TWI637986B - Stretchable transistor - Google Patents

Abstract

The present invention relates to a stretchable crystal element comprising a surface creped fluoroelastomer as a substrate, and further comprising a fluoroelastomer having a surface wrinkle as a The dielectric layer, the present invention significantly increases the mechanical compliance of the stretchable field effect transistor by using a fluoroelastomer having self-crosslinking surface wrinkles as the substrate and dielectric layer. In addition, the stretchable transistor has a high and stable mobility after 2000 cycles of 30% isoaxial stretching.

Description

Stretchable transistor component

The present invention relates to a stretchable transistor element, and more particularly to a transistor element comprising a surface creped fluoroelastomer as a substrate.

Stretchable electronic components are attracted by their potential for use in wearable or biomedical products, such as stretchable display devices, deformable artificial sensors, skin electronics for human-machine interfaces, and the like. The concern of many scientists. Field effect transistors (FETs) are a very important component in the application of stretchable electrons, and they are required to have a characteristic that the electronic properties are not significantly lowered under a high tensile state. Several methods have been applied to the preparation of stretchable field effect transistors, for example, using a stretchable conductive connector to bond component units fixed to a hard substrate, or a buckle caused by pre-stretching of an elastic substrate. The structure is to adjust the applied stress and the like. In contrast to the above method, a transistor composed of a stretchable material can enhance the function of the device while being subjected to stress, and the transistor is called an intrinsically stretchable transistor (IST). ). IST has a simple manufacturing process and is compatible with planar circuits. Due to the high mechanical compliance and low cost-large area manufacturing advantages of conjugated polymers, their choice as active layer channels is considered suitable for IST. In addition, the balance between the pressure tolerance and electronic properties of the conjugated polymer can be achieved by precisely controlling the space-filling structure and the alkyl group to increase the solubility group. However, at present for the semi-crystalline conjugated polymer, the occurrence of microcracks is still observed during the stretching process.

The following are three methods currently used to suppress microcracking during stretching, including:

Prior art (1), the soft segment was incorporated into a rigid polymer structure. The mechanical compliance can be increased by introducing a longer soft alkyl side chain into the conjugated polymer. In addition, in hard rod-flexible block copolymers, such as polyethylene (PE) and stereoregular poly(3-hexylthiophene) (P3HT), it is also shown that the soft segment can be reduced in the stretched form. Extensive stress. However, the resistance of the above materials to stress is still insufficient for use in stretchable applications.

Prior Art (2), Polymer and Elastomer Mix: Unyong and his research team have published that P3HT is mixed with polystyrene-block-poly(ethylene-co-butene)-block-polystyrene SEBS. Active channel. However, this method requires precise control of the microphase separation of the P3HT nanofibers in the rubber matrix, and wherein the mobility of the charges is limited due to the insulating properties of the elastomer.

Prior art (3), using elastic electrodes and dielectrics: Bao and his partners used embedded carbon nanotubes as the source and drain electrodes in polyurethane (PU) and as spin-coated PUs as gates Extreme dielectric layer. The formation of microcracks in the semiconductor is suppressed by good adhesion between P3HT and PU.

From the above, it is known that stretchable field effect transistors currently using conjugated polymers are mainly concentrated in the polythiophene system. The above device still has a low hole mobility ((10 ^-2 ~10 ^-3 (cm ² V ^-1 S ^-1 ))) and cannot be industrialized, and its tensile period cannot exceed 1000 defects. Therefore, there is a need to develop a new strategy to reduce the stress accumulated in repeated deformation of a stretchable electronic device having a semi-crystalline conjugated polymer as an active layer.

The inventor of the present invention discovered the above problems faced by the prior art in order to solve the above problems. SUMMARY OF THE INVENTION A primary object of the present invention is to provide a stretchable transistor element comprising a surface-wrapped fluoroelastomer as a substrate.

In a preferred embodiment, the fluoroelastic system in which the surface is creased is formed by a crosslinking action.

In another preferred embodiment, the fluoroelastomer having the surface wrinkle is further included as a dielectric layer.

In another preferred embodiment, wherein the fluoroelastomer system is polymerized from a monomer selected from the group consisting of perfluoroolefins, perfluorovinyl ethers, halogenated fluoroolefins, and partially fluorinated olefin-containing hydrogen-containing monomers. .

In another preferred embodiment, the fluoroelastomer system comprises polyvinylidene fluoride (VDF) and hexafluoropropylene (HFP) copolymer, TFE/propylene copolymer, TFE/propylene/VDF copolymer, TFE/ VDF/HFP copolymer, TFE/perfluoromethyl vinyl ether (PMVE) copolymer, TFE/CF ₂ =CFOC ₃ F ₇ copolymer, TFE/CF ₂ =CFOCF ₃ /CF ₂ =CFOC ₃ F ₇ copolymer , TFE/CF ₂ =C(OC ₂ F ₅ ) ₂ copolymer, TFE/ethyl vinyl ether (EVE) copolymer, TFE/butyl vinyl ether (BVE) copolymer, TFE/EVE/BVE copolymer , VDF/CF ₂ =CFOC ₃ F ₇ copolymer, ethylene/HFP copolymer, TFE/HFP copolymer, CTFE/VDF copolymer, TFE/VDF copolymer, TFE/VDF/PMVE/ethylene copolymer or TFE/VDF /CF ₂ =CFO(CF ₂ ) _{3 The} OCF ₃ copolymer crosslinks to form a crosslink.

