Low-voltage Organic Field-effect Transistors Research Articles

Compact Model Analysis for Low Voltage OFETs with Electrolytic Gate Dielectrics: Toward a Universal Model for Poly(3-Hexylthiophene) P3HT OFETs

The lightweight with flexibility and low-cost processing engineered the rapid growth of organic field-effect transistors (OFET) in the past three decades. Suitable compact models and parameter extraction methods are being developed to further the use of OFETs in integrated circuits, where stimulations are required to optimize the device performance. To simplify the parameter extraction, metaheuristic approaches are usually made, which otherwise is a cumbersome process. Following these, here investigations are made with the help of such a compact model to extract the operational parameters of P3HT (poly (3-hexylthiophene) based OFETs with electrolytic gate dielectrics using the genetic algorithm (GA) method. The result show that the compact model that was essentially developed in line with the successful models for inorganic material based FETs, can be used as an excellent framework for simulating low voltage OFETs made with both low and high mobility organic semiconductors. Mobility and threshold voltage calculated from the extracted parameters using GA for the two devices having mobility value differences of more than four orders are found to be nicely fitting with the experimental values. These results assume significance to the organic electronic industry as this facilitates the real-time circuit application of OFETs. KEYWORDS: Modeling, Low voltage OFET, Genetic algorithm, Ionic liquid, P3HT

Thermal Sensing Characteristics of Low-Voltage n-Channel Organic Field-Effect Transistors With Triple Layers of Naphthalenediimide-Containing Conjugated Polymer and Gate-Insulating Polymers

Organic field-effect transistors (OFETs) were fabricated with n-type naphthalenediimide-based conjugated polymer (N2200) as a channel layer and poly(methyl methacrylate) (PMMA)/poly(vinyl alcohol) (PVA) as a gate-insulating layer. The OFETs with the N2200/PMMA/PVA triple layers were operated with an n-channel mode at low voltages (≤5 V) and their electron mobility reached ca. 0.63 cm2/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}\cdot \text{s}$ </tex-math></inline-formula> at a drain voltage of 5 V. The drain current of OFETs was gradually increased as the temperature of channel region increased from 25 °C to 80 °C, whereas no shift in threshold voltage was measured upon the temperature variation. The relative thermal sensitivity of devices was almost linearly increased with the temperature, while a two-stage behavior by a border of ca. 35 °C was measured for specific thermal sensitivity. The present n-channel OFETs exhibited excellent thermal sensing performances upon repeated approaching/retracting tests using a heat source.

Pinaceae Fir Resins as Natural Dielectrics for Low Voltage Operating, Hysteresis‐Free Organic Field Effect Transistors

AbstractNatural dielectrics are emerging nowadays as a niche selection of materials for applications targeting biocompatibility and biodegradability for electronics and sensors within the overall effort of scientific community to achieve sustainable development and to build environmental consciousness. The two natural resins analyzed in this study, silver fir and Rocky mountain fir demonstrate robust dielectric properties and excellent film forming capabilities, while being trap free dielectrics in high‐performance organic field effect transistors (OFETs) operating at voltages as low as 1 V. Immense research possibilities are demonstrated through the avenue of inorganic nanofillers insertions in the natural resins film, that opens the door for fabrication of very low voltage OFETs with high dielectric constant insulating layers.

Brewers’ spent grain (BSG)-based green dielectric materials for low-voltage operating solution-processed organic field-effect transistors

A brewers’ spent grain (BSG) based dielectric material was used in organic field-effect transistors (OFETs). The fabricated devices showed a maximum hole mobility of 2.30 cm2 V−1 s−1.

Performance Comparison of Low-Voltage non-Ionic Gel Organic Field Effect Transistors with Gold and PEDOT:PSS Gate Electrodes

