Polymer Gate Dielectrics Research Articles

Solution-processable low-voltage carbon nanotube field-effect transistors with high-k relaxor ferroelectric polymer gate insulator

Achieving energy-efficient and high-performance field-effect transistors (FETs) is one of the most important goals for future electronic devices. This paper reports semiconducting single-walled carbon nanotube FETs (s-SWNT-FETs) with an optimized high-k relaxor ferroelectric insulator P(VDF-TrFE-CFE) thickness for low-voltage operation. The s-SWNT-FETs with an optimized thickness (∼800 nm) of the high-k insulator exhibited the highest average mobility of 14.4 cm2 V−1s−1 at the drain voltage (I D) of 1 V, with a high current on/off ratio (I on/off >105). The optimized device performance resulted from the suppressed gate leakage current (I G) and a sufficiently large capacitance (>50 nF cm−2) of the insulating layer. Despite the extremely high capacitance (>100 nF cm−2) of the insulating layer, an insufficient thickness (<450 nm) induces a high I G, leading to reduced I D and mobility of s-SWNT-FETs. Conversely, an overly thick insulator (>1200 nm) cannot introduce sufficient capacitance, resulting in limited device performance. The large capacitance and sufficient breakdown voltage of the insulating layer with an appropriate thickness significantly improved p-type performance. However, a reduced n-type performance was observed owing to the increased electron trap density caused by fluorine proportional to the insulator thickness. Hence, precise control of the insulator thickness is crucial for achieving low-voltage operation with enhanced s-SWNT-FET performance.

Polymeric gate insulators to induce synaptic photoresponse of organic transistors

Polymeric gate insulators to induce synaptic photoresponse of organic transistors

Combination of Polymer Gate Dielectric and Two-Dimensional Semiconductor for Emerging Field-Effect Transistors

Two-dimensional (2D) materials are considered attractive semiconducting layers for emerging field-effect transistors owing to their unique electronic and optoelectronic properties. Polymers have been utilized in combination with 2D semiconductors as gate dielectric layers in field-effect transistors (FETs). Despite their distinctive advantages, the applicability of polymer gate dielectric materials for 2D semiconductor FETs has rarely been discussed in a comprehensive manner. Therefore, this paper reviews recent progress relating to 2D semiconductor FETs based on a wide range of polymeric gate dielectric materials, including (1) solution-based polymer dielectrics, (2) vacuum-deposited polymer dielectrics, (3) ferroelectric polymers, and (4) ion gels. Exploiting appropriate materials and corresponding processes, polymer gate dielectrics have enhanced the performance of 2D semiconductor FETs and enabled the development of versatile device structures in energy-efficient ways. Furthermore, FET-based functional electronic devices, such as flash memory devices, photodetectors, ferroelectric memory devices, and flexible electronics, are highlighted in this review. This paper also outlines challenges and opportunities in order to help develop high-performance FETs based on 2D semiconductors and polymer gate dielectrics and realize their practical applications.

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.

Impact of polymer gate dielectric capacitance and gate leakage current on solution-based polymer organic thin film transistor

The polymer dielectric material plays a vital role in a solution-based organic thin-film transistor (OTFT), leading to higher performance, lower operating voltage, lesser gate leakage, and higher operating frequency. In this work, crosslinked polymer gate dielectric is used to be suitable for the photolithography process and integrated circuit applications. The impact of variation of crosslinker in the polymer dielectric on OTFT performance in terms of the electrical properties such as dielectric constant and dielectric leakage current is studied. The set of electrical characterizations is performed for the crosslinked dielectrics to get the optimum value of the crosslinker. In addition, the shadow mask-based OTFT is fabricated to evaluate the gate capacitance and the gate current leakage. The extracted model parameters from characterisation of dielectric and photolithography-based OTFT is used in spice level-1 model to simulate the characteristics of the fabricated OTFTs.

