Organic semiconducting polymers have opened a new paradigm for soft electronics due to their intrinsic flexibility and solution processibility. However, the contradiction between the mechanical stretchability and electronic performances restricts the implementation of high-mobility polymers with rigid molecular backbone in highly deformable devices. Here, we report the realization of high electronic performance and high stretchability on curvilinear polymer microstructures fabricated by solution-processing capillary-gradient-mediated assembly method. Curvilinear polymer microstructure arrays are fabricated with highly ordered molecular packing, precisely controlled geometry and alignment, and wafer-scale homogeneity, leading to high hole mobilities of 4.3 and 2.6 cm2 V− 1 s− 1 under zero and 100% strain, respectively. Fully stretchable field-effect transistors and logic circuits can be integrated through all-solution process using assembled curvilinear microstructure semiconducting channels, organic dielectrics and carbon-nanotube electrodes. Based on these fully stretchable devices, 92% preservation of carrier mobility is realized after 1000 stretch-release cycle under 50% strain. Long-range homogeneity is demonstrated with the narrow distribution of height, width, mobility, on-off ratio and threshold voltage across a four-inch wafer. This solution-assembly method provides a platform for wafer-scale and reproducible integration of high-performance soft electronic devices and circuits based on conjugated organic semiconductors.
Article
Wafer-scale integration of stretchable semiconducting polymer microstructures via capillary gradient
https://doi.org/10.21203/rs.3.rs-121537/v1
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published 01 Dec, 2021
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organic semiconducting polymers
stretchable semiconducting materials
Stretchable semiconducting materials are of great interest for soft and deformable electronics toward applications such as physiological monitoring1, bioelectronic interfaces2, robotics3 and implantable biomedical devices4, 5. Mechanical flexibility is feasible by structural engineering of rigid inorganic semiconductors6, 7 and employing intrinsically elastic polymers8. For instance, ultrathin nanomembranes9, nanowires10, 3D mesostructures11 and kirigami patterns12 have rendered rigid inorganics, such as silicon6 and III-V semiconductors13, 14, with mechanical flexibility. Semiconducting polymers with inherently low modulus and solution processability afford a competitive approach to realize scalable fabrication of flexible devices with enhanced stretchability and high integration density. However, trade-offs between electronic performances and mechanical flexibility restrict the practical applications of semiconducting polymers. The fundamental issue is that considerable stretchability requires deformable components, such as flexible side chains/backbones15 and elastomer blends16, while high mobility demands a rigid π-conjugated molecular structure and ordered packing to suppress the conformational and energetic disorder17–19. Therefore, intrinsically stretchable polymers usually possess a relatively low carrier mobility originating from defect- and disorder-induced carrier localization, and high-mobility rigid polymers experience serious degradation of electronic performances under high deformation24.
The concept of geometry engineering, which has been extensively studied to create stretchable wavy20, 21, fractal22, 23 and kirigami geometries24, 25 based on inorganic materials, is hopeful to accommodate the challenge in the fabrication of high-mobility and stretchable semiconducting polymers. In striking contrast to inorganics with versatile top-down lithography techniques, solution-processing methods, which are regarded with unique advantages of low cost and high productivity26, 27, involve an explicit compromise between stretchability and electronic performances for the patterning of stretchable polymer microstructures. Specifically, precise fabrication of complex microstructures demands patterning of liquid films or droplets in high resolution, which poses a challenge to attain ordered molecular packing due to the uncontrollable microfluidic dynamics and mass transport28–30. High crystallinity and ordered packing of polymer molecules are feasible by introducing directional microfluids in assembly process31, 32, while this strategy presents restricted versatility for microstructure fabrication. In addition, wafer-scale integration of desired microstructures with ordered molecular packing has not yet been realized in solution process. Reaching high packing order, stretchability, scalability and solution processibility simultaneously will opens up access to high-performance and low-cost soft electronic devices.