Low-voltage non-ionic gel organic-field effect transistors (NIGOFETs) with two kinds of gate electrode materials namely gold (Au) and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) formulation were fabricated in top-gate bottom-contact geometry to investigate the effects of gate electrodes on the electrical performance of the OFETs. In addition, three kinds of gate dielectrics were used for both types of transistors to understand the effects more thoroughly. As a result, it can be deduced from the data that NIGOFETs with Au gate electrodes (Au-NIGOFETs) display better performance considering higher mobility and on-to-off current ratio (ION/IOFF) as well as lower Subthreshold Swing (SS) of them. Besides, the threshold voltage (VTH) effects-free drain currents (IDS) of the Au-NIGOFETs surpasses those of the PEDOT:PSS formulation gated NIGOFETs (Pedot-NIGOFETs). This is probably due to having greater WF gate electrode (in our case Au) provides less injection barrier eventually leads to relatively unimpeded charge transportation. Nevertheless, Au-NIGOFETs interestingly proves to have further negative VTH and lower off-current (IOFF), which may be attributed to lower electrical resistivity (ρ) of the Au leading to denser charge carrier traps formation along with intensified charge carrier induction at the semiconductor-dielectric interface when the gate-to-source voltage (VGS) is less than VTH. However, because of the same reason, when VGS exceeds the VTH for example, IDS of Au-NIFOFET1 starts to increase in such a quick manner that enabling it to have higher ION/IOFF and lower SS.

Nanodielectrics approaches to low-voltage organic transistors and circuits

In this review, advances in nanoscale dielectric materials for organic field-effect transistors (OFETs) are summarized. OFETs are highly promising device units for ultra-thin, light-weight, flexible, and wearable electronics systems, while the operating voltages of the reported devices are in many cases much higher than what is relevant to modern technological applications. Key aspects behind this issue are clarified in terms of basic transistor device physics, which translate into the important motivations for realizing nanodielectric-based low-voltage OFETs. Different possibilities of a device design are explained in detail by introducing important recent publications on each material class. Finally, several forward-looking remarks on the integration of nanodielectrics into next-generation OFETs are provided.

Low Operating Voltage Organic Field-Effect Transistors with Gelatin as a Moisture-Induced Ionic Dielectric Layer: The Issues of High Carrier Mobility.

We have developed low-voltage (<2 V) flexible organic field-effect transistors (OFETs) with high carrier mobility using gelatin as a moisture-induced ionic gate dielectric system. Ionic concentration in the gelatin layer depends on the relative humidity condition during the measurement. The capacitance of the dielectric layer used for the calculation of field-effect carrier mobility for the OFETs crucially depends on the frequency at which the capacitance was measured. The results of frequency-dependent gate capacitance together with the anomalous bias-stress effect have been used to determine the exact frequency at which the carrier mobility should be calculated. The observed carrier mobility of the devices is 0.33 cm2/Vs with the capacitance measured at frequency 20 mHz. It can be overestimated to 14 cm2/Vs with the capacitance measured at 100 kHz. The devices can be used as highly sensitive humidity sensors. About three orders of magnitude variation in device current have been observed on the changes in relative humidity (RH) levels from 10 to 80%. The devices show a fast response with a response and recovery times of ∼100 and ∼110 ms, respectively. The devices are flexible up to a 5 mm bending radius.

Organic FETs using biodegradable almond gum as gate dielectric: A promising way towards green electronics

Abstract Green electronics is an emerging field of research which aims to manufacture devices in an environmentally friendly and sustainable way. Usually, the involved electronic materials are naturally occurring and non-toxic. Also, they can be processed using simple, low energy deposition processes and fabrication techniques. In this work, we present low voltage organic field-effect transistors (OFETs) using almond gum (AG) as the gate dielectric. AG is a natural, biodegradable insulator material that can be directly collected from almond trees and used without any further purification. Moreover, AG possesses interesting properties such as water solubility, ease of processing, good insulation, low leakage current, good film quality, and high capacitance making it a promising dielectric for OFET devices. Bottom gate/bottom contact p-channel OFETs have been processed on glass substrates with poly (3,6-di (2-thien-5-yl)-2,5-di (2-octyldodecyl)-pyrrolo [3,4-c] pyrrole-1,4-dione)thieno [3,2-b] thiophene) (DPPTTT) polymethyl methacrylate (PMMA) blend as the active layer and gold as the source and drain electrodes. The transistors operate at low voltage (VGS ≤ 3 V), with threshold voltages Vth as low as −0.8 V, saturated field effect mobilities μsat above 0.75 cm2 V−1 s−1, subthreshold swings SS around 270 mV/dec and ON/OFF current ratio equal to 103. The combined favourable properties of both almond gum and low voltage operated OFET devices have a high potential to pave a way towards using naturally occurring, biodegradable electronic materials in future disposable sensors or throwaway, low-end electronics.