In another preferred embodiment, the method further includes depositing a gate electrode layer over the substrate and an active layer stacked over the dielectric layer.

In another preferred embodiment, the gate electrode layer is formed of a stretchable conductive polymer.

In another preferred embodiment, the conductive polymer is a polythiophene polymer, a poly-p-phenylene vinyl polymer, a polyfluorene polymer, a phthalocyanine derivative (H2Pc, CuPc). , ZnPc, etc.) or a porphyrin derivative.

In another preferred embodiment, wherein the active layer exhibits a wave structure.

In another preferred embodiment, the active layer is an N-type or P-type organic small molecule, an organic polymer, or a mixture of organic small molecules and an organic polymer, and may be, for example, PSeDPP, P3HT or PCBM.

In another preferred embodiment, the polyvinylidene fluoride (VDF) and hexafluoropropylene (HFP) are in the presence of benzammonium oxide (BPO) and tripropylene isomeric cyanuric acid (TAIC). Cross-linking.

In summary, the present invention produces a highly efficient and essentially stretchable organic TFT by a fluoroelastomer substrate having a self-reticulated surface by a crosslinking reaction. The present invention also applies this material to the gate electrode, exhibiting low leakage current and good mechanical compliance. The CNT and PU/PEOT:PSS mixture is applied to a stretchable source/drain electrode. The substrate can be dissipated by the applied stress on the semiconductor, and the conjugated polymer film can be deformed into a wrinkle structure after stretching to make it highly resistant under pressure. After 100% stretching, the transistor still maintains a high mobility of ~0.73 (cm ² V ^-1 S ^-1 ) mobility, 10 ⁴ open-close ratio; the device has 2000 times of 30% isoaxial stress. After the stretching cycle, it still has excellent electrical performance.

Figure 1 (a) is a chemical structure example of the fluoroelastomer of the present invention, the chemical structure of PSeDPP and PII2T; (b) a schematic view of the surface pleats of the fluoroelastomer; (c) in the case of a fixed boundary, The in-plane stress generated by the different cross-linking densities of the top and bottom surfaces; (d) the stress-strain behavior test results of the fluoroelastomer and PDMS as the substrate, respectively.

2 is a fluoroelastomer prepared by adding a crosslinking agent and heating to 120 ° C without a boundary restriction, and respectively applying (a) 0% stress (b) 50% of the same axial stress.

Fig. 3 is a fluoroelastomer prepared by heating to 120 ° C without a crosslinking agent and having a boundary restriction, respectively, (a) 0% stress (b) 50% of the same axial stress.

4(a) is a schematic view showing a transfer of a PSeDPP film to a surface wrinkle substrate and deformation into a wrinkle structure; (b) an SEM image of the fluoroelastomer before 50% coaxial stretching; (c) SEM image of the fluoroelastomer after 50% coaxial stretching; (d) SEM image of the PSeDPP film on the elastomer after 50% coaxial stretching; (e) the PSeDPP film on the elastomer, SEM image after 50% coaxial stretching; (f) cross-sectional image of PSeDPP film on elastomer substrate before 50% coaxial stretching; (g) PSeDPP film on elastomer substrate at 50% coaxial Profile image after stretching.

Figure 5 is an SEM image of an SEM image of a PSeDPP film on a PDMS substrate via (a) 0% stress (b) at 50% coaxial stretching.

Figure 6 is an AFM image of the (a) high mode (b) phase mode (c) 3D topological mode of the PSeDPP film after being stretched under different stresses and transferred back to the wafer by the fluoroelastomer.

Figure 7 is a graph showing the effect of (a) PSeDPP film on PDMS substrate (b) PSeDPP film on fluoroelastomer substrate after stress applied to its structure and morphology.

Figure 8 shows the effect on the structure and morphology after stress application. The results of different tensile stress ratios of the P3HT film on the fluoroelastomer substrate were observed.

Figure 9 is an overview of the preparation of the device, including (a) a schematic of the manufacturing process and (b) an image of stretching the device to 30%.

Figure 10 is a graph showing the results of measuring the capacitance of the fluoroelastomer at different frequencies.

Figure 11 (a) is a cross-sectional SEM image of the stretchable device of the present invention; (b) SEM image of the top surface after 0% stretching, (c) 50% coaxial phase stretching.

Figure 12 is a (a) typical output curve and (b) transfer curve of the stretchable device under no applied pressure.

Figure 13 is the mobility of PSeDPP under stress-applying state (a) typical transmission characteristics of a TFT device in a specific tensile stress, and the stretching direction is parallel to the direction of charge flow (V _d = -80 V) or (b) The extension direction is perpendicular to the typical transmission characteristics of the state in which the charge flows. (c) A plot of I _open , I _off, and mobility versus applied stress, where the stress direction is parallel to the current direction and (d) the stress direction is perpendicular to the current direction.

