Wen-Yan Yin

Circuit Modeling and Performance Analysis of Multi-Walled Carbon Nanotube Interconnects

Metallic carbon nanotubes (CNTs) have received much attention for their unique characteristics as a possible alternative to Cu interconnects in future ICs. Until this date, while almost all fabrication efforts have been directed toward multiwalled CNT (MWCNT) interconnects, there is a lack of MWCNT modeling work. This paper presents, for the first time, a detailed investigation of MWCNT-based interconnect performance. A compact equivalent circuit model of MWCNTs is presented for the first time, and the performance of MWCNT interconnects is evaluated and compared against traditional Cu interconnects, as well as Single-Walled CNT (SWCNT)-based interconnects, at different interconnect levels (local, intermediate, and global) for future technology nodes. It is shown that at the intermediate and global levels, MWCNT interconnects can achieve smaller signal delay than that of Cu interconnects, and the improvements become more significant with technology scaling and increasing wire lengths. At 1000- global or 500- intermediate level interconnects, the delay of MWCNT interconnects can reach as low as 15% of Cu interconnect delay. It is also shown that in order for SWCNT bundles to outperform MWCNT interconnects, dense and high metallic-fraction SWCNT bundles are necessary. On the other hand, since MWCNTs are easier to fabricate with less concern about the chirality and density control, they can be attractive for immediate use as horizontal wires in VLSI, including local, intermediate, and global level interconnects.

Crosstalk Prediction of Single- and Double-Walled Carbon-Nanotube (SWCNT/DWCNT) Bundle Interconnects

The crosstalk effects in single- and double-walled carbon-nanotube (SWCNT and DWCNT) bundle-interconnect architectures are investigated in this paper. Some modified equivalent-circuit models are proposed for both SWCNT and DWCNT bundles, where capacitive couplings between adjacent bundles are incorporated. These circuit models are further used to predict the performance of SWCNT and DWCNT bundle interconnects in comparison with the Cu wire counterpart at all interconnect levels for advanced future technology generations. It is found that, compared with the SWCNT bundle, the DWCNT bundle interconnect can lead to a reduction of crosstalk-induced time delay, which will be more significant with increasing bundle length, while the peak voltage of the crosstalk-induced glitch in SWCNT and DWCNT bundle interconnects is in the same order as that of Cu wires. Due to the improvement in time delay, it is numerically confirmed that the DWCNT bundle interconnect will be more suitable for the next generation of interconnect technology as compared with the SWCNT bundle counterpart.

A Miniaturized Dual-Band Frequency Selective Surface (FSS) With Closed Loop and Its Complementary Pattern

A single-layer substrate frequency selective surface (FSS) made of miniaturized elements is proposed, with two controllable passbands obtained. Each FSS element consists of a loop wire on the top metal layer and its complementary pattern etched at the bottom one, which provides two transmission poles separated by a transmission zero. An equivalent circuit model is given for predicting the characteristics of the designed FSS, and a good agreement between the simulated and measured transmission coefficients is obtained. Furthermore, the cases of oblique wave incidence and cascading FSSs are also measured and examined.

Signal Transmission Analysis of Multilayer Graphene Nano-Ribbon (MLGNR) Interconnects

Signal transmission characteristics of some multilayer graphene nano-ribbon (MLGNR) interconnects are studied in this paper, with an equivalent single-conductor (ESC) model implemented for the analysis of their transient responses. In this model, both capacitive and inductive couplings between adjacent GNR layers are treated appropriately. According to the derived transfer function using the fourth-order approximation, the output voltage waveforms are predicted for both 14- and 22-nm technology nodes. In particular, the effects of Fermi level of MLGNR on the time delay of the transmitted rectangular pulse are examined and compared. Based on the decoupled partially differential equations (PDEs) for the common and differential modes of voltage wave propagation in the edge-coupled MLGNR interconnects, their output voltage responses are also predicted for different technology nodes, which are useful for the evaluation of on-chip signal integrity or EMC and EMI issues of MLGNR-built transmission lines for the future ICs.