In this work, we develop a platform to fabricate stretchable polymer microstructures by steering capillary gradient for realizing ordered microfluid dynamics and precise patterning simultaneously. High crystallinity, complicated curvilinear geometries and wafer-scale homogeneity are simultaneously achieved in polymer microstructures by optimizing the capillary-gradient-induced three sequential stages: breaking and trapping of liquids into micro-reservoirs, directional liquid transport into capillary bridges, and confined growth of polymer structures in capillary bridges. Due to the curvilinear structures with ordered molecular packing, high stretchability and carrier mobility are realized simultaneously based on these curvilinear structures. High mobilities of 4.3 and 2.1 cm2 V− 1 s− 1 are realized by using high-k Al2O3 and stretchable organic dielectrics, respectively. Based on a fully stretchable device configuration with solution-processed semiconducting channels, gate dielectrics and electrodes, 92% preservation of mobility after 1,000 stretch-release cycles under 50% strain and direct integration of 2000 stretchable transistors with a device density of 400 cm− 2 are achieved. Wafer-scale uniformity are further demonstrated by a narrow distribution of height, width, mobility, on-off-ratio and threshold voltage by careful statistics over 4000 sites on a four-inch wafer.
Capillary-gradient-mediated assembly of curvilinear polymer architectures. The capillary gradient is realized by employing programmable topographical templates with curvilinear micropillars fabricated by lithography and reactive-ion etching (Supplementary Fig. 1). The geometrical parameters of curvilinear micropillars include central angle θ, curvature radius R and inter-pillar distance G (Supplementary Fig. 2), which can be optimized to achieve scalable fabrication of high-quality curvilinear structures. Central angle θ was designed as 90o, 180o and 270o to accommodate the fabrication of curvilinear microstructures with different stretchability. Assembly of polymer structures were performed by confining a liquid thin film of precursor solution between a topographical template and a target substrate (see Supplementary Fig. 3 and Method). Through in situ fluorescence microscopy observations, a sequential dewetting process can be observed in confined liquid films: receding of liquid firstly occurs between the curvilinear micropillars, resulting in localization of liquid into inner arc to form discrete microreservoirs; with further evaporation of liquid, directional dewetting from microreservoirs to tops of micropillars yields pinned capillary bridges; finally, the confined growth of polymers in capillary bridges produces curvilinear microstructures (see Schematic illustration in Fig. 1a, b, Supplementary Fig. 3 and time sequential optical micrographs in Supplementary Fig. 4-6). This process is driven by the gradient of capillary pressure, which can be expressed as33,
where γ is surface tension of liquid, θY is the contact angle, d is the diameter of capillary tube. Driven by capillary pressure, liquid tends to concentrate in the position with a smaller capillary size (i.e. d) in evaporation process. By rationally designing the geometrical parameters of curvilinear micropillars, directional transport of liquid can occur from the gaps between micropillars to microreservoirs, which finally localize on the tops of micropillars to form capillary bridges. For the dewetting process from microreservoirs to the tops of micropillars, we observed near 100% formation of capillary bridges, which can be attributed to the large capillary-pressure contrast between the microreservoirs and capillary bridges. The height of microreservoirs is ca. 20 μm, while capillary bridges on the tops of micropillars feature a sub-micrometer height, yielding over 20-fold higher capillary pressure in capillary bridges. The lattice Boltzmann method (LBM) simulations also validate the directional liquid transport from microreservoirs to capillary bridges (Supplementary Fig. 7).
Successful liquid dewetting from inter-micropillar gaps to microreservoirs is crucial for the uniformity of as-prepared polymer microstructures at long range. Efficient trapping of liquid in microreservoirs enables nearly equivalent liquid volume and mass of polymer molecules at each arc (Fig. 1d, e), resulting in polymer microstructures with homogeneous size (Fig. 1f). In contrast, a broad size distribution of polymer microstructures can be observed in the system without trapping of liquid in microreservoirs (Supplementary Fig. 8), which is caused by the fluctuation of polymer concentration in dewetting process. The concentration of polymers firstly increases with the evaporation of solvents and then sustain a saturated state with the deposition of polymer microstructures, which finally decreases with the exhaustion of polymers in solution.
