Abstract
In this paper, the memristive switching behavior of Cu/ HfO2/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. HfO2 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 (Von, Ion, and Vreset) 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 Von of 3.0 V (±0.3) and mean reset voltage Vreset of −1.1 V (±0.5) over 50 consecutive sweep cycles. These devices exhibit a large Roff/Ron window (up to 104), 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 Ron 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.
Highlights
Among a plethora of different dielectric materials exhibiting resistive switching behavior[13,14,15], HfO2 has received much interest from the scientific community owing to its compatibility with the CMOS technology, low operating voltage, high dielectric constant and high thermodynamic stability[16,17,18]
Too little of PVP cannot prevent the macroscopic cracks that are induced by the thermal shrinkage which is caused by the densification of the metal oxide network, whilst high polymer contents, may induce a porogenic templating effect, by generating voids through liquid expulsion via phase separation[49]
This paper presented a novel and cost-effective sol-gel spin-coating method for the fabrication of memristive devices consisting of a (TE)-Cu/HfO2/p++ Si-(BE) stack
Summary
Among a plethora of different dielectric materials exhibiting resistive switching behavior[13,14,15], HfO2 has received much interest from the scientific community owing to its compatibility with the CMOS technology, low operating voltage, high dielectric constant and high thermodynamic stability[16,17,18]. Various techniques can be used to deposit HfO2 layers, including the atomic layer deposition (ALD)[19,25,27,28,29], pulsed laser deposition[30], metal organic and chemical vapor deposition (MOCVD or CVD)[31], physical deposition by magnetron sputtering[20,32,33,34] and more recently, sol-gel spin-coating method[35,36,37,38,39,40,41,42,43,44]. The ALD, CVD and sputtering techniques all provide a relatively good control over the deposited material properties and high yield. The statistical significance of the differences observed in the log(Ron) values is evaluated as a qualitative performance indicator of the gamma ray transducing capability of these memristive devices
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