Ding Ruixue

Microtrenching effect of SiC ICP etching in SF6/O2 plasma

Inductively coupled plasma (ICP) etching of single crystal 6H-silicon carbide (SiC) is investigated using oxygen (O2)-added sulfur hexafluoride (SF6) plasmas. The relations between the microtrenching effect and ICP coil power, the composition of the etch gases and different bias voltages are discussed. Experimental results show that the microtrench is caused by the formation of a SiFxOy layer, which has a greater tendency to charge than SiC, after the addition of O2. The microtrenching effect tends to increase as the ICP coil power and bias voltage increase. In addition, the angular distribution of the incident ions and radicals also affects the shape of the microtrench.

Working mechanism of a SiC nanotube NO2 gas sensor

The working mechanism of sensors plays an important role in their simulation and design, which is the foundation of their applications. A model of a nanotube NO2 gas sensor system is established based on an (8, 0) silicon carbide nanotube (SiCNT) with a NO2 molecule adsorbed. The transport properties of the system are studied with a method combining density functional theory (DFT) with the non-equilibrium Greens function (NEGF). The adsorbed gas molecule plays an important role in the transport properties of the gas sensor, which results in the formation of a transmission peak near the Fermi energy. More importantly, the adsorption leads to different voltage current characteristics of the sensor to that with no adsorption; the difference is large enough to detect the presence of NO2 gas.

Circuit modeling and performance analysis of SWCNT bundle 3D interconnects

Metallic carbon nanotubes (CNTs) have been proposed as a promising alternative to Cu interconnects in future integrated circuits (ICs) for their remarkable conductive, mechanical and thermal properties. Compact equivalent circuit models for single-walled carbon nanotube (SWCNT) bundles are described, and the performance of SWCNT bundle interconnects is evaluated and compared with traditional Cu interconnects at different interconnect levels for through-silicon-via-based three dimensional (3D) ICs. It is shown that at a local level, CNT interconnects exhibit lower signal delay and smaller optimal wire size. At intermediate and global levels, the delay improvement becomes more significant with technology scaling and increasing wire lengths. For 1 mm intermediate and 10 mm global level interconnects, the delay of SWCNT bundles is only 49.49% and 52.82% that of the Cu wires, respectively.

Impedance matching for the reduction of signal reflection in high speed multilevel three-dimensional integrated chips

In high speed three-dimensional integrated circuits (3D ICs), through silicon via (TSV) insertion causes impedance discontinuities along the interconnect-TSV channel that results in signal reflection. As demonstrated for a two-plane interconnect structure connected by a TSV, we incorporate an appropriate capacitance at the junction to mitigate the signal reflection with gigascale frequencies. Based on 65 nm technology and S-parameter analysis, the decrease of signal reflection can be 189% at the tuned frequency of 5 GHz. Extending this method to the five-plane interconnect structure further, the reduction of signal reflection can achieve 400%. So we could broaden this method to any multilevel 3D interconnect structures. This method can also be applied to a circuit with tunable operating frequencies by digitally connecting the corresponding matching capacitance into the circuit through switches. There are remarkable improvements of the quality of the transmitting signals.

Influence of Temperature on the Conductivity of Multi-walled Carbon Nanotube Interconnects

We propose a new conductivity model of multi-walled carbon nanotube (MWCNT) interconnects considering the influence of temperature. For each shell of MWCNT interconnects, it may present the property of ballistic transport or may suffer from acoustic photo and optical phonon (OP) scattering depending on their mean free paths (MFPs) and the wire length. Furthermore, since the MFPs are proportional to the shell diameter, five regions exist in the wire length in which the factors influencing the conductivity are determined. Thus the conductivity is modeled in five cases according to their lengths, and the final obtained model is a 5-piecewise function. By using this model, the influence of temperature on the conductivity is examined and analyzed. It is shown that the conductivity demonstrates different, changing behaviors with the increase of temperature in the five cases. Additionally, the influence of OP scattering on the conductivity does not need to be taken into account at room temperatures, whereas this influence will produce a decline region in the conductivity at high temperatures.

Through-silicon-via crosstalk model and optimization design for three-dimensional integrated circuits

Through-silicon-via (TSV) to TSV crosstalk noise is one of the key factors affecting the signal integrity of three-dimensional integrated circuits (3D ICs). Based on the frequency dependent equivalent electrical parameters for the TSV channel, an analytical crosstalk noise model is established to capture the TSV induced crosstalk noise. The impact of various design parameters including insulation dielectric, via pitch, via height, silicon conductivity, and terminal impedance on the crosstalk noise is analyzed with the proposed model. Two approaches are proposed to alleviate the TSV noise, namely, driver sizing and via shielding, and the SPICE results show 241 mV and 379 mV reductions in the peak noise voltage, respectively.

Reduction of signal reflection along through silicon via channel in high-speed three-dimensional integration circuit

The through silicon via (TSV) technology has proven to be the critical enabler to realize a three-dimensional (3D) gigscale system with higher performance but shorter interconnect length. However, the received digital signal after transmission through a TSV channel, composed of redistribution layers (RDLs), TSVs, and bumps, is degraded at a high data-rate due to the non-idealities of the channel. We propose the Chebyshev multisection transformers to reduce the signal reflection of TSV channel when operating frequency goes up to 20 GHz, by which signal reflection coefficient (S11) and signal transmission coefficient (S21) are improved remarkably by 150% and 73.3%, respectively. Both the time delay and power dissipation are also reduced by 4% and 13.3%, respectively. The resistance-inductance-conductance-capacitance (RLGC) elements of the TSV channel are iterated from scattering (S)-parameters, and the proposed method of weakening the signal reflection is verified using high frequency simulator structure (HFSS) simulation software by Ansoft.

Design of a novel dual pathway ESD protection device using ISE-TCAD

A novel dual pathway electrostatic discharge (ESD) protection device based on 0.6µm CMOS p-well technology has been designed and fabricated according to the ISE-TCAD simulation tool and the C-R method. The new device was verified by a multi-project wafer (MPW) fabrication and tested by the transmission line pulse (TLP) generator system. The results show that new device has lower trigger voltage, smaller chip area and a higher ESD failure voltage compared with those of gate grounded NMOS (ggNMOS) protection circuits with the same MPW. The voltage up to 5KV under human-body mode (HBM) test has been obtained.

Electronic Transport Properties of (7,0) Semiconducting Carbon Nanotube

Electronic transport properties of a finite (7,0) carbon nanotube (CNT) coupled to Au (111) surfaces are investigated with a fully nonequilibrium Greens functions method combined with the density functional theory. The results show that the coupling effect between the CNT and Au electrode plays an important role in the transport properties, which leads to the formation of a high plateau in the transmission spectrum around Fermi energy. In addition, the current-voltage characteristic of the (7,0) CNT coupled to Au electrodes is different from an isolated (7,0) CNT.