Given that efficient trapping of liquid into microreservoirs is significant for the long-range uniformity of polymer microstructures, we carefully studied the liquid dewetting in curvilinear micropillars with different geometrical parameters by experimental observations and computational fluidic dynamics (CFD) simulations. The dewetting dynamics were observed in micropillars with central angle θ of 90o,180o and 270o, curvature radius of arc from 5 to 100 μm and interpillar distance from 5 to 20 μm (Supplementary Fig. 9, 10). According to the criteria of trapped liquid in microreservoirs, the dewetting results are summarized in Figure 1c. These results indicate that increased interpillar gap distance G and decreased curvature radius R benefit the trapping of liquid into microreservoirs (Fig. 1c), which can be understood as high local capillary pressure in microreservoir region steers the liquid trapping. To develop better understanding to this trapping process, CFD simulations were carried out (Supplementary Fig. 11, Supplementary Movie 1). According to our analysis, liquid trapping occurs when the length of liquid front, which is proportional to interpillar gap distance G, is larger than the opening distance of curvilinear arc, which is a function of curvature radius R and central angle θ (see details in Supplementary Note 1). A threshold gap distance for liquid trapping can be calculated, shown as the solid lines in Figure 1c. The calculated threshold gap distance is proportional to the curvature radius R, which is well consistent with the experimental results.
By rational design of the micropillars, sequential dewetting from interpillar gaps via microreservoirs to capillary bridges boosts the large-scale fabrication of curvilinear polymer microstructures with long-range uniformity. A presentative semiconducting polymer, poly(3-hexylthiophene) (P3HT) were firstly employed to demonstrate the fabrication of curvilinear microstructures. As shown in scanning electron microscopy (SEM) images (Fig. 1f, Supplementary Fig. 12), the as-prepared P3HT curvilinear microstructures with different geometrical parameters exhibit homogeneous size and smooth surface. The long-range uniformity and reproducibility of curvilinear structures are demonstrated by optical micrographs with different magnification (Supplementary Fig. 13-15). AFM topography illustrates that a curvilinear microstructure exhibits uniform height of ca. 270 nm, width of ca. 600 nm and smooth top surface with low root mean square roughness of 0.436 nm (Fig. 1g). The crystallinity and crystallographic orientation of P3HT microstructures were determined by grazing-incidence wide angle X-ray scattering (GIWAXS) (Fig. 1h). GIWAXS pattern of P3HT curvilinear microstructures shows a series of rings along the qz axis, which can be assigned to the (h00) reflections of lamella layer structure. The diffraction ring lying on the qxy axis, corresponding to a facet with distance of 3.7 Å, can be attributed to the (010) reflections of π-π stacking34. This result indicates that the P3HT molecules exhibit a pure edge-on packing configuration with π-π stacking direction along the conductive channel, which benefits the charge-carrier transport in organic field-effect transistors (OFETs). In contrast, spin-coated thin films show small grains with disordered molecular packing and low crystallinity, which are reflected by the SEM image and GIWAXS pattern (Supplementary Fig. 16).
The curvilinear microstructures are also demonstrated on two additional conjugated polymers, p-type poly[2,5-bis(2-decyltetradecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-5,5’-di(thiophen-2-yl)-2,2’-(E)-2-(2-(thiophen-2-yl)vinyl)thiophene] (PDVT-10) and n-type poly{[N,N’-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5’-(2,2’-bithiophene)} (P(NDI2OD-T2)). High-quality curvilinear microstructures with smooth surface and homogeneous size are demonstrated. High crystallinity is demonstrated by sharp diffraction rings in GIWAXS patterns (Supplementary Fig. 17). To precisely tune the size of the curvilinear structures, the influence of arc angle, arc radius and precursor concentration on the size of microstructures were investigated. The curvilinear microstructures with arc angle θ= 270o and radius from 5 to 100 μm are presented in Supplementary Fig. 18a. The size of the curvilinear microstructures is proportional to the volume of semiconducting polymer solution trapped in each microreservoir, which can be demonstrated by large width on the position with large microreservoir volume (Supplementary Fig. 18b). The width and height are proportional to the concentration of the precursor solution and radius of arc angle, which is demonstrated by theoretical analysis and experimental results (Supplementary Note 2, Supplementary Fig. 19). The width of microstructures can also be controlled by using micropillars with different widths (Supplementary Fig. 20).
