High-Performance Low-Voltage Thin-Film Transistors: Experimental and Simulation Validation of Atmospheric Pressure Plasma-Assisted Li5AlO4 Metal Oxide Solution Processing

Metal oxide materials processed using solution methods have garnered significant attention due to their ability to efficiently and affordably create transparent insulating layers or active channel layers on various substrates for thin-film transistors (TFTs) used in modern electronics. The key properties of TFTs largely depend on how charge carriers behave near the thin layer at the semiconductor and dielectric interface. Effectively controlling these characteristics offers a straightforward yet effective approach to enhancing device performance. In this study, we propose a novel strategy utilizing atmospheric pressure plasma (APP) treatment to modulate the electrical properties of dielectric thin films and the interfaces between dielectric and semiconductor layers in TFTs processed by using solution methods. Through APP exposure, significant improvements in key TFT parameters were achieved for solution-processed TFTs. Interface states have been reduced from 1013 to 1011 cm-2, and the on/off current ratio has increased from 103 to 106 while maintaining a high field-effect mobility of 34 cm2 V-1 s-1. Additionally, UV-visible spectroscopy and X-ray analysis have confirmed the effectiveness of APP treatment in controlling interface states and traps, leading to overall performance enhancements in the TFTs. Furthermore, our experimental findings have been systematically validated using technology computer-aided design (TCAD) simulations of fabricated TFTs.

Stretchable Semiconducting Polymers with Hydrogen-Bonding-Capable Conjugation Breakers: Synthesis and Application in Organic Thin-Film Transistors

Diketopyrrolopyrrole (DPP)-based conjugated copolymers are important organic semiconductors for applications in high-efficiency organic thin-film transistors (OTFTs). However, the direct application of these polymers with rigid backbones in stretchable devices has limitations. In this study, we designed and synthesized three kinds of DPPBT-based copolymers, DPPBT-A1, DPPBT-A3, and DPPBT-A5, which have amide-coupled alkylene conjugation breakers capable of hydrogen bonding. Linkers with different segment lengths were copolymerized with DPP and bithiophene (BT) backbone units. A DPP-based copolymer with alternating BT moieties, DPPBT, was synthesized as a reference fully conjugated copolymer. The synthesized polymers with freely rotational backbone linkers have sufficient flexibility to develop ordered phase domains, even in thin films, in comparison to the reference copolymer. However, the introduction of the conjugation breakers, which disconnect the intramolecular π-π overlapping, tends to decrease the hole mobility (μ) from 0.76 to 0.20 cm2 V-1 s-1 in the corresponding OTFT devices. The TFT fabricated using DPPBT-A3 showed a mobility of 0.50 cm2 V-1 s-1, and the mobility value did not show a significant change even when elongated by more than 50%. Therefore, the molecular design strategy of introducing amide-coupled alkylene conjugation breakers into conjugated polymer chains can contribute significantly to the development of high-mobility stretchable conjugated polymers in future.

The Effect of Alkyl Chain Length in Organic Semiconductor and Surface Polarity of Polymer Dielectrics in Organic Thin-Film Transistors (OTFTs)

The interface between dielectric and organic semiconductor is critically important in determining organic thin-film transistor (OTFT) performance. Surface polarity of the dielectric layer can hinder charge transport characteristics, which has restricted utilization of polymeric dielectric materials containing polar functional groups. Herein, the electrical characteristics of OTFTs are analyzed depending on the alkyl chain length of organic semiconductors and surface polarity of polymer dielectrics. High-performance dibenzothiopheno[6,5-b:6',5'-f]thieno[3,2-b]thiophene (DBTTT) and newly synthesized its alkylated derivatives (C6-DBTTT and C10-DBTTT) are utilized as organic semiconductors. As dielectric layers, non-polar poly(1,3,5-trimethyl-1,3,5-trivinylcyclitrisiloxane) (pV3D3) and poly(2-cyanoethyl acrylate-co-diethylene glycol divinyl ether) [p(CEA-co-DEGDVE)] with polar cyanide functionality are utilized. The fabricated OTFTs with pV3D3 commonly exhibit the excellent charge transport characteristics. In addition, the OTFT performance is improved with lengthening the alkyl chain in organic semiconductors, which can be attributed to the molecular orientation of semiconductors. On the other hand, non-alkylated DBTTT OTFTs with polar p(CEA-co-DEGDVE) show relatively poor electrical characteristics, while their performance is drastically enhanced with the alkylated DBTTTs. The ultraviolet photoelectron spectroscopy (UPS) reveals that surface polarity of the dielectric layer can be abated with alkyl chain in organic semiconductors. It is believed that this study can provide a useful insight to optimize dielectric/semiconductor interface to achieve high-performance OTFTs.

