Polyimide Layer Research Articles

Adhesion–delamination phenomena at the interfaces of the dielectric layer

Fan-out wafer-level packaging (FOWLP) has been developed as an enhancement of standard wafer-level packaging solutions and is being intensively researched nowadays. However, issues of delamination remain unsolved. This study focuses on the interfacial characteristics between polyimide (PI) and redistribution layers (RDL) of the FOWLP to decrease the concerns in delamination. The problems of delamination were addressed through simulation and experimentation. In the simulation, the FOWLP package model was established by using the finite element analysis ANSYS software. The results showed various ways to reduce the residual stress, such as by adding a pre-baking process before reflow or by changing the thickness of each PI layer. These ways can effectively reduce the maximum residual stress of the FOWLP and improve the issue of delamination. Moreover, through plasma treatment with the different levels of powers and gases, the adhesion between PI and RDL can improve the overall strengthening of the FOWLP structure. While, in the experimental process, Taguchi design of experiment was utilized to determine the optimal process parameters and key factors. The physical and chemical properties were analyzed, such as the surface roughness via Atomic Force Microscope (AFM) and the surface material compounds by X-ray Photoelectron Spectroscopy (XPS). The relationship between the roughness and delamination was examined.

An optically transparent multi-electrode array for combined electrophysiology and optophysiology at the mesoscopic scale

Objective. A number of tissue penetrating opto-electrodes to simultaneously record and optogenetically influence brain activity have been developed. For experiments at the surface of the brain, such as electrocorticogram (ECoG) recordings and surface optogenetics, fewer devices have been described and no device has found widespread adoption for neuroscientific experiments. One issue slowing adoption is the complexity and fragility of existing devices, typically based on transparent electrode materials like graphene and indium-tin oxide (ITO). We focused here on improving existing processes based on metal traces and polyimide (PI), which produce more robust and cost-effective devices, to develop a multi-electrode array for optophysiology. Approach. The most widely used substrate material for surface electrodes, PI, has seen little use for optophysiologicalμECoG/ECoG arrays. This is due to its lack of transparency at optogenetically relevant short wavelengths. Here we use very thin layers of PI in combination with chrome-gold-platinum electrodes to achieve the necessary substrate transparency and high mechanical flexibility in a device that still rejects light artifacts well. Main results. The manufactured surface arrays have a thickness of only 6.5 µm, resulting in 80% transparency for blue light. We demonstrate immunity against opto-electric artifacts, long term stability and biocompatibility as well as suitability for optical voltage imaging. The biocompatible arrays are capable of recording stable ECoGs over months without any measurable degradation and can be used to map the tonotopic organization of the curved rodent auditory cortex. Significance. Our novel probes combine proven materials and processing steps to create optically near-transparent electrode arrays with superior longevity. In contrast to previous opto-electrodes, our probes are simple to manufacture, robust, offer long-term stability, and are a practical engineering solution for optophysiological experiments not requiring transparency of the electrode sites themselves.

Flexible and Integrated Sensing Platform of Acoustic Waves and Metamaterials based on Polyimide-Coated Woven Carbon Fibers.

Versatile, in situ sensing and continuous monitoring capabilities are critically needed, but challenging, for components made of solid woven carbon fibers in aerospace, electronics, and medical applications. In this work, we proposed a unique concept of integrated sensing technology on woven carbon fibers through integration of thin-film surface acoustic wave (SAW) technology and electromagnetic metamaterials, with capabilities of noninvasive, in situ, and continuous monitoring of environmental parameters and biomolecules wirelessly. First, we fabricated composite materials using a three-layer composite design, in which the woven carbon fiber cloth was first coated with a polyimide (PI) layer followed by a layer of ZnO film. Integrated SAW and metamaterials devices were then fabricated on this composite structure. The temperature of the functional area of the device could be controlled precisely using the SAW devices, which could provide a proper incubation environment for biosampling processes. As an ultraviolet light sensor, the SAW device could achieve a good sensitivity of 56.86 ppm/(mW/cm2). On the same integrated platform, an electromagnetic resonator based on the metamaterials was demonstrated to work as a glucose concentration monitor with a sensitivity of 0.34 MHz/(mg/dL).