Stretchability and electronic performance. To evaluate the stretchability, the curvilinear polymer microstructures were firstly fabricated onto a rigid substrate followed by transferring to stretchable polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) elastomer (see Method and schematics in Fig. 2a, Supplementary Fig. 21). The stretchability was firstly estimated by observing the morphology of P3HT curvilinear microstructures under different applied strains (Supplementary Fig. 22-24). For the curvilinear microstructures with central angle of 270o, no obvious cracks can be observed under 100% strain along both horizontal and vertical directions (Supplementary Fig. 24). The crack free microstructures under 100% strain are also validated by AFM images (Supplementary Fig. 25). In contrast, microstructures with central angle of 90o and 180o presents limited stretchability (Supplementary Fig. 22, 23). Spin-coated thin films and line-shaped microstructures experience serious damage under 100% strain (Supplementary Fig. 26). The limited stretchability is rationalized by the stress-strain curves, illustrating that the damage of a bulky P3HT belt occurs with strain below 40% (Supplementary Fig. 27). Finite element analysis (FEA) of curvilinear microstructures under 100% strain presents the spatial distribution of stress (Fig. 2b). The stress can be effectively released by deformation of curvilinear microstructures, yielding calculated stress below 10 MPa under 100% strain, which is well below the damage stress of ca. 20 MPa. These results demonstrate that the curvilinear microstructures endow exotic stretchability to the conjugated semiconducting polymers with limited intrinsic flexibility.
Electronic transport properties were measured by contacting with gold electrodes to form a OFET device with bottom-gate bottom-contact configuration (Fig. 2a, see Method for details). The curvilinear microstructures were fabricated based on three representative semiconductors, including n-type P(NDI2OD-T2), p-type P3HT and PDVT-10 (Fig. 2c, e, g). No crack and damage can be observed in these three polymer microstructures under 100% applied strain along horizontal and vertical directions (Fig. 2d, f, h), demonstrating considerable stretchability of these curvilinear microstructures. The electronic transport performances were measured to directly evaluate the stretchability of OFET devices based on curvilinear microstructures. By comparing the transfer curves of devices under different strains (Fig. i-k), the electronic transport is well preserved under 100% strain parallel and perpendicular to the channel direction. The primary mobility of PDVT-10 curvilinear microstructures is 4.3 cm2 V-1 s-1, which is high than 1.1 cm2 V-1 s-1 on spin-coated thin films (Supplementary Fig. 28). The 4-fold higher mobility in curvilinear microstructures can be attributed to the improved crystallinity and ordered molecular packing, which has been demonstrated by GIWAXS characterizations (Fig. 1h, Supplementary Fig. 17 and 28). Under 100% strain along and perpendicular to the channel direction, the mobilities of 2.6 and 2.1 cm2 V-1 s-1 can be realized in PDVT-10 curvilinear microstructures, respectively. For assembled straight PDVT-10 wires, a primary mobility of 3.9 cm2 V-1 s-1 can be achieved, whereas no electronic signal can be measured under 100% strain and 390-fold decrease of mobility occurs after the release of the strain (Supplementary Fig. 29), indicating serious damage of straight wires in stretch process. For P3HT, PDVT-10, P(NDI2OD-T2) curvilinear microstructures, over 40% preservation of mobility can be achieved under 100% strain (Fig. 2l-n), indicating the robust stretchability of these curvilinear microstructures.
Fully stretchable electronics based on curvilinear microstructures. The reliable stretchability of these curvilinear microstructures permits the construction of fully stretchable electronics. These flexible electronic devices with a top-gate top-contact configuration were fabricated by transferring PDVT-10 curvilinear structures onto SEBS elastomer followed by coating with SEBS and stretchable carbon nanotubes (CNTs) as flexible gate dielectrics and electrodes, respectively (Supplementary Fig. 21, 31, see Method for detailed discussion). The optical micrographs demonstrate the successful transfer of curvilinear microstructures onto SEBS substrate and the AFM image illustrate the high quality of patterned SEBS dielectrics (Supplementary Fig. 31c). 112 fully stretchable OFETs can be fabricated onto SEBS substrate (Fig. 3b) and a zoom-in optical image presents the alignment of semiconducting curvilinear microstructures, CNT electrodes and SEBS gate dielectrics (Fig. 3c). As shown in Fig. 3d, this fully stretchable OFET shows a primary carrier mobility of 2.1 cm2 V−1 s−1 and an on-off ratio of 104. The electronic performance is well preserved under 100% strain parallel and perpendicular to the channel direction. By statistics of 40 devices, an average mobility of 1.5 cm2 V−1 s−1 can be achieved based on this fully stretchable configuration (Fig. 3e). To evaluate the stretchability, the OFET device was measured under cyclic stretch and release with maximum strain of 50%. The OFET presents 92% preservation of mobility after 1000 cycles (Fig. 3f, Supplementary Fig. 32), indicating the robustness of the stretchability.
