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The carrier multiplication phenomenon involves hot carriers, which gain kinetic energy while accelerating to equilibrium with the established avalanching electric fields, and is typically explained via the local avalanche model. This work presents two vertical Ge-on-Si avalanche photodetectors fabricated in a separate absorption, charge, and multiplication configuration. Uniformity in materials, doping densities, and device dimensions is maintained, except for the multiplication width, which is used as a control parameter to manipulate avalanching fields under identical electric biasing and illumination schemes. Nonlocal carrier multiplication model is implemented during analysis of the extracted current-voltage signatures under small and large reverse biasing arrangements. For such an APD characterized by thinner multiplication region $\left ({{W_{m}=0.1 ~\mu m}}\right)$ , reduced linear and Geiger-mode multiplication regimes are perceived to be at play, outperforming the device having thicker multiplication region in almost all related figures of merit, e.g., responsivity $(22.58 \mathrm {A/W})$ , photo-to-dark current ratio $(\sim {10}^{5})$ , normalized photo-to-dark current ratio $(2.5\times {10}^{9} \mathrm {W}^{-1})$ , specific detectivity $(7.45\times {10}^{12}\mathrm {Jones})$ , and noise equivalent power $(\sim 2.42\times {10}^{-15} \mathrm {W/}\sqrt {\mathrm {Hz}})$ . The enhanced performance characteristics are due to excessively strong avalanching fields, reduced thermal charge density, and negligible dead space compared to its counterpart characterized by thicker multiplication width.

This article presents a 39 GHz transceiver front-end chipset for 5G multi-input multi-output (MIMO) applications. Each chip includes two variable-gain frequency-conversion channels and can support two simultaneous independent beams, and the chips also integrate a local-oscillator chain and digital module for multi-chip extension and gain-state control. To improve the radio-frequency performance, several circuit-level improvement techniques are proposed for the key building blocks in the front-end system. Furthermore, an advanced low-temperature co-fired ceramic process is developed to package the 39 GHz dual-channel transceiver chipset, and it achieves low packaging loss and high isolation between the two transmitting (TX)/receiving (RX) channels. Both the chip-level and system-in-package (SIP)-level measurements are conducted to demonstrate the performance of the transceiver chipset. The measurement characteristics show that the TX SIP provides 11 dB maximum gain and 10 dBm saturated output power, while the RX SIP achieves 52 dB maximum gain, 5.4 dB noise figure, and 7.2 dBm output 1 dB compression point. Single-channel communication link testing of the transceiver exhibits an error vector magnitude (EVM) of 3.72% and a spectral efficiency of 3.25 bit·s−1·Hz−1 for 64-quadrature amplitude modulation (QAM) modulation and an EVM of 3.76% and spectral efficiency of 3.90 bit·s−1·Hz−1 for 256-QAM modulation over a 1 m distance. Based on the chipset, a 39 GHz multi-beam prototype is also developed to perform the MIMO operation for 5G millimetre wave applications. The over-the-air communication link for one- and two-stream transmission indicates that the multi-beam prototype can cover a 5–150 m distance with comparable throughput.

An efficient transmission line model of high-speed cables is established, to predict its response at a high-frequency region (up to 20 GHz). Especially, an appropriate conformal mapping technique is applied to formulate the per-unit-length parameters of high-speed cables. Moreover, the skin and proximity effects of the conducting wires and the outer shield are derived in the closed form. As a result, the AC resistance/ inductance of all the conducting materials due to the skin and proximity effects are accurately incorporated for both layered and unlayered conductors. Furthermore, the mixed-mode S-parameters are precisely predicted for both balanced and unbalanced transmission line cables in the high-frequency region. In addition, the effects of the nonuniformities and cable geometry deformation on the mode conversions are also investigated. The proposed model is firstly validated with commercial software tools, COMSOL, FEKO, and HFSS; then, we further performed physical measurements to verify our new algorithm.

Thermal crosstalk in a highly integrated RRAM array due to the self-heating effect is one of the most critical issues affecting device reliability. In this paper, two types of “thermal-house” structures are proposed to optimize the thermal management of the RRAM array. An in-house developed parallel simulator is employed to study the performance of the proposed thermal house structures in terms of resistance ratio and crosstalk temperature. It is demonstrated that the proposed thermal house structures can help to reduce thermal crosstalk in high-density RRAM arrays. Some suggestions are also provided for further improving the thermal management capability of the thermal houses as well.

A hybrid finite volume-finite element method which can avoid overestimation of volume shared by each vertex in the meshing grid is proposed to solve the diffusive transport governed continuity equation. The simulation results demonstrate that the improved algorithm can eliminate unphysical distortions as compared to the conventional Scharfetter Gummel method. Based on the proposed algorithm, a parallel-computation simulator is developed for large-scale electrothermal simulation of resistive random access memory (RRAM) arrays, in which the domain decomposition method and J parallel adaptive unstructured mesh applications infrastructure are adopted. The validity, speedup, and scalability of the parallel simulator are investigated on the TianHe-2 supercomputer. Based on the simulated results, the electrothermal characteristics and reliability analysis of large-scale RRAM arrays are investigated in detail.

