Interconnect Applications Research Articles

Molecular dynamics work on thermal conductivity of SiGe nanotubes.

SiGe nanotubes (SiGeNTs) hold significant promise for applications in nanosolar cells, optoelectronic systems, and interconnects, where thermal conductivity is critical to performance. This study investigates the effects of length, diameter, temperature, and axial strain on the thermal conductivity of armchair and zigzag SiGeNTs through molecular dynamics simulations. Results indicate that thermal conductivity increases with sample length due to ballistic heat transport and decreases with temperature as phonon scattering intensifies. Axial strain transitions from compression to tension enhance phonon propagation, improving conductivity. Chirality affects conductivity, with zigzag SiGeNTs consistently outperforming armchair structures, while diameter exhibits negligible impact. Non-equilibrium molecular dynamics simulations were conducted using the LAMMPS package with the Tersoff potential to model Si-Ge interactions. Thermal conductivity was computed via Fourier's law, with the system divided into regions for controlled heat input and dissipation. Lengths, diameters, temperatures (100-500K), and axial strains (- 6% to + 9%) were varied systematically. Phonon spectrum analysis was performed using Fourier transforms of velocity autocorrelation functions to compute.

Topological bound states in the continuum in a non-Hermitian photonic system.

Topological insulators and bound states in the continuum represent two fascinating topics in the optical and photonic domain. The exploration of their interconnection and potential applications has emerged as a current research focus. Here, we investigated non-Hermitian photonics based on a parallel cascaded-resonator system, where both direct and indirect coupling between adjacent resonators can be independently manipulated. We observed the emergence of topological Fabry-Pérot bound states in the continuum in this non-Hermitian system, and theoretically validated its robustness. We also observed topological phase transitions and exceptional points in the same system. By elucidating the relationship between topological insulators and bound states in the continuum, this work will enable various applications that harness the advantages of bound states in the continuum, exceptional points, and topology. These applications may include optical delay and storage, highly robust optical devices, high-sensitivity sensing, and chiral mode switching.

On-chip topological transport of integrated optical frequency combs

Optical frequency combs in integrated photonics have widespread applications in high-dimensional optical computing, high-capacity communications, high-speed interconnects, and other paradigm-shifting technologies. However, quantum frequency combs with high-dimensional quantum states are vulnerable to decoherence, particularly in the presence of perturbations such as sharp bends. Here we experimentally demonstrate the robust on-chip topological transport of quantum frequency combs in valley photonic crystal waveguides. By measuring the time correlations and joint spectral intensity of the quantum frequency combs, we show that both quantum correlations and frequency entanglement remain robust against sharp bends, owing to the topological nature of the quantum valley Hall effect. We also demonstrate that dissipative Kerr soliton combs with a bandwidth of 20 THz maintain their spectral envelope and low-noise properties even in the presence of structure perturbations. These topologically protected optical frequency combs offer robust, complex, highly controllable, and scalable light sources, promising significant advances in high-dimensional photonic information processing.

Enhancing Cu interconnect reflow in back-end-of-line metal wiring with ultrathin Co liners

Abstract This research investigates the gap-fill characteristics of Cu in back-end-of-line (BEOL) interconnects, focusing on Co liner deposition using chemical vapor deposition (CVD) and cyclic-CVD (C-CVD). Providing superior gap-fill characteristics for BEOL interconnect applications is important. Three methods—CVD, C-CVD, and a combination of the two—were compared in terms of their effects on Cu reflow and electrical performance. CVD exhibited the lowest resistivity (44 μΩ cm at 10 nm thickness) and the fewest carbon impurities, confirmed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Atomic force microscopy (AFM) revealed that CVD produced the smoothest surface (Rq ~0.5 nm), enabling better adhesion and uniform Cu reflow. At 300°C, Co liners deposited by CVD achieved void-free Cu–Mn filling in 20 nm trenches, which showed CVD to outperform other methods. These findings highlight CVD as the most effective technique for precise Co liner deposition, ensuring reliable Cu interconnects in advanced semiconductor nodes.