Modified I-shaped hexa-band near perfect terahertz metamaterial absorber

PurposeA novel and simple six-band metamaterial absorber is proposed in the terahertz region, which is composed of an I-shaped absorber and circular ring with four gaps and a continuous metal ground plane separated by only 0.125 mm polyimide dielectric substrate. Initially, I-shaped resonator gives three bands at 0.4, 0.468 and 0.4928 THz with the absorptivity of 99.3%, 97.9% and 99.1%, respectively. The purpose of this paper is to improve the number of bands, for which the authors added the circular ring with four gaps, so the simulated metamaterial absorber exhibited six absorption peaks at 0.3392, 0.3528, 0.3968, 0.4676, 0.4768 and 0.492 THz, with the absorption rate of 91.4%, 94.2%, 94.9%, 90.3%, 77.5% and 97.4%, respectively. The surface current distribution and angle independence are explained for all the six frequencies which are used to analyze the absorption mechanism clearly. Structure maximum uses the squares and circles, so it will make the fabrication easy. The multiband absorbers obtained here have potential applications in many engineering technology, thermal radiation, material detection and imaging and optoelectronic areas.Design/methodology/approachThis paper presents the design of the six-band metamaterial absorber which is from the I-shaped resonator and circular ring with four gaps and the metallic ground plane separated by the 0.125 polyimide dielectric substrate. The absorber exhibited six absorption peaks at 0.3392, 0.3528, 0.3968, 0.4676, 0.4768 and 0.492 THz, with the absorption rate of 91.4%, 94.2%, 94.9%, 90.3%, 77.5% and 97.4%, respectively. From the fabrication point of view, the proposed six-band metamaterial absorber has a very simple geometrical structure, and it is very easy to be fabricated.FindingsThe authors present a new and simple design of six-band absorber based on an I-shaped absorber and circular ring with four gaps and a metallic ground plane separated by a polyimide layer having the thickness of 0.125 mm. Six different resonance absorption peaks are found at 0.3392, 0.3528, 0.3968, 0.4676 , 0.4768 and 0.492 THz. Surface current distribution and angle independence plot have been studied to understand the absorption behavior of the designed terahertz metamaterial absorber.Originality/valueThe multiband absorbers obtained here have potential applications in many engineering technology, thermal radiation, material detection, security, sensors, imaging and optoelectronic areas.

Broadband Adjustable Terahertz Absorption in Series Asymmetric Oval-Shaped Graphene Pattern

We propose a broadband adjustable graphene absorber in terahertz regime. A prototype is designed to verify the terahertz absorption characteristics by a layer of a periodic array of series asymmetric oval-shaped graphene patterns on polyimide and bottom layer of metal plate. The absorber with 92% absorption and the bandwidth ranging from 3.39 THz to 5.96 THz can be achieved. By changing the Fermi level of graphene, the bandwidth and absorption can be flexibly adjusted. The absorption remains above 92% in the range of 0~40o incident angle. Using these characteristics, the simple absorber has broad application prospects in the fields of filter and switch in terahertz region.

Melt fluidity and thermal property of thermosetting siloxane-containing polyimide resins and their organic/inorganic hybrid characteristics