Impact of compact TiO2 interface modification on the crystallinity of perovskite solar cells

The effect of TiO2 interfacial morphology on perovskite crystallinity was investigated by modifying the micro and nanoscale surface roughness of compact TiO2. While surface treatments of the compact TiO2 layer are recognized as effective strategies to enhance the photovoltaic performance of perovskite solar cells, the discussion regarding the crystallinity of perovskite atop TiO2 has been limited. In this study, we explored the impact of micro and nano scale interface morphology on perovskite crystal formation and its subsequent effects on device performance. Surprisingly, despite the absence of noticeable voids at the interface between the compact TiO2 and perovskite layers, the perovskite crystal morphology exhibited significant improvement following either micro or nanoscale interfacial modification. This enhancement ultimately led to improved photoconversion efficiency and reduced I-V hysteresis. These results emphasize the importance of underlayer surface morphology in the perovskite crystallization and suggest that the presence of grain boundaries within the perovskite layer may also contribute to I-V hysteresis in perovskite solar cells.

Low-Operating-Voltage Two-Dimensional Tin Perovskite Field-Effect Transistors with Multilayer Gate Dielectrics Based on a Fluorinated Copolymer

The fabrication of organic-inorganic perovskite field-effect transistors (FETs) with polymer gate dielectrics is challenging because of the solvent corrosion and wettability issues at interfaces. A few polymers have been integrated into perovskite transistors; however, these devices have high operating voltages due to low dielectric constants. Herein, poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE) with a high dielectric constant is introduced into bottom-gate phenylethylammonium tin iodide perovskite [(PEA)₂SnI₄] FETs. Polytetrafluoroethylene (PTFE) and cross-linked poly(4-vinylphenol) (PVP) (CL-PVP) are used to address the issues of solvent corrosion and wettability. We design the PVDF-TrFE/PTFE and PVDF-TrFE/PTFE/CL-PVP dielectric layers, where the ferroelectric properties of PVDF-TrFE are reduced by PTFE. The (PEA)₂SnI₄ FETs operate at relatively low gate voltages, exhibiting good overall performance with average hole mobilities of 0.42 and 0.36 cm² V^-1 s^-1. Our findings provide a feasible strategy for constructing low-operating-voltage perovskite FETs with large-dielectric-constant ferroelectric polymers as gate dielectrics by a solution processing technique.

Poly(ionic liquid) Gating Materials for High-Performance Organic Thin-Film Transistors: The Role of Block Copolymer Self-Assembly at the Semiconductor Interface

The widespread realization of wearable electronics requires printable active materials capable of operating at low voltages. Polymerized ionic liquid (PIL) block copolymers exhibit a thickness-independent double-layer capacitance that makes them a promising gating medium for the development of organic thin-film transistors (OTFTs) with low operating voltages and high switching speed. PIL block copolymer structure and self-assembly can influence ion conductivity and the resulting OTFT performance. In an OTFT, self-assembly of the PIL gate on the semiconducting polymer may differ from bulk self-assembly, which would directly influence electrical double-layer formation. To this end, we used poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2)) as a model semiconductor for our OTFTs, on which our PILs exhibited self-assembly. In this study, we explore this critical interface by grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM) of P(NDI2OD-T2) and a series of poly(styrene)-b-poly(1-(4-vinylbenzyl)-3-butylimidazolium-random-poly(ethylene glycol) methyl ether methacrylate) (poly(S)-b-poly(VBBI⁺[X]-r-PEGMA)) block copolymers with varying PEGMA/VBBI⁺ ratios and three different mobile anions (where X = TFSI^-, PF₆^-, or BF₄^-). We investigate the thin-film self-assembly of block copolymers as a function of device performance. Overall, a mixed orientation at the interface leads to improved device performance, while predominantly hexagonal packing leads to nonfunctional devices, regardless of the anion present. These PIL gated OTFTs were characterized with a threshold voltage below 1 V, making understanding of their structure-property relationships crucial to enabling the further development of high-performance gating materials.