Shape‐Deformable and Locomotive MXene (Ti3C2Tx)‐Encapsulated Magnetic Liquid Metal for 3D‐Motion‐Adaptive Synapses

AbstractOwing to their unique surface chemistry, room‐temperature pseudoliquidity, and high electrical conductivity, gallium‐based liquid metals (LMs) exhibit multifunctionality. To grant deformable and self‐flowing characteristics to LMs, magnetic particles are incorporated for precisely controlling the LM motion and shape deformability. However, LM surface‐adhesion and corrosivity hinders the integration of LMs into complex circuits and devices owing to potential alloying with other metals and contamination of their surroundings. In this study, a highly conductive Ti3C2Tx (MXene)‐encapsulated magnetic LM (MX–MLM) is developed using a feasible fabrication method. The MX–MLM comprises magnetic particles suspended within its core and self‐assembled MXene flakes on the surface to maintain the nonwettability and high electrical conductivity of a liquid droplet. The noncorrosivity and increased magnetism of the MX–MLM enable nonstick magnetic‐field‐induced locomotion and shape deformation on various surfaces including metals, oxides, and polymers. Furthermore, the MX–MLM exhibits recyclability and magnetic‐field‐induced self‐healing. To demonstrate its functionality, the MX–MLM is employed as a magnetointeractive, shape‐deformable, and locomotive top gate electrode in a transistor fabricated using a ferroelectric polymer gate insulator. The device exhibits excellent magnetointeractive synaptic capability for detecting and learning 3D path information.

Direct self-assembled monolayers treatment on the polar polymer dielectric towards ultra-flexible organic field-effect transistors

• A direct SAM treatment on the polar polymer gate dielectric without any preprocess is introduced. • A hysteresis-free OFET with a high mobility of 1.51 cm 2 V −1 s −1 was achieved. • An ultra-flexible OFET was fabricated and presented a stable electrical performance under deformations. Surface treatment for the polymer gate dielectric plays a significant role in achieving the high-performance flexible field-effect transistors. In this work, the direct SAM treatment on the polar polymer gate dielectric is introduced and the effects on the electrical performance of OFETs are investigated. After an appropriate SAM treatment for the polar polymer dielectric, the mobility can be improved and the hysteresis and interfacial trap states are decreased obviously. Moreover, the SAM treated polymer dielectric is used to achieve the ultra-flexible OFET successfully, with a stable electrical performance under various deformations. These results demonstrate that the direct SAM treatment on polar polymer dielectric is a promising strategy for the high-performance flexible organic transistors, presenting the huge potential for the next-generation flexible electronics.

Organic field-effect transistors with low-temperature curable high-k hybrid gate dielectrics

We report a low-voltage-operated organic field-effect transistor that uses a hybrid gate insulator that has a high dielectric constant k. The gate insulator consists of a high-k polymer cyanoetylated pullulan (CEP) that can be efficiently cross-linked by glycidoxypropyltrimethoxysilane (GOPTMS) at low temperature (∼110 °C). The very low curing temperature is below the glass transition temperature T g of conventional plastic substrates for plastic electronics, and is therefore compatible with many plastic substrates for plastic electronics. The cross-linking is very efficient in that only 1/10 (w:w) GOPTMS: CEP produced densely cross-linked thin films with a smooth surface, good insulating property, high capacitance density and high k. The devices functioned at low voltage, and exhibited charge carrier mobility ∼1.83 cm2 V−1 s−1, and steep substheshold swing ∼88 mV dec−1. These results imply that high quality polymer gate insulators are achievable at low temperature with a very small fraction of blended crosslinking agents; this characteristic offers a method to achieve portable all-plastic flexible electronics that function at low voltage.

Low-power high-mobility organic single-crystal field-effect transistor

Evolving flexible electronics requires the development of high-mobility and low-power organic field-effect transistors (OFETs) that are crucial for emerging displays, sensors, and label technologies. Among diverse materials, polymer gate dielectrics and two-dimensional (2D) organic crystals have intrinsic flexibility and natural compatibility with each other for OFETs with high performance; however, their combination lacks non-impurity and non-damage construction strategies. In this study, we developed a desirable OFET system using damage-free transfer of 2D organic single crystal, dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene on a unique polymer dielectric layer, poly(amic acid) (PAA). Benefiting from the unique PAA surface nanostructure and the long-range ordered characteristics of the 2D organic single crystal, the resulting OFETs show remarkable performance with high mobility and low operating voltage of 18.7 cm2 V−1 s−1 and −3 V, respectively. The result indicates that combining polymer gate dielectric with 2D organic single crystal using a high-quality method can produce flexible electronic devices with high performance.