A series of thermosetting siloxane-containing polyimide resins were synthesized by incorporating of bis(p-aminophenoxy)dimethylsilane or bis(p-aminophenoxy)tetramethyldisiloxane with various concentrations into formulated oligoimides. These thermosetting polyimide resins exhibited good combination of processability and thermal resistance. It was found that siloxane-containing oligoimides provided significant advantages over unmodified oligoimides, relative to melt fluidity and processing window, due to the flexibility of D[(CH3)2SiO2/2] siloxy units. The siloxane-containing polyimide resins cured at 380 °C revealed relatively higher glass transition temperatures (Tg) than that of unmodified polyimides, despite the incorporation of flexible siloxane segment in oligoimides. Dynamic mechanical analysis and microstructure investigation suggested that some D[(CH3)2SiO2/2] siloxy units in the surface layer of polyimide transformed into T[CH3SiO3/2] and Q[SiO4/2] siloxy units in the curing procedure besides crosslinking of phenylethynyl groups, due to oxidation crosslinking of siloxane. That led to inorganic silica-like structures formed in situ, and inter-connected by organic polyimide segments. This organic/inorganic hybrid characteristics endowed polyimide resins with enhanced thermal property. After post-curing at 450 °C, D[(CH3)2SiO2/2] siloxy units completely transformed into T[CH3SiO3/2] and Q[SiO4/2] siloxy units, and the polyimide reins gave the Tg even exceeding 550 °C. Meanwhile, the corresponding T700 carbon fiber reinforced composite presented excellent mechanical property and durability at the temperature as high as 500 °C.

Conjugated polyimide-coated carbon nanofiber aerogels in a redox electrolyte for binder-free supercapacitors

Boosting the energy density of supercapacitors without sacrificing power density and lifespan, requires ingenious electrode materials outfitting both sufficient assessable surface area and fast electrochemical reaction kinetics. Herein, hierarchically porous core-sheath nanoarchitecture was elaborately designed, via a robust support-coating strategy using a cellulose-derived porous carbon aerogel as the conductive 3D skeleton to support a uniform coating of conjugated polyimide. The inner carbon aerogel skeleton ensures a fast electron transfer and the outer conjugated polyimide layer affords abundant micropores and sufficient active sites, hence enriching the charge storage in such a porous core-sheath nanoarchitecture. The as-designed electrode was then applied to a redox electrolyte-assisted supercapacitor (RESC) with the KI-doped H2SO4 redox electrolyte. Due to the redox electrolyte further expediting the electrochemical reaction kinetics, the as-fabricated RESC delivers an ultrahigh electrode specific capacitance of 1139F g−1 at 5 A g−1, high energy density of 94 Wh kg−1 at a well-maintained power density, and long-term capability with 90% capacitance retention after 10,000 cycles at 100 A g−1. The successful construction of high-performance electrode materials and RESC in this work opens a new insight into the development of the state-of-the-art energy storage systems.

Electrospun PTFE/PI bi-component membranes with robust 3D superhydrophobicity and high water permeability for membrane distillation

Membrane distillation (MD) is an attractive membrane process for seawater and brine water desalination. One of the main obstacles for MD application is the absence of an effective MD membrane with high water permeability and an excellent salt rejection. This work proposes a novel design strategy of hydrophobic/hydrophilic bi-component membranes for MD by electrospinning and calcination. Unlike the conventional dual-layer hydrophobic/hydrophilic membranes, the bi-component membrane developed in this work is composed of multiple layers of hydrophilic polyimide (PI) nanofibers and hydrophobic polytetrafluoroethylene (PTFE) microclusters, which interweave with each other in the entire membrane. The optimal hydrophobic/hydrophilic bi-component membrane #PTFE/PI-2 shows robust three-dimensional (3D) superhydrophobic and self-cleaning properties. It exhibits a highly competitive permeation flux of 42 ± 3 L m−2 h−1 and an excellent salt rejection above 99.9% in a 400-h continuous DCMD operation when the feed solution was synthetic seawater with a NaCl concentration of 3.5 wt% at 60 °C. Moreover, it is able to achieve an outstanding water flux of 40 ± 2 L m−2 h−1 and a salt rejection over 99.9% when the feed solution was brine water with a NaCl concentration of 25 wt%. The high vapor permeability of #PTFE/PI-2 should be attributed to the high membrane porosity, negligible mass transfer resistance of PI nanofibers and more effective water evaporation area on its superhydrophobic surface. Meanwhile, the excellent anti-wetting property should be due to a unique 3D superhydrophobicity constructed by multiple layers of PTFE microclusters.

