Polystyrene-block-poly(methylmethacrylate) composite material film as a gate dielectric for plastic thin-film transistor applications (original) (raw)
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Journal of Electronic Materials, 2020
In this study, we present two regioregular poly(3-hexylthiophene-2,5-diyl) (rr-P3HT)-based top-gate bottom-contact configured organic thin-film transistors (OTFTs) using poly(a-methyl acrylate) (PMA) and poly(methyl methacrylate) (PMMA) polymers separately as gate insulators for comparison. In order to compare only the performance of the dielectrics, the other parts of the devices were kept qualitatively and quantitatively identical. Unlike PMMA, PMA is flexible, and flexibility is a desirable property for an OTFT. Thus, utilizing PMA can be advantageous if it supports higher performance of the transistor. In this respect, the electronic parameters of the fabricated devices were extracted from transfer and output characteristics to determine the performance of PMA in OTFT applications. Results showed that the mobility of the OTFT with PMA (PMA-OTFT) was nearly three times greater than that of the OTFT with PMMA (PMMA-OTFT), while the PMA-OTFT threshold voltage (V TH) was slightly less than that of the PMMA-OTFT, which was likely because of the greater effective capacitance (C EFF) of the PMA layer compared to that of the PMMA layer. This is the main advantage of the PMA. On the other hand, the major downside is found in the reduced onto off current (I ON /I OFF) and increased subthreshold swing originating from a huge off-current (I OFF), implying the existence of a large gate leakage current. Increasing the thickness of the PMA layer could reduce such large gate leakage current. However, this would lead to additional increase in the OTFT operating voltage. Therefore, further studies are required to improve the insulating property of the PMA polymer in order to substitute it for the PMMA.
… Applied Materials & …, 2012
An organic−organic blend thin film has been synthesized through the solution deposition of a triblock copolymer (Pluronic P123, EO 20 −PO 70 −EO 20 ) and polystyrene (PS), which is called P123−PS for the blend film whose precursor solution was obtained with organic additives. In addition to having excellent insulating properties, these materials have satisfied other stringent requirements for an optimal flexible device: lowtemperature fabrication, nontoxic, surface free of pinhole defect, compatibility with organic semiconductors, and mechanical flexibility. Atomic force microscope measurements revealed that the optimized P123−PS blend film was uniform, crack-free, and highly resistant to moisture absorption on polyimide (PI) substrate. The film was well-adhered to the flexible Au/Cr/PI substrate for device application as a stable insulator, which was likely due to the strong molecular assembly that includes both hydrophilic and hydrophobic effects from the high molecular weights. The contact angle measurements for the P123−PS surface indicated that the system had a good hydrophobic surface with a total surface free energy of approximately 19.6 mJ m −2 . The dielectric properties of P123−PS were characterized in a cross-linked metal− insulator−metal structured device on the PI substrate by leakage current, capacitance, and dielectric constant measurements. The P123−PS film showed an average low leakage current density value of approximately 10 −10 A cm −2 at 5−10 MV cm −1 and large capacitance of 88.2 nF cm −2 at 1 MHz, and the calculated dielectric constant was 2.7. In addition, we demonstrated an organic thin-film transistor (OTFT) device on a flexible PI substrate using the P123−PS as the gate dielectric layer and pentacene as the channel layer. The OTFT showed good saturation mobility (0.16 cm 2 V −1 s −1 ) and an on-to-off current ratio of 5 × 10 5 . The OTFT should operate under bending conditions; therefore flexibility tests for two types of bending modes (tensile and compressive) were also performed successfully.
Solution processable bilayered gate dielectric towards flexible organic thin film transistors
Organic Electronics, 2015
In this study, we have successfully explored the potential of a new bilayer gate dielectric material, composed of Polystyrene (PS), Pluronic P123 Block Copolymer Surfactant (P123) composite thin film and Polyacrylonitrile (PAN) through fabrication of metal insulator metal (MIM) capacitor devices and organic thin film transistors (OTFTs). The conditions for fabrication of PAN and PS-P123 as a bilayer dielectric material are optimized before employing it further as a gate dielectric in OTFTs. Simple solution processable techniques are applied to deposit PAN and PS-P123 as a bilayer dielectric layer on Polyimide (PI) substrates. Contact angle study is further performed to explore the surface property of this bilayer polymer gate dielectric material. This new bilayer dielectric having a k value of 3.7 intermediate to that of PS-P123 composite thin film dielectric (k $ 2.8) and PAN dielectric (k $ 5.5) has successfully acted as a buffer layer by preventing the direct contact between the organic semiconducting layer and high k PAN dielectric. The OTFT devices based on a,x-dihexylquaterthiophene (DH4T) incorporated with this bilayer dielectric, has demonstrated a hole mobility of 1.37 Â 10 À2 and on/off current ratio of 10 3 which is one of the good values as reported before. Several bending conditions are applied, to explore the charge carrier hopping mechanism involved in deterioration of electrical properties of these OTFTs. Additionally, the electrical performance of OTFTs, which are exposed to open atmosphere for five days, can be interestingly recovered by means of re-baking them respectively at 90°C.
