Printed Memristors for Memory, Computing and Hardware Security

Memristors are two-terminal electronic devices whose resistance can be changed upon the application of an electrical field. The device could be potentially used for non-volatile memory, novel computing paradigms, and hardware security. Currently, most of the reported memristors are fabricated by traditional thin film techniques such as vacuum deposition methods, photolithography, or CMOS-compatible processes. Additive manufacturing techniques like inkjet or laser printing have only recently been demonstrated to be feasible for memristor fabrication. This has the advantage of efficient material usage, cost-effectiveness, and rapid prototyping capability.<br/><br/>We demonstrate three types of memristors fabricated either by inkjet printing or laser printing. The first device is a fully inkjet-printed symmetric Ag/ZnO/Ag structure which shows digital resistive switching. Our utilized ZnO precursor ink is water-based and requires a post-deposition annealing step. The fully inkjet-printed memristor exhibits excellent parameters such as a high R_off/R_on ratio of 10⁷, a long retention time of over 10⁴ seconds, good endurance, and almost forming-free characteristics, which are advantageous for non-volatile memory applications. The second device is partially inkjet-printed and based on Ag/WO_3-x/Au. The device itself can be probed dynamically by applying a bias to exhibit digital resistive switching, caused by conductive filaments, or it can be operated as an analog resistive switching device without forming a conducting filament. The analog resistive switching properties are utilized to mimic the behavior of a biological synapse or neuron. This includes short-term plasticity, metaplasticity, and integration of several input signals. The third presented device is a fully laser-printed memristor formed by Ag and Pt as the electrodes and ZnO as the active layer. The semiconductor ZnO is converted from a novel precursor ink through local laser-induced hydrothermal synthesis. In addition, the memristors are integrated into a 6×6 fully-laser printed crossbar structure and successfully utilized for physical unclonable function (PUF) implementation.<br/><br/>In summary, we have demonstrated inkjet-printed and laser-printed memristors fabricated in a facile, rapid, and material-efficient approach. The introduced printed memristors show excellent device performance and are hence promising candidates for applications in non-volatile memory, neuromorphic computing, and hardware security.