Novel Capacitive-Based Sensor Technology for Augmented Proximity Detection

In this paper, the authors developed a capacitive-based sensor technology for high-range proximity detection, composed of multiple active units. The single sensor unit consists of a multi-layer compliant structure with a coplanar plate capacitor configuration. A prototype, composed of two single active units, was designed using, for each one, conductive electrodes printed on a polyimide layer and positioned in the middle of soft polymeric insulating substrates, either acting as shock-absorber and for sensor electrical and mechanical protection. For an in-depth theoretical analysis of the physical capacitive principle, a conditioning electronic circuit (i.e. data collection, conversion, amplification and filtering modules) was built in order to collect a digital voltage output proportional to the variable sensed capacitance. Experiments were performed to characterize the single capacitive sensor and the multi-unit sensor technology (i.e. curve of response, dynamic response, accuracy and precision). The results confirmed the outcomes originally achieved through FEM simulations and the effectiveness of the technology in high-range detection. Using a combination of two active sensor units, an operating range was achieved of up to 15 times the performance of a single commercial capacitive sensor with comparable dimensions.

Molecular Ordering Behavior of Lyotropic Chromonic Liquid Crystals on a Polyimide Alignment Layer

Coating-type polarizing films with high dichroic ratio (DR) and polarization efficiency in the visible region were fabricated using a solution of ternary lyotropic chromonic liquid crystals (LCLCs). Optical characteristics of these anisotropic LCLC polarizing films were then determined. DR increased with increasing LCLC concentrations. Molecular ordering of these LCLCs on a rubbed polyimide (PI) layer increased because LCLC molecules' orientation was enhanced by the dielectric anisotropy effect from rubbing the surface of the PI. In addition, this study demonstrated how the interaction between liquid crystal aggregates and the PI surface with different LCLC solutions correlated with LCLC molecular orientations on the PI which significantly depended on whether the coating direction of the LCLC solution was parallel or perpendicular to the PI rubbing direction. It was found that ordering direction at high LCLC concentrations was determined by shearing direction of the LCLC solution coating whereas the ordering direction at low LCLC concentrations was governed by the dielectric anisotropy effect from PI rubbing direction.

