Translartion. Region: Russians Fedetion –
Source: Novosibirsk State University – Novosibirsk State University –
Research staff Analytical and technological research center “High technologies and nanostructured materials” Physics Department of NSU studied the mechanism of charge transport in metal-insulator-conductor structures based on germanosilicate glasses. They were the first in the world to discover the memristor effect or “memory effect” in these materials, studied their optoelectric properties, and are now investigating the processes that occur in them during the flow of current. The results of the research were published in the highly rated scientific journal of the first quartile Applied Physics Letters (Charge transport mechanism in [GeOx](z)[SiO2](1-z) based MIS structures, HTTPS: //d.org/10.1063/5.0240239).
Silicon oxide is the most common dielectric, it is used to produce various microcircuits. Silicon-germanium glasses are a mixture of silicon oxide and germanium oxide. Previously, scientists studied silicon oxides or germanium oxides separately. Scientists from the NSU ATIC FF were the first to decide to combine the properties of these two substances. Germanium oxide is characterized by low binding energy. This means that a memristor created using this material will be easier to switch and therefore will be more energy efficient. Silicon oxide has a more stable structure, so it is more durable and long-lasting – it can “survive” a greater number of rewriting cycles, which makes it suitable for use in the creation of new, more reliable memory elements. These qualities, inherent in two different compounds, were combined in germanosilicate glasses.
— Our research group has been studying germanosilicate glasses for over five years. At that time, we were the first in the world to discover the memristor effect in them, in other words, the memory switching effect, when a sample of germanosilicate film switches from one resistance state to another. And these states are stored for quite a long time. We observed several thousand switchings and came to the conclusion that it was necessary to study the mechanisms of transport transfer in such materials in order to further optimize the design of memristors based on them.
Our colleagues previously studied the mechanisms of transport transfer in silicon oxides and germanium oxides, but we decided to study them in a mixture of these compounds. In our article, we described the results of our work aimed at deepening the study of this new material and its main characteristics, as well as establishing the physics and root cause of its properties observed by us. We need to understand the mechanisms that operate for germanosilicate film materials and find out what processes occur in them during the passage of current, – explained Vladimir Volodin, a leading researcher at the Laboratory of Functional Diagnostics of Low-Dimensional Structures for Nanoelectronics, Department of the ATIC, Physics Faculty, NSU, a leading researcher at the A.V. Rzhanov Institute of Semiconductor Physics, SB RAS, professor of the Department of General Physics, Doctor of Physical and Mathematical Sciences.
To conduct the experiments, films of four compositions with different ratios of germanium and silicon oxides were grown. Then the scientists made special MIS structures (metal-insulator-semiconductor) with a very thin layer of germanosilicate glass and began conducting temperature studies of the current-voltage characteristics – the dependence of the current on the voltage. In this case, the researcher sets the voltage and then records the dependence of the current in the sample as it changes. The studies were conducted in a certain temperature range – from room temperature to 102 ° C. This range corresponds to the operating temperatures of the memristors. Based on these dependencies, the scientists modeled the properties of the studied samples, approximating the current-voltage characteristics using existing conductivity models. They used 8 recognized models of electrical conductivity in the world. One of them – the Current Limited by Space Charge (CLCS) – unlike the others, showed the most realistic parameters.
— Using the TLC, we can theoretically predict the parameters of the future memristor as one of the new memory types. We also have the ability, based on the TLC model, to more accurately determine the electric voltage and switching, that is, the operating range of the device we are modeling. In addition, we can predict the currents in each specific sample based on the parameters of its chemical composition, the thickness of the dielectric layers, and other specified model parameters. By superimposing different models on the measured volt-ampere dependence, in the TLC model we determined the energy and concentration of traps involved in charge transport quite accurately. We studied a series of samples with different ratios of germanium oxide and silicon oxide. And according to this dependence, we found that with an increase in the proportion of silicon oxide in the samples, the depth of the traps monotonically decreases. We determined that the concentration of traps does not change, at least not noticeably. More significant changes – by an order of magnitude or more – could become a reason for a negative assessment of the applicability of the model, rejecting its validity, the impossibility of applying it to calculations and experimental values, which would be an undesirable result, said Ivan Yushkov, a junior research fellow at the Laboratory of Functional Diagnostics of Low-Dimensional Structures for Nanoelectronics at the ATIC PF NSU, and a postgraduate student at the A. V. Rzhanov Institute of Semiconductor Physics of the Siberian Branch of the Russian Academy of Sciences.
The significance of the study is that its results allow researchers to determine the parameters of a memristor theoretically without growing a nanostructure. In addition, the main charge transport mechanism for most memristive dielectrics is also the SCLC. Firstly, this confirms that the SCLC model is applicable in silicon-germanium oxide films, as is mainly the case with memristors, and secondly, using such a model, it is possible to predict the parameters of future structures and devices, or at least regulate the parameters relative to the layered sample being grown.
-Our study is of value for fundamental science, because we received the mechanisms of transport in these films the first in the world, but there is also practical significance: no one has yet explored German-Slacat glasses with this composition, but we would like to get modern memory elements from this material, which would exceed the usual flash memory in the number Circulation cycles, durability, effectiveness and reliability. Currently, the technologies have reached the line when humanity from the flash memory squeezed the “maximum”: the maximum number of rewriting cycles, the maximum duration of use, the maximum volumes in the container per element have been achieved. Further, using the same technology, it is not possible to multiply the memory parameters of electronic devices. A new type of memory, like a membrane, can help overcome these restrictions. There are other types of memory, but it is the membrane that differs in that when it is used, it is possible to increase the number of rewriting cycles compared to flash memory. The flash memory has a maximum of 10⁶ rewriting cycles, and the membrane has up to 10¹2. In addition, there are publications in which the authors show that the memoristors have one more brief cycle in terms of duration: if the flash memory has a microsekud share, then the membrane has dozens of nanoseconds or even piccicals, that is, a thousand and a million times faster, respectively. So with the help of membrane, memory can become much more “fast -acting,” explained Ivan Yushkov.
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