A Sub-20 nm Organic/Inorganic Hybrid Dielectric for Ultralow-Power Organic Thin-Film Transistor (OTFT) With Enhanced Operational Stability

Organic/inorganic hybrid materials are utilized extensively as gate dielectric layers in organic thin-film transistors (OTFTs). However, inherently low dielectric constant of organic materials and lack of a reliable deposition process for organic layers hamper the broad application of hybrid dielectric materials. Here, a universal strategy to synthesize high-k hybrid dielectric materials by incorporating a high-k polymer layer on top of various inorganic layers generated by different fabrication methods, including AlO_x and HfO_x , is presented. Those hybrid dielectrics commonly exhibit high capacitance (>300 nF·cm^-2 ) as well as excellent insulating properties. A vapor-phase deposition method is employed for precise control of the polymer film thickness. The ultralow-voltage (<3 V) OTFTs are demonstrated based on the hybrid dielectric layer with 100% yield and uniform electrical characteristics. Moreover, the exceptionally high stability of OTFTs for long-term operation (current change less than 5% even under 30 h of voltage stress at 2.0 MV·cm^-1 ) is achieved. The hybrid dielectric is fully compatible with various substrates, which allows for the demonstration of intrinsically flexible OTFTs on the plastic substrate. It is believed that this approach for fabricating hybrid dielectrics by introducing the high-k organic material can be a promising strategy for future low-power, flexible electronics.

Patterning an Erosion-Free Polymeric Semiconductor Channel for Reliable All-Photolithography Organic Electronics

Reliable patterning of organic semiconductors (OSCs) with high uniformity is essential to all-photolithography organic electronics. However, the majority of cross-linked OSCs experience performance fluctuations after photolithography because of the inherent vulnerability of low-ordered regions. Herein, we develop an anti-solution penetration photolithography process to achieve the reliable patterning of the OSC layer for all-photolithography integrated organic electronics. Using a thick and highly cross-linked semiconductor film and a low-solubility developer, an erosion-free semiconductor channel is obtained with a high mobility of up to 1.254 cm² V^-1 s^-1 and a uniform threshold voltage close to zero. Compared with existing all-photolithography organic circuits, the unit logic gate area consumption is lower by 1-3 orders of magnitude at 0.0069 mm², while the transistor density is higher by 1-2 orders of magnitude at 6780 Tr cm^-2. The miniaturized organic inverters maintain uncompromised voltage gains, and the 15-stage organic ring oscillators feature higher oscillation frequencies, making them promising for applications in wide-ranging integrated organic circuits.

NO2-Affinitive Conjugated Polymer for Selective Sub-Parts-Per-Billion NO2 Detection in a Field-Effect Transistor Sensor

Conjugated polymers (CPs) have provided versatile semiconducting implements for the development of soft electronic devices. When three CPs with the same conjugated framework but different side chains were adopted in the field-effect transistor (FET) sensor for NO₂ detection, the response to NO₂ showed an opposite tendency to the charge carrier mobility of each CP. Morphological and structural characterizations revealed that the flexible glycol side chain enhances NO₂ affinity as well as prevents the formation of lamellar stacking of the CP chains, thereby providing routes for the facile diffusion of NO₂. Additionally, theoretical calculations for CP-NO₂ complex formation at the molecular level support the relatively low energy barrier for inter-chain transition of NO₂ between the glycol-based conjugated frameworks, which implies the spontaneous internal diffusion of NO₂ to the semiconductor-dielectric interface in the FET-based sensor. As a result, the CP with a NO₂-affinitive morphology exhibited an exceptional sensitivity of 13.8%/ppb upon NO₂ (100 ppb) exposure for 50 s and provided excellent selectivity to the FET-based sensor toward other environmentally abundant harmful gases, such as SO₂, CO₂, and NH₃. In particular, the theoretic limit of detection reached down to 0.24 ppb, which is the lowest value ever reported for organic FET-based NO₂ gas sensors.

Metal phthalocyanines: thin-film formation, microstructure, and physical properties

Metal phthalocyanines (MPcs) are an abundant class of small molecules comprising of a highly conjugated cyclic structure with a central chelated metal ion. Due to their remarkable chemical, mechanical, and thermal stability MPcs have become popular for a multitude of applications since their discovery in 1907. The potential for peripheral and axial functionalization affords structural tailoring to create bespoke MPc complexes for various next generation applications. Specifically, thin-films of MPcs have found promising utility in medical and electronic applications where the need to understand the relationship between chemical structure and the resulting thin-film properties is an important ongoing field. This review aims to compile the fundamental principles of small molecule thin-film formation by physical vapour deposition and solution processing focusing on the nucleation and growth of crystallites, thermodynamic and kinetic considerations, and effects of deposition parameters on MPc thin-films. Additionally, the structure-property relationship of MPc thin-films is examined by film microstructure, morphology and physical properties. The topics discussed in this work will elucidate the foundations of MPc thin-films and emphasize the critical need for not only molecular design of new MPcs but the role of their processing in the formation of thin-films and how this ultimately governs the performance of the resulting application.