The scalable fabrication of curvilinear microstructures, dielectrics and CNT electrodes also allows for the construction of large-area device arrays for wearable electronics. 2000 stretchable OFETs were fabricated onto SEBS substrate in an area of ca. 2×2 cm2 (Supplementary Fig. 33) and these device arrays are stable under 100% strain (Supplementary Fig. 34). These OFET arrays can serve as wearable electronic devices due to the its fully stretchable nature (Supplementary Fig. 35). Due to the scalable fabrication techniques, fully stretchable logic circuits can be constructed based on curvilinear microstructures. A NAND logic gate was fabricated by connecting six OFETs (Fig. 3g, Supplementary Fig. 36). By sweeping the two inputs VA and VB, a low output voltage of near zero can be observed only when the two inputs are at high voltage of 30 V, indicating the NAND logic function (Fig. 3i). Stretchable semiconducting channels, gate dielectrics and CNT electrodes enable logic function under 100% strain (Fig. 3h, i). Due to the curvilinear microstructures with long-range uniformity and high ordered molecular packing, scalable integration of stretchable electronic device arrays is realized based on semiconducting polymers. Compared to previous reports, our methodology provides an approach to overcomes the trade-offs between electronic performance, stretchability and scalability (Supplementary Table 1).
Wafer-scale uniformity and deterministic patterning. Given that the sequential dewetting and efficient trapping of liquid in microreservoirs permit the fabrication of long-range uniform curvilinear structures, we sought to demonstrate wafer-scale fabrication of stretchable polymer microstructures. Fig. 4a shows curvilinear structures fabricated onto 4-inch silicon wafer. To evaluate the long-range uniformity, we measured both geometric and electronic-transport figures of merits across 21 different positions on this wafer. Typical AFM images extracted from these 21 different positions show uniform width and height of curvilinear microstructures at long range (Fig. 4b). FETs were fabricated based on these curvilinear microstructures using a top-contact bottom-gate configuration and transfer curves extracted from ca. 4000 devices from these 21 positions illustrate narrow distribution of on and off currents (Fig. 4c). Based on these devices in different positions, figures of merit, including mobility, on-off ratio and threshold voltage were extracted. Spatial distribution profiles of height, width, mobility, on-off ratio and threshold voltage illustrates long-range uniformity and reproducibility of both geometric and electronic parameters across the 4-inch wafer (Fig. 4d-h). By statistics of these parameters, an average height of 74.0 ± 6.0 nm, width of 0.81 ± 0.09 μm, mobility of 3.3 ± 0.3 cm2 V-1 s-1, on-off ratio of (7.7 ± 1.3) × 106, and threshold voltage of -0.23 ± 0.05 V can be extracted. The narrow distributions of these parameters indicate high uniformity of these curvilinear microstructures in wafer scale.
This technique can be further extended to fabricate 2D curvilinear networks by rational design of templates. For instance, 2D meshes constructed by curvilinear wires with central angle of 180o and 270o can be successfully fabricated (Fig. 4i, j, Supplementary Fig. 37). This sequential dewetting strategy can be further employed to the fabrication of multi-order hierarchical fractal patterns (Fig. 4k). The sequential dewetting process is driven by capillary gradient, yielding homogeneous distribution of liquid into capillary bridges (Supplementary Fig. 38).
In conclusion, high-quality stretchable curvilinear microstructures of semiconducting polymers have been realized at wafer scale by steering capillary gradient. Ordered molecular packing and designable curvilinear microstructures are demonstrated based on three different polymers, leading to a high mobility of 4.3 cm2 V− 1 s− 1 and well-preserved electronic performance under 100% strain and less than 8% degradation of performance after 1000 stretch-release cycles under 50% strain. This method also boosts the integration of fully stretchable FET and logic gate arrays. Controllable dewetting dynamics and efficient trapping of liquid in microreservoirs enable long-range uniformity of curvilinear microstructures, which is reflected by narrow distributions of height, width, mobility, on-off ratio and threshold voltage at wafer scale. It is anticipated that this solution-processing approach benefits the large-scale and high-throughput integration of wearable electronic devices, which is not restricted by molecular design.
