An ultra-deep TSV technique enabled by the dual catalysis-based electroless plating of combined barrier and seed layers

Silicon interposers embedded with ultra-deep through-silicon vias(TSVs)are in great demand for the heterogeneous integration and packaging of opto-electronic chiplets and microelectromechanical systems(MEMS)devices.Considering the cost-effective and reliable manufacturing of ultra-deep TSVs,the formation of continuous barrier and seed layers remains a crucial challenge to solve.Herein,we present a novel dual catalysis-based electroless plating(ELP)technique by tailoring polyimide(PI)liner surfaces to fabricate dense combined Ni barrier/seed layers in ultradeep TSVs.In additional to the conventional acid catalysis procedure,a prior catalytic step in an alkaline environment is proposed to hydrolyze the PI surface into a polyamide acid(PAA)interfacial layer,resulting in additional catalysts and the formation of a dense Ni layer that can function as both a barrier layer and a seed layer,particularly at the bottom of the deep TSV.TSVs with depths larger than 500μm and no voids are successfully fabricated in this study.The fabrication process involves low costs and temperatures.For a fabricated 530-μm-deep TSV with a diameter of 70μm,the measured depletion capacitance and leakage current are approximately 1.3 pF and 1.7 pA at 20 V,respectively,indicating good electrical properties.The proposed fabrication strategy can provide a cost-effective and feasible solution to the challenge of manufacturing ultra-deep TSVs for modern 3D heterogeneous integration and packaging applications.

Programmable van-der-Waals heterostructure-enabled optoelectronic synaptic floating-gate transistors with ultra-low energy consumption

Van der Waals(vdW)heterostructures provide a unique opportunity to develop various electronic and optoelectronic devices with specific functions by designing novel device structures,especially for bioinspired neuromorphic optoelectronic devices,which require the integration of nonvolatile memory and excellent optical responses.Here,we demonstrate a programmable optoelectronic synaptic floating-gate transistor based on multilayer graphene/h-BN/MoS2 vdW heterostructures,where both plasticity emulation and modulation were successfully realized in a single device.The dynamic tunneling process of photogenerated carriers through the as-fabricated vdW heterostructures contributed to a large memory ratio(105)between program and erase states.Our device can work as a functional or silent synapse by applying a program/erase voltage spike as a modulatory signal to determine the response to light stimulation,leading to a programmable operation in optoelectronic synaptic transistors.Moreover,an ultra-low energy consumption per light spike event(~2.5 fJ)was obtained in the program state owing to a suppressed noise current by program operation in our floating-gate transistor.This study proposes a feasible strategy to improve the functions of optoelectronic synaptic devices with ultra-low energy consumption based on vdW heterostructures designed for highly efficient artificial neural networks.

Integrating surface and interface engineering to improve optoelectronic performance and environmental stability of MXenebased heterojunction towards broadband photodetection

Two-/three-dimensional(2D/3D)heterojunction-based photodetectors have attracted much attention due to their highly efficient photoelectric conversion driven by the built-in electric field for high-speed photoresponse.However,a large dark current induced by unexpected surface states at the interface between 2D materials and 3D bulks is widely observed in such structures,greatly degrading their optoelectronic performance.Herein,a heterojunction of proton acid HCl treated MXene(H-MXene)/TiO_(2)/Si via integrating surface and interface engineering is fabricated,which exhibits decreased dark current and improved environmental stability.A feasible strategy to optimize the interface properties between MXene and Si is proposed by an in-situ oxidation process of MXene into TiO_(2),resulting in a suppressed dark current as well as high specific detectivity.Benefitting from the enhanced light absorption of MXene on the bulk Si substrate,the photoresponse of as-fabricated devices in the near-infrared region is also elevated.Moreover,the treatment of proton acid HCl on the surface of MXene brings better conductivity and environmental stability due to the decreased layer spacing of MXene,which is further confirmed by both experimental and theoretical methods.This work opens a unique way to comprehensively boost the optoelectronic performance of MXene-based photodetectors.

Anisotropic electrical properties of aligned PtSe_(2) nanoribbon arrays grown by a pre-patterned selective selenization process

This study proposes a feasible and scalable production strategy to naturally obtain aligned platinum diselenide(PtSe_(2))nanoribbon arrays with anisotropic conductivity.The anisotropic properties of two-dimensional(2D)materials,especially transition-metal dichalcogenides(TMDs),have attracted great interest in research.The dependence of physical properties on their lattice orientations is of particular interest because of its potential in diverse applications,such as nanoelectronics and optoelectronics.One-dimensional(1D)nanostructures facilitate many feasible production strategies for shaping 2D materials into unidirectional 1D nanostructures,providing methods to investigate the anisotropic properties of 2D materials based on their lattice orientations and dimensionality.The natural alignment of zigzag(ZZ)PtSe_(2) nanoribbons is experimentally demonstrated using angle-resolved polarized Raman spectroscopy(ARPRS),and the selective growth mechanism is further theoretically revealed by comparing edges and edge energies of different orientations using the density functional theory(DFT).Back-gate field-effect transistors(FETs)are also constructed of unidirectional PtSe_(2) nanoribbons to investigate their anisotropic electrical properties,which align with the results of the projected density of states(DOS)calculations.This work provides new insight into the anisotropic properties of 2D materials and a feasible investigation strategy from experimental and theoretical perspectives.

A robust lateral shift free(LSF)electrothermal micromirror with flexible multimorph beams

Electrothermal bimorph-based scanning micromirrors typically employ standard silicon dioxide(SiO_(2))as the electrothermal isolation material.However,due to the brittle nature of SiO_(2),such micromirrors may be incapable to survive even slight collisions,which greatly limits their application range.To improve the robustness of electrothermal micromirrors,a polymer material is incorporated and partially replaces SiO_(2) as the electrothermal isolation and anchor material.In particular,photosensitive polyimide(PSPI)is used,which also simplifies the fabrication process.Here,PSPIbased electrothermal micromirrors have been designed,fabricated,and tested.The PSPI-type micromirrors achieved an optical scan angle of±19.6°and a vertical displacement of 370μm at only 4 Vdc.With a mirror aperture size of 1 mm×1 mm,the PSPI-type micromirrors survived over 200 g accelerations from either vertical or lateral directions in impact experiments.In the drop test,the PSPI-type micromirrors survived falls to a hard floor from heights up to 21 cm.In the standard frequency sweeping vibration test,the PSPI-type micromirrors survived 21 g and 29 g acceleration in the vertical and lateral vibrations,respectively.In all these tests,the PSPI-type micromirrors demonstrated at least 4 times better robustness than SiO_(2)-type micromirrors fabricated in the same batch.