Improvement of device performance of Ph-BTBT-10 field-effect transistors fabricated on a HfO2/alicyclic polyimide double-layered gate insulator

We report on the FET properties of 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10) on a HfO2/alicyclic polyimide double-layered gate insulator at an elevated temperature. The patterning of semiconductor and polymeric insulator layers is also discussed using the surface selective deposition of solution onto the wettable region (self-assembled monolayer-coated oxide layer) and unwettable region (bare metal oxide layer) obtained by vacuum ultraviolet light (172 nm) irradiation. A multilayered film of 20–30 nm thick Ph-BTBT-10 and a double-layered gate insulator consisting of 30–40 nm thick alicyclic polyimide on high-k metal oxide films leads to a reduction in the operating voltage and the interfacial trap density at the gate insulator interface. The mobility of the FETs was improved from 0.4 to 2.4 cm2 V−1 s−1 by thermal annealing of Ph-BTBT-10 at 120 °C due to the transition from a monolayer to a bilayer structure and the use of alicyclic polyimide as the polymer gate insulator.

Hybrid La2O3-cPVP Dielectric for Organic Thin Film Transistor Applications

In this work, we have studied the electrical performance of cross-linked polyvinyl phenol (cPVP) modified lanthanum oxide (La2O3) bilayer dielectric film in pentacene thin film transistors (TFT). A simple spin-coating and room temperature operated cross-linking reaction of the hydroxyl moieties of PVP and the nitrogen groups of PMF were carried out to form the cross-linked PVP. The deposition of a thin 30 nm cPVP layer over the La2O3 layer provided a low leakage current (<10−7 A cm−2), causing a reduction in the interface trap density. Besides, the modified surface properties of the La2O3 layer were favorable for the growth of pentacene organic semiconductors. As a result, the current on-off ratio and the sub-threshold slope was improved from 104 and 1.0 V/decade to 105 and 0.67 V/decade. The La2O3∕cPVP pentacene TFT operated at −10 V also exhibited improvement in the field-effect mobility to 0.71 cm2 Vs−1 from 0.48 cm2 Vs−1 for the single-layer La2O3 (130 nm) device. Thus, our work demonstrates that the rare earth oxide La2O3 with cPVP is an excellent dielectric system in the context of emerging transistors with hybrid polymer gate dielectrics.

Influence of Polymer Gate Dielectric on Organic Field‐Effect Transistors: Interdependence of Molecular Weight, Solvent Polarity, and Surface Energy—A Case Study with PMMA and Pentacene

AbstractThe semiconductor/dielectric interface controls the performance of organic field‐effect transistors (OFETs). Herein, the influence of both the molecular weight and the polarity of the solvent of a poly(methyl methacrylate) (PMMA)‐based gate dielectric on the performance of pentacene OFETs is systematically investigated, by studying surface energy, surface roughness, morphology, leakage current, and capacitance of the dielectric. Various existing views on the role of the surface energy are considered while deriving a correlation. Larger pentacene grains are observed when the film is grown on high molecular weight‐PMMA films cast from high dipole moment‐solvent. The electrical properties of the corresponding OFETs show great improvement compared to those of OFETs fabricated with low molecular weight‐PMMA film as the gate dielectric, irrespective of the solvent. The authors attribute this enhanced performance to the increased surface energy of the polymeric dielectric which turns out to be a strong function of its molecular weight and the dipole moment of the solvent. Bias‐stress measurements on the OFETs confirm this correlation.

Heterogeneous Functional Dielectric Patterns for Charge-Carrier Modulation in Ultraflexible Organic Integrated Circuits.

Flexible electronics have gained considerable attention for application in wearable devices. Organic transistors are potential candidates to develop flexible integrated circuits (ICs). A primary technique for maximizing their reliability, gain, and operation speed is the modulation of charge-carrier behavior in the respective transistors fabricated on the same substrate. In this work, heterogeneous functional dielectric patterns (HFDP) of ultrathin polymer gate dielectrics of poly((±)endo,exo-bicyclo[2.2.1]hept-ene-2,3-dicarboxylic acid, diphenylester) (PNDPE) are introduced. The HFDP that are obtained via the photo-Fries rearrangement by ultraviolet radiation in the homogeneous PNDPE provide a functional area for charge-carrier modulation. This leads to programmable threshold voltage control over a wide range (-1.5 to +0.2V) in the transistors with a high patterning resolution, at 2V operational voltage. The transistors also exhibit high operational stability over 140 days and under the bias-stress duration of 1800s. With the HFDP, the performance metrics of ICs, for example, the noise margin and gain of the zero-VGS load inverters and the oscillation frequency of ring oscillators are improved to 80%, 1200, and 2.5kHz, respectively, which are the highest among the previously reported zero-VGS -based organic circuits. The HFDP can be applied to much complex and ultraflexible ICs.