Assembly of curvilinear semiconductor microstructure arrays. P-type semiconducting polymers P3HT (Mn: 100 kDa) and PDVT-10 (Mn: 65 kDa), and N-type semiconducting polymer P(NDI2OD-T2) (PolyeraActivInk™ N2200, Mn: 63.8 kDa) were used in this study. The polymers were dissolved in chloroform at a concentration of 5 mg mL− 1. A 10 µL droplet of polymer solution was dropped onto the curvilinear template and covered by the target substrate, yielding a capillary-bridge assembly system. The assembly system was kept at room temperature for 24 hours to evaporate the organic solvents. After the total evaporation of solvents, the semiconductor microstructure arrays were generated onto the target substrate.
We developed two methods to transfer curvilinear semiconductor microstructures to the stretchable SEBS substrate: 1) The curvilinear semiconductor microstructures were firstly assembled on the SiO2 surface by using the capillary-bridge assembly. Next, SEBS 1221 with a concentration of 300 mg mL− 1 was spin-coated on the SiO2 surface at 1000 rpm for 60 s. The curvilinear semiconductor microstructures embedded in SEBS substrates was released from SiO2 surface by dipped into ethanol solution. 2) The 10 nm Cr/100 nm Cu were deposited on the silicon surface as a sacrificial layer by the e-beam evaporation. The curvilinear semiconductor microstructures were firstly assembled on the Cu surface using capillary bridge lithography. Next, SEBS 1221 with a concentration 300 mg mL− 1 was spin-coated on the copper surface at 1000 rpm for 60 s. The curvilinear semiconductor arrays were transferred from the sacrificial copper film to SEBS substrates using FeCl3 solution. Compared with the first method, the second method is appropriate for transferring polymer microstructures, which strongly adhere to the SiO2 substrate.
Morphological and crystallographic characterizations. Optical and fluorescence microscope images of the dewetting process and as-formed polymer microstructures were obtained by an optical microscope (Vision Engineering Co., UK). The structures of the curvilinear micropillar templates and the morphology of curvilinear polymer microstructure arrays were investigated by the SEM (Hitachi, S-4800, Japan). The AFM images and surface roughness data were measured by the Nanoscope IIIa instrument (Bruker, ICON2-SYS, Germany). The GIWAXS data were obtained at 1W1A Diffuse X-ray Scattering Station, Beijing Synchrotron Radiation Facility (BSRF-1W1A) with an incidence angle of 0.2°. The tensile strength of P3HT belts (1 mm × 6 µm × 20 mm) and SEBS belts (1 mm × 20 µm × 20 mm) was measured by dynamic mechanical analysis (DMA, Q800,TA instrument, US) with a stretching rate of 0.2 mm min− 1.
Observation and simulation of the dewetting process. To in-situ observe the dewetting process in the gap between adjacent curvilinear micropillars, a polymer, poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) with green fluorescence, was added into the solution. The dewetting process was observed by a fluorescent microscope (Vision Engineering Co., UK). COMOSOL Multiphysics was used to simulate the dewetting behavior. The contact angle the silicon pillar is ca. 0o. The surface tension is set as 28.8 mN m− 1. The radius of central arc pillar is 10 µm. The defined minimum spacing between two pillars is 15 µm.
Finite element analysis. COMOSOL Multiphysics was used to study the mechanical response of the curvilinear semiconductor microstructures on the stretchable SEBS substrate. In our simulation, a curvilinear P3HT microstructure with the exposed top surface, was modeled by four-node composite shell elements, which was embedded in the SEBS 1052 substrate and has the arc angle of 270o, arc radius of 5 µm, width of 600 nm and thickness of 400 nm. Displacement boundary conditions were applied to both edges of the substrate to produce uniaxial tension of the substrates. The material parameters of SEBS and P3HT are ESEBS = 1 MPa and νSEBS = 0.49, and EP3HT = 28 MPa and νP3HT = 0.35, respectively. Here, E is the elastic modulus and ν is the Poisson’s ratio.
The electrical measurements using soft contact lamination method. The high k gate dielectric layer Al2O3 (50 nm) was deposited on the surface of highly doped Si by atomic-layer-deposition (ALD) method. The electrical performance of stretchable curvilinear semiconductor microstructures was measured through the bottom-gate bottom-contact OFET by the soft contact lamination: Al2O3 film as the high k gate dielectric, highly doped Si as the gate electrode, and Au film on the top as source and drain electrodes.