Scalable Processing of Low Voltage Organic Field Effect Transistors With a Facile Soft-Contact Coating Approach

A soft-contact coating (SCC) method, using a rotatable steel sheet as the meniscus guide, is developed for depositing organic semiconductors (OSCs). The method is used to fabricate bottom-gate bottom-contact organic-field effect transistors (OFETs) using blended solution of small molecule OSC and polymer binder. During the coating process, the meniscus guide maintains very weak contact force to the substrate surface, avoiding damages to the pre-fabricated electrodes. Even at a fast coating speed of 20 mm/s, well controlled crystallization can be achieved to form low sub-gap density of the states (DOS) channels for low voltage OFETs of excellent uniformity. The fabricated low voltage OFETs on plastic substrate in full solution processes exhibit high mobility reaching $1.5 ~{\text {cm}}^{{2}}\cdot \,\,\text{V}^{\text {-1}}\cdot \,\,\text{s}^{\text {-1}}$ , and a small threshold voltage dispersion less than 250 mV for measured 159 devices.

Amorphous Indium-Gallium-Zinc-Oxide Transistor Used Ion Gel Dielectric for Low Driving Voltage and Easy Processing

Transistors using organic materials are attracting huge attention in the market today due to their low cost and possibility of solution process. Moreover, since the organic materials used in transistors are intrinsically flexible, they are believed to be essential elements for the realization of flexible devices such as stretchable displays, rollable displays, and wearable devices. In most cases, however, because of the low dielectric constant of organic materials, the operating voltage of the transistor is very high when the organic materials are used as the gate dielectric layer. When the operating voltage of the transistor is high, two serious problems can occur. First, the high operating voltage can cause increased power consumption of the transistor. It is a fatal drawback that reduces the applicability to wireless device applications because in the case of wireless electronic equipment, lifetime of battery is limited. Also, as the operating voltage increases, additional gate driver integrated circuits are required to control the driving voltage. This leads to the increased process complexity, and reduces the price competitiveness of the device. Therefore, it can be said that the possibility of mass production and functionality of transistors using organic materials will increase by solving these two problems. As a result, various studies have been focused on solving these problems by reducing the thickness of dielectric or choosing unique organic material with high dielectric constant [2] [3]. In order to solve above problems, we proposed the transistors based on ion gel dielectric, which has high capacitance. Ion gel refers to the substance in which ionic liquid is trapped in the polymer matrix [1]. When the voltage is applied to the electrode, the ion gel forms an electric double layer (EDL) at the interface with the electrode. Since EDL forms a capacitor with thickness of several nanometers, the ion gel has a very high capacitance above 1μF/cm2 [1]. From the capacitance-frequency curve measurement of Metal-Ion gel insulator-Metal capacitor (MIM), it was confirmed that the capacitance of ion gel increased as the amount of ionic liquid in ion gel increased. In addition, MIM showed the capacitance around 1μF/cm2 even if the ionic liquid content was very small. In the case of the transistor structure, the transistor was easy to fabricate because the gate electrode was deposited on the same substrate as the source-drain electrode. The active layer had the width of 20μm and the length of 160μm. The gate leakage current of the transistor increased with increasing the amount of ionic liquid in the ion gel. By optimizing the amount of ionic liquid to control gate leakage current, the ionic liquid was chosen 3% relative to the polymer in terms of mass and the gate leakage current was reduced to several tens of picoampere. The transfer characteristic represented that turn-on-voltage was near -1V and on-off ratio was 3.93·104 when the gate voltage was swept from -4V to 4V. This result shows that the transistor can operate with well-behaved electrical property even at small driving voltage near 4V. The transistor made by simple fabrication with ion gel dielectric showed outstanding electrical characteristics with low driving voltage around 4V and this result will pave the way for the next generation of flexible devices. [1] Wang, H., Wang, Z., Yang, J., Xu, C., Zhang, Q., & Peng, Z. (2018). Ionic Gels and Their Applications in Stretchable Electronics. Macromolecular rapid communications, 39(16), 1800246. [2] Yoon, M. H., Yan, H., Facchetti, A., & Marks, T. J. (2005). Low-voltage organic field-effect transistors and inverters enabled by ultrathin cross-linked polymers as gate dielectrics. Journal of the American Chemical Society, 127(29), 10388-10395. [3] Hung, C. C., Wu, H. C., Chiu, Y. C., Tung, S. H., & Chen, W. C. (2016). Crosslinkable high dielectric constant polymer dielectrics for low voltage organic field‐effect transistor memory devices. Journal of Polymer Science Part A: Polymer Chemistry, 54(19), 3224-3236. This research was supported by Nano·Material Technology Development Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Science, ICT and Future Planning (2016M3A7B4905609) Figure 1

