Abstract
The Resistive RAM (RRAM) technology is currently in a level of maturity that calls for its integration into CMOS compatible memory arrays. This CMOS integration requires a perfect understanding of the cells performance and reliability in relation to the deposition processes used for their manufacturing. In this paper, the impact of the precursor chemistries and process conditions on the performance of HfO2 based memristive cells is studied. An extensive characterization of HfO2 based 1T1R cells, a comparison of the cell-to-cell variability, and reliability study is performed. The cells’ behaviors during forming, set, and reset operations are monitored in order to relate their features to conductive filament properties and process-induced variability of the switching parameters. The modeling of the high resistance state (HRS) is performed by applying the Quantum-Point Contact model to assess the link between the deposition condition and the precursor chemistry with the resulting physical cells characteristics.
Highlights
Resistive Random Access Memories (RRAM) gathered increasing interest in the last years[1,2]
The physical analysis as X-Ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) of the HfO2 films were performed after finalizing the complete CMOS process flow
At the deposition temperature of 150 °C, the HfO2 film was grown in the amorphous state, which remains stable at post-annealing temperatures of 400 °C27
Summary
In order to study the impact of the HfO2 deposition condition on the switching behavior systematically, the pristine currents of the memristive devices at 1 Volt are investigated primarily. The films deposited by the process conditions C and D are the ones where the pristine currents (see Fig. 3) are the largest caused by the high carbon content and the low oxygen concentration in the HfO2 layers. Considering the variances, illustrated, devices B still demonstrate the lowest values and the highest stability during cycling, confirming that the carbon content plays a fundamental role on cells’ performance and reliability[21] This means, when the conductive filaments in the devices B are correctly formed, the subsequent set and reset operations are not impacted by carbon impurities, resulting in reduced dispersion of the switching voltage values. This negative impact could be related to the creation of partially formed filaments involving carbon defects, which prevent the complete growth of the oxygen vacancy based conductive filament growth. By applying the QPC model to the DC-switching curves, the variability is affected by he microstructure of the deposited dielectric film as well as its carbon content
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