Resistivity scaling of porous MoP narrow lines

The resistivity scaling of copper (Cu) interconnects with decreasing dimensions remains a major challenge in the downscaling of integrated circuits. Molybdenum phosphide (MoP) is a triple-point topological semimetal (TSM) with low resistivity and high carrier density. With the presence of topologically protected surface states that should be defect-tolerant and electron backscatter forbidden, MoP nanowires have shown promising resistivity values compared to Cu interconnects at the nanometer scale. In this work, using template-assisted chemical vapor conversion and standard fabrication techniques that are industry-adoptable, we report the fabrication of porous but highly crystalline MoP narrow lines with controlled sizes and dimensions. We examine the influence of porosity, thickness, and cross-section area on the resistivity values of the fabricated MoP lines to further test the feasibility of MoP for interconnect applications. Our work presents a facile approach to synthesizing TSM nanowires with different dimensions and cross sections, enabling experimental investigations of their predicted unconventional resistivity scaling behavior. Finally, our results provide insight into the effects of porosity on the resistivity of these materials on the nanometer scale.

Meter-Scale Long Connectorized Paper-like Polymer Waveguide Film for 100 Gbps Board-Level Optical Interconnects Application.

We design and fabricate meter-scale long connectorized paper-like flexible multimode polymer waveguide film with a large bandwidth-length product (BLP) for board-level optical interconnects application. The measured BLP of the multimode waveguide is greater than 57.3 GHz·m at a wavelength of 850 nm under the strictest overfilled launch condition with a maximum length of 2.1 m and 10-dB insertion loss. The fabricated waveguide films are as flexible as regular printing paper and can be conveniently interfaced with standard mechanically transferable (MT) fiber connectors with low loss. The average insertion loss of the connectorized waveguide is about 0.042 dB/cm with inter-channel crosstalk as low as -46.4 dB, and the bending loss is less than 1 dB at a bending radius of 1 mm under the overfilled launch condition. We also demonstrate a vertical-cavity surface-emitting laser (VCSEL)-based single-lane 100 Gbps PAM4 transmission. Our results show that the meter-scale long paper-like polymer waveguide film has both excellent optical properties and large bandwidth and is ideal for high-speed board-level optical interconnects application with a single-lane data rate of 100 Gbps and beyond, especially those that have a strict requirement on the length of connection and compactness.

Net 30-Tb/s bidirectional IM/DD optical interconnect over 19-core fiber enabled by WDM uplink/downlink twin-SSB PAM-4 transmission.

High-capacity optical interconnects with short reach are hugely demanded driven by the exponential growth of data traffic. In this work, four-channel wavelength division multiplexing (WDM) uplink/downlink twin single-sideband (twin-SSB) signals are implemented by a wavelength selective switch (WSS) at once, which simplifies the structure of multi-channel SSB transmitters and reduces the cost of high-capacity optical interconnect. Compared to a double sideband scheme, it has been experimentally proven that the performance of SSB transmission over standard single-mode fiber (SSMF) at C-band with an ultra-high baud rate has been greatly improved, which has the ability to effectively overcome the power fading induced by chromatic dispersion in an intensity modulation and direct detection (IM/DD) system. Besides, Rayleigh backscattering cross talk introduced by the same wavelengths in single-fiber bidirectional transmission is avoided by the proposed uplink/downlink twin-SSB scheme, which achieves 0.5-dB receiver sensitivity improvement compared to the conventional scheme. Finally, whtat is believed to be a record C-band 36.48-Tb/s PAM-4 4λ WDM IM/DD bidirectional optical interconnect is successfully demonstrated over 1-km 19-core fiber under a 20% soft-decision forward error correction (SD-FEC) threshold of 2.4×10-2 for beyond net 30-Tb/s large-capacity optical interconnection application.