Synthesis and characterization of a perfluorocyclobutane-containing cross-linked polyimide gate insulator for thin film transistor

We have synthesized a thermally curable polymeric gate insulator (TFVOB-SPI) through the modification of soluble polyimide (SPI) using a 4-(1,2,2-trifluorovinyloxy)benzoyl (TFVOB) chloride. The thermal cross-linking of TFVOB-SPI was done and prepared the cross-linked TFVOB-SPI thin film having the perfluorocyclobutane (PFCB) structure. The PFCB structure was formed by the radical mediated thermal cycloaddition of trifluorovinyl ether of TFVOB. The cross-linked TFVOB-SPI showed excellent thermal stability up to 495 °C with only 5% weight loss and excellent chemical resistance to common organic solvents. The pentacene thin-film transistor (TFT) with the cross-linked TFVOB-SPI as a gate dielectric exhibited a field effect mobility of 0.28 cm2/Vs with almost no hysteresis during the TFT operation.

Strategies for Chemical Sensing Using High Purity Semiconducting Single-Walled Carbon Nanotube Electronic Devices

Semiconducting single-walled carbon nanotubes (sc-SWCNTs) are attractive in chemical sensing [1] because of their peculiarities: As they present a single atom-thick wall and a quasi 1D form factor, sc-SWCNTs are especially sensitive to their surroundings' electrostatics. Moreover, their band gap of approximately 1 eV is much greater than room-temperature thermal energy while being in a convenient range for electronic applications. Also, their electronic structure exhibits van Hove singularities (sharp spikes in the density of states) that drastically alters their conductivity and optical properties when charge carriers are injected. Although sc-SWCNT electronic devices are very sensitive, they lack in selectivity and they usually need to be functionalized to implement a lock-and-key detection mechanism.In this talk, we will present various strategies for chemical sensing using enriched sc-SWCNTs. We will discuss the advantages and disadvantages of using sc-SWCNTs in electronic chemical sensing devices. Sub-ppm ammonia sensing will be demonstrated using a sc-SWCNT material wrapped with a decomposable polymer in a chemiresistor configuration. [2] Also using chemiresistors, CO2 detection has been achieved by designing a SWCNT-wrapping polymer with specific interactions. [3] Finally, we will present a strategy to differentiate the response of sensor elements to a variety of volatile analytes by changing the polymer gate dielectrics in a three-terminal bottom gate chemitransistor configuration. [4] This methodology opens the way to the implementation of sc-SWCNT-based chemitransistors in a printed cross-reactive sensor array.

Simulation of two-transistor parallel and series circuits for gas sensing validated by experimental data

Organic field effect transistors (OFETs) in parallel and series circuit configurations are simulated and tested for gas sensing activity. The devices are based on PQT12 and PQTS12 organic semiconductor thin films. A two-dimensional finite element simulation methodology is implemented. It is assumed that traps due to defects and grain boundaries are uniformly distributed throughout the semiconductor film. Gaussian trap distributions are used in the simulation. Gas sensing is accounted for by a doping-dependent hopping mobility model in the organic active material. Interface traps and charges at the interface between the polymer channel and gate insulator are incorporated. Transistors in both parallel and series configurations are studied. Compared to individual OFET-based sensors, the circuit configuration achieves significantly increased sensitivity to analyte, as indicated by the simulation and in agreement with experimental observations. This supports the concept of combining transistors to enhance analyte sensitivity and provides a method for advance screening of combinations of OFETs for high signal-to-drift ratios. The absolute value of drain currents for series circuits is lower than that of parallel circuits; however, the series circuits display higher analyte sensitivity.

Solution Processed Organic Transistors on Polymeric Gate Dielectric with Mobility Exceeding 15 cm2 V−1 s−1

Herein, 6,6′ bis (trans‐4‐pentylcyclohexyl)‐dinaphtho[2,1‐b:2′,1′‐f ]thieno[3,2‐b]thiophene (5H‐21DNTT)—a solution‐processable derivative of DNTT—is characterized and studied for its potential as a crystalline solution‐processed organic semiconductor to achieve high mobility and stable organic thin‐film transistor (OTFT) operation. The performance of a bottom‐gate, bottom‐contact OTFT with a 5H‐21DNTT semiconductor is analyzed with different polymeric organic gate dielectrics via various solution‐processed techniques. In comparison to other polymeric gate dielectrics, Parylene C exhibited a superior performance for 5H‐21DNTT OTFT devices, and the OTFT devices show a remarkable average mobility of 10.9 cm2 V−1 s−1, as well as a maximum mobility exceeding 15 cm2 V−1 s−1, with a 100% reliability factor.

