Carbon material-based nanoelectronics

In this dissertation, I discuss the solution for the major challenge for carbon nanotube-based nanoelectronics, and explore the radio frequency application of carbon-based material including graphene and nanotube.;Chapter 1 is a brief introduction of carbon nanotube and graphene in electronics field as the foundation for the whole dissertation. Chapter 2 to 5 report the work I have finished in the past four and half years. Chapter 6 discusses the future directions of carbon-based nanoelectronics.;Chapter 2 reports a method we developed to obtain predominantly semiconducting nanotubes from direct CVD growth. By using isopropanol as the carbon feedstock, semiconducting nanotube purity of above 90% is achieved, which is unambiguously confirmed by both electrical and micro-Raman measurements. Mass spectrometric study was performed to elucidate the underlying chemical mechanism.;Chapter 3 presents a scalable method for fabrication of self-aligned graphene transistors by defining T-shaped gate on top of graphene, followed by self-aligned source and drain formation by depositing Pd with the T-gate as a shadow mask. This transistor design provides significant advantages such as elimination of misalignment, reduction of access resistance by minimizing ungated graphene, and reduced gate charging resistance. To achieve high yield scalable fabrication, we have combined the use of large-area graphene synthesis by chemical vapor deposition, wafer scale transfer, and e-beam lithography to deposit T-shaped top gates. The fabricated transistors with gate lengths in the range of 110 to 170 nm exhibited excellent performance with peak current density of 1.3 mA/mum and peak transconductance of 0.5 mS/mum, which is one of the highest transconductance values reported. In addition, the T-gate design enabled us to achieve graphene transistors with extrinsic current-gain cut-off frequency of 23 GHz and maximum oscillation frequency of 10 GHz. These results represent important steps toward self-aligned design of graphene transistors for various applications.;In Chapter 4, we introduce the self-aligned fabrication method for carbon nanotube RF transistors. In this way, the channel length can be scaled down to 140 nm which enables quasi ballistic transport, and the gate dielectric is reduced to 2-3 nm aluminum oxide, leading to quasi quantum capacitance operation. A current-gain cut-off frequency (ƒt) up to 22 GHz and a maximum oscillation frequency (ƒmax) of 10 GHz are demonstrated. Furthermore, the linearity properties of nanotube transistors are characterized by using the 1-dB compression point measurement with positive power gain for the first time, to our knowledge. Our work reveals that the importance and potential of separated semiconducting nanotubes for various RF applications.;Chapter 5 discusses about the aligned nanotube transistor study and further explores radio frequency circuit application of aligned nanotube array transistors. We constructed T-gate aligned nanotube array RF transistors with the extrinsic current-gain cut-off frequency of 25 GHz as the best on-chip performance for nanotube RF transistors reported to date. Correspondingly, the intrinsic current-gain cut-off frequency of 102 GHz was achieved after de-embedding, which is among the highest value for nanotube-based RF transistors.;In Chapter 6, future direction on carbon-based material nanoelectronincs is briefly discussed. In the field of radio frequency (RF) electronics, RF device design can be further optimized for better performance. Noise figure is another important figure of merit for RF transistors and circuits beside linearity. With the excellent transistor performance achieved in previous work, I propose to further realize amplifier circuit with positive gain such as low noise amplifier (LNA) and power amplifier (PA). Through combing the CMOS technology platform with the carbon-based radio frequency transistors, we can study the CMOS-Carbon hybrid radio frequency circuit to fulfill the advantage of the low cost for traditional CMOS technology and the high performance provided by carbon-based nanomaterial. It will be meaningful to further analyze the noise figure of the carbon nanotube-based as the important parameter of nanotube RF transistors. As an interesting topic, flexible analog electronics based on nanotube material based on T-gate design may have the potential in higher performance in flexible electronics field.;In summary, this dissertation starts from the material synthesis and preparation to the device and circuit application of carbon-based material. The electronic application shows the great potential of carbon-based material in the nanoelectronics and radio frequency electronics. It can be predicted that carbon-based material nanoelectronics is very promising for beyond silicon electronics due to the unique electronic properties. (Abstract shortened by UMI.).