Demonstration of a three-active-section DFB laser with photon-photon resonance and detuned loading effects to obtain enhanced bandwidth and maintained high output power

Enhancement of the modulation bandwidth of the directly modulated semiconductor laser has attracted tremendous attention for applications in optical fiber communication and optical interconnects. However, modulation bandwidth is enhanced by some special technology such as integrating the active region or passive region regularly, which lead to low power and complex fabrication. Here we design and demonstrate a monolithic integrated three-active-section distributed feedback (TAS-DFB) laser with enhanced bandwidth theoretically and experimentally. The laser includes three sections: the DFB section, feedback section and active phase section. The three sections share the same multiple quantum-well structure. To enhance the modulation bandwidth beyond the intrinsic modulation bandwidth, both photon-photon resonance (PPR) and detuned loading (DL) effects are utilized to achieve over 55 GHz. The active phase section shows promise in achieving high bandwidth with PPR and relatively high output power of ∼ 10 mW at 25 °C under continuous-wave (CW) operation simultaneously. The fabrication process of the TAS-DFB laser is simplified due to the conventional and identical active layer structure.

Characteristics of metallic coated ultra-short semiconductor Fabry-Pérot lasers

Fabry-Pérot (F–P) lasers have attracted significant attention due to their extensive applications in optical communication and precision measurement fields. However, traditional F–P lasers are relatively large in size and face challenges in directly achieving single-mode lasing, which limits their applications. In this study, we employ a metallic coating layer to significantly enhance the light confinement of the F–P cavity, thereby substantially reducing the cavity length of the F–P laser. We have experimentally developed an F–P laser with a cavity length of approximately 6.8 μm, successfully achieving single-mode lasing at room temperature. The lasing mode exhibits an ultra-narrow linewidth of 0.06 nm and a relative high side-mode suppression ratio exceeding 30 dB, along with good linear polarization. Additionally, we propose a type of on-chip integrated laser based on metallic-coated F–P cavities, characterized by high coupling efficiency and large fabrication tolerances. Simulation results indicate that the coupling efficiency for double-ended and single-ended output waveguides reaches 79% and 55%, respectively. The metallic-coated ultra-short F–P lasers have great potential for applications in on-chip optical interconnects and photonic integrated chip systems.

Sputtered quaternary alloy coating of Fe4CoNiCu for solid oxide fuel cell steel interconnects application

A quaternary Fe4CoNiCu alloy coating is applied on SUS 430 steel substrate for solid oxide fuel cell (SOFC) interconnects application via magnetron sputtering technology. The oxidation behavior of the coated steels is investigated in air at 800 °C. During initial oxidation, Fe and Co in the alloy coating is oxidized preferentially, forming Fe-rich oxide. Ni is oxidized to NiO by inward diffusion of oxygen. Slight Cu diffuses to or near the surface of the oxide scale to form CuO. Some Cu reacts with Fe3O4 to form CuFeO2 inside the oxide scale. The alloy coating is thermally converted into a quaternary spinel coating of (Fe,Co,Ni,Cu)3O4 with a small quantity of CuO existing on the surface and a protective Cr2O3 layer is formed at the steel/coating interface. The (Fe,Co,Ni,Cu)3O4 spinel layer effectively inhibits the growth of Cr2O3 layer and the outward diffusion of Cr. The scale ASR is 13.08 mΩ cm2 at 800 °C after 1680 h oxidation.

