Printed and flexible sensors are in the focus of recent efforts to establish the advantages of low-cost manufacturing techniques such as screen printing or inkjet printing for printed electronical applications. Devices based on conductive carbon nanotube (CNT) networks within polymeric matrices such as polydimethylsiloxane (PDMS) are already exceeding mere technological demonstrations. Therefore, we investigate the application-oriented behaviour of fully inkjet-printed CNT/PDMS strain sensors under different conditions such as short-and long-term performance. The sensors exhibit a quasi-linear piezoresistive behaviour with vanishing hysteresis to tensile strain. Significant differences in the resistive response between compressive and tensile strain suggest complex re-orientation mechanisms of CNTs inside the matrix. No clear indication for this phenomenon could be observed in the evolution of the CNT network resistance during fatigue measurements within an uncured or cured PDMS matrix, where both scenarios exhibit no visual degradation. However, these measurements over thousands of cycles show different permanent changes in the overall device resistance exhibiting damages but also recovery in the network. Considering these findings facilitates the development of printed sensor devices.

With the rapid proliferation of consumer electronics in our day to day lives, there is an ever increasing demand for flexible electronic devices which are low cost, easy to fabricate and deliver reliable performance. In this work, we report fabrication of symmetric poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)/WO 3 /PEDOT:PSS memory cells by inkjet printing on transparent, flexible polyethylene naphthalate (PEN) substrates. The cells show resistive switching behavior with two stable resistance states. The current conduction across the interface between the PEDOT:PSS electrode and dielectric WO 3 is determined by localized filamentary features which is space charge limited in the high resistance state, facilitated through the migration of oxygen vacancies at low voltages (<2 V) whereas Schottky emission dominates the current conduction for higher voltages (>2 V). The cells show good retentivity and endurance (>6000 cycles). The cells are entirely sinter free and no electroforming is required to activate them. These characteristics make them suitable for the next generation of flexible non-volatile memory devices.

Printable and flexible memory devices are attracting a lot of interest in several emerging technological applications for the development of flexible electronics, such as interconnections/wearables/smart devices for IoT. In this work, we report on the fabrication of flexible, transparent, and fully inkjet-printed resistive random access memory cells (ReRAM) using PEDOT: PSS/ZnO/PEDOT: PSS structures. The electrical characteristics were studied, including the determination of SCLC as the dominant charge transport mechanism. In addition, the bending performance and the transparency of the devices was tested in order to confirm the reliable operation and reproducibility of the cells. The switching for the printed structures of PEDOT:PSS/ZnO/PEDOT:PSS was led through the formation and dissolution of a stable oxygen vacancy filament, as confirmed by conductive atomic force microscopy. While the conduction mechanism for the high resistance state (HRS) was attributed to the space charge limited conduction (SCLC) mechanism. The switching of the memory cells, their endurance and retention properties were analyzed and indicated the stability of the HRS and low resistance state (LRS) for more than 104 cycles and 105 s comparable to ZnO-based ReRAM produced by clean-room techniques. The study of the mechanical flexibility of the cells shows that up to 700 bending cycles can be reached without significantly changing the switching characteristics.

In recent years, photoacoustic generators based on multiwalled carbon nanotubes (MWCNT) and polydimethylsiloxane (PDMS) are manufactured in a variety of ways, which influences the properties of the generators with respect to frequency bandwidth, sound wave pressure, robustness, and reproducibility. Due to the high optical absorption of MWCNTs and the high thermal expansion coefficient of PDMS, this combination is ideally suited for use as a photoacoustic generator. This study presents a novel method to produce photoacoustic generators based on long‐term stable MWCNT and PDMS inks with a high reproducibility by means of inkjet‐printing. The MWCNT‐PDMS layers (thicknesses of 2–4 µm), printed directly onto the distal end face of a multimode glass fiber, show a good homogeneity and low optical transmission (19–21%). After the preparation of the fiber pieces, the inkjet printer performs all steps automatically in a time period of 30–60 s per layer. The generated ultrasonic pressure (0.39–0.54 MPa) and frequency bandwidth (1.5–12.7 MHz) can be measured at a distance of ≈4 mm with a laser fluency of 12.7 mJ cm−2. These highly reproducible printed photoacoustic generators can be well used for nondestructive material testing and medical applications.

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