Organic-based field effect transistors for protein detection fabricated by inkjet-printing

Abstract Biosensors based on Organic Field-Effect Transistors (OFETs) have attracted increasing attention due to the possibility of rapid, label-free, and inexpensive detection. Among all the different possibilities, inkjet-printed top-gate organic Field Effect Transistors-Based Biosensors (BioFETs) using a polymeric gate insulator have been seldom reported. In this work, a systematic investigation in terms of topographical and electrical characterization was carried out in order to find the optimal fabrication process for obtaining a reliable polymer insulator. Previous studies have demonstrated that the best electrical performance arises from the use of the perfluoropolymer Cytop™[12,13,14]. Consequently, a simple immobilization protocol was used to ensure the proper attachment of a model biomolecule onto the Cytop's hydrophobic surface whilst keeping its remarkable insulating properties with gate current in the range of dozens of pico-amperes. The top-gate inkjet-printed BioFETs presented in this study operate at threshold voltages in the range of 1–2 V and show durability even when exposed to oxygen plasma, wet amine functionalization treatments, and aqueous media. As a preliminary application, the inkjet-printed top-gate BioFETs is used for monitoring an immunoreaction by measuring changes in the drain current, paving the way for further use of this device in the immunosensing field.

Strategies for Chemical Sensing Using High Purity Semiconducting Single-Walled Carbon Nanotube Electronic Devices

Semiconducting single-walled carbon nanotubes (sc-SWCNTs) are attractive in chemical sensing [1] because of their peculiarities: As they present a single atom-thick wall and a quasi 1D form factor, sc-SWCNTs are especially sensitive to their surroundings’ electrostatics. Moreover, their band gap of approximately 1 eV is much greater than room-temperature thermal energy while being in a convenient range for electronic applications. Also, their electronic structure exhibits van Hove singularities (sharp spikes in the density of states) that drastically alters their conductivity and optical properties when charge carriers are injected. Although sc-SWCNT electronic devices are very sensitive, they lack in selectivity and they usually need to be functionalized to implement a lock-and-key detection mechanism.In this talk, we will present various strategies for chemical sensing using enriched sc-SWCNTs. We will discuss the advantages and disadvantages of using sc-SWCNTs in electronic chemical sensing devices. Sub-ppm ammonia sensing will be demonstrated using a sc-SWCNT material wrapped with a decomposable polymer in a chemiresistor configuration. [2] Also using chemiresistors, CO2 detection has been achieved by designing a SWCNT-wrapping polymer with specific interactions. Finally, we will present a strategy to differentiate the response of sensor elements to a variety of volatile analytes by changing the polymer gate dielectrics in a three-terminal bottom gate chemitransistor configuration. [3] This methodology opens the way to the implementation of sc-SWCNT-based chemitransistors in a printed cross-reactive sensor array.

Impact of Hydrogen Bonds Limited Dipolar Disorder in High-k Polymer Gate Dielectric on Charge Carrier Transport in OFET.

The paper contributes to the characterization and understanding the mutual interactions of the polar polymer gate dielectric and organic semiconductor in organic field effect transistors (OFETs). It has been shown on the example of cyanoethylated polyvinylalcohol (CEPVA), the high-k dielectric containing strong polar side groups, that the conditions during dielectric layer solidification can significantly affect the charge transport in the semiconductor layer. In contrast to the previous literature we attributed the reduced mobility to the broader distribution of the semiconductor density of states (DOS) due to a significant dipolar disorder in the dielectric layer. The combination of infrared (IR), solid-state nuclear magnetic resonance (NMR) and broadband dielectric (BDS) spectroscopy confirmed the presence of a rigid hydrogen bonds network in the CEPVA polymer. The formation of such network limits the dipolar disorder in the dielectric layer and leads to a significantly narrowed distribution of the density of states (DOS) and, hence, to the higher charge carrier mobility in the OFET active channel made of 6,13-bis(triisopropylsilylethynyl)pentacene. The low temperature drying process of CEPVA dielectric results in the decreased energy disorder of transport states in the adjacent semiconductor layer, which is then similar as in OFETs equipped with the much less polar poly(4-vinylphenol) (PVP). Breaking hydrogen bonds at temperatures around 50 °C results in the gradual disintegration of the stabilizing network and deterioration of the charge transport due to a broader distribution of DOS.