System of nano-silver inkjet printed memory cards and PC card reader and programmer

This work describes the development of inkjet printed, low-cost memory cards, and complementary pair of memory card reader and card reader/programmer for PCs. This constitutes a complete system that can be used for various applications. The memory cards are manufactured by inkjet printing nano-silver ink on photo paper substrate. The printed memory structures have an initial high resistance that can later be programmed to specific values representing data on the cards, the so called Write Once Read Many (WORM) memories. The memory card reader measures the resistance values of the memory cells and reads it back to the computer by USB connection. Using multiple resistance levels that represent different states it is possible to have a larger number of selectable combinations with fewer physical bits compared to binary coding. This somewhat counters one of the limitations of resistive memory technology that basically each cell needs one physical contact. The number of possible states is related to the resolution of the reader and the stability of the WORM memory.     

高精度数码喷墨打印技术及在印刷电子上的应用

文章介绍了高精度数码喷墨打印技术的设备,材料和打印工艺及其在印刷电子上的应用。重点介绍了纳米银墨水的结构、性能、烧结条件和电性能以及打印性能及其在制备导电线路上的应用,探讨了喷头孔径及基材的表面性能对打印线路的影响。最后,介绍了挠性PCB的打印。     

R2R gravure and inkjet printed RF resonant tag

The fabrication of passive circuitry by gravure and inkjet printing is studied. A chipless inductively coupled RF resonant tag is analyzed as a test structure. A floating-bridge layout is employed to provide high yield when fabricated by roll-to-roll (R2R) printing. The conducting first layer and insulating second layer are R2R gravure printed with silver nanoparticle ink and a thermally cross-linkable dielectric ink, respectively. Above 10 MS/m conductivity is obtained for the first layer, which passes three times through the 5 m long drying unit at 5 m/min speed. The floating bridge is inkjet printed with silver nanoparticle ink and the prototype tag is measured over a reading distance of ca. 2 cm. An equivalent circuit model is presented and the model parameters are optimized to obtain a best fit to the measured frequency response. This indirect measurement provides an estimate of 4.3 μm for the thickness of the dielectric layer sandwiched between the conducting top and bottom layers. Application possibilities for the all-printed RF resonant tag are outlined.     

Inkjetting dielectric layer for electronic applications

Printed electronics is expected to increase its market share significantly in near future. The emerging applications include e.g. display applications, RFID tags, and photovoltaic applications. A benefit of printing is the additive character of the process, which means that material is deposited only the amount that is needed. Digital printing increases flexibility of the process, because circuits are manufactured directly from a digital file, which removes need of fixed masks or patterned screens for each layout. Formation of a multilayer circuitry requires printing of conductive and insulative layers. This paper focuses on printing of a dielectric layer with an inkjet printer. Six sigma DMAIC approach was applied during the process characterization and analysis. The study began by defining the process parameters and evaluating their importance to the outputs. Highest rated parameters were taken into consideration and a design of experiments was established. Measured values were analyzed and it was observed which parameters had the highest effect on the outputs. The results were further verified and it was observed that electrically the printed structures were successful.     

The design challenge in printing devices and circuits: Influence of the orientation of print patterns in inkjet-printed electronics

We present a morphological and electrical analysis of inkjet-printed two-dimensional films of silver nanoparticle inks arranged at different orientation to the raster-scan-based printing process. Different parameters causing morphological and functional irregularities in the inkjet-deposited films as a function of their orientation to the printing process are introduced in detail and the relevance for the field of printed electronics is discussed. Researchers have demonstrated the manufacturing of various microelectronic devices using inkjet printing. Nearly all of the devices are based on simple rectilinear geometries. Usually, these geometries have a preferential orientation that is exactly (i) along the deposition process or exactly (ii) perpendicular to the deposition process. So far, it was assumed that the geometrical and functional characteristics are identically for the both cases. However, we show empirically that this is not the case and help to understand the conditions that lead to the differences.     

Control of on-demand nanoliter drop volume and jetting velocity in piezoelectric inkjet printing

Consistent dosages placed with high accuracy onto the substrate are critical for drop-on-demand (DoD) inkjet printing to be adopted in additive manufacturing and device characterization. Practically, the consistency of drop volume and drop jetting velocity is subject to process uncertainties, such as fluctuations of applied pressure and variations in printheads, for which open-loop approaches are unable to compensate. In this work, a stochastic process model of the relation between two control parameters of a firing waveform and two output features, drop volume and drop jetting velocity, is developed from standard printhead calibration data. An image-based control strategy based on a projection-based one-step-ahead Kalman estimator for model parameters estimation is proposed to regulate the drop volume and the drop jetting velocity. The effectiveness of the proposed control strategy is experimentally validated for three inks with broad properties. By including input boundary layers, an order of magnitude improvement in reducing drop volume and jetting velocity variations is also experimentally demonstrated.     