Figure 14 is a diagram showing the current leakage phenomenon of a stretchable FET device under stress.

Figure 15 is a graph showing the current leakage of a stretchable transistor using a crosslinked fluoroelastomer substrate without a crosslinked dielectric layer.

Figure 16 shows the mechanical durability of a PSeDPP-based retractable FET at 30% stress. (a) Typical transmission characteristics of a TFT device under a specific tensile stress and a tensile direction parallel to a charge flow direction (V _d = -80 V) or (b) a tensile direction perpendicular to a charge flow direction characteristic. (c) A plot of I _open , I _off, and mobility versus applied stress, where the stress direction is parallel to the current direction and (d) the stress direction is perpendicular to the current direction.

Figure 17 is a field effect transistor characteristic in a stretched state. (a) When the applied stress is parallel to the direction of charge flow, the field effect transistors are respectively at different stress mobility; (b) when the applied external stress is parallel to the charge flow direction, the field effect transistors are respectively at different stresses. Mobility; (c) the cycle of the stretchable field effect transistor after release after applying 2000 times of 30% tensile stress, and the stress direction is parallel to the charge flow direction, the mechanical durability of the device; (d) the pullable Extensible field effect transistor is applied in 2000 The mechanical durability of the device after the 30% tensile stress release cycle, and the stress direction is perpendicular to the charge flow direction.

The term "a" or "an" as used in this document may be used in the scope of the patent application or in the specification, but may also mean one or more or at least one.

Stretchable transistor element of the invention

It is an object of the present invention to provide a stretchable transistor element comprising a surface creped fluoroelastomer as a substrate.

In a preferred embodiment, the fluoroelastic system in which the surface is creased is formed by a crosslinking action.

In another preferred embodiment, the fluoroelastomer having the surface wrinkle is further included as a dielectric layer.

In another preferred embodiment, wherein the fluoroelastomer may comprise one or more interpolymerized units derived from at least two major monomers. Examples of suitable candidates for the principal monomer or of such include perfluoroolefins (e.g., tetrafluoroethylene (TFE) and hexafluoropropylene (HFP), having the formula, or any of CF ₂ = CF-Rf perfluoroolefin of, Wherein Rf is fluoro or a perfluoroalkyl group having from 1 to 8, in some embodiments from 1 to 3 carbon atoms, perfluorovinyl ether (for example, perfluoroalkyl vinyl ether (PAVE) and perfluoro) Alkoxyalkyl vinyl ether (PAOVE), halogenated fluoroolefins (eg, chlorotrifluoroethylene (CTFE)), such as olefins (eg, ethylene and propylene), and partially fluorinated olefins (eg, vinylidene fluoride (eg, vinylidene fluoride) Hydrogen-containing monomer of VDF), pentafluoropropene and trifluoroethylene. Those skilled in the art will be able to select a suitable amount of specific interpolymerized units to form a fluoroelastomer.

In some embodiments, the polymerized units derived from the non-fluorinated olefin monomer are at most A 25 mole percent fluoropolymer, in some embodiments up to 10 mole percent or up to 3 mole percent, is present in the fluoroelastomer. In some embodiments, the polymeric unit derived from at least one of the PAVE or PAOVE monomers is at most 50 mole percent fluoropolymer, in some embodiments at most 30 mole percent or at most 10 mole percent The amount is present in the fluoroelastomer.

As described above, the fluoroelastomer is preferably, but not limited to, polyvinylidene fluoride (VDF) and hexafluoropropylene (HFP) copolymer, TFE/propylene copolymer, TFE/propylene/VDF copolymer, TFE/VDF. /HFP copolymer, TFE/perfluoromethyl vinyl ether (PMVE) copolymer, TFE/CF ₂ =CFOC ₃ F ₇ copolymer, TFE/CF ₂ =CFOCF ₃ /CF ₂ =CFOC ₃ F ₇ copolymer, TFE/CF ₂ =C(OC ₂ F ₅ ) ₂ copolymer, TFE/ethyl vinyl ether (EVE) copolymer, TFE/butyl vinyl ether (BVE) copolymer, TFE/EVE/BVE copolymer, VDF/CF ₂ =CFOC ₃ F ₇ copolymer, ethylene/HFP copolymer, TFE/HFP copolymer, CTFE/VDF copolymer, TFE/VDF copolymer, TFE/VDF/PMVE/ethylene copolymer or TFE/VDF/ The CF ₂ =CFO(CF ₂ ) ₃ OCF ₃ copolymer crosslinks to form a crosslink.

In another preferred embodiment, the method further includes depositing a gate electrode layer over the substrate and an active layer stacked over the dielectric layer.

In another preferred embodiment, the gate electrode layer is formed of a stretchable conductive polymer.

