Drop‐on‐demand inkjet printing of highly viscous fluids represents a highly attractive emerging technology for advanced material deposition. The jetting of viscous inks, such as concentrated polymer solutions and nanoparticle suspensions, is a key enabling technology for many industrial applications, ranging from microelectronics to biomedicine and ceramics manufacturing. Currently available standard inkjet printers typically operate in a relatively narrow viscosity range (up to 16 mPa s), and alternative drop‐on‐demand printing techniques (such as laser‐induced forward transfer) present limited industrial applicability. In this context, the development of a piezoelectric‐driven printhead capable of jetting high‐viscosity fluids is of great interest. Herein, a prototype of such a device is presented and its performance is evaluated using model fluids at increasing viscosities. Specifically, the dependence of emitted droplets’ properties on jetting parameters is evaluated and linked to the physical characteristics of the system. In optimal conditions, piezoelectric jetting of solutions characterized by viscosities in excess of 200 cP is achieved. Finally, as an applicative example, the jetting of functional inks is attempted. A ZnO suspension and a poly(3,4‐ethylenedioxythiophene) (PEDOT) based solution are successfully jetted to demonstrate the applicability of the developed printhead to the deposition of ceramic suspensions and concentrated polymer solutions.

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The emerging wearable electronics integrated into textiles are posing new challenges both in materials and micro-fabrication strategies to produce textile-based energy storage and power source micro-devices. In this regard, inkjet printing (IJP) offers unique features for rapid prototyping for various thin-film (2D) devices. However, all-inkjet-printed capacitors were very rarely reported in the literature. In this work, we formulated a stable Ti3C2 MXene aqueous ink for inkjet printing current-collector-free electrodes on TPU-coated cotton fabric, together with an innovative inkjet-printable and UV-curable solvent-based electrolyte precursor. The electrolyte was inkjet-printed on the electrode’s surface, and after UV polymerization, a thin and soft gel polymer electrolyte (GPE) was obtained, resulting in an all-inkjet-printed symmetrical capacitor (a-IJPSC). The highest ionic conductivity (0.60 mS/cm) was achieved with 10 wt.% of acrylamide content, and the capacitance retention was investigated both at rest (flat) and under bending conditions. The flat a-IJPSC textile-based device showed the areal capacitance of 0.89 mF/cm2 averaged on 2k cycles. Finally, an array of a-IJPSCs were demonstrated to be feasible as both a textile-based energy storage and micro-power source unit able to power a blue LED for several seconds.

Over the past decades, the semiconductor industry managed to continuously increase performance at an impressive, steady rate by scaling all parts of the integrated devices to nanometer-size dimensions, thereby enormously increasing the number of transistors on the chip as well as decreasing the dimensions of the metallization [1]. Presently, Cu constitutes the largest material fraction as conductor in damascene trenches which can be deposited by electrochemical deposition (ECD) or electroless deposition (ELD) [2 – 6]. For next-generation interconnects, the material properties (electromigration) of Cu render it unreliable for producing ever more performant chips. Additionally, the necessity of a diffusion barrier layer for Cu strongly increases line resistance and negatively impacts device performance upon further down-scaling. Recently, various alternative metals, such as ruthenium, rhodium, and molybdenum, have been studied and start to be implemented to tackle performance losses due to the small dimensions of the metal structures [7 – 9]. Consequently, both wet-chemical deposition as well as controlled etching of these metals has become of interest [10 – 12]. In our contribution, we present results of the development of an electroless deposition bath for rhodium, using ruthenium (II) hexammine as reducing agent. An electrochemical characterization of the anodic and cathodic reactions involved was performed in hydrochloric acid and ammonium chloride solutions. The stability of Rh3+ and [Ru(NH3)6]2+ was monitored using UV-vis spectroscopy. It was found that under oxygen-free conditions the hexammine complex can be kept stable in the ammonium-containing solution. Initially, deposition experiments were performed on PVD-Pt blanket thin films, for which a non-uniform coverage was observed. Therefore, to enhance the nucleation of the ELD process, we first deposited a thin Rh layer by electrochemical deposition, after which Rh was deposited using our ELD bath. Transmission electron microscopy and elemental mapping was used to characterize the morphology and chemical composition, respectively. Upon thermal treatment (forming gas, 420 °C, 20 min) crystal grain growth was observed. Acknowledgements The authors would like to thank the partners of IMEC's Industrial Affiliation Program (IIAP) on Advanced Interconnects. References [1] D. Josell, S.H. Brongersma, and Z. Tőkei, Annual Review of Materials Research 39, 231 (2009), https://doi.org/10.1146/annurev-matsci-082908-145415 [2] Copper Electrodeposition for Nanofabrication of Electronics Devices, K. Kondo, R.N. Akolkar, D.P. Barkey, and M. Yokoi (editors), Springer (2014) [3] Y. Shacham-Diamand, T. Osaka, Y. Okinaka, A. Sugiyama, and V. Dubin, Microelectronic Engineering 132, 35 (2015), http://dx.doi.org/10.1016/j.mee.2014.09.003 [4] L. Yu, L. Guo, R. Preisser, and R. Akolkar, Journal of The Electrochemical Society 160 D3004 (2013), http://dx.doi.org/10.1149/2.002312jes [5] K. Venkatraman, A. Joi, Y. Dordi, and R. Akolkar, Electrochemistry Communications 91, 45 (2018), https://doi.org/10.1016/j.elecom.2018.05.007 [6] F. Inoue, H. Philipsen, A. Radisic, S. Armini, Y. Civale, P. Leunissen, M. Kondo, E. Webb, and S. Shingubara, Electrochimica Acta 100, 203 (2013), https://doi.org/10.1016/j.electacta.2013.03.106 [7] K. Sankaran, S. Clima, M. Mees, C. Adelmann, Z. Tőkei, and G. Pourtois, Interconnect Technology Conference / Advanced Metallization Conference (IITC/AMC), 2014 IEEE International (2014), https://doi.org/10.1109/IITC.2014.6831868 [8] L.G. Wen, P. Roussel, O.V. Pedreira, B. Briggs, B. Groven, S. Dutta, M. Popovici, N. Heylen, I. Ciofi, K. Vanstreels, F.W. Østerberg, O. Hansen, D.H. Petersen, K. Opsomer, C. Detavernier, C. Wilson, S. Van Elshocht, K. Croes, J. Bömmels, Z. Tőkei, and C. Adelmann, ACS Applied Materials & Interfaces 8, 26119 (2016), https://doi.org/10.1021/acsami.6b07181 [9] S. Dutta, S. Kundu, A. Gupta, G. Jamieson, J.F. Gomez Granados, J. Bömmels, C. Wilson, Z. Tőkei, and C. Adelmann, IEEE Electron Device Letters 38, 949 (2017), https://doi.org/10.1109/LED.2017.2709248 [10] Y. Gong and R. Akolkar, Journal of The Electrochemical Society, 167, 062510 (2020), http://dx.doi.org/10.1149/1945-7111/ab864b [11] H. Philipsen and W. Monnens, Electrochimica Acta 274, 306 (2018), https://doi.org/10.1016/j.electacta.2018.04.093 [12] H. Philipsen, N. Mouwen, S. Teck, W. Monnens, Q.T. Le, F. Holsteyns, and H. Struyf, Electrochimica Acta 306, 285 (2019), https://doi.org/10.1016/j.electacta.2019.03.065