Tuning the viscosity of halogen free bulk heterojunction inks for inkjet printed organic solar cells

For the solution processing of organic photovoltaics on an industrial scale, the exclusion of halogenated solvents is a necessity. However, the limited solubility of most semiconducting polymer/fullerene blends in non-halogenated solvents results in ink formulations with low viscosities which poses limitations to the use of roll-to-roll compatible deposition processes, such as inkjet printing. We propose to add polystyrene as a rheological modifier to increase the viscosity of bulk heterojunction (BHJ) non-halogenated inks. The printing and performance of P3HT/PCBM photoactive layer inks are characterized as a function of polystyrene concentration and three different molecular weights. Addition of 1 wt% polystyrene provided a near two-fold gain in viscosity, with the largest viscosity gains coming from the polymer with the highest molecular weight. However, this coincided with greater viscoelastic behavior, which reduced the jetting performance of the inks. Differences in solvent compatibility of the polystyrene/P3HT/PCBM ternary blend resulted in phase separation upon layer drying, whereby polystyrene segregated to the layer-air interface to form an isolated domain or network like topology. Nevertheless, a 1.7-fold increase in dynamic viscosity was obtained for devices with printed BHJ layers containing polystyrene at the expense of a 20% reduction in OPV performance. The improved viscosity and good printing behavior achieved with small additions of polystyrene demonstrates its potential to overcome the limited viscosity resulting from typical non-halogenated ink formulations for semiconducting polymers. These results offer a step forward to the industrialization of inkjet printing as an effective deposition technique for functional layers of organic electronics.     

High-brightness perovskite quantum dot light-emitting devices using inkjet printing

The performance of perovskite quantum dot light-emitting diodes (PeQLEDs) has been rapidly enhanced recently, but the devices are still stuck in the stage of using small-scale solution processes, such as spin-coating. In this work, we report the realization of high performance PeQLEDs by using inkjet printing technique. We demonstrate the preparation of a printable perovskite quantum dot ink by using a hybrid solvent consisting of high boiling solvent dodecane and low boiling solvent n-octane. A universal strategy for eliminating coffee rings during inkjet printing of perovskite inks is developed based on the modulation of ink formulation, and the stacking model of perovskite quantum dot in a pixel pit structure is proposed. The inkjet-printed PeLEDs exhibit a low turn-on voltage of 2.7 V, a brightness of 10992 cd/m² at 6.6 V and a maximum current efficiency of 8.67 cd/A, which is by far the highest value reported for inkjet-printed PeLEDs. The results pave a way for future realization of high performance pixelated PeLED displays with inkjet printing technique.     

Air stable complementary polymer circuits fabricated in ambient condition by inkjet printing

Air stable complementary polymer inverters were demonstrated by inkjet printing of both top-gate electrodes and the semiconductors in ambient conditions. The p-type and n-type polymer semiconductors were also thermally annealed in ambient conditions after printing. The good performance of circuits in ambient condition shows that the transistors are not only air-stable in term of ambient humidity and oxygen, but also inert to ion migration through dielectrics from the printed gate. The result obtained here has further confirmed the feasibility of fabrication of low-cost polymer complementary circuits in a practical environment.     

数字喷墨打印技术在PCB抗蚀层制作中的初步研究

随着数字喷墨打印设备和纳米油墨的不断发展,喷墨打印技术在PCB制作中得到了越来越广泛的应用。目前市场上主要包括三个方面的应用：抗蚀层、字符、阻焊。文章通过市场调研,成本评估和工艺能力评估重点研究了喷墨打印技术在线路抗蚀层制作中的应用。结果发现喷墨打印技术相对于传统的线路制作工艺具有一定的成本优势和线路制作能力。     

纳米导电油墨及其在印刷天线中的应用

文章以印刷RFID天线作为印刷电子技术的应用实例,介绍了利用纳米导电油墨印刷RFID天线的优势、进展与发展展望。     

Flexible organic phototransistors based on a combination of printing methods

Highly photosensitive organic phototransistors (OPTs) are successfully demonstrated on a flexible substrate using all-solution process as well as a combination of printing methods which consist of roll-to-plate reverse offset printing (ROP), inkjet printing and bar coating. Excellent electrical switching characteristics are obtained from heterogeneous interfacial properties of the reverse-offset-printed silver nanoparticle electrode and the inkjet-printed p-channel polymeric semiconductor. In particular, the OPTs exhibit remarkably photosensitivity with a photo-to-dark current ratio exceeding 5 orders. This optoelectronic properties of the combinational printed OPTs are theoretically and experimentally studied, and found the comparable tendency. In addition, excellent mechanical stability is observed with up to 0.5% of strain applied to the OPTs. Hence, by manufactured with a combination of various graphic art printing methods such as roll-to-plate ROP, inkjet printing, and bar coating, these devices are very promising candidates for large-area and low-cost printed and flexible optoelectronics applications.     

