Overview of carbon-based circuits and systems

This paper presents an overview of the state of the art on carbon-based circuits and systems made up of carbon nanotubes and graphene transistors. A tutorial description of the most important devices and their potential benefits and limitations is given, trying to identify their suitability to implement analog and digital circuits and systems. Main electrical models reported so far for the design of carbon-based field-effect devices are surveyed, and the main sizing parameters required to implement such devices in practical integrated circuits are analyzed. The solutions proposed by cutting-edge integrated circuits and devices are discussed, identifying current trends, challenges and opportunities for the circuits and systems community1

Carbon Nanotube Interconnect Modeling for Very Large Scale Integrated Circuits

In this research, we have studied and analyzed the physical and electrical properties of carbon nanotubes. Based on the reported models for current transport behavior in non-ballistic CNT-FETs, we have built a dynamic model for non-ballistic CNT-FETs. We have also extended the surface potential model of a non-ballistic CNT-FET to a ballistic CNT-FET and developed a current transport model for ballistic CNT-FETs. We have studied the current transport in metallic carbon nanotubes. By considering the electron-electron interactions, we have modified two-dimensional fluid model for electron transport to build a semi-classical one-dimensional fluid model to describe the electron transport in carbon nanotubes, which is regarded as one-dimensional system. Besides its accuracy compared with two-dimensional fluid model and Lüttinger liquid theory, one-dimensional fluid model is simple in mathematical modeling and easier to extend for electronic transport modeling of multi-walled carbon nanotubes and single-walled carbon nanotube bundles as interconnections. Based on our reported one-dimensional fluid model, we have calculated the parameters of the transmission line model for the interconnection wires made of single-walled carbon nanotube, multi-walled carbon nanotube and single-walled carbon nanotube bundle. The parameters calculated from these models show close agreements with experiments and other proposed models. We have also implemented these models to study carbon nanotube for on-chip wire inductors and it application in design of LC voltage-controlled oscillators. By using these CNT-FET models and CNT interconnects models, we have studied the behavior of CNT based integrated circuits, such as the inverter, ring oscillator, energy recovery logic; and faults in CNT based circuits

Current transport modeling of carbon nanotube field effect transistors for analysis and design of integrated circuits

The purpose of this study was to develop a complete current transport model for carbon nanotube field effect transistors (CNT-FETs) applicable in the analysis and design of integrated circuits. The model was derived by investigating the electronic structure of carbon nanotubes and using basic laws of electrostatics describing a field effect transistor. We first derived analytical expressions for the carrier concentration in carbon nanotubes for different chiral vectors (n,m) by studying and characterizing their electronic structure. Results showed a strong relation to the diameter and wrapping angle of carbon nanotubes. The charge distribution in a CNT-FET is characterized from the charge neutrality and potential balance conditions. Mathematical techniques are used to derive analytically approximated equations describing the carbon nanotube potential in terms of the terminal voltages. These equations are validated by comparing them with the respective numerical solutions; furthermore, the expressions for the carbon nanotube potential are used to derive current transport equations for normal and subthreshold operations. Threshold and saturation voltages expressions are each derived in the process and the I-V characteristics for CNT-FETs are calculated using different combinations of chiral vectors. Results showed a strong dependence of the I-V characteristics on the wrapping angle and diameter of carbon nanotubes, as expected from the carrier concentration modeling. Results were also compared with available experimental data showing close agreement within the limitations and approximations used in the analysis. In addition, the current model equations were used to generate the voltage transfer characteristics for basic logic circuits based on complementary CNT-FETs. The voltage transfer characteristics exhibit characteristics similar to the voltage transfer characteristics of standard CMOS logic devices, with a sharp transition near the logic threshold voltage depending on the input conditions. A small-signal radio frequency (rf) model was also developed and it is shown to have cut-off frequencies in the upper GHz range with a strong dependence on the chiral vector and corresponding transconductance (gm). Finally, due to the rapid growth of carbon nanotubes as bio- and chemical sensing devices, we have also presented, using our current model equations, possible methods to interpret and analyze CNT-FETs when utilized as biosensors

Highly ordered nanowire arrays on plastic substrates for ultrasensitive flexible chemical sensors

