electronic devices.

Research of aging test on high Tg colorless polyimide

AbstractFor the past few years, colorless polyimide (CPI) has been drawn much attention for its application in transparent electronics. The high temperature (even to 450°C) process of the preparation of organic light‐emitting diode display (OLED) device may have huge challenges on the properties of CPI, so we designed a series of aging test experiments to study the influence of test temperature and atmosphere on the high transparency percentages (Tr%) of CPI films with structure of Glass/SiO2/CPI/SiO2. As the aging temperature increased from 430 to 450°C and then to 470°C, the Tr% of the film decreased significantly. Comparing with the sample without aging, the transmission losses were 0.22%, 1.42%, and 4.82% for the films aging with 430, 450, and 470°C in N2 atmosphere, respectively. Additionally, aging in nitrogen resulted in less Tr% loss (1.22%) compared with air (1.42%). This research offers insights into how to maintain the high Tr% of CPI films during high‐temperature processing. Furthermore, it supports the development of more durable and reliable CPI‐based components for OLED displays and other transparent electronic devices. This can lead to advancements in the performance of these devices, potentially extending their lifespan and broadening their range of applications.

Variation in the Bandgap of Amorphous Zinc Tin Oxide: Investigating the Thickness Dependence via In Situ STS.

Amorphous transparent conducting oxides (a-TCOs) have seen substantial interest in recent years due to the significant benefits that they can bring to transparent electronic devices. One such material of promise is amorphous ZnxSn1-xOy (a-ZTO). a-ZTO possesses many attractive properties for a TCO such as high transparency in the visible range, tunable charge carrier concentration, electron mobility, and only being composed of common and abundant elements. In this work, we employ a combination of UV-vis spectrophotometry, X-ray photoemission spectroscopy, and in situ scanning tunneling spectroscopy to investigate a 0.33 eV blue shift in the optical bandgap of a-ZTO, which we conclude to be due to quantum confinement effects.

Highly Transparent Red Organic Light-Emitting Diodes with AZO/Ag/AZO Multilayer Electrode.

Free-form factor optoelectronics is becoming more important for various applications. Specifically, flexible and transparent optoelectronics offers the potential to be adopted in wearable devices in displays, solar cells, or biomedical applications. However, current transparent electrodes are limited in conductivity and flexibility. This study aims to address these challenges and explore potential solutions. For the next-generation transparent conductive electrode, Al-doped zinc oxide (AZO) and silver (AZO/Ag/AZO) deposited by in-line magnetron sputtering without thermal treatment was investigated, and this transparent electrode was used as a transparent organic light-emitting diode (OLED) anode to maximize the transparency characteristics. The experiment and simulation involved adjusting the thickness of Ag and AZO and OLED structure to enhance the transmittance and device performance. The AZO/Ag/AZO with Ag of 12 nm and AZO of 32 nm thickness achieved the results of the highest figure of merit (FOM) (Φ550 = 4.65 mΩ-1) and lowest roughness. The full structure of transparent OLED (TrOLED) with AZO/Ag/AZO anode and Mg:Ag cathode reached 64.84% transmittance at 550 nm, and 300 cd/m2 at about 4 V. The results demonstrate the feasibility of adopting flexible substrates, such as PET, without the need for thermal treatment. This research provides valuable insights into the development of transparent and flexible electronic devices.

Robust large area molecular junctions based on transparent and flexible electrodes

Towards transparent and flexible large area molecular electronic devices.