Control of Reactions on Bipolar Electrodes Using Ion-Selective Membranes

IntroductionBipolar electrochemistry is an attractive technique to realize simultaneous multiplexed detection. In bipolar electrochemical systems, a potential gradient is formed in a solution. When an isolated electrode (bipolar electrode: BPE) that is not in contact with an external device is placed in the potential gradient, potential difference is generated at the interface between the BPE and the solution (Figure 1(A)), which can be a motive force to make anodic and cathodic reactions to proceed on the BPE (Figure 1(B)) [1]. The progress of reduction reactions on the cathodic pole can be measured by coupling the reaction with electrochemiluminescence (ECL) [2]. Although the simple single electrode configuration is attractive in realizing a large array of BPEs, an issue is that the interfacial potential difference on the BPE is not controlled intentionally. In other words, the potential profile in the solution can vary as expressed by 1, 2, and 3, although the potential difference between the two poles is the same for all cases (Figure 1(C)). To solve this problem, we used an ion-selective membrane (ISM) on a part of the BPE. The ISM has an effect to fix the interfacial potential difference there without current generation through the interface (Figure 1(D)). Method Arrays of BPEs were formed with platinum (Pt) or gold (Au). An ISM was formed on a part of each BPE. The surface of the BPE was insulated with polyimide layer except for the anodic and cathodic poles and the active area of the ISM. We previously tested the use of thin-film Ag/AgCl instead of the ISM. However, a problem was that current flowed through the interface due to its non-polarized nature, affecting the ECL intensity. With regard to this, current does not flow through the ISM/solution interface. The location of the ISM was changed with BPEs of the same length (Figure 2(A)). Otherwise, BPEs of different lengths were fabricated, and the location of the ISM was kept constant between the ISM and the cathodic pole (Figure 2(B)).The active areas on the BPEs were cleaned and the cleanliness was checked by taking cyclic voltammograms (CV) in a solution containing 100 mM KCl and 10 mM K3[Fe(CN)6]. To form the ISM, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS) was first coated on an exposed area of the BPE. To form the ISM, 20 µl of Na+ ionophore cocktail containing 89.5% 2-Nitrophenyl octyl ether, 10.0% sodium ionophore II, and 0.5% sodium tetraphenylborate (w/w) (Sigma-Aldrich (Japan)) was dissolved in 79.3% polyvinyl chloride (PVC) and tetrahydrofuran (PVC/THF) solution. The solution was dropped onto the PEDOT/PSS layer to form the ISM and was dried.Figure 3 shows the setup used for the experiment. Pt wires (diameter: 0.5 mm) were used for the driving electrodes. The distance between the driving electrodes was 30 mm. For ECL, 10 mM PBS (pH 6.9) containing 5.0 mM tripropylamine (TPA) and 1.0 mM [Ru(bpy)3]2+ was used. As an analyte, oxygen dissolved in the solution was used. To change the interfacial potential difference at the ISM, Na+ ions of different concentrations were added to the solution. Before injecting the solution in the reaction chamber, the solution was stirred for at least 30 min to saturate air. Pictures of ECL were taken immediately after the application of the voltage with 60 s exposure. The experiments were conducted at 25°C. Results and Conclusions The potential of the ISM was checked using a BPE with an ISM by measuring the potential in NaCl solutions of various concentrations with respect to a commercial liquid junction Ag/AgCl electrode. Figure 4 shows the dependence of the potential of the ISE on the concentration of Na+ ions. The slope was 59.0 mV/decade, which was very close to the value expected from the Nernst equation. The effect of placing the ISM on a part of the BPE was investigated using BPEs of the same length. ECL intensity changed depending on the location of the ISM (Figure 5). Figure 6 shows ECL observed using BPEs of different length maintaining the distance between ISM and the cathodic pole. In both cases, the effect of placing the ISM was clearly observed and the ECL intensity was strongest when the distance between the ISM and the anodic pole is longer. These results indicate that the ECL intensity can actually be controlled by the ISM. We have tested other electrode configurations. The results will also be presented.The potential control developed in this study is also effective to control the electrode potentials in closed BPE systems in which solutions are separated in different compartments.

Wirebond Process Improvement through Silicon Die Polyimide Removal

This study aims to develop polyimide etching process on the silicon die after decapsulation to resolve the wire shear issue during ball shear data gatherings. The shear strength of the ball is affected by the presence of polyimide insulator during ball shearing process, due to the polyimide layer of the silicon die being coplanar with the ball height of the wire. Experimentation and statistical analysis were done on units with and without polyimide coating, with Sodium Hydroxide (NaOH) used to remove the excess polyimide. Results revealed that silicon dice without polyimide coating resulted to better reading in terms of ball shear.

Controlling thermal conductivities and electrical insulation properties of carbon nanofiber/polyimide composites using surface coating techniques

AbstractIn the present work, sandwich‐structured composite sheets consisting of a core layer of carbon nanofiber (CNF)/polyimide (PI) and an outer layer of either pristine PI or hexagonal boron nitride (hBN)/PI were proposed and characterized for the possibility that they could enhance the effective thermal conductivity (TC) of PI composite sheets while also retaining their electrical insulation properties. The sandwiched structures were prepared using a dip coating method. The electrical insulation properties were evaluated via the breakdown voltage (BDV) of direct current. By using hBN with an average size of 0.5 μm as filler for the outer layer, a composite sheet with a highly effective level of TC was prepared. The BDV achieved more than 2 kV, when the outer layer had a total thickness of approximately more than 60 μm even at 30 vol% of hBN_0.5 content. The tensile strengths of the sandwich‐structured sheets indicated the values between each single layer of the 10 vol%‐CNF/PI and hBN_0.5/PI composites.

