Large area polymer semiconductor sub-microwire arrays by coaxial focused electrohydrodynamic jet printing for high-performance OFETs.

Large area and highly aligned polymer semiconductor sub-microwires were fabricated using the coaxial focused electrohydrodynamic jet printing technology. As indicated by the results, the sub-microwire arrays have smooth morphology, well reproducibility and controllable with a width of ~110 nm. Analysis shows that the molecular chains inside the sub-microwires mainly exhibited edge-on arrangement and the π-stacking direction (010) of the majority of crystals is parallel to the long axis of the sub-microwires. Sub-microwires based organic field effect transistors showed high mobility with an average of 1.9 cm2 V-1 s-1, approximately 5 times higher than that of thin film based organic field effect transistors. In addition, the number of sub-microwires can be conveniently controlled by the printing technique, which can subsequently concisely control the performance of organic field effect transistors. This work demonstrates that sub-microwires fabricated by the coaxial focused electrohydrodynamic jet printing technology create an alternative path for the applications of high-performance organic flexible device.

Simulation of Cone-Jet and Micro-Drip Regimes and Printing of Micro-Scale Patterns on PET Substrate.

The fabrication of various micro-patterns on polymer insulating substrates is a current requirement in micro-electromechanical system (MEMS) and packaging sectors. In this paper, we use electrohydrodynamic jet (E-Jet) printing to create multifaceted and stable micro-patterns on a polyethylene terephthalate (PET) substrate. Initially, simulation was performed to investigate optimized printing settings in phase field physics for the usage of two distinct functional inks. A series of simulation experiments was conducted, and it was determined that the following parameters are optimised: applied pressure of 40 kPa, high pulse voltage of 1.95 kV, low dc voltage of 1.60 kV, duty cycle of 80%, pulse frequency of 60 Hz, printing height of 0.25 mm, and printing speed of 1 mm/s. Then, experiments showed that adjusting a pressure value of 40 kPa and regulating the SEMICOSIL988/1 K ink to print micro-drops on a polymer substrate with a thickness of 1 mm prevents coffee staining. The smallest measured droplet size was 200 µm. Furthermore, underfill (UF 3808) ink was driven with applied pressure to 50 kPa while other parameters were left constant, and the minimum size of linear patterns was printed to 105 µm on 0.5-mm-thick PET substrate. During the micro-drip and cone-jet regimes, the consistency and diameter of printed micro-structures were accurately regulated at a pulse frequency of 60 Hz and a duty cycle of 80%.

Numerical modeling and analysis of coaxial electrohydrodynamic jet printing.

Coaxial electrohydrodynamic jet (CE-Jet) printing is an encouraging method for fabrication of high-resolution micro and nanostructures in MEMS systems. This paper presents a novel simulation work based on phase field method which is considered as a precise technique in fluid dynamics. The study explores influence of various parameters such as applied voltage, needle-substrate distance, dynamic viscosity, relative permittivity, needle size and flow rate on stability and resolution of CE-Jet morphologies. The morphology of CE-Jet exhibits that width of cone-jet profile and printed structures on substrate were directly proportional to relative permittivity and flow rate. In addition, it was inversely proportional to dynamic viscosity and applied voltage. The study examine that CE-Jet length of inner liquid is inversely proportional to needle-substrate distance in same time. It was later verified in experimental study by producing stable CE-Jet morphology with 300 µm diameter using optimized parameters (i.e., DC voltage 7.0 kV and inner liquid flow rate 400 nl/min) as compared to other validation studies such as 400 µm and 500 µm. The CE-Jet printing technique investigates significant changes in consistency and stability of CE-Jet morphologies and makes Jet unique and comparable when adjustment accuracy reaches 0.01 mm. PZT sol line structures with a diameter of 1 µm were printed directly on substrate using inner needle (diameter of 120 µm). Therefore, it is considered as a powerful tool for nano constructs production in M/NEMS devices.

Fabrication and Characterization of a Microscale Piezoelectric Vibrator Based on Electrohydrodynamic Jet Printed PZT Thick Film.

This paper proposes a novel way of preparing a PZT thick film micro vibrator using the electrohydrodynamic jet (E-Jet) printing technique. Initially, a micro piezoelectric vibrator was simulated and designed for obtaining optimized structure, which has a total thickness of less than 600 µm. Subsequently, the PZT thick film element was directly printed on the elastic body using the E-Jet printing. This method avoids the glue fabrication process involved in the bulk piezoelectric fabrication, thus avoiding the limits of voltage drops, isolating and absorbing amplitude usually occurred in the vibrator having glue interface. It was observed that B02 and B03 modes were generated at frequencies of 29.74 and 79.14 kHz, respectively, and the amplitudes of B02 and B03 modes were 406 and 176 nm, respectively. The error between the simulation and test result in the B03 modal is only 0.35%, which indicates the accuracy of the simulation analysis and the fabrication process. The PZT thick film traveling-wave micro vibrator successfully realized bidirectional rotation of a rotor, with a maximum speed of 681 rpm, which also shows a linear relationship between excitation voltage and rotary speed. This paper provides an effective method for preparing a micro piezoelectric vibrator for MEMS ultrasonic devices, which simplifies the manufacturing process and enhances the performance of the piezoelectric vibrator.

Electrohydrodynamic jet 3D printing of PCL/PVP composite scaffold for cell culture.

Controlled printing of biodegradable and bioresorbable polymers at desired 3D scaffold is of great importance for cell growth and tissue regeneration. In this work, a novel electrohydrodynamic jet 3D printing technology with the resultant effect of electrohydrodynamic force and thermal convection was developed, and its feasibility to fabricate controllable filament composite scaffolds was verified. This method introduces an effective thermal field under the needle to simultaneously enhance the ink viscosity, jetting morphology controllability and printing structure solidify. The fabrication mechanisms of thermal convection on jetting morphology and printed structures feature were investigated through theoretical analysis and experimental characterization. Under optimized conditions, a stable and finer jet was formed; then with the use of this jet, various 3D structures were directly printed at a high aspect ratio ~30. Furthermore, the PCL/PVP composite scaffolds with the controllable filament diameter (~10 µm) which is closed to living cells were printed. Cell culture experiments showed that the printed scaffolds had excellent cell biocompatibility and facilitated cellular proliferation in vitro. It is a great potential that the developed electrohydrodynamic jet 3D printing technology might provide a novel approach to directly print composite synthetic biopolymers into flexibly scale structures for tissue engineering applications.