Comparison of Electronic Parameters of Low Voltage Organic Field-Effect Transistors with Novel Gel Gate Insulators

Comparison of Electronic Parameters of Low Voltage Organic Field-Effect Transistors with Novel Gel Gate Insulators

Realizing low-voltage operating crystalline monolayer organic field-effect transistors with a low contact resistance

Monolayer crystals of 1,4-bis((5′-hexyl-2,2′-bithiophen-5-yl)ethynyl)benzene (HTEB) and their applications in low-voltage operating OFETs with a low bulk injection resistance (Rc,bulk) are presented.

Graphene Oxide/Polystyrene Bilayer Gate Dielectrics for Low-Voltage Organic Field-Effect Transistors

Here, we report on the use of a graphene oxide (GO)/polystyrene (PS) bilayer as a gate dielectric for low-voltage organic field-effect transistors (OFETs). The hydrophilic functional groups of GO cause surface trapping and high gate leakage, which can be overcome by introducing a layer of PS—a hydrophobic polymer—onto the top surface of GO. The GO/PS gate dielectric shows reduced surface roughness and gate leakage while maintaining a high capacitance of 37.8 nF cm−2. The resulting OFETs show high-performance operation with a high mobility of 1.05 cm2 V−1 s−1 within a low operating voltage of −5 V.

Subthreshold-Operated Low-Voltage Organic Field-Effect Transistor for Ion-Sensing System of High Transduction Sensitivity

A combination of the ion-sensitive organic field-effect transistor (ISOFET) transducer with silicon chips can utilize the strengths of both technologies for developing ubiquitous sensor systems. For optimal design of such a system, the transduction sensitivity of the ISOFET needs to be maximized. In this article, OFETs of different subthreshold swing (SS) values are fabricated using a solution processed organic semiconductor and dielectric materials to experimentally prove the dependence of the transduction sensitivity on the SS. Further ion-sensing measurement results show that the OFET of small SS (80mVdec) realized by both large gate dielectric capacitance and significantly reduced subgate density of states at the channel can help to achieve similar sensitivity with that of the silicon FET but with two-order lower power consumption.

Stability improvement in flexible low-voltage organic field-effect transistors with complementary polymeric dielectrics

The stability in terms of electrical, mechanical and thermal performance, is highly desirable for practical application of flexible electronics. Here, we report the stability improvement for pentacene-based flexible organic filed-effect transistors (OFETs) with complementary polymeric dielectrics, in which the net structured cross-linked poly(4-vinylphenol) (cPVP) layer was sandwiched between two ultrathin poly-(methyl methacrylate) (PMMA) layers. The core-shell-like structured dielectrics showed improved electrical insulating property by tuning the surface morphology and termination of the pinholes, enabling a 4 V-driven flexible OFET device with a high mobility of 0.72 cm 2 /V and excellent bias-stress stability in air. Under the tensile bending strain, the relationship between the parallel/vertical bending directions, dynamic or static bending modes and device performances were quantitatively investigated. Moreover, this flexible OFETs has a thermal operation margin up to at least 90 °C. The interfacial compatibility between the top PMMA layer and Pentacene was responsible for the enhanced stability performances. Our approach provides future possibilities of using hybrid polymeric dielectrics for highly stable flexible OFETs. • Complementary polymeric dielectrics were proposed for rational design of highly stable flexible OFETs. • Collaborative improvements in bias-stress stability, mechanical stability and thermal stability were realized. • Complementary polymeric dielectrics afford enhanced interfacial compatibility. • Ultrathin PMMA film served as both modification and buffering layer.

Intrinsically ionic conductive cellulose nanopapers applied as all solid dielectrics for low voltage organic transistors

Biodegradability, low-voltage operation, and flexibility are important trends for the future organic electronics. High-capacitance dielectrics are essential for low-voltage organic field-effect transistors. Here we report the application of environmental-friendly cellulose nanopapers as high-capacitance dielectrics with intrinsic ionic conductivity. Different with the previously reported liquid/electrolyte-gated dielectrics, cellulose nanopapers can be applied as all-solid dielectrics without any liquid or gel. Organic field-effect transistors fabricated with cellulose nanopaper dielectrics exhibit good transistor performances under operation voltage below 2 V, and no discernible drain current change is observed when the device is under bending with radius down to 1 mm. Interesting properties of the cellulose nanopapers, such as ionic conductivity, ultra-smooth surface (~0.59 nm), high transparency (above 80%) and flexibility make them excellent candidates as high-capacitance dielectrics for flexible, transparent and low-voltage electronics.