The Quinonoid Zwitterion Interlayer for the Improvement of Charge Carrier Mobility in Organic Field-Effect Transistors

The interface between the semiconductor and the dielectric layer plays a crucial role in organic field-effect transistors (OFETs) because it is at the interface that charge carriers are accumulated and transported. In this study, four zwitterionic benzoquinonemonoimine dyes featuring alkyl and aryl N-substituents were used to cover the dielectric layers in OFET structures. The best interlayer material, containing aliphatic side groups, increased charge carrier mobility in the measured systems. This improvement can be explained by the reduction in the number of the charge carrier trapping sites at the dielectric active layer interface from 10¹⁴ eV⁻¹ cm⁻² to 2 × 10¹³ eV⁻¹ cm⁻². The density of the traps was one order of magnitude lower compared to the unmodified transistors. This resulted in an increase in charge carrier mobility in the tested poly [2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno [3,2-b]thiophene)] (DPPDTT)-based transistors to 5.4 × 10⁻¹ cm² V⁻¹ s⁻¹.

Facile Photo-cross-linking System for Polymeric Gate Dielectric Materials toward Solution-Processed Organic Field-Effect Transistors: Role of a Cross-linker in Various Polymer Types

Energy-efficient solution-processed organic field-effect transistors (OFETs) are highly sought after in the low-cost printing industry as well as for the manufacture of flexible and other next-generation devices. The fabrication of such electronic devices requires high-functioning insulating materials that are chemically and mechanically robust to avoid lowering insulating properties during the device fabrication process or utilization of devices. In this study, we report a facile, fluorinated, UV-assisted cross-linker series using a fluorophenyl azide (FPA), which reacts with the C-H groups of a conventional polymer. This demonstrates the application of the cross-linked films in OFET gate dielectrics. The effects of the cross-linkable chemical structure of the FPA series on the cross-linking chemistry, photopatternability, and dielectric properties of the resulting films are investigated for low/high-k or amorphous/crystalline polymeric gate dielectric materials. The characteristics of insulating layers and behavior of OFETs containing these cross-linked gate dielectrics (for example, leakage current density (J), hysteresis, and charge trap density) depend on the polymer type. Furthermore, an organic-based complementary inverter and various printable OFETs with excellent electrical characteristics are successfully fabricated. Thus, these reported cross-linkers that enable the solution process and patterning of well-developed conventional polymer dielectric materials are promising for the realization of a more sustainable next-generation industrial technology for flexible and printable devices.

Molecular Semiconductors for Logic Operations: Dead-End or Bright Future?

The field of organic electronics has been prolific in the last couple of years, leading to the design and synthesis of several molecular semiconductors presenting a mobility in excess of 10 cm² V^-1 s^-1 . However, it is also started to recently falter, as a result of doubtful mobility extractions and reduced industrial interest. This critical review addresses the community of chemists and materials scientists to share with it a critical analysis of the best performing molecular semiconductors and of the inherent charge transport physics that takes place in them. The goal is to inspire chemists and materials scientists and to give them hope that the field of molecular semiconductors for logic operations is not engaged into a dead end. To the contrary, it offers plenty of research opportunities in materials chemistry.

Ultrathin ZrOx-Organic Hybrid Dielectric (EOT 3.2 nm) via Initiated Chemical Vapor Deposition for High-Performance Flexible Electronics

A one-step synthesis method is introduced and used to form an ultrathin, homogeneous organic-inorganic hybrid dielectric film with a high dielectric constant (high-k), based on initiated chemical vapor deposition. The hybrid dielectric is synthesized from tetrakis-dimethyl-amino-zirconium and 2-hydroxyethyl methacrylate, which are a high-k inorganic material and a soft organic material, respectively. A detailed material analysis on the synthesized ZrO_x-organic hybrid (Zr-hybrid) is performed. The Zr-hybrid dielectric has a high dielectric constant of nine, leading to a film equivalent oxide thickness (EOT) as low as 3.2 nm, which is the lowest EOT obtained from a flexible dielectric layer to date. The leakage current density (J) is no larger than 6 × 10^-7 A/cm² at 2 MV/cm, and the breakdown field (E_break) was ∼3.3 MV/cm. The J of the Zr-hybrid dielectric remains almost constant even under the 2.5% strain condition, while that of the ZrO₂ dielectric breaks down electrically at a tensile strain of less than 1.0%. The Zr-hybrid dielectric shows an energy band gap in the range of 5.2-5.4 eV and exhibits a sufficient valence band offset of around 3.0 eV with a pentacene organic semiconductor. The gate stack of the Zr-hybrid dielectric/pentacene semiconductor shows decent metal-oxide-semiconductor field-effect transistor performance even under a tensile strain of 1.67%, indicating that the Zr-hybrid is a promising gate dielectric for advanced flexible electronic applications.

