Kangwei Zhang

Improvement of resistive switching characteristics in ZrO2 film by embedding a thin TiOx layer.

The stabilization of the resistive switching characteristics is important to resistive random access memory (RRAM) device development. In this paper, an alternative approach for improving resistive switching characteristics in ZrO(2)-based resistive memory devices has been investigated. Compared with the Cu/ZrO(2)/Pt structure device, by embedding a thin TiO(x) layer between the ZrO(2) and the Cu top electrode, the Cu/TiO(x)-ZrO(2)/Pt structure device exhibits much better resistive switching characteristics. The improvement of the resistive switching characteristics in the Cu/TiO(x)-ZrO(2)/Pt structure device might be attributed to the modulation of the barrier height at the electrode/oxide interfaces.

Bipolar one diode–one resistor integration for high-density resistive memory applications

Different from conventional unipolar-type 1D-1R RRAM devices, a bipolar-type 1D-1R memory device concept is proposed and successfully demonstrated by the integration of Ni/TiOx/Ti diode and Pt/HfO2/Cu bipolar RRAM cell to suppress the undesired sneak current in a cross-point array. The bipolar 1D-1R memory device not only achieves self-compliance resistive switching characteristics by the reverse bias current of the Ni/TiOx/Ti diode, but also exhibits excellent bipolar resistive switching characteristics such as uniform switching, satisfactory data retention, and excellent scalability, which give it high potentiality for high-density integrated nonvolatile memory applications.

Investigation on the RESET switching mechanism of bipolar Cu/HfO2/Pt RRAM devices with a statistical methodology

The RESET switching of bipolar Cu/HfO2/Pt resistance random access memory (RRAM) is investigated. With a statistical methodology, we systematically analyze the RESET voltage (VRESET) and RESET current (IRESET). VRESET shows a U-shape distribution as a function of RON according to the scatter plot of the raw experimental data. After data correction by a series resistance (RS), VRESET is nearly constant, while IRESET decreases linearly with RCF. These behaviours are consistent with the thermal dissolution model of RESET. Moreover, the IRESET and VRESET distributions are strongly affected by the RON distribution. Using a ?resistance screening? method, the IRESET and VRESET distributions are found to be compatible with the Weibull distribution model. The Weibull slopes of the VRESET and IRESET distributions are independent of RCF, indicating that the RESET point corresponds to the initial phase of conductive filament (CF) dissolution, according to our cell-based model for the unipolar RESET of RRAM devices. The scale factor of the VRESET distributions is roughly constant, while that of the IRESET distributions scale with 1/RCF. Accordingly, the RESET switching of the HfO2-based solid electrolyte memory is compatible with the thermal dissolution mechanism, improving our understanding on the physics of resistive switching of RRAM devices.

Unexpected surface implanted layer in static random access memory devices observed by microwave impedance microscope

Real-space mapping of doping concentration in semiconductor devices is of great importance for the microelectronics industry. In this work, a scanning microwave impedance microscope (MIM) is employed to resolve the local conductivity distribution of a static random access memory sample. The MIM electronics can also be adjusted to the scanning capacitance microscopy (SCM) mode, allowing both measurements on the same region. Interestingly, while the conventional SCM images match the nominal device structure, the MIM results display certain unexpected features, which originate from a thin layer of the dopant ions penetrating through the protective layers during the heavy implantation steps.

Investigation of One-Dimensional Thickness Scaling on

Scaling is a key issue for resistive switching (RS) memory before commercialization. In this letter, we reveal the impact of electrode diffusion on the device performance as the thickness of RS material scaled. Serious deterioration of on/off ratio and device yield was observed when the material thickness scaled below 3 nm. A new method of two-step electrode deposition accompanied with reoxidization process was employed to overcome this problem. Significant improvements of device performance such as forming free, low RESET current (~1 μA), high on/off ratio (>; 100) and 100% device yield were achieved thereafter.

\hbox{Cu/HfO}_{x}/\hbox{Pt}

In this paper, the effect of a low constant current stress (CCS) treatment on the performance of a Cu/ZrO2/Pt resistive switching device is investigated. The conductance of the device increases about two orders of magnitude after CCS treatment, indicating that some defects are introduced into the ZrO2 matrix and the CCS treatment can be regarded as an electrical doping process. Benefiting from these introduced defects, better resistive switching performance is obtained after CCS treatment, including low forming voltage, low reset current, uniform resistive switching and good endurance characteristics.

Resistive Switching Device Performance

The RESET switching of an oxide-based bipolar solid electrolyte memory with the Cu/HfO₂/Pt structure is studied in this work. The parameters of the RESET point defined at the maximum of the RESET current evolution, RESET voltage (V_RESET) and RESET current (I_RESET), are analyzed with a statistical method. The experimental raw data show a U-shape relation between VRESET and the ON-state resistance (R_ON). After data correction by a series resistance (R_S), V_RESET is roughly constant and the RESET current (IRESET) is inversely proportional to R_ON. These behaviors are in agreement with the thermal dissolution model of RESET. The further statistical analyses in terms of Weibull distributions show that the R_ON distribution has a strong influence on the I_RESET and V_RESET distributions. By using a “resistance screening” method, the I_RESET and V_RESET distributions are found to be compatible with a Weibull model. The Weibull slopes of the I_RESET and V_RESET are independent on R_ON, indicating that the RESET point corresponds to the initial phase of CF dissolution, according to our cell-based RESET model for the unipolar VCM (valence change mechanism) device. On the other hand, the scale factor of the V_RESET distribution (V_RESET63%) is roughly constant, while the scale factor of the I_RESET (I_RESET63%) is inversely proportional to R_ON, which is consistent with the thermal dissolution model of RESET and our cell-based RESET model. The RESET switching of the studied oxide-based bipolar solid electrolyte memory is dominated by the thermal dissolution mechanism.