A differential probe-fed liquid crystal (LC)-based frequency tunable circular-ring patch antenna is presented. Besides, cavity model is extended to analyze the LC-based antenna for the differential operation. According to the cavity model, the permittivity and loss tangent of the LC are extracted from the measured differential reflection coefficients. Acceptable agreements among the measurement, simulation, and calculation for differential impedances, reflection coefficients, and radiation patterns are obtained and also validate the extraction method and model. More importantly, the extended cavity model can provide a deep physical insight into the LC-based antenna.

Due to its ultrathin feature, graphene has been recently proposed as diffusion barrier layer for Cu wires. This paper is geared toward developing an equivalent single-conductor (ESC) transmission-line (TL) model for analysis of Cu-graphene interconnects, i.e., Cu wires encapsulated with graphene barriers. Based on the ESC TL model, electrical performances of Cu-graphene interconnects are examined and evaluated. It is shown that the time delay and temperature rise can be reduced by replacing the conventional diffusion barriers in the Cu/low-k interconnect with the graphene barriers.

In this paper, a compact passive equalizer for differential transmission channel is designed in TSV-based three-dimensional integrated circuits (3-D ICs). The compact size of the equalizer is achieved by a square shunt metal line. Three simplified odd-mode half circuit models are proposed for ground-signal-signal-ground (G-S-S-G) type TSVs, differential on-interposer interconnects, and differential channels, respectively. Those simplified models merely consist of frequency-independent elements and can accurately predict the differential insertion losses up to 20 GHz. Moreover, the electrical parameters of the proposed serial resistance-inductance (RL) type equalizers are derived from the system transfer functions and optimized by virtue of the time-domain inter-symbol interference cancellation technique. Further, the geometrical parameters of the RL equalizers are calculated by using a genetic algorithm based multi-objective optimization method. Finally, the performance of the designed RL equalizer is validated by both frequency- and time-domain simulations for 20 Gb/s high-speed differential signaling.

This paper deals with the fabrication of an inductorless wideband low-noise amplifier (LNA). The LNA includes two branches in parallel: a common-source (CS) path and a common-gate (CG) path. The CS path is responsible for providing enough power gain, while the CG path is used to achieve the input impedance matching. To eliminate the noise contribution of the CG path, the noise cancellation technique is applied. Therefore, the overall noise figure (NF) is improved. The phase mismatch between the two paths is also quantitatively analyzed to investigate its effect on gain and NF. The analytical results agree well with the simulation results. The LNA has been fabricated by a commercial 0.18-μm CMOS process. The measurement results show that the LNA has achieved a maximum gain of 14.5 dB with 1.7-GHz 3-dB gain bandwidth and a minimum NF of 3 dB. The tested input 1-dB gain compression point (IP1 dB) is -10.4 dBm at 1 GHz and the input third-order intercept point is 0.25 dBm. With 1.8-V supply, the LNA draws only 6-mA dc current.

An improved multifilamentary conduction model for the reset process in resistive random access memory (RRAM) is constructed by considering the stochastic distribution of oxygen vacancies (Vo). In this context, conduction filaments (CFs) have different Vo densities and diffusion barriers. Fully coupled multiphysics simulations of RRAM with three CFs are performed using the time domain finite difference method to self-consistently solve the current transport, heat conduction, and Vo transport equations. The simulated I-V characteristics agree well with experiment. Since the three CFs have different thermal diffusion barriers, as in previous studies, they rupture at different applied voltages. Evolution of each CF in the reset process is investigated: from when its electrical conductivity is linearly dependent to when it is exponentially dependent on Vo density.

Electromagnetic (EM) waves with orbital angular momentum (OAM) provide a new degree of freedom for channel multiplexing to improve the capacity of wireless communication. For OAM-based systems, it is important to design specific configurations to generate vortex radios. In this paper, a reconfigurable reflectarray antenna is proposed with independent control of dual polarizations. A reflective cell is proposed by properly assigning the variable capacitances of four varactors, which are placed between metal square rings of each unit. The varactors of each unit are divided into two groups and the capacitance value of each group controls the reflection phase for a single linear polarization. By using the equivalent circuit model, the reflective units and array can be designed efficiently. Smooth phase variation and good reflection efficiency are achieved. Then, the reflectarray is set into sectors and a simple phase-shifting surface model is used to generate vortex beam. Each sector is realized with reflective units satisfying desired reflection phases for different modes. This kind of OAM-generating method can reduce the required variation range of reflection phase and provide more choices for a specific OAM mode combination with dual polarization, which is helpful to reduce mutual coupling between the two linear polarizations. Finally, full-wave simulations show that the 0, ±1, ±2 modes of vortex beam are successfully generated at 3.5 GHz with arbitrary combination in dual-polarization, which is also supported by OAM modes purity and reflection efficiency analysis. Therefore, in our design, the reconfigurable OAM and spin angular momentum (SAM), related with polarization, can be utilized simultaneously and independently for high-capacity wireless communication.

As the interconnect delay exceeds the gate delay, the integrated circuit (IC) technology has evolved from a transistor-centric era to an interconnect-centric era. Conventional metallic interconnects face several serious challenges in aspects of performance and reliability. To address these issues, nanocarbon materials, including carbon nanotube (CNT) and graphene, have been proposed as promising candidates for interconnect applications. Considering the rapid development of nanocarbon interconnects, this paper is dedicated to providing a mini-review on our previous work and on related research in this field.