Recent Efforts in Understanding and Improving the Nonideal Behaviors of Organic Field-Effect Transistors

Over the past three decades, the mobility of organic field-effect transistors (OFETs) has been improved from 10-5 up to over 10 cm2 V-1 s-1, which reaches or has already satisfied the requirements of demanding applications. However, pronounced nonideal behaviors in current-voltage characteristics are commonly observed, which indicates that the reported mobilities may not truly reflect the device properties. Herein, a comprehensive understanding of the origins of several observed nonidealities (downward, upward, double-slope, superlinear, and humped transfer characteristics) is summarized, and how to extract comparatively reliable mobilities from nonideal behaviors in OFETs is discussed. Combining an overview of the ideal and state-of-the-art OFETs, considerable possible approaches are also provided for future OFETs.

High-k Fluoropolymer Gate Dielectric in Electrically Stable Organic Field-Effect Transistors

A detailed study of a high-k fluoropolymer gate dielectric material, poly(vinylidene fluoride- co-hexafluoropropylene) [P(VDF-HFP)], is presented as a guide to achieve low operational voltage and electrically stable device performance. The large dipole moment of C-F dipoles in P(VDF-HFP) is responsible for its high dielectric constant as well as its potentially ferroelectric behavior that must be minimized to avoid hysteretic current-voltage characteristics. A range of material grades and processing conditions are explored and are shown to have a significant effect on the degree of hysteresis observed in device-transfer characteristics. The percentage of HFP monomer in the P(VDF-HFP) dielectric has an effect on gate-dependent mobility induced by disorder at the semiconductor-dielectric interface. Most importantly, we present the considerations that must be made to achieve optimal performance in multiple device architectures of organic field-effect transistors when using P(VDF-HFP) as a dielectric layer.

Molecularly Aligned Hexa- peri-hexabenzocoronene Films by Brush-Coating and Their Application in Thin-Film Transistors

The facile Chinese brush-coating method was used to prepare oriented thin films of hexa- peri-hexabenzocoronene (HBC) derivatives on the silicon substrate. As a result of the directional solution-coating, the D_{3 h}-symmetry (HBC-1,3,5-Ph-C12) and the C₁-symmetry (HBC-1,2,4-Ph-C12) derivatives displayed an anisotropic alignment, with mostly edge-on orientation on SiO₂ surfaces modified with various silane-based monolayers. On these silane-modified surfaces, the higher symmetry molecule HBC-1,3,5-Ph-C12 developed a hexagonally packed superstructure, which provided greater π orbital overlap and presumably the electronic coupling between neighboring molecules. In particular, the use of an octyltrichlorosilane (OTS)-modified surface enabled brush-coated thin films to have higher anisotropic orientation, crystallinity, and favorable molecular arrangement. In contrast, the growth of the hexagonal packing of low-symmetry derivative HBC-1,2,4-Ph-C12 was only achieved on the phenyltrichlorosilane and OTS surfaces. Thin-film transistors based on these brush-coated films gave a maximum mobility of 0.1 and 0.056 cm² V^-1 s^-1, which are 2 orders of magnitude improvement over the devices with unoriented films prepared by spin-coating. The results indicate that the molecular packing of discotic liquid crystals on the silane-modified surface is sensitively influenced by the molecular symmetry, which affects intermolecular interactions as well as molecule/surface interactions. This study provides a simple way to fabricate aligned films for HBC derivatives for transistor application.

Flexible Organic Thin Film Transistors Incorporating a Biodegradable CO2-Based Polymer as the Substrate and Dielectric Material

Employing CO₂-based polymer in electronic applications should boost the consumption of CO₂ feedstocks and provide the potential for non-permanent CO₂ storage. In this study, polypropylene carbonate (PPC) is utilized as a dielectric and substrate material for organic thin film transistors (OTFTs) and organic inverter. The PPC dielectric film exhibits a surface energy of 47 mN m⁻¹, a dielectric constant of 3, a leakage current density of less than 10⁻⁶ A cm⁻², and excellent compatibility with pentacene and PTCDI-C8 organic semiconductors. Bottom-gate top-contact OTFTs are fabricated using PPC as a dielectric; they exhibits good electrical performance at an operating voltage of 60 V, with electron and hole mobilities of 0.14 and 0.026 cm² V⁻¹ s⁻¹, and on-to-off ratios of 10⁵ and 10³, respectively. The fabricated p- and n-type transistors were connected to form a complementary inverter that operated at supply voltages of 20 V with high and low noise margins of 85 and 69%, respectively. The suitability of PPC as a substrate is demonstrated through the preparation of PPC sheets by casting method. The fabricated PPC sheets has a transparency of 92% and acceptable mechanical properties, yet they biodegraded rapidly through enzymatic degradation when using the lipase from Rhizhopus oryzae.

