Filament-type HfO₂-based RRAM has been considered as one of the most promising candidates for future non-volatile memories. Further improvement of the stability, particularly at the “OFF” state, of such devices is mainly hindered by resistance variation induced by the uncontrolled oxygen vacancies distribution and filament growth in HfO₂films. We report highly stable endurance of TiN/Ti/HfO₂/Si-tip RRAM devices using a CMOS compatible nanotip method. Simulations indicate that the nanotip bottom electrode provides a local confinement for the electrical field and ionic current density; thus a nano-confinement for the oxygen vacancy distribution and nano-filament location is created by this approach. Conductive atomic force microscopy measurements confirm that the filaments form only on the nanotip region. Resistance switching by using pulses shows highly stable endurance for both ON and OFF modes, thanks to the geometric confinement of the conductive path and filament only above the nanotip. This nano-engineering approach opens a new pathway to realize forming-free RRAM devices with improved stability and reliability.

Electrochemical impedance spectroscopy (EIS) is of fundamental importance for characterization and monitoring of rechargeable batteries in automotive, energy storage, and electronics sectors. In this article, a low-complexity practical system for EIS of batteries is presented, and the uncertainty associated with its measurement results is analyzed. The system is based on a voltage-controlled current generator and the acquisition of current and voltage signals from the battery under test. Arbitrary current waveforms can be generated, and thus the system is flexible and reconfigurable. In particular, a broadband multisine excitation signal is used, enabling faster measurements with respect to the conventional stepped sine approach. The proposed system is characterized by repeated measurements on a 18 650 lithium-ion battery. Moreover, it is validated by comparison with a commercial benchtop instrument, and with the ground truth provided by a discrete component Randles circuit. Results show that the system is able to accurately and repeatably measure the impedance of a battery in a wide frequency range from 0.05 Hz to 1 kHz. Furthermore, it provides results that are consistent with the commercial instrument and with the ground truth of the $R$ – $C$ Randles circuit. Therefore, the proposed system using the broadband multisine method is suitable for implementing fast and inexpensive monitoring capabilities in smart battery management systems.

Online diagnostic of lithium-ion battery (LIB) cells may have significant impact on chemical energy storage systems. Electrochemical impedance spectroscopy (EIS) is widely used for the characterization of LIBs and could be the most appropriate technique for online diagnostic, but its response time should be shortened. This work investigates the usage of multisine excitation to shorten the measurement time and simplify the hardware implementation for EIS of battery cells. Two types of multisine binary sequences are considered: sigma–delta modulated multisine sequences (SDMSs) and maximum length binary sequences (MLBSs). Their applicability to online and in situ EIS monitoring is evaluated by designing a measurement architecture also suitable to be implemented in a system-on-chip. The calibrated measurement system is compared with a benchtop reference instrument, reporting an RMSE deviation smaller than 5% in the frequency range of interest 1–200 Hz. The realized system is then used for online monitoring of the discharge process of a commercial 18650 LIB cell. The two proposed sequences are compared in terms of accuracy using a digital battery emulator circuit. Both the sequences demonstrated to be suitable for fast measurement and simple hardware integration, enabling online in situ EIS monitoring at cell level.