In the above, the material of the conductive polymer is not limited, and as the material of the conductive polymer, a polythiophene polymer, a poly-p-phenylene vinyl polymer, or a polyfluorene can be preferably used. A conductive polymer such as a polymer, or a low molecular organic compound exhibiting p-type semiconductor properties such as a phthalocyanine derivative (H2Pc, CuPc, ZnPc, etc.) or a porphyrin derivative. In particular, polyethylene dioxythiophene (Polyethylene) which is a polythiophene-based polymer can be preferably used. Dioxythiophene, PEDOT), or polystyrene sulfonate (PSS) added to PEDOT, more preferably PU/PEDOT:PSS.

In another preferred embodiment, wherein the active layer exhibits a wave structure.

In the above, the material of the active layer is not particularly limited, and may be a semiconductor commonly used as an active layer in the field of the invention, including N-type or P-type organic small molecules, organic polymers, or small organic molecules. And a mixture of organic polymers. The material of the organic small molecule is, for example, pentacene. Organic semiconductor polymer poly-(3-hexylthiophene, P3HT), polyacrylic acid (PAA), etc.; however, it is preferred to use conjugated polymers such as: PSeDPP, P3HT, PCBM, F8T2.

In another preferred embodiment, the fluoroelastomer system is formed by crosslinking the monomers in the presence of benzophenone oxide (BPO) and tripropylene isomeric cyanuric acid (TAIC).

In the present invention, the terms "curing" and "curable" generally link the polymers together via a covalent chemical bond via a crosslinking molecule or group to form a network polymer. Therefore, in the present invention, the terms "cured" and "crosslinked" are used interchangeably. The cured or crosslinked polymer is generally characterized as insoluble, but is expandable in the presence of a suitable solvent.

In the present invention, the solvent which can be used in the practice of the present invention has a boiling point and, if necessary, can be cured using a cured fluoroelastomer manufactured by the curable composition disclosed herein by a normal drying procedure using heat or reduced pressure. Solvents useful in the practice of the invention do not include ionic liquids. In some embodiments of any of the foregoing embodiments, including the curable compositions disclosed herein, the solvent has a boiling point in the range of from 30 °C to 200 °C. If the boiling point of the solvent is lower than 30 ° C, it is difficult to maintain a consistent solid content during, for example, the coating process. If the boiling point of the solvent is higher than 200 ° C, it is difficult to remove the solvent after the fluoroelastomer is cured, if necessary. Examples of solvents which can be used in the practice of the invention include ketones, esters, Carbonates and formates, such as tert-butyl acetate, 4-methyl-2-pentanone, n-butyl acetate, ethyl acetate, 2-butanone, ethyl formate, methyl acetate, cyclohexanone, Dimethyl carbonate, acetone and methyl formate. In some embodiments, the solvent comprises acetone, 2-butanone, 4-methyl-2-pentanone, cyclohexanone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, n-butyl acetate, At least one of t-butyl acetate or dimethyl carbonate. In some embodiments, the solvent comprises at least one of ethyl acetate or methyl acetate. In some embodiments including any of the embodiments of the curable compositions disclosed herein, the solvent is not an alcohol. Alcohols tend to be particularly hazardous to peroxide curing.

In curing the fluoroelastomer, it is usually necessary to include a crosslinking agent. Such crosslinkers can be used, for example, to provide enhanced mechanical strength in the final cured composition. Accordingly, in some embodiments, the curable composition of the present invention further comprises a crosslinking agent. Those skilled in the art will be able to select conventional crosslinkers based on the desired physical properties. Examples of useful crosslinking agents include triallyl isocyanurate (TAIC), tris(methyl)allyl cyanurate (TMAIC), tris(meth)allyl cyanurate, polyisocyanate Triallyl urate (poly TAIC), xylylene-bis(diallyl isocyanurate) (XBD), N,N'-meta-phenylbissuccinimide, phthalic acid Diallyl ester, propylene (diallylamine)-symmetric triazine, triallyl phosphite, 1,2-polybutadiene, ethylene glycol diacrylate, diethylene glycol diacrylate and CH ₂ =CH-R _f1 -CH=CH ₂ , wherein R _f1 is a perfluoroalkylene group having 1 to 8 carbon atoms. The crosslinking agent is typically present in an amount from 1% to 10% by weight, relative to the weight of the curable composition. In some embodiments, the crosslinker is present in a range from 2% to 5% by weight relative to the weight of the curable composition.