An optically semi-transparent liquid antenna with slot-coupled feeding for future wireless communication systems

To meet the needs of optically transparent camouflage and concealment in the military field, as well as to improve the aesthetics and flexibility of wireless electronic devices. In this paper, a rectangular wideband liquid antenna with medium transparency and a hollowed-out center is proposed. The antenna is fabricated by using 3D printing technology and is primarily composed of a hollowed-out rectangular resin container, a transparent ionic liquid, and a non-transaprent slot-coupled feeding structure. By removing the center of the resin container and filling it with air, a resonator is formed that merges a rectangular ring with air. This method decreases the equivalent relative permittivity of the entire resonator and expands the operating bandwidth. Experimental results show that the antenna has an impedance bandwidth of 7 GHz-8.25 GHz, a relative bandwidth of 16.4%, a optical transparency of 84.57% and a maximum gain of 9.5dBi at 8 GHz. The proposed antenna has potential applications in electronic countermeasures, multimode composite guidance, 5G communication, and transparent electronic devices.

Approaching Theoretical Limits in the Performance of Printed P-Type CuI Transistors via Room Temperature Vacancy Engineering.

Development of a novel high performing inorganic p-type thin film transistor could pave the way for new transparent electronic devices. This complements the widely commercialized n-type counterparts, indium-gallium-zinc-oxide (IGZO). Of the few potential candidates, copper monoiodide (CuI) stands out. It boasts visible light transparency and high intrinsic hole mobility (>40 cm2 V-1 s-1 ), and is suitable for various low-temperature processes. However, the performance of reported CuI transistors is still below expected mobility, mainly due to the uncontrolled excess charge- and defect-scattering from thermodynamically favored formation of copper and iodine vacancies. Here, a solution-processed CuI transistor with a significantly improved mobility is reported. This enhancement is achieved through a room-temperature vacancy-engineering processing strategy on high-k dielectrics, sodium-embedded alumina. A thorough set of chemical, structural, optical, and electrical analyses elucidates the processing-dependent vacancy-modulation and its corresponding transport mechanism in CuI. This encompasses defect- and phonon-scattering, as well as the delocalization of charges in crystalline domains. As a result, the optimized CuI thin film transistors exhibit exceptionally high hole mobility of 21.6 ± 4.5 cm2 V-1 s-1 . Further, the successful operation of IGZO-CuI complementary logic gates confirms the applicability of the device.

Theoretical Study of Doping in GaOOH for Electronics Applications

GaOOH, having a bandgap of 4.7–4.9 eV, can be regarded as one of several ultrawide-bandgap (UWBG) semiconductors, although it has so far mainly been used as a precursor material of Ga2O3. To examine the possibility of valence control and application in electronics, impurity levels in GaOOH are investigated using the first-principles density-functional theory calculation. The density values of the states of a supercell including an impurity atom are calculated. According to the results, among the group 14 elements, Si is expected to introduce a shallow donor level, i.e., a free electron is introduced. On the other hand, Ge and Sn introduce a localized state about 0.7 eV below the conduction band edge, and thus cannot act as an effective donor. While Mg and Ca can introduce a free hole and act as a shallow acceptor, Zn and Cd introduce acceptor levels away from the valence band. The transition metal elements (Fe, Co, Ni, Cu) are also considered, but none of them are expected to act as a shallow dopant. Thus, the results suggest that the carrier concentration can be controlled if Si is used for n-type doping, and Mg and Ca for p-type doping. Since GaOOH can be easily deposited using various chemical techniques at low temperatures, GaOOH will potentially be useful for transparent electronic devices.

Large-scale, high-transparency, ultra-thin ITO membranes with robust conductivity and flexibility

Ultra-thin ITO films exhibit excellent optical properties but poor electrical properties, which greatly limit further applications in the field of optoelectronic devices. In this study, a large-area (4 inches) ITO thin film with a thickness of 10 nm was prepared on a flexible Mica substrate. The film shows low resistivity (1.32×10−4 Ω·cm), high carrier concentration (2.2 × 1021 cm−3), high optical transparency (>98.1%), and an atomic-level flat surface. XPS characterization and first principles calculations prove that the van der Waals interface between ITO and Mica can induce a higher concentration of oxygen vacancies in the ultra ITO thin film, which is the reason for its remarkable conductivity enhancement. In addition, the ITO/Mica flexible film exhibits excellent durability and recyclability, maintaining its photoelectric properties at a high bending radius of 2.5 mm and tens of thousands of bending cycles. This study will provide an important experimental basis for the further development and application of large-area, ultra-thin ITO films in flexible transparent electronic devices.