RSC Advances
In this paper, we fabricated high performance flexible pentacene-based OFETs with low-k polymethylmethacrylate (PMMA, k=3.5) and high-k dielectrics cross-linked poly(4-vinylphenol) (PVP, k= 4.1) as double gate insulator layers on poly(ethylene terephthalate) (PET) plastic substrate. The field-effect mobility (μ) of flexible pentacene-based OFETs was greatly increased from 0.66 cm 2 V-1 s-1 to 1.51 cm 2 V-1 s-1 , meanwhile, their high electrical insulating properties were also well maintained which resulted in high ON/OFF current ratio of 10 5. The control experiments showed that the high performance flexible OFETs were mainly attributed to the PMMA/PVP double dielectric layers which not only have high electrical insulating property but also favor the growth of pentacene films. The flexible OFETs still showed excellent mechanical flexibility when they were bent 1000 successive mechanical bending cycles and held under the bending state for 2 hours at a radius of 3.5mm. In addition, the flexible OFETs also showed high thermal stability, which exhibited the mobility of 0.72cm 2 /Vs, the positive shift direction of VTH, the ON/OFF current ratio of 10 5 after heating to 100°C for 2 hours in the atmosphere. Our results suggested that the PMMA/PVP double dielectric films were very suitable for the dielectric layer of the flexible OFETs.
Characteristics and applications of Polymeric Thin Film Transistor: Prospects and challenges
2011
Polymeric Thin Film Transistors (PTFTs) have undergone extraordinary improvements during the last decade. PTFTs which are also termed as Organic Thin Film Transistor (OTFT) are promising devices for future development of variety of low-cost and large-area electronics applications such as activematrix displays and flexible microelectronics. Organic transistors show high mobility, high-speed and high-current characteristics and are suitable for driver elements of flexible displays. This paper reviews recent progress in materials, fabrication processes, advances in device designs and applications related to PTFTs/ OTFTs. The performance of PTFTs/OTFTs is evaluated in terms of on/off current ratio, threshold voltage, subthreshold slope, power dissipation, switching time, driving capability and effective mobility. Various analytical models such as charge transport phenomena in organic solids and resulting models of PTFTs/OTFTs are reviewed. The paper thoroughly discusses the applications of OTFTs in various fields. Prospects, challenges and limitations are also discussed. Recently, polymer thin film transistors area has emerged as a field of intense research activities with emphasis on fundamental concepts and practical applications.
Bending Effect of Organic Field-Effect Transistors with Polyimide Gate Dielectric Layers
Japanese Journal of Applied Physics, 2005
We manufactured markedly flexible pentacene field-effect transistors (FETs) on a polyethylenenaphthalate base film with polyimide gate dielectric layers, with a mobility of 0.3 cm2/Vs and an on/off ratio of 105. The electric performance of DC current–voltage characteristics was measured by applying compressive and tensile strains while reducing the bending radius down to 3 mm. It was found that the compressive strain leads to an increase in mobility of 10% induced by the change in strain of up to 1.4±0.1%, although the tensile strain leads to a decrease in mobility of 10%. To elucidate the origin of the enhancement of mobility under the compressive strain, we also investigated the strain dependence of capacitance–voltage characteristics for a pentacene channel layer, and almost no change was observed. Our results suggest that the strains markedly affect the spacing between pentacene molecules rather than the number of induced carriers.
The application of a high-k polymer in flexible low-voltage organic thin-film transistors
Although much progress has been made in the study of high-mobility organic semiconductors in recent years, one major challenge for organic thin film transistors (OTFTs) in real applications is the relatively high operating voltage, which is mainly related to the gate dielectric of the OTFT. Here we show the application of a high-k poly(vinylidene fluoride-trifluoroethylene-chlorofloroethylene) (P(VDF-TrFE-CFE)) as the gate dielectric of flexible low-voltage pentacene OTFTs for the first time. The performance of the OTFTs is optimized by modifying the surface of P(VDF-TrFE-CFE) films with various thin polymer films by a solution process. The flexible OTFTs show excellent performance at the operating voltage of 4 V and good stability after 1000 bending tests. It is expected that P(VDF-TrFE-CFE) is a suitable gate dielectric for low-voltage OTFTs based on various small-molecule organic semiconductors because P(VDF-TrFE-CFE) terpolymer films can be easily modified with different thin polymer films by a solution process.
Applied Physics Letters, 2009
We demonstrate low-voltage, solution-processed organic transistors on rough plastic substrates with a carrier mobility over 0.2 cm2/V s, a turn-on voltage of near 0 V, and a record low subthreshold slope of ∼80 mV/decade in ambient conditions. These exceptional characteristics are attributed to (1) a device stacking architecture with a conducting polymeric gate and a double layered dielectric composed of low-temperature cross-linked poly(4-vinylphenol), (2) a low interface trap density achieved by modifying the dielectric surface with a phenyl-terminated self-assembled monolayer from 4-phenylbutyltrichlorosilane, and (3) controlled crystallization of a small-molecule organic semiconductor film with favorable charge transport microstructure and a low bulk trap density as deposited by an optimized solution-shearing process. The device performance under different operating voltages was also examined and discussed.