Contacts between Two- and Three-Dimensional Materials: Ohmic, Schottky, and p–n Heterojunctions

After a decade of intensive research on two-dimensional (2D) materials inspired by the discovery of graphene, the field of 2D electronics has reached a stage with booming materials and device architectures. However, the efficient integration of 2D functional layers with three-dimensional (3D) systems remains a significant challenge, limiting device performance and circuit design. In this review, we investigate the experimental efforts in interfacing 2D layers with 3D materials and analyze the properties of the heterojunctions formed between them. The contact resistivity of metal on graphene and related 2D materials deserves special attention, while the Schottky junctions formed between metal/2D semiconductor or graphene/3D semiconductor call for careful reconsideration of the physical models describing the junction behavior. The combination of 2D and 3D semiconductors presents a form of p-n junctions that have just marked their debut. For each type of the heterojunctions, the potential applications are reviewed briefly.

Perfectly matched layer-absorbing boundary condition for left-handed materials

The perfectly matched layer (PML) absorbing boundary condition (ABC) is extended to truncate the boundary of left-handed materials in the Finite-Difference Time-Domain (FDTD) simulation. The uniaxial material parameters are given in the frequency domain, and discretized in the FDTD update procedure by means of the Z-Transform technique. The effectiveness of the PML is demonstrated by numerical results.

Performance Prediction of Carbon Nanotube Bundle Dipole Antennas

A theoretical investigation is carried out for predicting radiation characteristics of single-walled carbon nanotube (SWCNT) bundle dipole antennas based on the distributed circuit parameters and the model of an SWCNT, where the cross section of bundles can be in a circular and a rectangular geometry, respectively. The current distributions in such novel antennas are predicted to investigate the effects of bundle cross-sectional size, tube diameter, tube length, and operating frequency. Furthermore, comparative studies are performed to show the geometry- and frequency-dependent radiation resistance, far-field pattern, and radiation efficiency of some typical bundle dipole antennas, which are numerically confirmed to outperform an SWCNT antenna by 30-40 dB in radiation efficiency.

A Novel Microstrip Filter Using Three-Mode Stepped Impedance Resonator (TSIR)

A novel microstrip filter using three-mode stepped impedance resonator (TSIR) is presented, with its coupling scheme given so as to accurately predict its desired performance. A T-type open stub is introduced into the design of a miniaturized TSIR. It is shown that the developed filter exhibits quasi-elliptic characteristics with sharp skirt and wide stopband. Good agreements are obtained between its measured and simulated S-parameters.

Evanescent-Mode Substrate Integrated Waveguide (SIW) Filters Implemented with Complementary Split Ring Resonators

A new type of evanescent-mode substrate integrated waveguide (SIW) bandpass fllter is presented in this paper, with complementary split ring resonators (CSRRs) introduced on the top or bottom metal planes of the waveguide. Both positive and negative couplings are obtained between the CSRRs by changing their locations and orientations. In comparison with conventional SIW fllters, the proposed fllters are compact since their passbands are below the cutofi frequency of SIW. A third- and a fourth-order cross-coupled fllter prototypes were designed using standard PCB technology. They operate at the same central frequency of 3.8GHz, with their fractional bandwidths of 15% and 20%. The proposed fllters have a wide upper stopband as the cutofi frequency of TE10-mode in the SIW is much higher than the central frequency. Their good performance is demonstrated by both the simulated and measured S-parameters.

18.5% efficient graphene/GaAs van der Waals heterostructure solar cell

The honeycomb connection of carbon atoms by covalent bonds in a macroscopic two-dimensional scale leads to fascinating graphene and solar cell based on graphene/silicon Schottky diode has been widely studied. For solar cell applications, GaAs is superior to silicon as it has a direct band gap of 1.42 eV and its electron mobility is six times of that of silicon. However, graphene/GaAs solar cell has been rarely explored. Herein, we report graphene/GaAs solar cells with conversion efficiency (Eta) of 10.4% and 15.5% without and with anti-reflection layer on graphene, respectively. The Eta of 15.5% is higher than the state of art efficiency for graphene/Si system (14.5%). Furthermore, our calculation points out Eta of 25.8% can be reached by reasonably optimizing the open circuit voltage, junction ideality factor, resistance of graphene and metal/graphene contact. This research strongly support graphene/GaAs hetero-structure solar cell have great potential for practical applications.