Direct Effect of Dielectric Surface Energy on Carrier Transport in Organic Field-Effect Transistors

The understanding of the characteristics of gate dielectric that leads to optimized carrier transport remains controversial, and the conventional studies applied organic semiconductor thin films, which introduces the effect of dielectric on the growth of the deposited semiconductor thin films and hence only can explore the indirect effects. Here, we introduce pregrown organic single crystals to eliminate the indirect effect (semiconductor growth) in the conventional studies and to undertake an investigation of the direct effect of dielectric on carrier transport. It is shown that the matching of the polar and dispersive components of surface energy between semiconductor and dielectric is favorable for higher mobility. This new empirical finding may show the direct relationship between dielectric and carrier transport for the optimized mobility of organic field-effect transistors and hence show a promising potential for the development of next-generation high-performance organic electronic devices.

Constant-current corona triode adapted and optimized for the characterization of thin dielectric films

This work describes an enhanced corona triode with constant current adapted to characterize the electrical properties of thin dielectric films used in organic electronic devices. A metallic grid with a high ionic transparency is employed to charge thin films (100 s of nm thick) with a large enough charging current. The determination of the surface potential is based on the grid voltage measurement, but using a more sophisticated procedure than the previous corona triode. Controlling the charging current to zero, which is the open-circuit condition, the potential decay can be measured without using a vibrating grid. In addition, the electric capacitance and the characteristic curves of current versus the stationary surface potential can also be determined. To demonstrate the use of the constant current corona triode, we have characterized poly(methyl methacrylate) thin films with films with thicknesses in the range from 300 to 500 nm, frequently used as gate dielectric in organic field-effect transistors.

Interface studies of well-controlled polymer bilayers and field-effect transistors prepared by a mixed-solvent method

The properties of semiconductor/dielectric interfaces are crucial to the performance of polymer field-effect transistors. The key to fabricating high-performance polymer transistors by spin-coating is solving solvent corrosion issues, wherein the solvent of the top polymer produces a rough interface or damage on the underlying polymer layer during deposition. Herein, we propose a mixed-solvent method that employs a mixture of an orthogonal solvent of the underlying polymer and a good solvent of the top polymer as the solvent of the top polymer to prepare polymer bilayers and produce a comparative study of the trap density at the semiconductor/dielectric interface of the corresponding transistor. By changing the ratio of orthogonal solvent to good solvent, namely the degree of orthogonality of the mixed solvent with respect to the underlying polymer, the interface and film qualities of polymer bilayers can be well controlled. We applied this method to spin-coat poly(3-hexylthiophene) (P3HT) on poly(methylmethacrylate) (PMMA) with a mixture of cyclohexane (orthogonal solvent) and chloroform (good solvent). The results of morphology characterizations and electrical property studies indicate the optimal ratio of cyclohexane to chloroform for preparing high-quality P3HT/PMMA bilayers for field-effect conduction is 7 : 3. Transistors based on the optimal bilayers with a bottom-gate/top-contact configuration and a long channel length show good performance. The trap density at the P3HT/PMMA interface is evaluated to be 3.6 × 10¹² cm⁻² eV⁻¹ from the subthreshold swing, characterizing the distribution of the interface trap levels across the bandgap in P3HT. Furthermore, based on deviations from ideality in the capacitance–voltage characteristics of the metal–insulator–semiconductor capacitor in the device, the traps at the interface are found to be acceptor-type, with the trap density determined to be 2.3 × 10¹¹ cm⁻². This value is in a good agreement with that estimated from the subthreshold swing.

A mixture of an orthogonal solvent of the bottom polymer and a good solvent of the top polymer is used as the solvent of the top layer to prepare polymer bilayers. The trap densities at the semiconductor/dielectric interface of the corresponding transistor are evaluated.

On-surface synthesis of a 2D boroxine framework: a route to a novel 2D material?

The synthesis of a 2D boroxine covalent framework is described, which exhibits promising morphological and electronic properties.