Understanding the deformation creep and role of intermetallic compound-microstructure in Sn-Ag-Cu solders

Tin-based alloys are commonly used in lead-free solder joints in electronic interconnection applications, where creep can limit joint reliability. In this work, directionally solidified bulk solder alloys of different compositions (pure tin, SAC105 and SAC305) are mechanically tested under a constant load for each composition at room temperature to understand mechanical creep performance and quantify the role of different content of Ag3Sn and Cu6Sn5 intermetallic compounds (IMCs) in terms of secondary creep strain rate, microstructural evolution, and total amount of accumulated strain. In this work, microstructures are fabricated using directional solidification to promote a systematic variation in IMC sizes, shapes, and distributions within similar crystal orientations of the primary β-Sn matrix. Analysis of creep data indicates that secondary creep is dominated by obstacle-controlled dislocation motion. This is further confirmed by electron backscatter diffraction (EBSD) analysis, which reveals that the formation of subgrains and internal structure, correlating to the initial microstructure of the sample, i.e. changes in secondary dendrite arm spacing (λ2) and eutectic intermetallic spacing (λe). The experimental observations are supported further by crystal plasticity simulations that explicitly model the presence of IMCs within the Sn-based samples and show the dependence of the secondary creep rate upon the IMC content, and therefore be beneficial for the possible future composition design in solders.

Low-temperature Cu-Cu direct bonding with ultra-large grains using highly (110)-oriented nanotwinned copper

With the application of Cu-Cu direct bonding technology in high-performance electronic devices, improving bonding reliability is essential for achieving high-density 3D IC integration. In this study, we innovatively applied highly (110)-oriented perpendicular nanotwinned Cu (p-ntCu) to achieve Cu-Cu direct bonding at low temperature and pressure. The anisotropic growth of p-ntCu during annealing at 200 °C resulted in the formation of ultra-large grains, which could improve the conductivity of the electrodeposited Cu film. Two Cu films were bonded at 200–250 °C with 2 MPa pressure for 1 h, and there was almost no void at the bonding interface. Anisotropic grain growth occurred within the bonding joint and grain boundary migration was observed at the bonding interface. The shear strength after bonding at 250 °C was measured as 58.3 MPa on average, indicating a relatively high quality of such Cu-Cu bonding. The p-ntCu can achieve Cu-Cu bonding and improve the conductivity by anisotropic grain growth at low temperature and pressure, which has great potential for Cu interconnect applications.

Single-fundamental-mode cryogenic (3.6 K) 850-nm oxide-confined VCSEL

Cryogenic oxide-confined vertical-cavity surface-emitting laser (VCSEL) has promising application in cryogenic optical interconnect for cryogenic computing. In this paper, we demonstrate a cryogenic 850-nm oxide-confined VCSEL at around 4 K. The cryogenic VCSEL with an optical oxide aperture of 6.5 μm in diameter can operate in single fundamental mode with a side-mode suppression-ratio of 36 dB at 3.6 K, and the fiber-coupled output power reaches 1 mW at 5 mA. The small signal modulation measurements at 298 and 292 K show the fabricated VCSEL has the potential to achieve a high modulation bandwidth at cryogenic temperature.

Unconventional magnetoresistance and resistivity scaling in amorphous CoSi thin films

The resistivity scaling of Cu electrical interconnects represents a critical challenge in Si CMOS technology. As interconnect dimensions reach below 10 nm, Cu resistivity increases significantly due to surface scattering. Topological materials have been considered for application in ultra-scaled interconnects (below 5 nm), due to their topologically protected surface states that have reduced electron scattering. Recent theoretical work on the topological chiral semimetal CoSi suggests that this material could offer lower resistivity than Cu at dimensions smaller than 10 nm. Here we investigate the scaling trend of textured and amorphous CoSi thin films, deposited by molecular beam epitaxy in a thickness range between 2 and 82.5 nm. Contrary to predictions of standard resistivity models, we report here a reduction in resistivity for thin amorphous CoSi films, which is instead consistent with surface-dominated transport. Moreover, magnetotransport measurements reveal significant enhancement of the magnetoresistance in scaled films, highlighting the complex transport mechanisms present in these highly disordered films at thicknesses of a few nanometers.