Up-scaling of the manufacturing of all-inkjet-printed organic thin-film transistors: Device performance and manufacturing yield of transistor arrays

All-inkjet-printed thin-film transistors (TFTs) have been demonstrated in literature using mainly laboratory inkjet equipment, simple one-channel layout and only a low number of manufactured TFT devices. We report on the development and the up-scaling of the manufacturing of all-inkjet-printed TFT arrays using industrial inkjet equipment. The manufacturing of the TFTs was carried out in ambient condition without the need for cleanroom environments or inert atmospheres and at a maximum temperature of 150 °C enabling the use of flexible polymer films as substrate. Arrays of 924 TFTs were manufactured on an area of about DIN A4 (297 × 420 mm²). This allows the consideration of statistics, e.g. to determine the process yield as a function of device design and layout. We present process yields for all-inkjet-printed TTFs up to 82% demonstrating the potential of the developed all-inkjet-printing process.     

High-speed operation in printed organic inverter circuits with short channel length

We have demonstrated fast operation of printed organic inverter circuits. We employ a soluble organic semiconducting material which has high field-effect mobility and ink-jet printed source/drain electrodes with short channel length. Appropriate concentration of the semiconducting solution and modification layer of source/drain electrodes improve both mobility and on/off ratio. The fabricated transistors with a short channel length (4 μm) exhibit excellent mobility (1.2 cm²/V s), high on/off ratio (>10⁵) and operational stability. The diode-load inverter with a narrow channel and low parasitic capacitance operate at 8 kHz at 20 V. These results will lead to significant progress in applications of printed organic circuits.     

Inkjet printed micropump actuator based on piezoelectric polymers: Device performance and morphology studies

All inkjet printed piezoelectric actuators based on poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF–TrFE)) for applications as pump actuators in microfluidic lab-on-a-chip systems (LOC) are manufactured and investigated in terms of their morphology and actuator performance. Furthermore, a pump demonstrator with an all-printed P(VDF–TrFE) actuator is characterized here for the first time. The actuators are manufactured in a fully additive and flexible way by successive inkjet printing of a P(VDF–TrFE) film sandwiched between two silver electrodes on a polyethylene terephthalate (PET) substrate. Different from most current micropumps where actuator elements are fabricated separately, no additional joining step is required in the manufacturing approach employed here. Actuator performance is investigated by measurements of piezoelectric d₃₁ coefficients as well as remanent polarization P_rem for different thermal treatments of the as-printed P(VDF–TrFE) films. A strong dependence of the device performance on the annealing temperature is found with maximum values for d₃₁ and P_rem of approximately 10 pm V⁻¹ and 5.8 μC cm⁻², respectively. Morphology investigations of the printed films by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Atomic Force Microscopy (AFM) indicate an increased degree of crystallinity of the piezoelectric β-phase for samples annealed at temperatures above 110 °C, which coincides with improved device performance. A basic pumping function with pump rates of up to 130 μL min⁻¹ is demonstrated, which is promising for future applications in LOC. Furthermore, the process chain and characterization presented here can be employed to design and manufacture also other P(VDF–TrFE)-based devices and allows the combination with additional printed on-chip functionalities in future LOC.     

A comparative assessment of surface microstructure and electrical conductivity dependence on co-solvent addition in spin coated and inkjet printed poly(3,4-ethylenedioxythiophene):polystyrene sulphonate (PEDOT:PSS)

This study focuses on the fabrication of poly(3,4-ethylenedioxythiophene):polystyrene sulphonate (PEDOT:PSS) thin films by inkjet printing and investigates the developed surface morphology and electrical conductivity of the printed films as a function of the concentration of dimethyl sulfoxide (DMSO), added as conduction enhancing co-solvent, and Surfynol, added as a surfactant. The printed films are compared with PEDOT:PSS films fabricated by the traditional spin coating technique. Measurements of the surface tension justify including surfactant as a processing additive, where addition of 1% Surfynol results in substantial decrease of the surface tension of the PEDOT:PSS solution, whilst it also increases film surface roughness by an order of magnitude for both fabrication methods. The addition of 5 wt% DMSO is shown to result in a 10³ decrease in sheet resistance for both spin coated and inkjet printed films with both processing routes demonstrating decrease in surface roughness and coarsening of PEDOT grains as a function of the co-solvent concentration, whilst X-ray photon spectroscopy showed an increase in the surface PEDOT to PSS ratio from 0.4 to 0.5. Inkjet printed films have lower sheet resistance than the corresponding spin coated films, whilst atomic force microscopy reveals a coarser surface morphology for the inkjet printed films. The findings in this work point out at the decrease of sheet resistance due to coarsening of PEDOT grains which is linked to a decrease of surface roughness for small RMS values associated with the PEDOT grains. However, the higher surface roughness generated when Surfynol surfactant was added was not detrimental to the film’s in-plane conductivity due to the fact that these higher roughness values were unrelated to the PEDOT grains.     