Preparation example

The crystal element of the invention

A method of preparing a fluoroelastomer is to dissolve a fluoropolymer in MEK at a concentration of 300 mg/ml to prepare a fluoroelastomer in a weight ratio of a fluoroelastomer: BPO:TAIC=100:2:6. The solution was cast into a glass petri dish and allowed to evaporate at 30 ° C and then cured at 120 ° C for 1 hour. The final thickness of the substrate was 400 μm. The PU was diluted to 40 mg/ml with Milli-Q water. PEDOT:PSS (10 mg/ml) was previously mixed with 10 wt% DMSO and 1 wt% Zonyl FS-300 (fluorosurfactant (purchased from Sigma-Aldrich (US)). During the mixing process, the diluted PUD was stirred at high speed. At the same time, PEDOT:PSS was added dropwise. Before the spray coating was used as the gate electrode, the mixture of the polymer was filtered through a syringe filter (pore size: 0.2 μm) by dissolving in trifluoroethylene. The OTS solution was spin-coated to prepare a tantalum wafer having an OTS self-assembled layer, and then ammonium hydroxide vapor was applied. The fluoropolymer having the same crosslinking rate as the substrate was subjected to MEK (140 mg/mL) at 1000 rpm. Spin-coated and deposited on a TISS-coated wafer. PSeDPP dissolved in chlorobenzene (15 mg/mL) was also spin coated onto the OTS-coated wafer and used in a two-step procedure, including: 0 rpm, 60 s, and (2) 120 rpm, and accelerated at 600 rpm s ^{-1 for} 30 seconds. The resulting dielectric layer was manually transferred to a PU/PEDOT:PSS electrode at 50 ° C and a gentle pressure was applied for 10 seconds. PSeDPP Also transferred to the dielectric layer in the same manner. CNTs (Sigma Aldrich) in chloroform at a concentration of 0.214 mg/mL, with ultrasound Solutions of 60 minutes to a spray coating process, the substrate was heated on a hot plate to line 60 ℃, using a channel length and a width of 100um 200um the shadow mask, so that the source and drain electrode pattern.

Characteristic analysis method

The thickness of the polymer film was measured using a microfigure measuring instrument (Surfcorder ET3000, Otaru Research Institute Co., Ltd. (Japan)). The morphological change of the semiconductor layer was observed by a field emission scanning electron microscope (FE-SEM, JEOL JSM-6330F). The SEM sample was measured for image properties, first sputtered with platinum, and the analysis was run at 10 kV acceleration. The PU/PEDOT:PSS sheet resistance is measured using a four-point probe structure coupled to a Keithley 2400 power measurement unit. The electrical properties of the stretchable device of the present invention were measured by a Keithley Model 4200 Semiconductor Parameter Analyzer. The inventors of the present invention obtained the OFET parameter-field-effect mobility μ _FET (cm ² V ^-1 s ^-1 ) in the saturation region by the following Equation 1, the on/off ratio (I _on / _off ), and Threshold voltage ( V _th ): Where I _d is the drain current, V _g is the gate current, V _th is the threshold voltage, μ is the hole mobility, W is the channel width, L is the channel length, and C _tot is the dielectric per unit area. capacitance.

Example

The invention is described in detail in the following examples, but these examples are not intended to limit the scope of the invention.

Surface wrinkle fluoroelastomer of the present invention

1(a) and 1(b) will be described together. The fluoropolymer having a curing active terminal monomer (CSM) can be easily cross-linked by BPO and TAIC by a solution process. For example, the chemical formula of the fluoropolymer containing VDF and HFP is as shown in FIG. (a) is shown.

With the elastomer substrate manufactured by the extrusion or molding method, a substrate having both self-wrinkled surface and mechanical compliance can be prepared by the solution-processed system of the above-described preparation example. Figure 1 (b) shows that the process of producing an autogenous wrinkle structure on a substrate is based on the following mechanisms: (1) The surface crosslinks have a lower density than the bottom surface. During the heating process, since the solvent is evaporated from the surface, the polymer in the surface region becomes non-soluble, so that the crosslinking reaction rate is slowed down. Therefore, the bottom region is crosslinked to a greater extent than the surface region. Another possibility It is because the free radicals generated by the decomposition of BPO may react with oxygen directly in the top region, which leads to a lower cross-linking reaction in the top region than in the bottom region. Wrinkles are caused by internal stresses caused by the difference in density of the crosslinking reaction. (2) The boundary restriction of the culture dish causes the polymer to generate thermal compression stress during thermal expansion.

Test the effects of boundary limits and crosslinkers on the cross-linking reaction

Description will be made with reference to Fig. 1 (c), Fig. 2 and Fig. 3 together. The fluoroelastomers were prepared under the following conditions:

Example 1: A cross-linking agent was added and heated to 120 ° C with boundary restrictions, and the prepared fluoroelastomer was as shown in Fig. 1 (c).

Comparative Example 1: A cross-linking agent was added and heated to 120 ° C without boundary restrictions, and the prepared fluoroelastomer was as shown in FIG. 2 .

Comparative Example 2: A fluorine-containing elastomer prepared by heating was added to 120 ° C without a crosslinking agent as shown in Fig. 3 .

From the experimental results, it was found that the pleated structure produced by the crosslinking reaction of the fluoroelastomers of Comparative Example 1 and Comparative Example 2 was not as remarkable as the results of the boundary restriction of Example 1 and the addition of a crosslinking agent.

Comparison of mechanical properties of different elastomer materials

Referring to Figure 1(d), the difference in mechanical properties of the fluoroelastomer of the present invention and the commercially available elastomeric poly-dimethyloxane (PDMS) at different crosslinking ratios was tested. The Young's module values for fluoroelastomers, PDMS (15:1) and PDMS (20:1) were 16.18, 6.28 and 5.42 (MPa), respectively.

