Ultralong carbon nanotubes (CNTs) are in huge demand in many cutting-edge fields due to their macroscale lengths, perfect structures, and extraordinary properties, while their practical application is limited by the difficulties in their mass production. Herein, we report the synthesis of ultralong CNTs with a dramatically increased yield by a simple but efficient substrate interception and direction strategy (SIDS), which couples the advantages of floating-catalyst chemical vapor deposition with the flying-kite-like growth mechanism of ultralong CNTs. The SIDS-assisted approach prominently improves the catalyst utilization and significantly increases the yield. The areal density of the ultralong CNT arrays with length of over 1 cm reached a record-breaking value of ∼6700 CNTs mm-1, which is 2-3 orders of magnitude higher than the previously reported values obtained by traditional methods. The SIDS provides a solution for synthesizing high-quality ultralong CNTs with high yields, laying the foundation for their mass production.
Pressure sensors based on field-effect transistor mechanism has received a lot of attention from researchers, which can effectively suppress low contrast and crosstalk effects. In this paper, we demonstrate a pressure sensor based on carbon nanotube field-effect transistors and three-dimensional conformal force-sensitive top electrode with high sensitivity and easy integration. The high mobility field-effect transistor sensors were prepared using carbon nanotube films with 99.9999% semiconductor concentration as the channel material. Conformal carbon nanowall film on pyramidal micro-structure arrays worked as force-sensitive top electrode, the field-effect transistor sensor shows a sensitivity of 1019.19 kPa-1, much higher than piezoresistive sensor (the sensitivity of about 377.73 kPa-1) and capacitive sensor (the sensitivity of 115.78 kPa-1). And the sensitivity and range of the sensor can be adjusted by the force-sensitive layer orientation design. Additionally, the sensor’s response time is less than 30ms, the recovery time is about 30ms. The field-effect pressure sensor could detect ultra-low pressure (about 1.3 mg) of the chrysanthemum petals, and also could record the dynamic crawling process of the insect.
In this work, for the first time, we present a fully functional 3D stackable 1kb one-CNTFET-one-RRAM (1T1R) array with carbon nanotube (CNT) CMOS peripheral circuits. The 1T1R cells were fabricated with 1024 CNT NFETs and Ta 2 O 5 -based multi-bit RRAMs, while the peripheral circuits consisted of 747 CNT PFETs and 875 NFETs for the word line (WL) 7:128 decoder and 128 drivers. The entire array was fabricated using a low-temperature (≤300°C) process, enabling multiple layers of CNTFET/RRAM arrays to be vertically stacked in the BEOL to boost the integration density and chip functionality. Furthermore, this 1T1R digital memory array was then used as a BEOL buffer macro and monolithically 3D (M3D) integrated with another 128kb HfO 2 -based analog RRAM array and Si CMOS logic to accelerate the computing-in-memory (CIM). The fabricated M3D-CIM chip consisted of three functional layers, whose structural integrity and proper function was validated by extensive structural analysis and electrical measurements. To highlight the advantages of this M3D-CIM architecture, typical neural networks such as multi-layer perceptron (MLP) and ResNET32 were implemented, achieving a GPU-equivalent classification accuracy of up to 96.5% in image classification tasks while consuming 39× less energy. Therefore, this work demonstrates the tremendous potential of the CNT/RRAM-based M3D-CIM architecture for various artificial intelligence (AI) applications.
Wafer-scale fabrication of transistors is the prerequisite for practical applications of carbon nanotube (CNT) based electronics. In this work, we fabricated top-gated thin film transistors (TFTs) based on solution-derived CNT film prepared on a 2 in. substrate through a photolithography based process. In particular, we improved the gate dielectric layer in CNT TFTs through using a thin thermal oxidized Y2O3 film as a buffer layer before the growth of high-κHfO2 layer. The introduction of the Y2O3 film significantly enhanced the performance of CNT TFTs, including the improved on-state current and transconductance, lowered threshold voltage and subthreshold swing, and drastically enhanced carrier mobility, owing to the reduction of the interface state density and scattering centers. Quantitative extraction of the interface state density based on either capacitance-voltage measurements or subthreshold swing data further demonstrates that the introduction of the Y2O3 interlayer reduces the interface state density from 9.24 × 1012 cm−2 to 4.63 × 1012 cm−2 in the gate insulator.
The excellent performance and radiation-hardness potential of carbon nanotube (CNT) field effect transistors (CNTFETs) have attracted wide attention. However, top-gate structure CNTFETs, which are often used to make high-performance devices, have not been studied enough. In this paper, the total ionizing dose (TID) effect of the top-gate structure CNTFETs and the influence of the substrate on top-gate during irradiation are studied. The parameter degradation caused by the irradiation- and radiation-damage mechanisms of the top-gate P-type CNTFET were obtained by performing a Co-60 γ-ray irradiation test. The results indicate that the transfer curves of the top-gate P-type CNTFETs shift negatively, the threshold voltage and the transconductance decrease when TID increases, and the subthreshold swing decreases first and then increases with the increase in TID. The back-gate transistor is constructed by using the substrate as a back-gate, and the influence of back-gate bias on the characteristics of the top-gate transistor is tested. We also test the influence of TID irradiation on the characteristics of back-gate transistors, and reveal the effect of trapped charge introduced by radiation on the characteristics of top-gate transistors. In addition, the CNTFETs that we used have obvious hysteresis characteristics. After irradiation, the radiation-induced trapped charges generated in oxide and the OH groups generated by ionization of the CNT adsorbates aggravate the hysteresis characteristics of CNTFET, and the hysteresis window increases with the increase in TID.
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