Grains in Selectively Grown MoS2 Thin Films

Transition metal dichalcogenides (TMDCs) have recently been studied using various synthesis methods, such as chemical vapor deposition for large-scale production. Despite the realization of large-scale production with high material quality, a range of approaches have been made to solve the patterning issue of TMDCs focusing on the application of integrated devices; however, patterning is still under study to accurately represent nanoscale-sized patterns, as well as the desired positions and shapes. Here, an insulating substrate is treated selectively with O₂ plasma, and MoS₂ growth is induced in the superhydrophilic area. Selectively well-grown MoS₂ patterns are confirmed by atomic force microscopy and Raman and photoluminescence spectroscopy. In addition, the grain size, according to the growth size, and grain boundary are analyzed by annual dark field transmission electron microscopy (TEM) and spherical aberration-corrected scanning TEM to confirm the selective growth. An analysis of the device performance and the optical properties reveals an enhancement with increasing grain size. This method presents the path of the growth technique for patterning, as well as the direction that can be applied to devices and integrated circuits.

Proving Scalability of an Organic Semiconductor To Print a TFT-Active Matrix Using a Roll-to-Roll Gravure

Organic semiconductor-based thin-film transistors' (TFTs) charge-carrier mobility has been enhanced up to 25 cm²/V s through the improvement of fabrication methods and greater understanding of the microstructure charge-transport mechanism. To expand the practical feasibility of organic semiconductor-based TFTs, their electrical properties should be easily accessed from the fully printed devices through a scalable printing method, such as a roll-to-roll (R2R) gravure. In this study, four commercially available organic semiconductors were separately formulated into gravure inks. They were then employed in the R2R gravure system (silver ink for printing gate and drain-source electrodes and BaTiO₃ ink for printing dielectric layers) for printing 20 × 20 TFT-active matrix with the resolution of 10 pixels per inch on poly(ethylene terephthalate) (PET) foils to attain electrical properties of organic semiconductors a practical printing method. Electrical characteristics (mobility, on-off current ratio, threshold voltage, and transconductance) of the R2R gravure-printed 20 × 20 TFT-active matrices fabricated with organic semiconducting ink were analyzed statistically, and the results showed more than 98% device yield and 50 % electrical variations in the R2R gravure TFT-active matrices along the PET web.

Flexible, Low-Power Thin-Film Transistors Made of Vapor-Phase Synthesized High-k, Ultrathin Polymer Gate Dielectrics

A series of high-k, ultrathin copolymer gate dielectrics were synthesized from 2-cyanoethyl acrylate (CEA) and di(ethylene glycol) divinyl ether (DEGDVE) monomers by a free radical polymerization via a one-step, vapor-phase, initiated chemical vapor deposition (iCVD) method. The chemical composition of the copolymers was systematically optimized by tuning the input ratio of the vaporized CEA and DEGDVE monomers to achieve a high dielectric constant (k) as well as excellent dielectric strength. Interestingly, DEGDVE was nonhomopolymerizable but it was able to form a copolymer with other kinds of monomers. Utilizing this interesting property of the DEGDVE cross-linker, the dielectric constant of the copolymer film could be maximized with minimum incorporation of the cross-linker moiety. To our knowledge, this is the first report on the synthesis of a cyanide-containing polymer in the vapor phase, where a high-purity polymer film with a maximized dielectric constant was achieved. The dielectric film with the optimized composition showed a dielectric constant greater than 6 and extremely low leakage current densities (<3 × 10^-8 A/cm² in the range of ±2 MV/cm), with a thickness of only 20 nm, which is an outstanding thickness for down-scalable cyanide polymer dielectrics. With this high-k dielectric layer, organic thin-film transistors (OTFTs) and oxide TFTs were fabricated, which showed hysteresis-free transfer characteristics with an operating voltage of less than 3 V. Furthermore, the flexible OTFTs retained their low gate leakage current and ideal TFT characteristics even under 2% applied tensile strain, which makes them some of the most flexible OTFTs reported to date. We believe that these ultrathin, high-k organic dielectric films with excellent mechanical flexibility will play a crucial role in future soft electronics.

Tracking the Evolution of Polymer Interface Films during the Process of Thermal Annealing at the Domain and Single Molecular Levels using Scanning Tunneling Microscopy

Structural evolution of polymer (NTZ12) interface films during the process of annealing is revealed at the domain and single molecular levels using the statistical data measured from scanning tunneling microscopy images and through theoretical calculations. First, common features of the interface films are examined. Then, mean values of surface-occupied ratio, size and density of the domain are used to reveal the intrinsic derivation of the respective stages. Formation of new domains is triggered at 70 °C, but domain ripening is not activated. At 110 °C, the speed of formation of new domains is almost balanced by the consumption due to the ripening process. However, formation of new domains is reduced heavily at 150 °C but restarted at 190 °C. At the single molecular level, the ratio of the average length of linear to curved backbones is increased during annealing, whereas the ratios of the total length and the total number of linear to curved skeletons reaches a peak value at 150 °C. The two major conformations of curved backbones for all samples are 120° and 180° bending, but the ripening at 150 °C reduces 180° folding dramatically. Molecular dynamic simulations disclose the fast relaxing process of curved skeletons at high temperature.