A substrate with a higher Young's module value dissipates more stress and protects Semiconductor layer. Therefore, according to the above results, the use of a fluoroelastomer as a substrate compared to PDMS has a better effect.

Stretchable transistor element of the invention

PSeDPP film produces a consistent wrinkle structure with fluoroelastomer

Please refer to FIG. 4(a) to FIG. 4(f) for explanation. Fig. 4(a) is a schematic view showing the transfer of a PseDPP film (80 nm) to a surface-wrapped fluoroelastomer substrate. The PSeDPP film has two states on the surface of the wrinkle, including: Free-Standing (FS) and Semi-free-standing (SFS). The semi-support type means the portion of the bottom of the film that is supported by the substrate, while the unsupported type means that the film is suspended at the top or end of the substrate gap without any support. The unsupported surface can change the structure and characteristics of the polymer film. When the thickness of the film is less than 100 nm, the effect becomes stronger when it is a complete block.

According to research by Martín-González and its team, when the polymer film is unsupported, it is softer than the monolithic pattern due to its small spatial barrier. This effect, in turn, leads to the easy collapse of the PseDPP film. The pleats on the surface of the fluoroelastomer cause the conjugated polymer film in contact therewith to also produce the same pleated structure.

4(b) to (c) are SEM images of the fluoroelastomer substrate before and after elongation in the 50% axial direction. The initial random wrinkle structure has a distance of 1 μm and is consistent with the applied stress direction. It is worth noting that this wrinkle is much smaller than the wrinkles produced by the pre-stretching method previously studied ( Thin Solid Films 519, 818-822. (2012)). Before stretching, the PSeDPP film is only slightly wavy, as shown in Figure 4(d); however, when stretched by 50%, the PSeDPP film produces a distinct wrinkle structure, as shown in Figure 4(e). . The SEM cross-sectional images according to Figures 4(f) through 4(g) show that the structural changes produced by the PSeDPP film are consistent with the morphology of the wrinkle structure on the substrate. The value of the Young's module of the conjugated polymer and the elastic substrate is greatly different. The PSeDPP film tends to form a wrinkle structure to release the applied stress and reduce the total energy of the system to stabilize it. In addition, no microcracks were produced during the stretching process.

However, as shown in Fig. 5, in the case where the PSeDPP film is made of PDMS as a substrate, the initial state is smooth, but many minute cracks occur after stretching.

After stretching, the PSeDPP film is transferred back to the wafer by the fluoroelastomer under different stress forms.

This will be described together with reference to FIG. Since the image of the PSeDPP film on the corrugated substrate could not be obtained, the PSeDPP was transferred to the rigid SiO ₂ /Si substrate. Figure 6 shows the AFM pattern of PSeDPP at different degrees (0 to 80%) under the same axial stress. However, at different degrees, the wrinkles have different morphology, and there is still no microcrack on the film. The gap of the wrinkles is 400 to 800 nm, which is similar to the size of the gap in the SEM image. And it was confirmed that the PSeDPP has been modified into a wrinkled structure according to the rolling form shown by the 3D topology.

Microcracking on different elastic substrates

The description will be made with reference to FIG. The PSeDPP film prepared from PDMS and the fluoroelastomer was observed on a large scale by an optical microscope, and cracks or cracks on the surface were generated when stretched. As shown in Fig. 7(a), the PSeDPP film prepared on PDMS produced a crack of 10 μm width when 50% stress was applied; however, as shown in Fig. 7(b), it was prepared on a fluoroelastomer. The PSeDPP film has microcracks until the stretching exceeds 100%. This means that the mechanical compliance of PSeDPP on a fluoroelastomer substrate is twice that on a PDMS substrate. This phenomenon may be due to wrinkles on the fluoroelastomer, which slows the cracking of PSeDPP. Since the degradation on the fluoroelastomer is significantly less than the device, it is inferred that the fluoroelastomer is not the original cause of a significant decrease in equipment performance. because. It is speculated that the stretchability of the substrate may be improved due to the wrinkled surface of the substrate, and the applied stress may be released, resulting in an increase in adhesion between the PSeDPP and the fluoroelastomer.

Testing with different polymer materials on fluoroelastomers

Referring to Fig. 8, the description will be made together. In order to understand whether the fluoroelastomer can be applied to other polymer materials in addition to PSeDPP, the electronic properties of P3HT on the wrinkled surface were tested. Figure 8 shows the change in morphology of P3HT in the stretched state. The inventors have unexpectedly found that no significant microcracking was observed before stretching to 200%, which is superior to the experimental results of P3HT on PDMS substrates ( Chem. Mater. 26, 4544-4551. (2014), Adv. Mater. 26, 4253-4259. (2014)). From the above results, it is understood that the fluoroelastomer having a wrinkle structure can remarkably enhance the stretchability of the semi-crystalline conjugated polymer film.

Prepare the lower gate and top contact transistor

The description will be made with reference to FIG. Fig. 9(a) is a schematic view showing the structure of preparing a lower gate and a top contact transistor on a fluoroelastomer having wrinkles.

