In this paper, the memristive switching behavior of Cu/ HfO 2 /p ++ Si devices fabricated by an organic-polymer-assisted sol-gel spin-coating method, coupled with post-annealing and shadow-mask metal sputtering steps, is examined. HfO 2 layers of about 190 nm and 80 nm, are established using cost-effective spin-coating method, at deposition speeds of 2000 and 4000 rotations per minute (RPM), respectively. For two types of devices, the memristive characteristics ( V on , I on , and V reset ) and device-to-device electrical repeatability are primarily discussed in correlation with the oxide layer uniformity and thickness. The devices presented in this work exhibit an electroforming free and bipolar memory-resistive switching behavior that is typical of an Electrochemical Metallization (ECM) I-V fingerprint. The sample devices deposited at 4000 RPM generally show less variation in electrical performance parameters compared to those prepared at halved spin-coating speed. Typically, the samples prepared at 4000 RPM (n = 8) display a mean switching voltage V on of 3.0 V (±0.3) and mean reset voltage V reset of −1.1 V (±0.5) over 50 consecutive sweep cycles. These devices exhibit a large R off / R on window (up to 10 4 ), and sufficient electrical endurance and retention properties to be further examined for radiation sensing. As they exhibit less statistical uncertainty compared to the samples fabricated at 2000 RPM, the devices prepared at 4000 RPM are tested for the detection of soft gamma rays (emitted from low-activity Cs-137 and Am-241 radioactive sources), by assessing the variation in the on-state resistance value upon exposure. The analysis of the probability distributions of the logarithmic R on values measured over repeated ON-OFF cycles, before, during and after exposing the devices to radiation, demonstrate a statistical difference. These results pave the way for the fabrication and development of cost-effective soft-gamma ray detectors.

This study investigates the resistive switching (RS) behavior of Ag/HfO 2 (3 nm-thick)/SiO x (interfacial-layer)/Si devices. The findings are drawn from a systematic electrical and material characterization of the fabricated devices. Based on the current-time (I-t) and current-voltage (I-V) measurements, it is inferred that both metal and oxygen ion migration play a significant role in the switching events, leading to bipolar and unipolar switching modes depending on the biasing scheme. The results demonstrate two competing switching mechanisms taking place when the biasing voltage is increased beyond the RESET voltage in the bipolar mode. The devices are also shown to exhibit self-rectifying characteristics when the bias is applied to the Ag electrode. The proposed method of investigating the total charge passed through the device within the time to SET, during the I-t characterization, is particularly useful for identifying the current transport models governing the high-resistance state. The results reported in this manuscript provide useful insights into the control of RS behavior in this scientifically and technologically important material system. Developing a thorough understanding of the fundamental physics governing the observed RS behavior is a substantial step for the growing progress in the memristor device research, as well as for its potential exploitation in diverse CMOS-compatible applications.

This work reports on flexible cost-effective memristor device synthesis, using Pt/GO/Cu structure. The memristor is fabricated on flexible substrate and it preserves its switching ability at a bending angle of up to 60 • . Compared to the state of the art, in our fabrication method, the graphene oxide (GO) film is deposited directly to the device using spin coating. The fabricated memristor stack exhibits tunable volatility based on the used compliance current, which expands its application horizon for memory, computing and security schemes. In this work, the non-volatile regime along with the natural stochasticity of the switching behavior of the device, named SecureMem, are utilized for efficient true random number generation. A prototype of the full system interfacing with microcontroller is built to get SecureMem ready for integration with other circuits and systems. The randomness of the data generated by SecureMem prototype is confirmed by passing all National Institute of Standards and Technology tests without any post-processing or hardware overhead. SecureMem is considered a great asset as it provides new insights for highly efficient cost-effective hardware security in smart wearable devices.

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