A plastic electronic circuit based on low voltage, organic thin-film transistors for monitoring the X-Ray checking history of luggage in airports

Abstract A circuit based on low voltage Organic Field-Effect Transistors (OFETs) and conceived for monitoring the security check history of luggage in airport environment is reported. An OFET-based, direct X-Rays detector is used as sensing element and integrated in an organic circuit for digitization and memorization of the X-Ray exposure event. An integrated interface to a commercial RFID chip and antenna is also realized to allow remote readout of the circuit status. The operation mechanism of the circuit is described and a complete explanation of the strategy adopted for circuit design is reported. Simulations of the systems in Cadence® Virtuoso environment are presented: X-Ray response of the sensor is modelled, and the overall functionality of the detection and memorization schema are demonstrated. Fabrication and characterization of the circuit under X-Rays in laboratory environment are described. In particular, the correct functionality of the circuit is demonstrated, as well as its actual capability in driving the commercial RFID tag system. The robustness of the circuit to aging and exposure to X-Rays in operation conditions is finally discussed.

A Facile Photo-cross-linking Method for Polymer Gate Dielectrics and Their Applications in Fully Solution Processed Low Voltage Organic Field-effect Transistors on Plastic Substrate

A simple and effective photochemical method was developed for cross-linking of polymer gate dielectrics. Laborious synthetic processes for functionalizing polymer dielectrics with photo-cross-linkable groups were avoided. The photo-cross-linker, BBP-4, was added into host polymers by simple solution blending process, which was capable of abstracting hydrogen atoms from polymers containing active C―H groups upon exposure to ultraviolet (UV) radiation. The cross-linking can be completed with a relatively long wavelength UV light (365 nm). The approach has been applied to methacrylate and styrenic polymers such as commercial poly(methylmethacrylate) (PMMA), poly(iso-butylmethacrylate) (PiBMA) and poly(4-methylstyrene) (PMS). The cross-linked networks enhanced dielectric properties and solvent resistance of the thin films. The bottom-gate organic field-effect transistors (OFETs) through all solution processes on plastic substrate were fabricated. The OFET devices showed low voltage operation and steep subthreshold swing at relatively small gate dielectric capacitance.

Binary polymer composite dielectrics for flexible low-voltage organic field-effect transistors

Abstract Insulating polymers have been recognized as a promising class of gate dielectrics for organic field-effect transistors (OFETs). However, the relative permittivity of most single polymer dielectrics is quite fixed and too low to afford low-operating voltages of OFETs. For flexible low-voltage OFETs, dielectric tunable polymer composites are highly desirable. Here, a new type of binary polymer composite dielectrics is developed by incorporating a small amount of polyacrylic acid (PAA) into poly(methyl methacrylate) (PMMA) to reduce the operating voltage and enhance the device performance. The resulting dielectric layers deliver a tunable relative permittivity from 3.32 to 4.28 with an increase of PAA contents in the composite. As results, flexible OFETs using PMMA:PAA dielectrics show greatly improved mobility and reduced threshold voltages with a low-operating voltage below −5 V. The OFETs using the composite dielectric also exhibit excellent performance stability during mechanical bending tests with different radii, where the mobility can maintain 95% of its initial value over 5000 cycles under a bending radius of 5 mm. The tunable dielectric properties and high robustness of these novel dielectrics make them promising candidates for solution-processed low-voltage flexible OFETs with low power consumption.

Device engineering for high-performance, low-voltage operating organic field effect transistor on plastic substrate

Various aspects in device engineering were tackled to realize a high-performance, low-voltage operating organic field effect transistor on plastic substrate. Contact resistance between the active layer and metal electrodes was decreased by employing oxide interfacial layers. The anodization of the Al gate served as a high capacitance dielectric layer enabling low-voltage operation of the devices. Several polymers were investigated in passivating the surface of the oxide dielectric to decrease the interfacial trap densities and to enhance surface smoothness. Finally, using these optimum conditions, devices on plastic substrate were fabricated which yielded mobility higher than 2 cm2 V−1 s−1 without hysteresis, operating below 5 V, with the current on/off ratio higher than 106 and the prospect of various applications in organic electronics.