Linxi Dong

High-Frequency Analysis of Cu-Carbon Nanotube Composite Through-Silicon Vias

A high-frequency analysis of Cu-carbon nanotube (CNT) composite through-silicon vias (TSVs) is conducted. The electrical modeling of the Cu-CNT composite TSVs is performed, with the effective complex conductivity formulated for accurate characterization of kinetic inductance. It is shown that, after codepositing CNT with Cu, the electrical conductivity of the TSVs can be improved and the influence of kinetic inductance variation can be suppressed in comparison with the CNT TSVs. On the other hand, the Cu-CNT composite TSVs can exhibit little compromise in performance yet much enhanced reliability by comparison to the Cu counterpart. That is, the Cu-CNT composite TSVs can provide a better tradeoff between reliability and performance than the Cu and CNT counterparts.

Strain redistribution in free-standing bridge structure released from strained silicon-on-insulator

The strain evolution including relaxation and conversion during the fabrication of free-standing bridge structure, which is the building block for the gate-all-around transistor, has been investigated in strained silicon-on-insulator. Compared to the starting strained silicon-on-insulator substrate, the strain of the free-standing bridge structure transforms from the biaxial strain to the uniaxial strain after patterning and release due to its unique configuration, as suggested by UV-Raman spectroscopy. Furthermore, such uniaxial strain has strong correlation with the dimension of the suspended structure, and it is enhanced as the width of the free-standing bridge decreases and the size of the connected pad increases. For 0.5μm-wide free-standing bridge connected to the pad of 16 × 16 μm2, the maximum uniaxial tensile strain of 4.65% is obtained, which remarkably exceeds the levels that can be achieved by other techniques ever reported. The observed strain redistribution phenomenon is also analyzed by two...

The slope effect of a capacitive resonator profile fabricated by a DRIE process on the performance of an MEMS disk resonator

The thickness of a capacitive disk resonator can be increased by selecting a deep reactive ion etching (DRIE) process for reducing motional resistance. However, the DRIE process sometimes causes MEMS capacitive resonators to have a non-ideal profile. In this paper, the slope effect of a resonator profile fabricated by a DRIE process on the capacitance, electrostatic force, electrical stiffness, motional resistance and output current of the capacitive resonator is analyzed. The relation curves between these parameters and the sloped angle are obtained theoretically. The results show that the capacitance, electrostatic force, electrical stiffness and output current decrease as the sloped angle increases, but the motional resistance obviously increases. By capturing the electric field distribution of a capacitive resonator with different ratios of the gap to thickness by using FEM software ANSYS, the effects of slope angle and thickness on the natural frequency of the resonator are investigated. The analyzed results can provide the theoretical basis for designing high-performance MEMS disk resonators fabricated by the DRIE process.

Modeling and Characterization of Coaxial Through-Silicon Via With Electrically Floating Inner Silicon

In this paper, coaxial through-silicon via (C-TSV) is modeled and studied with the consideration of electrically floating inner silicon substrate. Nonlinear capacitances of the central via and the outer shielding shell are accurately captured by solving cylindrical Poisson equation. By employing symbolically defined device block, the nonlinear capacitances of the C-TSV with electrically floating inner silicon are combined into the equivalent circuit model, and their impacts on the electrical characteristics are examined.

High-Frequency Modeling of On-Chip Coupled Carbon Nanotube Interconnects for Millimeter-Wave Applications

This paper presents a high-frequency equivalent circuit model for on-chip coupled carbon nanotube (CNT) interconnects up to 100 GHz. By simplifying the circuit model, the S-parameters of on-chip coupled interconnects can be acquired and validated by comparing with the full-wave electromagnetic simulations. By virtue of effective complex conductivity, the high-frequency behaviors of coupled CNT interconnects are captured and studied, with the impacts of kinetic inductance treated appropriately.

Anchor Loss Variation in MEMS Wine-Glass Mode Disk Resonators Due to Fluctuating Fabrication Process

With increasing demand for high-frequency, high-quality factor (Q-factor) mechanical resonators, the Q-factor declining issue at high-frequency becomes increasingly prominent. This paper studies the performance variations of disk resonators under the wine-glass vibration mode due to the support beam offset that are caused by process deviations. The formula of the Q-factor in terms of the support loss is derived to further illustrate the change of the Q-factor caused by the beam offset. It is found that the impact of the extensional mode on the performance is more serious than that of the flexural mode, since the extensional mode may destruct the mode shape and decrease the radial size (i.e., amplitude) of the disk. Finally, some design methods on how to improve the Q-factor of the resonator are given. The numerical results show that there are, respectively, 0.07% and 13.7% increase in the resonant frequency and the disk radial size when the support beam offset is 4°, whereas the increase in the resonant frequency and the disk radial size becomes 0.96% and 69.8%, respectively, when the support beam offset reaches 16°. For the Q-factor, although the flexural-mode Q-factor, Qf, increases with increasing support beam offset, the overall Q-factor of the resonator still decreases due to the dominant extensional-mode loss. In the worst case, the largest decline reaches 27.11% from the zero offset position (where there is only flexural-mode loss) to the 16° offset position.