Transverse charge transport in inkjet printed poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)

Transverse (z) alignment of PEDOT grains was demonstrated in inkjet printed PEDOT:PSS. This explained the superior transverse charge conduction mode in inkjet printed PEDOT:PSS films, best fitted by the Efros-Shklovskii 1D-VRH (variable range hopping) model in this study compared with spin coated PEDOT:PSS films, which have demonstrated layers of generally in-plane aligned PEDOT:PSS grains. The findings of this study, regarding the microstructure of inkjet printed PEDOT:PSS films and their transverse charge transport model, justify measurements of the transverse conductivity of inkjet printed films in this study being 600 times higher than that of spin coated films. In addition, it was found that the addition of 5 wt% DMSO in the printing PEDOT:PSS ink lowers the workfunction by 3% approximately.     

Polylactic acid as a biodegradable material for all-solution-processed organic electronic devices

In this paper we report on the fabrication of spin-coated biodegradable polylactic acid (PLA) thin films to be used as substrates for the realisation of all-solution-processed organic electronic devices. The full mechanical and electrical characterisation of these substrates shows that they exhibit good mechanical and dielectric properties and are therefore suitable for the fabrication of disposable electronics. To demonstrate practically the functionality of such PLA thin films, organic electronic devices were realised on the top of them, exclusively by means of solution-process fabrication techniques and in particular inkjet-printing. Also, a photonic curing procedure is here presented as a means for sintering the conductive inks without heating up the PLA substrates. Two types of organic transistors were fabricated on the top of PLA: organic field-effect transistors (OFETs), where the PLA film was used not only as a substrate but also as the gate dielectric, and all-inkjet-printed organic electrochemical transistors (OECTs). The second typology of transistors exhibited one of the highest transconductance reported so far in the literature (up to 2.75 mS). This study opens an avenue for the fabrication of disposable, low-cost organic electronic devices.     

Significant effect of the molecular formula in silver nanoparticle ink to the characteristics of fully gravure-printed carbon nanotube thin-film transistors on flexible polymer substrate

Single-walled carbon nanotubes (SWNTs) are a valuable material for use in not only nanoelectronics but also printed electronics because of their stability, tunable operation speed, and scalability. However, the device characteristics of fully printed, SWNT-based thin film transistors (SWNT-TFTs) often have large variations, and the fundamental cause of these inconsistencies are not yet well understood. Therefore, fully printed SWNT-TFT-based electronic devices have not been practically realized in the market. In this study, the significant variation in the electrical parameters of printed SWNT-TFTs that is caused by minor molecular variations in the formulation of silver nanoparticle-based ink is reported. Strikingly, a very small difference in the chemical structure between ethylene glycol and diethylene glycol in the silver nanoparticle-based ink, which is used to print drain-source electrodes in the SWNT-TFTs, with everything else identical, induced a difference of approximately 70 meV in the barrier height between the drain-source electrodes and the SWNT layer at 300 K. The modification of the absorbed polymer binder in the silver nanoparticle ink due to the additive is the major cause of the observed barrier height difference. These results allow for a better understanding of the relationship between the ink rheology at the molecular level and the printed device properties, and enable a more precise design and control of device properties which will have profound impacts on printed electronic devices.     

An accurate method to determine the through-plane electrical conductivity and to study transport properties in film samples

The through-plane conductivity of a film sample is critically important because it largely affects the performance of batteries, capacitors, and thermoelectric devices. In this study, we developed a modified four-probe through-plane electrical conductivity measurement method using a coaxial structure. This method is general and works for free-standing film samples. We studied different samples including a steel sheet, highly oriented pyrolytic graphite, and conducting polymers. We confirmed metallic transportation in the steel sheet and hopping transportation in graphite in the through-plane direction by conducting low temperature measurements at 100 K. In the case of a conducting polymer poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate, the conductivity anisotropic ratio decreases with increasing in-plane conductivity. Temperature dependent measurements show two distinct activation energy regimes in the through-plane direction in PEDOT/PSS but almost no change in the in-plane electrical conductivity activation energy. This could be due to additional carrier paths that occur through the more disordered region (the PSS-rich region) in the through-plane direction. We also examined the Meyer–Neldel rule in PEDOT/PSS and concluded that PEDOT/PSS follows the anti-Meyer–Neldel rule, likely due to the high carrier density in the film.