Vertically-waveguide-coupled BaTiO₃-based microdisk optical resonator equipped with the functionality of resistive random-access memory (ReRAM)

The transparent ITO/BaTiO3/ITO Resistive Random-Access Memory (ReRAM) vertically integrated with bus waveguides situated underneath is successfully realized as a ReRAM-based microdisk resonator fabricated on lithium niobate (LiNbO3) substrate. The radio-frequency sputtering technique was adopted for the subsequent depositions of the transparent ITO and BaTiO3 layers, while a proton-exchange method was utilized to fabricate the bus waveguides immersed in LiNbO3. The ReRAM-based microdisk resonator thus designed and fabricated has the novel functionality of memory and optical spectral filtering combined dually. As the ReRAM microdisk resonator is electronically switched between the two different memory states, or the high-resistance state (HRS) and low-resistance state (LRS), the output spectral observed at both the through and drop ports are noticeably shifted with one another before and after subjecting the ReRAM to a required forming process. Specifically, the spectral shift associated with the LRS state of ReRAM between the through and drop port terminal was approximately 0.4 nm, while roughly 0.6 nm was measured with the HRS state of ReRAM between the same two terminals. The resultant light wave filtering allows the spectrum of the interest to be selectively tuned as the ReRAM device dimensions are varied. Utilizing the different thin-film materials for ReRAM fabrication may also prove beneficial for spectral tuning. In light of different spectral shifts observed, the particular memory state of ReRAM could uniquely be interrogated by an optical means. Our discovery heralds a new era for realizing one of the novel optical memory devices reported to date.