Vibration-Induced Errors in MEMS Tuning Fork Gyroscopes with Imbalance

This paper discusses the vibration-induced error in non-ideal MEMS tuning fork gyroscopes (TFGs). Ideal TFGs which are thought to be immune to vibrations do not exist, and imbalance between two gyros of TFGs is an inevitable phenomenon. Three types of fabrication imperfections (i.e., stiffness imbalance, mass imbalance, and damping imbalance) are studied, considering different imbalance radios. We focus on the coupling types of two gyros of TFGs in both drive and sense directions, and the vibration sensitivities of four TFG designs with imbalance are simulated and compared. It is found that non-ideal TFGs with two gyros coupled both in drive and sense directions (type CC TFGs) are the most insensitive to vibrations with frequencies close to the TFG operating frequencies. However, sense-axis vibrations with in-phase resonant frequencies of a coupled gyros system result in severe error outputs to TFGs with two gyros coupled in the sense direction, which is mainly attributed to the sense capacitance nonlinearity. With increasing stiffness coupled ratio of the coupled gyros system, the sensitivity to vibrations with operating frequencies is cut down, yet sensitivity to vibrations with in-phase frequencies is amplified.

Weak localization behavior observed in graphene grown on germanium substrate

Two dimensional electron systems (2DES) usually show the weak localization behavior in consequence of electron interaction in the limited dimension. Distinct from other 2DES, the monolayer graphene, due to the chirality, exhibits unique weak localization behavior sensitive to not only inelastic but also elastic carrier scattering. Grain boundaries, which usually exist in monolayer graphene, are apparently related to the elastic carrier scattering process, thus affecting the weak localization behavior. However, their effect is scarcely studied due to the lack of an ideal platform. Here, a complementary system consisting of both single-crystalline graphene grown on Ge (110) and poly-crystalline graphene grown on Ge (111) is constructed. From the comparison of magnetoresistivity measurements, the weak localization effect is found to be greatly enhanced for the poly-crystalline graphene on Ge(111) compared to the single-crystalline graphene on Ge(110). The degraded transport performance in graphene/Ge(111) is...

A compact planar ultra-wideband handset antenna with L-Shaped extended ground stubs

In this letter, a compact planar ultra-wideband mobile antenna with L-shaped extended ground stubs is presented. The proposed handset antenna consists of two planar meandered monopole radiating elements, i.e., main antenna and auxiliary antenna respectively, located at the diagonal corners of mobile phone printed circuit broad with standard size of 136 × 68mm2. Each radiating element is composed of two arms and a L-shaped extended ground stub, jointly achieving multiple resonances and ultra-wideband impedance matching with a compact size. The effect of the L-shaped ground stub is investigated in detail. The proposed antenna has a compact size of 31.4 × 12mm2, printed simple structure and full-band coverage (GSM850 and 1.6–5.4GHz) for wireless handsets systems, including GSM850, DCS1800, PCS1900, UMTS, LTE, WiMAX, and WLAN in 4G and 5G communication systems. The optimized antenna prototype is fabricated and measured. The measured results show that the reflection coefficients are less than −6 dB over the operating bands and the mutual coupling between two ports is less than −20 dB. Good agreement is obtained between the simulated and measured results. The results demonstrate that the proposed handset antenna has good characteristics of ultra-wideband, isolation, gain, and radiation pattern, and is a good candidate as a terminal antenna for handsets applications.

Strain analysis of free-standing strained silicon-on-insulator nanomembrane

Based on the ultra-thin strained silicon-on-insulator (sSOI) technology, by creatively using a hydrofluoric acid (HF) vapor corrosion system to dry etch the SiO2 layer, a large area of suspended strained silicon (sSi) nanomembrane with uniform strain distribution is fabricated. The strain state in the implemented nanomembrane is comprehensively analyzed by using an UV-Raman spectrometer with different laser powers. The results show that the inherent strain is preserved while there are artificial Raman shifts induced by the heat effect, which is proportional to the laser power. The suspended sSOI nanomembrane will be an important material for future novel high-performance devices.