Co-Electrodeposition of Ni/Co–W and Cu/Co–W Alloys on Type 445 Stainless Steel for Application in SOFC Interconnects

Co-Electrodeposition of Ni/Co–W and Cu/Co–W Alloys on Type 445 Stainless Steel for Application in SOFC Interconnects

Modeling and analysis of crosstalk induced effects in graphene-carbon nanotube composite interconnects

This paper proposes an equivalent circuit model for two-line coupled multilayer graphene nanoribbon - single-wall carbon nanotube (MLGNR-SWCNT) composite interconnects (MSCs), incorporating the effects of coupling capacitance and mutual inductance. We also examine the temperature-dependent crosstalk effect on the victim line of MSCs in the time domain using decoupling techniques and the ABCD parameter matrix approach. This analysis is conducted at the global level of 7 nm, 14 nm, and 22 nm technology nodes, comparing the performance of MSCs with MLGNR, SWCNT, and copper (Cu) interconnects, validated through HSPICE simulations. Our results reveal that the crosstalk delay of all interconnects induced by dynamic crosstalk exhibits superior performance in the in-phase crosstalk mode compared to the out-of-phase mode at room temperature. In particular, MSCs demonstrate less crosstalk delay in both crosstalk modes compared to SWCNT and Cu interconnects. In addition, we analyze the crosstalk delay of the victim line for two-line coupled MSCs at varying temperatures in out-of-phase crosstalk mode, comparing them with MLGNR, SWCNT, and Cu interconnects. Simulation results indicate that the crosstalk delay is temperature-dependent, increasing with rising temperatures, and the crosstalk delay of MSCs is the least of all interconnects. Furthermore, we investigate the crosstalk noise of MSCs induced by functional crosstalk at different temperatures, comparing it with MLGNR, SWCNT, and Cu interconnects. It is observed that the crosstalk noise peak remains constant with temperature changes across all interconnects; however, the holding time and width of crosstalk noise increases with rising temperatures and MSCs have the least crosstalk noise peak and crosstalk noise width of all interconnects. Also, numerical results exhibit that reducing interconnect temperature, SWCNT diameter, and edge roughness of MLGNR are effective strategies to diminish the crosstalk delay of MSCs. In addition, increasing line spacing is identified as an effective method to reduce crosstalk noise peak of MSCs of different lengths. The proposed model results show excellent agreement with HSPICE simulation data. Therefore, our analysis of crosstalk effect manifests that MLGNR-SWCNT composite can be a promising material to replace SWCNT and copper as an ideal material for global interconnect applications in thermally variable environments.

Terminated polymer waveguide with low coupling loss to single-mode fiber for 100 Gbps optical interconnects and beyond.

We designed and fabricated terminated polymer waveguides with low coupling loss to a standard single-mode fiber (SSMF) for 100 Gbps optical interconnects application and beyond. The mode field diameter of the polymer waveguide is designed to perfectly match that of the SSMF with a theoretical coupling loss as small as 0.07 dB. The fabricated polymer waveguides on FR-4 substrates exhibit both a low propagation loss of 0.32 dB/cm and a low coupling loss of less than 0.17 dB to SSMF at a wavelength of 1310 nm. These low loss values indicate good compatibilities with both printed circuit boards and fiber optics. Both single-lane 56 Gbaud (112 Gbps) and 60 Gbaud (120 Gbps) 4-level pulse amplitude modulation (PAM4) optical transmission using terminated polymer waveguides have been successfully demonstrated. The bit error ratio (BER) for PAM4 transmission at both data rates reached a level of 10-4 which is well below the forward error correction (FEC) limitation with a power penalty of less than 1 dB. The bandwidth of the test equipment rather than the polymer waveguide itself limits the high-speed optical interconnect performances in our experiments. The results imply that the polymer waveguide is a promising media for single-lane 100 Gbps optical interconnects application and beyond.

Effect of Mixed Morphology (Simple Cubic, Face-Centered Cubic, and Body-Centered Cubic)-Based Electrodes on the Electric Double Layer Capacitance of Supercapacitors.

