The switching ratio and stability of ITO/HfO₂/SiO₂/Ag memristors improved by SiO₂ functional layer

The randomness of conductive filament growth and rupture has always been a key factor affecting the switching ratio and stability of memristors. In this paper, an ITO/HfO₂/SiO₂/Ag memristor with an HfO₂/SiO₂ heterojunction as the functional layer was fabricated on an ITO substrate via magnetron sputtering. Compared to single-layer HfO₂ memristors, the switching ratio was improved by approximately 10 times, reaching a maximum of 50, and the switching ratio remained above 20 for over 6000 seconds, showing significant enhancement in stability. XPS analysis was performed on the device cross-section, obtaining both the full spectrum and the fine spectrum of the O1s energy level. The full spectrum showed that the Ag content in the SiO₂ functional layer was higher than that in the HfO₂ layer, and the O1s spectrum indicated a lower concentration of oxygen vacancies. Through fitting the device’s I-V curve to analyze its conduction mechanism, it was found that the conduction mechanism in the positive voltage region follows Ohmic conduction, while in the negative voltage region, it aligns with the space-charge-limited current mechanism. Based on this, a physical model was proposed to explain the reset/set memory behavior of the device. By varying the sputtering time to change the thickness of the SiO₂ layer and comparing the I-V characteristic curves for different sputtering times, the optimal sputtering time for SiO₂ was determined to be 10 minutes.