After a piezoelectric inkjet printhead jets the first droplet, the actuating membrane still vibrates, creating residual vibrations in the ink channel, which can degrade the inkjet printhead performance. For suppressing these vibrations, an optimized actuating voltage waveform with two pulses must be obtained, of which the first pulse is used for jetting and the second pulse is used to suppress the residual vibrations. In this study, the pressure history within the ink channel of a recirculating piezoelectric inkjet printhead was first acquired using lumped element modeling. Then, for suppressing residual vibrations, a bipolar voltage waveform was optimized via analysis of the tuning time ($t_{\mathrm{t}}$ ), dwell time ($t_{\mathrm{d}2}$), rising time ($t_{\mathrm{r}2}$), falling time ($t_{\mathrm{f}2}$), and voltage amplitude of the second pulse. Two voltage waveforms, Waveform 01 and Waveform 02, were optimized thereafter. In Waveform 01, $t_{\mathrm{t}}=2 \mathsf{\mu }\mathrm{s}, t_{\mathrm{d}2}=2 \mathsf{\mu }\mathrm{s}$, and $t_{\mathrm{r}2}$ and $t_{\mathrm{f}2}=1 \mathsf{\mu }\mathrm{s}$ were finalized as the optimal parameters; in the case of another waveform, the optimal parameters of $t_{\mathrm{d}2}$, $t_{\mathrm{r}2}$, and $t_{\mathrm{f}2}$ were found to be $4$, $1$, and $1 \mathsf{\mu }\mathrm{s}$, respectively. The optimal voltage amplitude of the second pulse was found to be 1/3 the amplitude of the first pulse. On the basis of our analysis, the tuning time in Waveform 01 is the most sensitive parameter, and the performance yielded is even poorer than that yielded by standard waveform, if not optimized. Therefore, the other waveform is recommended for the suppression of residual vibrations.

We present a polymer-assisted spin coating process used to fabricate high-density p-type CuBi₂O₄ (CBO) thin films. Polyvinylpyrrolidone (PVP) is introduced in the precursor solutions in order to promote uniform nucleation of CBO and prevent formation of the secondary phase, such as Bi₂O_3, by Bi³⁺ ion hydrolysis. Slow PVP molecule decomposition during the two-step annealing process, with a 1 M/0.5 M (Bi³⁺/Cu²⁺) metal ion concentration, enables optimum contact at the CBO/substrate interface by avoiding formation of voids. This resulted in the formation of non-porous, compact CBO thin films. The highest current density of the photoelectrochemical (PEC) oxygen reduction reaction is obtained with non-porous, compact CBO thin films due to unimpeded charge transport through the CBO bulk, as well as across the interface. When combined with silicon, the high-density CBO thin film investigated in this work is expected to provide new PEC tandem cell options to use for solar applications.

Flexible electrodes should have a good mechanical durability and electrical properties under even extreme bending and deformation conditions. We fabricated such an electrode using an inkjet printing system. In addition, annealing was performed under curing temperatures of 150, 170, and 190 °C to improve the electrical resistance performance of the electrode. Scanning electron microscopy, X-ray diffraction, nanoindentation, and surface profile measurements were performed to measure and analyze the electrode characteristics and the change in the shape of the coffee ring. The bending deformation behavior of the electrode was predicted by simulations. To confirm the bending durability of the flexible electrode according to different curing temperatures, the bending deformation and electrical resistance were simultaneously tested. It was found that the electrode cured at a temperature of 170 °C could endure 20,185 bending cycles and had the best durability, which was consistent with the predicted simulation results. Moreover, the average specific resistance before the electrode was disconnected was 13.45 μΩ cm, which is similar to the conventional electrode value. These results are expected to increase the durability and life of flexible electrodes, which can be used in flexible electronic devices, sensors, and wearable devices that are subjected to significant bending deformation.

Divinylsiloxane-bis-benzocyclobutene (DVS-BCB) has attracted significant attention as an intermediate bonding material, owing to its excellent properties. However, its applications are limited, due to damage to peripheral devices at high curing temperatures and unoptimized compressive pressure. Therefore, it is necessary to explore the compressive pressure condition for DVS-BCB bonding. This study demonstrates an optimization process for void-free DVS-BCB bonding. The process for obtaining void-free DVS-BCB bonding is a vacuum condition of 0.03 Torr, compressive pressure of 0.6 N/mm², and curing temperature of 250 °C for 1 h. Herein, we define two factors affecting the DVS-BCB bonding quality through the DVS-BCB bonding mechanism. For strong DVS-BCB bonding, void-free and high-density chemical bonds are required. Therefore, we observed the DVS-BCB bonding under various compressive pressure conditions at a relatively low temperature (250 °C). The presence of voids and high-density crosslinking density was examined through near-infrared confocal laser microscopy and Fourier-transform infrared microscopy. We also evaluated the adhesion of the DVS-BCB bonding, using a universal testing machine. The results suggest that the good adhesion with no voids and high crosslinking density was obtained at the compressive pressure condition of 0.6 N/mm². We believe that the proposed process will be of great significance for applications in semiconductor and device packaging technologies.

OER characteristics of K-doped NiCo₂O₄ catalyst and K doping control through simple hydrothermal synthesis.