Solution-processed transparent PVP:HfO2 hybrid dielectric films with low leakage current density and high k

Organicinorganic hybrid dielectric materials have attracted significant attention owing to their capacity to integrate the mechanical and electrical characteristics of organic and inorganic components. This paper presents the deposition of high-performance polyvinylpyrrolidone (PVP): hafnium oxide (HfO2) hybrid dielectric films at low temperature using the sol-gel method. Initially, the influence of precursor components on the surface morphology of single-component dielectric films was investigated. It is observed that the addition of FSO and acetic acid can result in smoother and more uniform surfaces for PVP and HfO2, respectively. Furthermore, based on these findings, we successfully prepared PVP:HfO2 hybrid dielectric films with surface roughness below 1 nm, high transmittance above 95% in the visible range (400–760 nm), and wide optical bandgaps exceeding 5.3 eV. The formation of PVP:HfO2 cross-linked network was identified through FTIR analysis, and a mechanism was proposed. Moreover, MIM devices were fabricated to determine the insulating performance of dielectric films. We found that the PVP:HfO2 hybrid dielectric films exhibit a significant reduction in leakage current density and a substantial increase in relative dielectric constant compared to the single-component dielectric films. In addition, with the increase in PVP concentration, the leakage current density first decreases and then increases, while the relative dielectric constant first increases and then decreases. After optimization, 0.5 wt% PVP:HfO2 hybrid dielectric film exhibits a low leakage current density of 5.89×10−8 A/cm2 @1 MV/cm and a high relative dielectric constant of 32.54. PVP:HfO2 hybrid dielectric films exhibit tremendous potential for applications in the realm of high-performance transparent electronic devices.

Crystallization of (Hf, Zr)O2 thin films via non-heating process and their application to ferroelectric-gate thin film transistors

HfO2-based ferroelectric materials do not necessarily require high-temperature annealing for crystallization, making them attractive for applications in transparent electronic devices on plastic or glass substrate. In this study, (Hf, Zr)O2 (HZO) films prepared via non-heating sputtering are investigated and their application to ferroelectric-gate thin-film transistors (TFTs) is demonstrated. The internal tensile stress induced by (In, Sn)O x (ITO) top-electrode deposition is found to promote the crystallization of HZO from the amorphous state to the ferroelectric phase. ITO/HZO (15–25 nm)/ITO capacitors prepared via the non-heating process exhibit ferroelectric hysteresis loops with remanent polarizations of 6–9 μC cm−2 and coercive fields of 0.6–1.1 MV cm−1. Ferroelectric-gate TFTs with a 10 nm thick ITO channel are also fabricated via the non-heating process. These TFTs show nonvolatile operation with an on/off ratio of ∼10. These findings demonstrate the potential of HZO for transparent devices on substrates with low thermal resistance prepared via the non-heating process.

Low-temperature polyol synthesis of millimeter-scale-length silver nanowires enabled by high concentration of Fe3+ for flexible transparent heaters