Supercapacitors store energy due to the formation of an electric double layer (EDL) at the interface of the electrodes and electrolyte. The present article deals with the finite element study of equilibrium electric double layer capacitance (EDLC) in the mixed morphology electrodes comprising all three fundamental crystal structures, simple cubic (SC), body-centered cubic (BCC), and face-centered cubic morphologies (FCC). Mesoporous-activated carbon forms the electrode in the supercapacitor with (C2H5)4NBF4/propylene carbonate organic electrolyte. Electrochemical interference is clearly demonstrated in the supercapacitors with the formation of the potential bands, as in the case of interference theory due to the increasing packing factor. The effects of electrode thickness varying from a wide range of 50 nm to 0.04 mm on specific EDLC have been discussed in detail. The interfacial geometry of the unit cell in contact with the electrolyte is the most important parameter determining the properties of the EDL. The critical thickness of the electrodes is 1.71 μm in all the morphologies. Polarization increases the interfacial potential and leads to EDL formation. The Stern layer specific capacitance is 167.6 μF cm-2 in all the morphologies. The maximum capacitance is in the decreasing order of interfacial geometry, as FCC > BCC > SC, dependent on the packing factor. The minimum transmittance in all the morphologies is 98.35%, with the constant figure of merit at higher electrode thickness having applications in the chip interconnects. The transient analysis shows that the interfacial current decreases with increasing polarization in the EDL. The capacitance also decreases with the increase of the scan rate.

Optimization of novel two-step curing method for die stack epoxy bonding to reduce voids in Ball Grid Array packages for high-density interconnect applications

This research explores the optimization of epoxy curing parameters to minimize void formation in 3-IC-Chip-MAPBGA packages, a subset of BGA packages, crucial components in high-density interconnect applications. The study utilizes a systematic approach involving design of experiments (DOE) assisted by statistical JMP tool to manipulate curing profiles, aiming to achieve void reduction while preserving adhesion properties. Various analytical techniques, including X-ray imaging, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), die shear strength tests, and C-Sam analysis for delamination, are employed to analyze void formation, material characteristics, mechanical properties, and structural integrity. The findings demonstrate that the sample with a 2nd step curing profile, identified as sample#3, which includes a ramp time of 15 min, a 1st step curing temperature of 90 °C with a soak time of 20 min, and a 2nd step ramp time of 20 min, exhibits the most favourable outcome in void reduction. This sample shows a notably lower void presence of 3.66 % and the highest die shear strength of 126 MPa. In contrast, the control sample, serving as a reference, displays a void percentage of 7.28 %, nearly twice as high as that of sample#3, and much lower die shear strength of 80 MPa at 25 °C. Adopting the curing profile of sample#3 also leads to a substantial 18.75 % reduction in cycle time compared to the control sample. The study highlights the importance of balancing curing parameters to mitigate void formation and maintain optimal mechanical properties, offering valuable insights for improving the reliability of high-density interconnect applications.

Optimization of electrophoretic deposition and thermal treatment of Cu–Mn spinel matrix for spinel/perovskite composite coating used as SOC metallic interconnect

The electrophoretic deposition of a mixture of copper-manganese spinel oxide matrix with perovskite oxide dispersion phase and subsequent two-step sintering was investigated as a means of obtaining a new spinel/perovskite composite coating for application in metallic interconnects for solid oxide cell (SOC) technologies. The effect of a number of factors was examined, including electrophoretic deposition parameters such as solvent type, time, voltage, and dispersant content as well as different heat treatment conditions on the quality of the matrix of the coating material. A solution of ethanol-acetone (25/75 v/v) and 2.0 g L−1 of iodine dispersant with a deposition time of 60 s and a voltage of 60 V provided the thickest, most uniform coating as deposited. SEM observations showed that a dense coating of Cu–Mn spinel was obtained after 8 h of reduction at 1000 °C followed by 6 h of oxidation at 850 °C. Selected preparation parameters were applied to deposit composite coatings with a Cu–Mn spinel matrix and the addition of LNF, LSC and LSCF perovskites.