Investigation of Resistive Switching Characteristics and Mechanisms of Strontium Zirconate Memory Devices
|關鍵字:||非揮發性記憶體;電阻式記憶體;鋯酸鍶;鈣鈦礦;Nonvolatile Memory;Resistive Random Access Memory;Strontium Zirconate;Perovskite|
With the popularity of the portable equipment such as mobile phone, digital camera, and MP3 player, the demand of nonvolatile memory has greatly increased in recent years. For ideal NVM devices, it is expected to possess the advantages of low operation voltage, low power consumption, high operation speed, high endurance, long retention time, nondestructive readout, simple structure, and low cost. However, there is no NVM device completely including the above properties up to now. Flash memory, the mainstream of NVM devices nowadays, suffers some severe issues including high operation voltage, high power consumption, and low operation speed. In addition, as the continuous device scaling down, it will meet the physical scaling limitation in the near future, further leading to poor retention time and coupling interference effect. Consequently, several high-potential candidates for the next-generation NVM application, including ferroelectric random access memory, magnetroresistive random access memory, phase change random access memory, and resistive random access memory (RRAM) have been proposed to replace flash memory. Among them, RRAM possesses the excellent advantages, including low operation voltage, low operation power, high operation speed, high scalability, good endurance, long retention time, nondestructive readout, simple structure, and low cost. As a result, RRAM has been investigated for the commercial NVM application. Chapter 1 introduces various types of novel memory devices and reviews current status of the resistive switching memory based on the material categories. Some important effects and the possible resistive switching mechanisms are organized and discussed in detail. The detailed experimental procedures of fabrication of SrZrO3 (SZO)-based memory devices, the principles of material analyses, and the related electrical measurements are all presented in Chapter 2 of this dissertation. In Chapter 3, the effects of vanadium doping on resistive switching characteristics and mechanism of RF-sputtered SZO-based thin films are investigated. The physical and electrical properties of SZO-based thin films, such as the forming voltage, turn-on voltage, HRS resistance, dielectric constant, and , are modulated by vanadium doping due to the suppression of oxygen vacancy formation. Although SZO thin films exhibited lower forming voltage and lower turn-on voltage than those of the vanadium-doped SZO thin films, the large dispersion of resistive switching parameters and the low device yield in SZO thin films limit their development in realizing the practical NVM application. In Chapter 4, the O2-600 oC RTA process is used to give a narrower distribution in the SZO bulk thin films, further reducing the large dispersion of resistive switching parameters and increasing the device yield in SZO thin films. O2-annealing process is reported to improve and stabilize resistive switching behavior of SZO-based memory devices, but it could increase forming voltage and turn-on voltage. In Chapter 5, embedding Pt metal layer into SZO thin films can significantly reduce forming voltage and turn-on voltage to -3.5 V and |2.3| V, respectively, due to the formation of Pt clusters. However, this E-Pt process is more complicated than the conventional process of silicon-based devices. In Chapter 6, the resistive switching region can be effectively reduced and localized within the oxygen-rich layer of SZO devices by the oxygen flow control process, leading to the low operation voltage and small dispersions of resistive switching parameters. Finally, Chapter 7 summarizes the finding and contributions of this dissertation and the future works are suggested for the further RRAM research.
|Appears in Collections:||Thesis|