Sacrificial layer-assisted one-step transfer printing for fabricating a three-layer dry electrode

A sacrificial-layer assisted one-step transfer printing method is presented to fabricate a three-layer dry electrode for detecting electrophysiological signals. First, an Au electrode layer was deposited on a silicon wafer covered by a Cu sacrificial layer. Then, a polyimide (PI) intermediate layer was patterned on the Au layer by a standard photolithography process, and subsequently the Au layer was patterned by wet etching, using the patterned PI layer as the etching mask. Finally, both the patterned Au layer and PI layer were transferred onto a stretchable film in one step to make a three-layer dry electrode by etching away the Cu sacrificial layer. This three-layer dry electrode exhibited excellent conformability and stretchability and low electrode-skin contact impedance. The performance of the three-layer dry electrode for long-term and dynamic electrocardiogram (ECG) monitoring was also examined. The quality of ECG signals was well maintained for 48 h, during which period the signal to noise ratio was kept at 40 dB. It was also found that the physical exercises had only slight effects on the ECG signal, where all features of the signal were clearly distinguishable when the volunteer ran at 5 km/h.

Fluorescence enhanced BA-LIFT for single cell detection and isolation

Laser bioprinting is a term that refers to a group of laser-based techniques for printing living cells with high precision and good viability. Most of these techniques are based on modifications of the standard laser induced forward transfer technique (LIFT). When it comes to printing living material, direct laser irradiation should be avoided, therefore an indirect LIFT technique comprising an energy absorption layer should be used. This work presents a blister actuated-LIFT (BA-LIFT) technique which uses a commercial polyimide tape as a uniform energy absorption layer. To increase the potential of the technique for cell selection and printing accuracy, we take advantage of the high optical transmission of the polyimide layer to implement an in-line fluorescence and conventional imaging vision system coaxial with the laser path. With this system and using the appropriate staining methodology it is possible to track and identify different cell types, selecting those to be transferred and tracking cell survival both in the donor and acceptor substrates. We studied the BA-LIFT printability map for sodium alginate and methylcellulose hydrogels in the fluence range from 6.1 to 2.0 J cm−2 together with the cell viability assessment measured by our fluorescence system. The study has revealed that less concentrated, therefore less viscose hydrogel shows better results with lower fluences, whereas hydrogels with higher concentrations present better results at higher fluences. Also, at low fluences 98 % of cell viability was obtained, besides both primary cells and cell lines keep their integrity, proliferating and functional activity. The technique was tested by tracking and targeting mouse hematopoietic progenitor stem cells transferred to assess colony forming units; moreover, natural killer cells were isolated and its activation in a stimulation media was tracked with the fluorescence system.

Use of Pulse-Height Spectroscopy to Characterize the Hole Conduction Mechanism of a Polyimide Blocking Layer Used in Amorphous-Selenium Radiation Detectors

We demonstrate the use of pulse-height spectroscopy (PHS) to extract the internal electric field of an amorphous-selenium (a-Se) detector having a polyimide (PI) blocking layer. PHS enables more accurate measurement of the internal electric field of the detector because single-photon interactions in radiation detectors do not distort the internal electric field significantly. We fabricated a set of a-Se detectors, each having a PI layer with different thicknesses, and measured instantaneous electric field within the a-Se and PI layers using PHS, as well as the dark current of each detector. We also investigated the detector response under X-ray pulse illumination to determine the optimal thickness of PI necessary to achieve the best photo-to-dark-current ratio for low radiation dose imaging applications. Finally, we represent an analytical model of the steady-state dark-current behavior and a hole conduction mechanism in PI, which incorporates the Poole–Frankel emission model, and compared our model with the experimental results. The PHS approach reported in this article can enable the selection and design of an optimal blocking layer material when integrated with the existing [e.g., a-Se and cadmium zinc telluride (CZT)] and emerging direct-conversion radiation semiconductors (e.g., PbO and TIBr).

