Recently, Prof. Zhang Min and Wang Xiaofang, the corresponding author and the first author of our research group, published the research results entitled “performance enhancement and mechanism exploration of all carbon nanotube memory with hydrogenation and dehydration through supercritical carbon dioxide” on carbon.
Carbon nanotubes based non-volatile memories (NVMs) with excellent electronic properties can provide high bit density and energy efficiency. But with the limit of the process conditions, obtaining steep flanks with large hysteresis is still a challenge, while it is the prerequisite for stable program/erase/read operations. Herein, we adopt a novel treatment of supercritical CO2 (SCCO2) fluids to improve the performance of all-carbon-nanotube thin-film transistor (A-CNT-TFT) memory elements. By the treatment, the transfer characteristics of the A-CNT-TFTs achieve a 13.20 V hysteresis window, which is larger than 50% of the whole sweeping-voltage range. The disappearance of hump effect greatly improves the switching characteristics. The material analysis confirms that the SCCO2 fluids can reduce the defects in dielectric layer sufficiently and strengthen the connection between channel and gate dielectric. Furthermore, it is proposed that existence of hydroxyl groups in the carbon nanotubes contributes dominantly to the mechanism for charge storage, and the SCCO2 treatment enhances the charge storage by increasing the number of the hydroxyl groups. The work shows that the low-temperature SCCO2 treatment can better improve the performance of A-CNT-TFTs, which provides a promising option for nonvolatile charge storage memory devices.
In conclusion, the switching performance and charge storage property of the A-CNT-TFTs can be enhanced by SCCO2 treatment. The large and stable gate hysteresis as well as the low gate leakage current enable these transistors to fit for the NVM applications. The A-CNT-TFT based memory devices after SCCO2 treatment show a retention time longer than 1600 s and stable endurance characteristics over 1000 times. Material analysis for the dielectric layer and electrical measurements for the device indicate that the SCCO2 treatment can effectively eliminate the defects in the dielectric layer and enhance the adhesion between SiO2 and CNTs. Additionally, we have analyzed the mechanisms causing the hysteresis, and proposed a novel model to understand the process, from which the hysteresis is mainly induced by the hydroxyl groups in the CNTs, which can be improved by the SCCO2 treatment.