Nitrogen-doped carbon nanotubes for self-powered memristive systems

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Abstract

Memristive devices are one of the promising candidates for creating neuromorphic systems due to the possibility of multilevel switching, low operating voltages and high scalability. However, as with any passive element, the memristor requires an external bias voltage to operate, which requires the inclusion of a power source in the circuit. In this regard, of great interest are works on the creation of self-powered memristive systems consisting of connecting in series a memristor and a nanogenerator that converts the energy of the external environment into electrical energy [1, 2]. Such a memristive system has a high potential for applications in aerospace and implantable electronics. At the moment, the first self-powered memristive and sensor systems based on metal oxides and piezoelectric nanogenerators (PENG) have already been developed [2]. The main problems in this area are to reduce the size of the nanogenerator and to match the output parameters of the nanogenerator and the input parameters of the memristor. In the framework of this work, these problems are being resolved by creating a self-powered memristive system based on nitrogen-doped carbon nanotubes (N-CNTs).

Previously, we studied the memristive properties of N-CNTs and showed that nanotubes demonstrate reproducible multilevel switching with a resistance ratio in the high- and low-resistance states (HRS/LRS) of about 4 ⋅ 105 [3, 4]. It was found that the memristive effect in N-CNTs is due to the incorporation of nitrogen atoms into the nanotube structure and the formation of an internal piezoelectric field [4]. As part of further studies, it was found that an array of vertically aligned N-CNTs is a promising material for creating PENG: the generated output voltage is hundreds of mV and the current generated by single nanotube reaches hundreds of nA [5]. The results obtained allow us to speak about the possibility of developing a self-powered memristive system by connecting in series a memristor and PENG based on N-CNTs.

To optimize the output characteristics of the PENG, in particular, the amplitude of the generated voltage, and the input switching voltage of the N-CNT-based memristor, studies were carried out to increase the piezoelectric response and reduce the switching voltage of the N-CNT resistance by changing the concentration of the dopant nitrogen in the nanotube growth process. It was found that it is necessary to grow N-CNTs with a doping nitrogen concentration of up to 12% and a high aspect ratio of length to diameter (more than 60) to create PENG with an output voltage of up to 2 V. These N-CNT parameters are provided at a low growth temperature (500–550 C°) and high ratio of acetylene and ammonia flows (1:5 - 1:6). On the contrary, the N-CNTs with a small aspect ratio (less than 30) and doping nitrogen concentrations of 4–6% are required for the manufacture of memristors with a minimum switching voltage (about 2 V), These N-CNT parameters are provided by increasing the growth temperature to 615 C° and reduction in growth time. The obtained results can be used in the development of self-powered memristive and sensor systems based on nitrogen-doped carbon nanotubes.

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Memristive devices are a promising candidate for creating neuromorphic systems because of their multilevel switching capability, low operating voltages, and high scalability. However, as with any passive element, the memristor necessitates an external bias voltage to operate, necessitating the incorporation of a power source in the circuit. Of considerable interest are studies involving the development of self-sustaining memristive systems that employ a memristor and a nanogenerator connected in series, which transforms energy from the surrounding environment into electrical energy [1, 2]. A memristive system shows significant potential for use in aerospace and implantable electronics. Currently, researchers have developed the initial self-powered memristive and sensor systems using metal oxides and piezoelectric nanogenerators (PENG) [2]. The major challenges in this field include downsizing the nanogenerator and ensuring that the output parameters of the nanogenerator match the input parameters of the memristor. In this study, we are addressing the aforementioned issues by developing a self-sustaining memristive system using nitrogen-doped carbon nanotubes (N-CNTs).

Previously, we investigated the memristive properties of N-CNTs and demonstrated their reproducible multilevel switching, with a resistance ratio in the high- and low-resistance states (HRS/LRS) of approximately 4×105 [3, 4]. Our findings revealed that the incorporation of nitrogen atoms into the nanotube structure and the formation of an internal piezoelectric field were responsible for the memristive effect in N-CNTs [4]. As part of our research, we discovered that an array of vertically aligned N-CNTs holds promise as a material for creating PENG. The resulting output voltage can reach hundreds of millivolts while the current generated by a single nanotube can exceed hundreds of nanoamperes [5]. These findings suggest the potential for developing a self-powered memristive system by connecting a memristor and a PENG based on N-CNTs in series.

To optimize the output characteristics of the PENG, specifically the amplitude of the generated voltage and the input switching voltage of the N-CNT-based memristor, experiments were conducted to enhance the piezoelectric response and lower the switching voltage of the N-CNT resistance. These experiments involved modifying the concentration of dopant nitrogen during the nanotube growth process. It is necessary to grow N-CNTs with a high aspect ratio of length to diameter (greater than 60) to create PENG with an output voltage of up to 2 V. The N-CNTs should be doped with nitrogen up to 12%, and growth should occur at a low temperature (500–550 °C) with a high ratio of acetylene and ammonia flows (1:5–1:6). On the other hand, the production of memristors with a minimum switching voltage (about 2 V) necessitates N-CNTs with a small aspect ratio (less than 30) and doping nitrogen concentrations of 4–6%. To obtain these N-CNT parameters, the growth temperature must be raised to 615 °C and the growth time reduced. The findings obtained could be used to fabricate nitrogen-doped carbon nanotube-based self-powered memristive and sensor systems.

ADDITIONAL INFORMATION

Authors’ contribution. All authors made a substantial contribution to the conception of the work, acquisition, analysis, interpretation of data for the work, drafting and revising the work, final approval of the version to be published and agree to be accountable for all aspects of the work.

Funding sources. The study was supported by the Russian Science Foundation grant No. 22-79-10163 at the Southern Federal University.

Competing interests. The authors declare that they have no competing interests.

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About the authors

M. V. Il'ina

Southern Federal University

Author for correspondence.
Email: mailina@sfedu.ru
Russian Federation, Taganrog

O. I. Soboleva

Southern Federal University

Email: mailina@sfedu.ru
Russian Federation, Taganrog

M. R. Polyvianova

Southern Federal University

Email: mailina@sfedu.ru
Russian Federation, Taganrog

O. I. Il'in

Southern Federal University

Email: mailina@sfedu.ru
Russian Federation, Taganrog

References

  1. Shi J, Wang Z, Tao Y, et al. Self-powered memristive systems for storage and neuromorphic computing. Front Neurosci. 2021;15:662457. doi: 10.3389/fnins.2021.662457
  2. Kim BY, Lee WH, Hwang HG, et al. Resistive switching memory integrated with nanogenerator for self-powered bioimplantable devices. Advanced Functional Materials. 2016;26(29):5211–5221. doi: 10.1002/adfm.201505569
  3. Il’ina MV, Il’in OI, Osotova OI, et al. Memristors based on strained multi-walled carbon nanotubes. Diamond and Related Materials. 2022;123:108858. doi: 10.1016/j.diamond.2022.108858
  4. Il’ina MV, Il’in OI, Osotova OI, et al. Memristive effect in nitrogen-doped carbon nanotubes. Nanobiotechnology Reports. 2021;16:821–828. doi: 10.1134/S2635167621060082
  5. Il’ina MV, Il’in OI, Osotova OI, et al. Pyrrole-like defects as origin of piezoelectric effect in nitrogen-doped carbon nanotubes. Carbon. 2022;190(312):348–358. doi: 10.1016/j.carbon.2022.01.014

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