Secondary electro-optic response induced by VOD875S dye in polymer stabilised liquid crystals

ABSTRACT Polymer stabilised liquid crystal, which has the scattering state and transparent state, is widely used in tunable optic devices. Here, we demonstrate a polymer stabilised liquid crystal device with secondary electro-optic response phenomenon. Doped VOD875S dye into the normal polymer stabilised liquid crystal, the transmittance of the scattering and transparent states is reduced; moreover, the transparent region can be extended beyond the electrode and the transmittance is increased again when the operating voltage is larger than a critical value. The effects of dye concentration, polyimide (PI) layer and surfactant concentration on the secondary electro-optic response phenomenon of PSLC film were studied. It was found that high dye concentration, no PI layer and high surfactant concentration can effectively reduce the critical voltage of the secondary electro-optic response phenomenon. The secondary electro-optic response phenomenon can be used in some smart devices.

Adhesion Properties of Electroplating Process Between Polyimide and Metal Layer for Polymer/Metal Hybrid Bonding

This article investigates the adhesion properties between the polyimide layers and the Ti/Cu layer after the electroplating process. The adhesion strength was evaluated by the four-point bending system, and the influence factors were confirmed by using different electroplating times and currents. The fracture interface after the four-point bending measurement was characterized, and the interface spectrum between the polyimide and the Ti/Cu layer was analyzed. The results showed that the modified polyimide-like material has better adhesion performance than the conventional polyimide. Moreover, the mechanism of degradation was proposed. As a result, the modified polyimide-like material can be applied in electroplating, a redistribution layer (RDL) formation, and packaging at the back-end-of-line processes.

Fabrication and Self-sensing Control of Soft Electrothermal Actuator

Soft electrothermal actuators have attracted wide attention due to their high flexibility, adaptability and light weight. These characteristics give them great potentials to be used in biomimetic and soft robotics applications. In this paper, an electrothermal actuator with directly printed microfilament heater was designed, fabricated and characterized. The soft actuator used polyimide (PI) and polydimethylsiloxane (PDMS) as the structural materials due to their large mismatch of thermal expansion. A microfilament heater was electrohydrodynamic (EHD) printed using a low melting point alloy Bi58/Sn42, and embedded in-between the PI and PDMS layers. The fabricated actuator achieved a maximum curvature of 1.0 cm−1 under a supply voltage as low as 3 V. Resistive self-sensing technology was used to sense the deflection of the actuator and to develop the closed-loop control of the actuator. The bending curvature of the actuator is resulted from the temperature change of the actuator, which can be detected by the electrical resistance change of the embedded heater as they are linearly related. A PID controller was designed for the closed-loop operation of the actuator. Compared with the open-loop operation, the closed-loop controlled actuator demonstrated more rapid and precise response. The developed electrothermal actuator was successfully demonstrated for applications as a soft lifter and soft gripper.

In Situ Synthesis of Ultrastable CsPbBr3 Perovskite Nanocrystals Coated with Polyimide in a CSTR System.

The poor stability of perovskite nanocrystals (NCs) is one of the major obstacles for their application in optoelectronic devices. Herein, we develop an easy in situ strategy for preparing polyimide (PI)-coated single-particle CsPbBr3 NCs in a continuous stirred-tank reactor system. Benefiting from the protection of the thick polyimide layer, these PI-coated CsPbBr3 NCs show excellent stability against severe environments such as water, heat, oxygen, and light. Meanwhile, time-resolved photoluminescence and ultrafast transient absorption spectroscopy revealed that the polyimide (PI) polymer contributes to passivating the surface defects of the CsPbBr3 NCs, giving CsPbBr3/PI NCs a higher photoluminescence quantum yield. Thanks to the performances of high luminescent efficiency and stability, these green-emitting perovskite CsPbBr3/PI NCs show promising potentials in the fields of solid-state lighting and display.