Silver nanowires (AgNWs) emerge as a promising candidate for flexible electronic devices. AgNWs with high aspect ratios improve the optoelectronic properties of transparent conductive electrodes. However, syntheses conducted at a high temperature usually produce AgNWs either too short or too thick. Here, we report a one-pot low-temperature polyol method using a high concentration of Fe(NO3)3 (up to 160 mM). Fe3+ was found to accelerate AgNWs growth by five times, possibly reduced to Fe2+ and functioning as an oxygen scavenger to preserve Ag seeds, allowing the synthesis to be conducted at as low as 70 °C, which was about 100 °C lower compared with a common polyol method. Low temperature suppressed excessive nucleation, producing AgNWs longer than 1100 μm. AgNWs were dispersed in an acidic solution and purified with a non-pressure filtration method. transparent conductive electrodes fabricated with long AgNWs on polyethylene terephthalate exhibited a sheet resistance of 7.8 Ω/sq at a transmittance of 95.0% without heat treatment. Transparent heaters of AgNWs on polyethylene terephthalate and polydimethylsiloxane substrates were heated to 79.1 °C at 3 V and 174.1 °C at 8 V power supply, respectively, and their application was demonstrated in a quick defogging process. The simple synthesis method of ultralong AgNWs may expand their applications in high-performance flexible transparent electronic devices.

Simultaneously achieving high transparency and applicable piezoelectricity in Sm-modified KNN-based lead-free ceramics

Transparent piezoelectric ceramics have drawn extensive concerns in recent years because of their electro-optical applications. However, it's challenging to achieve both high piezoelectricity and transparency simultaneously because of their intrinsic trade-off, especially for lead-free ceramics. In this work, the rare-earth element Sm is introduced into (K,Na)NbO3-based lead-free ceramics for improving transparency while keeping relatively high piezoelectricity. Ceramics with nominal compositions of [(Na0.57K0.43)0.94Li0.06][(Nb0.94Sb0.06-xSmx)0.95Ta0.05]O3 (x = 0 ∼ 0.005) are fabricated via the conventional solid-state reaction method. Even with pressureless sintering, the ceramic with Sm substitution content x = 0.004 possesses high transmittance of T = 63% in the visible light region (without anti-reflection coatings) and good piezoelectricity (d33 = 158 pC/N). The high transparency can be attributed to the presence of a pseudocubic phase and the significant elimination of domain walls by the Sm modification, while a coexistent orthorhombic-tetragonal phase structure at room temperature is responsible for its superior piezoelectric performance which outperforms other reported KNN-based transparent ceramics. Our results demonstrate that the as-fabricated ceramics are promising lead-free ferroelectric materials for transparent electronic device applications and this work provides insights for the further development of transparent piezoelectric ceramics.

Effect of Titanium Cation Doping on the Performance of In2O3 Thin Film Transistors Grown via Atomic Layer Deposition

Indium oxide semiconductors, as one of the channel materials for thin film transistors (TFTs), have been extensively studied. However, the high carrier concentration and excess oxygen defects of intrinsic In2O3 can cause the devices to fail to work properly. We overcame this hurdle by incorporating the titanium cation (Ti4+) into In2O3 via atomic layer deposition (ALD). The InTiOx TFTs with an In:Ti atomic ratio of 15:1 demonstrated excellent electrical and optical properties, such as a lower threshold voltage (Vth) of 0.17 V, a lower subthreshold swing (SS) of 0.13 V/dec., a higher Ion/Ioff ratio of 107, and a transmittance greater than 90% in the visible region. With the doping ratio increasing from 20:1 to 10:1, the mobility decreased from 9.38 to 1.26 cm2/Vs. The threshold voltage shift (ΔVth) of InTiO (15:1) under 5 V positive bias stress (PBS) for 900 s is 0.93 V, which is less than other devices. The improvement in stability with increasing Ti4+ concentrations is attributed to the reduction of oxygen defects. Therefore, these InTiO (15:1) TFTs with excellent performance show great potential for future applications in transparent electronic devices.