Precise Characterisation of Molecular Orientation in a Single Crystal Field-Effect Transistor Using Polarised Raman Spectroscopy

Charge transport in organic semiconductors is strongly dependent on the molecular orientation and packing, such that manipulation of this molecular packing is a proven technique for enhancing the charge mobility in organic transistors. However, quantitative measurements of molecular orientation in micrometre-scale structures are experimentally challenging. Several research groups have suggested polarised Raman spectroscopy as a suitable technique for these measurements and have been able to partially characterise molecular orientations using one or two orientation parameters. Here we demonstrate a new approach that allows quantitative measurements of molecular orientations in terms of three parameters, offering the complete characterisation of a three-dimensional orientation. We apply this new method to organic semiconductor molecules in a single crystal field-effect transistor in order to correlate the measured orientation with charge carrier mobility measurements. This approach offers the opportunity for micrometre resolution (diffraction limited) spatial mapping of molecular orientation using bench-top apparatus, enabling a rational approach towards controlling this orientation to achieve optimum device performance.

Silk Fibroin for Flexible Electronic Devices

Flexible electronic devices are necessary for applications involving unconventional interfaces, such as soft and curved biological systems, in which traditional silicon-based electronics would confront a mechanical mismatch. Biological polymers offer new opportunities for flexible electronic devices by virtue of their biocompatibility, environmental benignity, and sustainability, as well as low cost. As an intriguing and abundant biomaterial, silk offers exquisite mechanical, optical, and electrical properties that are advantageous toward the development of next-generation biocompatible electronic devices. The utilization of silk fibroin is emphasized as both passive and active components in flexible electronic devices. The employment of biocompatible and biosustainable silk materials revolutionizes state-of-the-art electronic devices and systems that currently rely on conventional semiconductor technologies. Advances in silk-based electronic devices would open new avenues for employing biomaterials in the design and integration of high-performance biointegrated electronics for future applications in consumer electronics, computing technologies, and biomedical diagnosis, as well as human-machine interfaces.

Organic Field-Effect Transistors Based on a Liquid-Crystalline Polymeric Semiconductor using SU-8 Gate Dielectrics onFlexible Substrates

In this work, the insulating properties of poly(4-vinylphenol) (PVP) and SU-8 (MicroChem, Westborough, MA, USA) dielectrics are analyzed and compared with each other. We further investigate the performance behavior of organic field-effect transistors based on a semiconducting liquid-crystal polymer (LCP) using both dielectric materials and evaluate the results regarding the processability. Due to the lower process temperature needed for the SU-8 deposition, the realization of organic transistors on flexible substrates is demonstrated showing comparable charge carrier mobilities to devices using PVP on glass. In addition, a µ-dispensing procedure of the LCP on SU-8 is presented, improving the switching behavior of the organic transistors, and the promising stability data of the SU-8/LCP stack are verified after storing the structures for 60 days in ambient air showing negligible irreversible degradation of the organic semiconductor.

Universal solution-processed high-k amorphous oxide dielectrics for high-performance organic thin film transistors

Solution-processed high-k ZrTiO_x dielectric films achieve a k value and capacitance of 53 and 467 nF cm⁻², and a low leakage current of 4 × 10⁻⁸ A cm⁻² with polymer modification. High-performance organic thin film transistors with a carrier mobility of 0.58 cm² V⁻¹ s⁻¹, and a low operating voltage of 6 V were realized with ZrTiO_x dielectric films.

Large-area, flexible imaging arrays constructed by light-charge organic memories

Existing organic imaging circuits, which offer attractive benefits of light weight, low cost and flexibility, are exclusively based on phototransistor or photodiode arrays. One shortcoming of these photo-sensors is that the light signal should keep invariant throughout the whole pixel-addressing and reading process. As a feasible solution, we synthesized a new charge storage molecule and embedded it into a device, which we call light-charge organic memory (LCOM). In LCOM, the functionalities of photo-sensor and non-volatile memory are integrated. Thanks to the deliberate engineering of electronic structure and self-organization process at the interface, 92% of the stored charges, which are linearly controlled by the quantity of light, retain after 20000 s. The stored charges can also be non-destructively read and erased by a simple voltage program. These results pave the way to large-area, flexible imaging circuits and demonstrate a bright future of small molecular materials in non-volatile memory.