The first step is to deposit the polymer PEDOT:PSS/PU mixture with conductivity as a gate electrode. It is based on the disclosure of previous studies ( Adv. Mater. 26, 3451-3458. (2014)) that water-soluble polyurethanes are added to form a highly stretchable conductor. In order to reduce the conductivity of the electrode in a stressed state, this embodiment uses a spray coating method to deposit a PU/PEDOT:PSS layer as a gate electrode. The surface resistance of PU/PEDOT:PSS (4:1) is 420 (Ω/sq). The second step is to transfer the dielectric layer and the PSeDPP layer from the self-assembled octadecyltrimethoxydecane modified germanium wafer to the PU/PEDOT:PSS film. The fluoroelastomer dielectric layer (thickness ~1 μm ) was crosslinked prior to transfer, and Figure 10 shows its capacitance (~6 nF/cm ² ) at different frequencies (1000-5000 Hz). The final step is to pattern the single-walled carbon nanotubes dispersed in chloroform by a shadow mask having a length of 100 μm and a width of 2000 μm, and patterning (SWCNT) as a drain and a source of the PSeDPP layer. As shown in Fig. 9(b), the carbon nanotube electrode does not damage the semiconductor layer as long as the deposition distance and temperature of the deposition are precisely controlled.

11(a), (b) and (c) are SEM images of the cross section of the transistor and SEM images of the surface of the device before and after stretching, respectively. From the above results, it is understood that even in the structure of the multilayer stack, each layer has been transformed into a wrinkled state.

Testing the electronic characteristics of a TFT device

The electronic characteristics of the TFT device having the wrinkled substrate were measured at room temperature using a probe station. As shown in Fig. 12(a), the push side has no significant junction resistance impedance in the output characteristic curve due to the top contact structure. For the field effect transistor, in the upper contact type structure, the ejection area is larger than that of the lower contact type device, so that the field effect mobility is higher and the junction resistance is lower. In addition, since the length of the channel used in the present invention is large, the junction resistance is not greater than the channel resistance. In addition, this device also exhibits well-defined typical current modulation. The characteristic of the hysteresis of I _d - V _g is shown in Fig. 12(b), which is a typical phenomenon which often occurs when a fluorine-containing base polymer dielectric layer is used.

The electronic characteristics of the device in the direction of parallel (Fig. 13 (a)) and vertical (Fig. 13 (b)) in the channel under unstretched and stretched conditions, respectively. Tables 1 and 2 show the electronic characteristics of the stretchable TFT.

Among them, the formula 1 is obtained in the saturated region. Considering the change in channel size during the stretching process, the width and length of the channel under stress are further measured in the present invention to obtain the correct mobility. When no external stress was applied, the carrier mobility of the saturated region of the PSeDPP device was 1.51 cm ² V ^-1 S ^-1 . When applying the same axial tensile stress, the device exhibits a typical stress-strain-dependent behavior, and the parallel and vertical mobility decreases from 1.51 to 0.37 and 0.13 cm ² V ^-1 after 100% stretching, respectively. S ^-1 . I _on the parallel direction compared to the large amount of decrease of the vertical direction, as shown, this behavior is due to increase the length and reduce the width of the active layer 13c caused to 13d. No microcracking was observed until 100% stress was applied. Therefore, the decrease in mobility may be caused by a change in the accumulation of polymer molecules. Separation of crystalline polymer segments occurs often after elongation of the amorphous (unshaped) chain, such that the elongated portion may be tilted as the layer is tilted toward the direction of stretching. In general, the wrinkled surface plays an important role in avoiding cracking, and the crack may cause a significant decrease in carrier mobility. Fig. 14 is a view showing a state in which a current leaks in the case where stress is applied. The current leakage is not significantly changed when a high degree of stress is applied, due to the cross-linking of the fluoropolymer dielectric, but in the absence of cross-linking, a large-scale current leakage occurs (see figure 15).

Figures 16(a) through 16(b) show the transfer curves in the parallel and perpendicular directions after a 30% stretching cycle. Tables 3 and 4 disclose the electronic properties obtained by testing the device in an unstretched state after stress relief. Figures 16(c) through 16(d) summarize the hole mobility, I _on and I _off values after a 2000% 30% stretch cycle. The threshold voltage increases as the applied stress increases due to the incomplete crosslinking of the fluoroelastomer substrate, and the channel length is also irreversibly increased in the endurance test. The shifting of the threshold voltage to the negative direction may result in more charge trapping in the interface due to the longer channel length. The parallel and vertical mobility was maintained at 0.482 and 0.732 (cm ² V ^-1 S ^-1 ) after 2000 cycles. It is possible that the parallel direction has a lower mobility due to the irreversible elongation of the substrate.