Fabrication and measurement of devices. The fully deformable OFET device was fabricated as follows: 1) The curvilinear semiconductor microstructures were transferred to SEBS 1221 substrate. 2) P3-SWCNT was dispersed in 2-propanol at concentration of 5 mg mL− 1. The CNT solution was spray-coated onto curvilinear microstructure arrays as source and drain electrodes by the pneumatic spray gun with a shadow mask. 3) A dextran solution (Mn: 5000, 40 wt% in water) was spin-coated on plasma-treated quartz glass slide at 1500 rpm for 20 s. The glass slide was then baked at 80 °C for 30 min. Then, the SEBS (H1052) solution (10 wt% in toluene) was spin-coated onto the sample at 1000 rpm for 60 s as a stretchable dielectric layer with a thickness of ca. 1.2 µm. The surface of the SEBS dielectric layer was modified by OTS to increase the dielectric performance. The dielectric layer is patterned via direct laser writing through a nanosecond, pulsed UV laser beam with the computer-assisted design. 4) The quartz glass substrates with the SEBS dielectric layer was laminated onto stretchable SEBS (H1221) substrate with curvilinear semiconductor microstructures with precise alignment. Then, the dielectric layer on the substrate was transferred onto the stretchable substrate by immersing the entire device in water to dissolve the sacrificial dextran layer. The device was thermally annealed at 80 °C in vacuum for 4 h to enhance the contact between the dielectric layer and the organic semiconductor layer. 5) Finally, a CNT layer was spray-coated through a metal shadow mask onto the dielectric layer as the gate electrode.
All of the electrical characteristics of the OFETs were measured with Keithley 4200A-SCS characterization system in an ambient environment at room temperature. The dielectric constants of SEBS 1052 were obtained by the capacitance measurement through an Agilent precision LCR meter E4980A. The carrier mobility in the saturation regime at gate voltage (VG) of -15 V could be calculated by,
where μ is the carrier mobility, L is defined as the channel length, W is the channel width, Ci is the capacitance of the gate dielectric layer per unit area and IDS is the current between the drain and source electrodes.
Author contributions
Y.Q., J.Y. and J.F. conceived the idea and designed the experiments. Y.Q. and J.Y. fabricated and characterized the polymer microstructures. J.Y. fabricated and measured the electronic devices. B.Z. conducted the simulations of microfluidic dynamics. H.G., L.W. and P.W. contributed to dielectric layer fabrication and transfer of microstructures. S.L. contributed to mechanical simulations. J.F., J.Y. and Y.W. wrote the manuscript. All authors discussed the results and commented on the manuscript.
Additional information
Supplementary information is available in the online version of the paper. Reprints and permissions information is available online at www.nature.com/reprints. Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Correspondence and requests for materials should be addressed to J.Y., J.F. and Y.W. (Emails: [email protected]; [email protected]; [email protected]).
Competing interests
The authors declare no competing interests.
- Park, S. et al. Self-powered ultra-flexible electronics via nano-grating-patterned organic photovoltaics. Nature 561, 516-521 (2018).
- Someya, T., Bao, Z. & Malliaras, G. G. The rise of plastic bioelectronics. Nature 540, 379-385 (2016).
- Kim, R.-H., et al. Waterproof AlInGaP optoelectronics on stretchable substrates with applications in biomedicine and robotics. Nat. Mater. 9, 929-937 (2010).
- Liu, Y., et al. Morphing electronics enable neuromodulation in growing tissue. Nat. Biotechnol. 38, 1031-1036 (2020).
- Lee, G.-H. et al. Multifunctional materials for implantable and wearable photonic healthcare devices. Nat. Rev. Mater. 5, 149-165 (2020).
- Khang, D.-Y. et al. A stretchable form of single-crystal silicon for high-performance electronics on rubber substrates. Science 311, 208-212 (2006).
- Kim, D.-H. et al. Stretchable and foldable silicon integrated circuits. Science 320, 507-511 (2008).
- Oh, J. Y., et al. Intrinsically stretchable and healable semiconducting polymer for organic transistors. Nature 539, 411-415 (2016).