The development of a robust method for integrating high-performance semiconductors on flexible plastics could enable exciting avenues in fundamental research and novel applications. One area of vital relevance is chemical and biological sensing, which if implemented on biocompatible substrates, could yield breakthroughs in implantable or wearable monitoring systems. Semiconducting nanowires (and nanotubes) are particularly sensitive chemical sensors because of their high surface-to-volume ratios. Here, we present a scalable and parallel process for transferring hundreds of pre-aligned silicon nanowires onto plastic to yield highly ordered films for low-power sensor chips. The nanowires are excellent field-effect transistors, and, as sensors, exhibit parts-per-billion sensitivity to NO_2, a hazardous pollutant. We also use SiO_2 surface chemistries to construct a 'nano-electronic nose' library, which can distinguish acetone and hexane vapours via distributed responses. The excellent sensing performance coupled with bendable plastic could open up opportunities in portable, wearable or even implantable sensors

Transistors as an Emerging Platform for Portable Amplified Biodetection in Preventive Personalized Point‐of‐Care Testing

The impressive improvement in biomolecular detection has gone from simple chemical methods to sophisticated high throughput laboratory machines capable of accurately measuring the complex biological components and interactions. In the following chapter, we focus our attention on transistor‐based devices as an emerging platform for easy‐to‐use, portable amplified biodetection for preventive personalized medical applications and point‐of‐care testing. Electronic sensing devices comprise biosensors based on field‐effect transistors (bio‐FETs) and organic electrochemical transistors (OECTs). Transistor sensing devices can transduce electronic and ionic signals thereby creating an effective human‐machine communication channel. In this chapter, we survey the progress done on the development of transistor innovative concepts to examine biological processes, i.e., biosensors integrated with textiles, flexible substrates, and biocompatible materials. Electrochemical and field‐effect transistors can operate at low voltages possibly serving for highly sensitive, selective, and real‐time sensing devices. The exploration of biosensors integrates different disciplines such as organic electronics, biology, electrochemistry, and materials science

Nano-Bio Hybrid Electronic Sensors for Chemical Detection and Disease Diagnostics

The need to detect low concentrations of chemical or biological targets is ubiquitous in environmental monitoring and biomedical applications. The goal of this work was to address challenges in this arena by combining nanomaterials grown via scalable techniques with chemical receptors optimized for the detection problem at hand. Advances were made in the CVD growth of graphene, carbon nanotubes and molybdenum disulfide. Field effect transistors using these materials as the channel were fabricated using methods designed to avoid contamination of the nanomaterial surfaces. These devices were used to read out electronic signatures of binding events of molecular targets in both vapor and solution phases. Single-stranded DNA functionalized graphene and carbon nanotubes were shown to be versatile receptors for a wide variety of volatile molecular targets, with characteristic responses that depended on the DNA sequence and the identity of the target molecule, observable down to part-per-billion concentrations. This technology was applied to increasingly difficult detection challenges, culminating in a study of blood plasma samples from patients with ovarian cancer. By working with large arrays of devices and studying the devices\u27 responses to pooled plasma samples and plasma samples from 24 individuals, sufficient data was collected to identify statistically robust patterns that allow samples to be classified as coming from individuals who are healthy or have either benign or malignant ovarian tumors. Solution-phase detection experiments focused on the design of surface linkers and specific receptors for medically relevant molecular targets. A non-covalent linker was used to attach a known glucose receptor to carbon nanotubes and the resulting hybrid was shown to be sensitive to glucose at the low concentrations found in saliva, opening up a potential pathway to glucose monitoring without the need for drawing blood. In separate experiments, molybdenum disulfide transistors were functionalized with a re-engineered variant of a μ-opiod receptor, a cell membrane protein that binds opiods and regulates pain and reward signaling in the body. The resulting devices were shown to bind opiods with affinities that agree with measurements in the native state. This result could enable not only an advanced opiod sensor but moreover could be generalized into a solid-state drug testing platform, allowing the interactions of novel pharmaceuticals and their target proteins to be read out electronically. Such a system could have high throughput due to the quick measurement, scalable device fabrication and high sensitivity of the molybdenum disulfide transistor