In order to demonstrate the compatibility of the fluoroelastomer system with other semiconductor materials, poly(isoindigo-bithiophene) PII2T and P3HT substrate FETs (field effect transistors) were also used for the active layer, as shown in FIG. Figures 17(a) through 17(b) show the tendency of the applied stress relative mobility. When 0% stress was applied to PII2T and P3HT, the mobility of the device reached 0.95 cm ² V ^-1 s ^-1 and 0.51 cm ² V ^-1 s ^{-1 , respectively} . Then, when 100% stress is applied, the mobility parallel to the current direction increases to 9×10 ^-3 cm ² V ^-1 s ^-1 and 2.8×10 ^-2 , respectively, and the mobility perpendicular to the current direction is respectively Increase to 8 × 10 ^-3 cm ² V ^-1 s ^-1 and 3.7 × 10 ^-2 cm ² V ^-1 s ^-1 . Both showed the same mobility trend as PSeDPP, and the mobility decreased by ~10% during the first stretching cycle to 100% stretching. The degradation of mobility is relatively fast due to the fact that the wrinkle structure is not formed when the film is transferred to the substrate. However, when stretched, the mobility remained at a relatively constant value until 2000 cycles of stretching. The devices using PII2T and P3HT have a mobility parallel to the current direction of 4×10 ^-2 cm ² V ^-1 s ^-1 and 5 × 10 ^-2 cm ² V ^-1 after 2000 stretching cycles. s ^-1 , the mobility perpendicular to the current direction is 3 × 10 ^-2 cm ² V ^-1 s ^-1 and 7 × 10 ^-2 cm ² V ^-1 s ^{-1 , respectively} .

In general, the corrugated structure will reduce the stress accumulated on the semiconductor and inhibit the formation of cracks in repeated cycles, so that it still has a high mobility after the fatigue test. In the present invention, the performance of the device can reach the requirement of driving the active organic electroluminescent diode display after 2000 complete cycles under the application of 30% stress, indicating that the substrate having wrinkles has a huge potential to be applied. In a stretchable organic TFT.

In summary, the present invention produces a highly efficient and essentially stretchable organic TFT by a fluoroelastomer substrate having a self-reticulated surface by a crosslinking reaction. The present invention also applies this material to the gate electrode, exhibiting low leakage current and good mechanical compliance. The CNT and PU/PEOT:PSS mixture is applied to a stretchable source/drain electrode. The substrate can dissipate the stress applied on the semiconductor, and the conjugated polymer film can be deformed into a wrinkled structure after stretching to make it highly resistant under stress. After 100% stretching, the transistor still maintains a high mobility of ~0.73 (cm ² V ^-1 S ^-1 ) mobility, 10 ⁴ open-close ratio; the device has 2000 times of 30% isoaxial stress. After the stretching cycle, it still has excellent electrical performance.

Claims (10)

A stretchable crystal element comprising a surface-wrapped fluoroelastomer fluoroelastomer as a substrate, the surface-wrapped fluoroelastomer system being formed by a cross-linking action. The stretchable crystal element of claim 1 further comprising the surface-wrapped fluoroelastomer as a dielectric layer. The stretchable crystal element of claim 1, wherein the fluoroelastomer system is selected from the group consisting of hydrogen-containing monomers derived from perfluoroolefins, perfluorovinyl ethers, halogenated fluoroolefins, and partially fluorinated olefins. The monomer is polymerized. The stretchable crystal element of claim 1, wherein the fluoroelastomer system is copolymerized with polyvinylidene fluoride (VDF) / hexafluoropropylene (HFP) copolymer, TFE / propylene copolymer, TFE / propylene / VDF , TFE/VDF/HFP copolymer, TFE/perfluoromethyl vinyl ether (PMVE) copolymer, TFE/CF ₂ =CFOC ₃ F ₇ copolymer, TFE/CF ₂ =CFOCF ₃ /CF ₂ =CFOC ₃ F ₇ copolymer, TFE/CF ₂ =C(OC ₂ F ₅ ) ₂ copolymer, TFE/ethyl vinyl ether (EVE) copolymer, TFE/butyl vinyl ether (BVE) copolymer, TFE/EVE /BVE copolymer, VDF/CF ₂ =CFOC ₃ F ₇ copolymer, ethylene/HFP copolymer, TFE/HFP copolymer, CTFE/VDF copolymer, TFE/VDF copolymer, TFE/VDF/PMVE/ethylene copolymer Or TFE/VDF/CF ₂ =CFO(CF ₂ ) ₃ OCF ₃ copolymer is formed by crosslinking. The stretchable transistor component of claim 2, further comprising a gate electrode layer deposited over the substrate and an active layer stacked over the dielectric layer. The stretchable transistor element of claim 5, wherein the gate electrode layer is formed of a stretchable conductive polymer. The stretchable crystal element of claim 6, wherein the conductive polymer is a polythiophene polymer, a poly-p-phenylene vinyl polymer, a polyfluorene polymer, a phthalocyanine derivative ( H2Pc, CuPc, ZnPc, etc.) or a porphyrin derivative. The stretchable transistor component of claim 5, wherein the active layer exhibits a wavy structure. The stretchable crystal element of claim 8, wherein the active layer is an N-type or P-type organic small molecule, an organic polymer, or a mixture of an organic small molecule and an organic polymer. A stretchable transistor element according to claim 3, wherein the fluoroelastomer system is formed by crosslinking the monomers in the presence of benzophenone oxide (BPO) and tripropylene isomeric cyanuric acid (TAIC).