- Ko, H. C. et al. A hemispherical electronic eye camera based on compressible silicon optoelectronics. Nature 454, 748-753 (2008).
- Gong, S. et al. A wearable and highly sensitive pressure sensor with ultrathin gold nanowires. Nat. Commun. 5, 3132 (2014).
- Xu, S. et al. Assembly of micro/nanomaterials into complex, three-dimensional architectures by compressive buckling. Science 347, 154-159 (2015).
- Lamoureux, A., Lee, K., Shlian, M., Forrest, S.R. & Shtein, M. Dynamic kirigami structures for integrated solar tracking. Nat. Commun. 6, 8092 (2015).
- Park, S.-I. et al. Printed assemblies of inorganic light-emitting diodes for deformable and semitransparent displays. Science 325, 977-981 (2009).
- Yoon, J. et al. GaAs photovoltaics and optoelectronics using releasable multilayer epitaxial assemblies. Nature 465, 329-333 (2010).
- Onorato, J., Pakhnyuk, V. & Luscombe, C.K. Structure and design of polymers for durable, stretchable organic electronics. Polymer J. 49, 41-60(2017).
- Shin, M. et al. Polythiophene nanofibril bundles surface-embedded in elastomer: a route to a highly stretchable active channel layer. Adv. Mater. 27, 1255-1261 (2015).
- Noriega, R., et al. A general relationship between disorder, aggregation and charge transport in conjugated polymers. Nat. Mater. 12, 1038-1044 (2013).
- Venkateshvaran, D. et al. Approaching disorder-free transport in high-mobility conjugated polymers. Nature 515, 384-388 (2014).
- Fratini, S., Nikolka, M., Salleo, A., Schweicher, G. & Sirringhaus, H. Charge transport in high-mobility conjugated polymers and molecular semiconductors. Nat. Mater. 19, 491-502 (2020).
- Lee, Y., et al. Deformable organic nanowire field-Effect transistors. Adv. Mater. 30, 1704401 (2018).
- Su, Y., et al. In-plane deformation mechanics for highly stretchable electronics. Adv. Mater. 29, 1604989 (2017).
- Fan, J.A., et al. Fractal design concepts for stretchable electronics. Nat. Commun. 5, 3266 (2014).
- Kim, J. et al. Stretchable silicon nanoribbon electronics for skin prosthesis. Nat. Commun. 5, 5747 (2014).
- Shyu, T. C. et al. A kirigami approach to engineering elasticity in nanocomposites through patterned defects. Nat. Mater. 14, 785-789 (2015).
- Blees, M. K. et al. Graphene kirigami. Nature 524, 204-207 (2015).
- Minemawari, H. et al. Inkjet printing of single-crystal films. Nature 475, 364-367 (2011).
- García de Arquer, F. P., Armin, A., Meredith, P. & Sargent, E. H. Solution-processed semiconductors for next-generation photodetectors. Nat. Rev. Mater. 2, 16100 (2017).
- Deegan, R. D. et al. Capillary flow as the cause of ring stains from dried liquid drops. Nature 389, 827-829 (1997).
- Marín, Á. G., Gelderblom, H., Lohse, D. & Snoeijer, J. H. Order-to-disorder transition in ring-shaped colloidal stains. Phys. Rev. Lett. 107, 085502 (2011).
- Huang, J., Kim, F., Tao, A. R., Connor, S. & Yang, P. Spontaneous formation of nanoparticle stripe patterns through dewetting. Nat. Mater. 4, 896-900 (2005).
- Diao, Y. et al. Solution coating of large-area organic semiconductor thin films with aligned single-crystalline domains. Nat. Mater. 12, 665-671 (2013).
- Xu, J. et al. Multi-scale ordering in highly stretchable polymer semiconducting films. Nat. Mater. 18, 594-601 (2019).
- De Gennes, P. G., Brochard-Wyart, F., & Quéré, D. Capillarity and Wetting Phenomena: Drops, Bubbles, Pearls, Waves (Springer Science & Business Media, 2013).
- Sirringhaus, H. et al. Two-dimensional charge transport in self-organized, high-mobility conjugated polymers. Nature 401, 685-688 (1999).
There is NO Competing Interest.
- SupplementaryInformation.docx
- SupplementaryMovie.avi
Supplementary Movie