La施主掺杂SrTiO_3单晶的阻变性能研究

以La施主掺杂SrTiO_3(La STO)单晶为样品,制备了Pt/LaSTO/In结构存储器件.通过一系列电学测试,发现该器件具有稳定的多级阻变现象,最大开关比为10~4;高低阻电流-电压关系曲线的拟合分析表明,高阻时存在界面势垒,而低阻时满足电子隧穿模型特性.电子顺磁共振研究表明LaSTO单晶内存在带正电的空穴缺陷中心.综合分析证明器件的高低阻之间的转变由界面空位缺陷导致的电子俘获与去俘获引起.此外发现光照会对LaSTO单晶的阻值产生影响.该实验结果为LaSTO单晶在阻变存储器件中的应用提供了理论和技术指导.

Resistance switching of La doped SrTiO3 single crystals

To date, there has not been a consensus about the resistance switching mechanism of donor-doped SrTiO₃. The La doped STO (LaSTO) single crystal is a donor-doped material and has an N-type conductivity since La³⁺ could easily substitute Sr²⁺. In this study, the Pt/LaSTO/In memory device is fabricated based on (100) LaSTO single crystal with 0.5 wt% La doping. Through a series of electrical tests, it is found that the Pt/LaSTO/In memory device has a stable multi-stage resistive switching property, and the maximum switching ratio is 10⁴. The fitting I-V curve at the high resistance state (HRS) shows that there is an interface barrier in the memory device. However, the fitting I-V curve at low resistance state (LRS) is consistent with the characteristic of the electron tunneling model. The spectrum of electron paramagnetic resonance (EPR) indicates that LaSTO single crystal has only one EPR signal of g=2.012. Considering the fact that Δg=g_obs-g_e (where g_obs is the g factor obtained from the sample, g_e=2.0023 is the free electron value) is positive, the signal can be regarded as being due to hole center. The hole center is positively charged and can trap electrons. Comprehensive analysis indicates that the transition between the HRS and LRS of the device can be explained by the modulation of Pt/LaSTO interface barrier, which is caused by the electron trapping and detrapping of interfacial vacancy defects. In addition, it is found that illumination could reduce the low resistance of the Pt/LaSTO/In device. This is due to the photo-generated carriers causing a tunneling current because of the narrow Schottky barrier when the Pt/LaSTO/In device is in the LRS. However, the Schottky barrier plays a leading role in HRS, so the change in carrier concentration, caused by illumination, does not lead to a significant change in current for HRS. The experimental results provide theoretical and technical guidance for the applications of LaSTO single crystals in resistive memory devices.