Multi-ratio optical thermometry and energy storage characteristics of Yb3+/Er3+/Tm3+ doped BaNb2O6 transparent glass-ceramics

• RE-doped BaNb 2 O 6 transparent glass ceramics (GCs) were fabricated firstly. • Realizing three-mode Up-conversion optical thermometry in the GCs. • The maximum S r-max and S a-max can reach 2.30% K –1 and 6.71‰ K –1 . • Achieving high W d of 0.99 J cm –3 and high P d of 225.3 MW cm –3 . • Multifunctional GCs can be used in optical sensing and energy storage fields. In order to meet the needs of new materials gradually developing towards miniaturization, integration, and light weight, multifunctional BaNb 2 O 6 : Yb 3+ /Er 3+ /Tm 3+ transparent glass-ceramics were successfully prepared by melt quenching and controllable crystallization. Its structure, luminescence, and energy transmission were studied. Using the opposite temperature dependence of the Tm 3+ emission band and the corresponding large energy level gap, a maximum relative sensitivity of 2.3% K –1 based on thermal coupling levels (TCLs) is obtained in a wide temperature range (298–673 K). The multi-ratio optical thermometry based on TCLs and non-TCLs is successfully realized by using the different emission bands of double emission centers, which makes it possible for self-reference optical temperature measurement modes. In addition, the transparent glass-ceramic exhibits excellent electrical properties under 700 kV cm –1 electric field: high discharge energy density ( W d = 0.99 J cm –3 ), huge instantaneous power density (225.3 MW cm –3 ), and ultra-fast discharge rate ( T 0.9 ≤ 15.8 ns). The prepared glass-ceramic is expected to be a new type of lead-free multifunctional photoelectric material for temperature sensors and transparent electronic devices.

Flexible, Stretchable, and Transparent MXene Nanosheet/Thermoplastic Polyurethane Films for Multifunctional Heating and Electromagnetic Interference Shielding

The development of multifunctional electromagnetic interference (EMI) shielding films with optical transparency is highly urgent as visual windows in modern optoelectronic devices. Herein, Ti3C2Tx nanosheet (MXene)-based transparent conductive films (TCFs) with thermoplastic polyurethane (TPU) as substrates were prepared by simple spraying, which was further applied in high-performance EMI shielding, Joule heating, and photothermal conversion. The comprehensive properties of the transparent MXene/TPU films can be optimized by adjusting the thickness of the MXene layer. The optimal TCF showed a sheet resistance of 119.1 Ω/sq, a transmittance of 43.1%, and an average EMI shielding effectiveness of 10.9 dB. Meanwhile, this TCF exhibited a stable EMI shielding performance to resist bending and stretching. Moreover, the multifunctional MXene/TPU film presented remarkable thermal management performances, including Joule heating (89.4 °C @ 7 V) and photothermal conversion (72 °C @ 100 mW/cm2) abilities. This work presents flexible and stretchable MXene-based TCFs with satisfactory EMI shielding performance and multisource thermal response behavior, which is promising for various transparent and flexible electronic devices.

High-mobility and low subthreshold swing amorphous InGaZnO thin-film transistors by in situ H2 plasma and neutral oxygen beam irradiation treatment

In this work, staggered bottom-gate structure amorphous In–Ga–Zn–O (a-IGZO) thin film transistors (TFTs) with high-k ZrO2 gate dielectric were fabricated using low-cost atmospheric pressure-plasma enhanced chemical vapor deposition (AP-PECVD) with in situ hydrogenation to modulate the carrier concentration and improve interface quality. Subsequently, a neutral oxygen beam irradiation (NOBI) technique is applied, demonstrating that a suitable NOBI treatment could successfully enhance electrical characteristics by reducing native defect states and minimize the trap density in the back channel. A reverse retrograde channel (RRGC) with ultra-high/low carrier concentration is also formed to prevent undesired off-state leakage current and achieve a very low subthreshold swing. The resulting a-IGZO TFTs exhibit excellent electrical characteristics, including a low subthreshold swing of 72 mV dec−1 and high field-effect mobility of 35 cm2 V−1 s−1, due to conduction path passivation and stronger carrier confinement in the RRGC. The UV–vis spectroscopy shows optical transmittance above 90% in the visible range of the electromagnetic spectrum. The study confirms the H2 plasma with NOBI-treated a-IGZO/ZrO2 TFT is a promising candidate for transparent electronic device applications.