Bottom-up Cu deposition in metallized through silicon vias (TSV) depends on a co-adsorbed polyether–Cl − suppressor layer that selectively breaks down within recessed surface features. This work explores Cu deposition when formation of the suppressor blocking layer is limited by the flux of Cl − . This constraint leads to a transition from passive surfaces to active deposition partway down the via sidewall due to coupling between suppressor formation and breakdown as well as surface topography. The impact of Cl − concentration and hydrodynamics on the formation of the suppressor surface phase and its potential-dependent breakdown is examined. The onset of suppression breakdown is related to the local Cl − coverage as determined by the adsorption isotherm or transport limited flux. A two-additive co-adsorption model is presented that correlates the voltammetric potential of suppression breakdown with the depth of the passive-active transition during TSV filling under conditions of transport limited flux and incorporation of Cl − . The utility of potential waveforms to optimize the feature filling process is demonstrated. At higher Cl − concentrations (≥80 μmol/L), sidewall breakdown during Cu deposition occurs near the bottom of the via followed by a shift to bottom-up growth like that seen at higher Cl − concentrations.

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This work examines the filling of Through Silicon Vias (TSV) by Ni deposition from a NiSO 4 + NiCl 2 + H 3 BO 3 electrolyte containing a branched polyethyleneimine suppressor. Feature filling occurs due to the interaction of transport limited suppressor adsorption and its consumption by potential dependent metal deposition. The interaction between surface topography and suppressor transport yields a sharp transition from passive to active deposition within the TSV. The transition is associated with significant incorporation of the suppressor, or its components, within the Ni deposit that results in grain refinement evident by electron backscatter diffraction (EBSD). Potential waveforms that progressively shift the location of the passive-active transition upward to optimize feature filling were examined. The evolution of feature filling and deposit microstructure are compared to predictions of a three-dimensional model that reflect critical behavior associated with suppressor-derived, S-shaped negative differential resistance (S-NDR). The model uses adsorption and consumption kinetics obtained from voltammetric measurements of the critical potential associated with suppression breakdown. Good agreement between experiment and simulation is demonstrated.

Microscopic, spatially controlled, and highly efficient bipolar electrochemistry can be performed on an electrically-floating macroscopic conductive substrate using a tool we call the Scanning Bipolar Cell (SBC). The operating principle for the SBC is that current follows the path of least resistance. A high ohmic potential drop can be generated in the electrolyte adjacent to the conductive substrate by using a moderate conductivity electrolyte with a microjet cell geometry, inducing localized charge transfer on the substrate beneath the microjet. The equal and opposite redox chemistry necessary for sustained bipolar electrochemistry is spread over the macroscopic far-field of the floating conductive substrate. We combine experiments and finite element simulations to demonstrate this system using reversible copper redox chemistry. Bipolar electrochemical coupling to the surface can be highly efficient in the SBC and is governed by the balance of interfacial charge transfer and solution ohmic resistances, as characterized by the Wagner number of the system. Bipolar electrochemistry-spatially segregated, equal and opposite reduction and oxidation on an electrically-floating conductor-is a widely recognized phenomenon that is being reinvigorated as a useful tool for new kinds of electrochemical applications.1-11 The driving force for bipolar electrochemistry is the ohmic potential variation in solution that forms during the passage of current in an electrochemical cell. When there is an appreciable ohmic potential drop through solution, and a conductor is in that potential gradient, the path of least resistance for current flow can sometimes be through the conductor via bipolar electrochemistry.Electrodeposition processes are among the most common domains for this new breed of engineering-oriented bipolar electrochemistry applications. For example, copper interconnects can be grown between two electrically isolated copper posts without any direct electrical contact by placing them in a solution with high ohmic resistance.1,2 This generates a large electric field that creates sufficient voltage across each post to drive copper reduction and the growth of material between them (since it is bipolar, there is an equal but opposite oxidation also occurring). Similarly, one can also use the equal and opposite nature of bipolar electrochemistry to make Janus type conducting particles that are differentially decorated based on the induced bias across the dimensions of the particle.3 Bipolar electrochemistry that employs a reversible electrodeposition/etching chemistry can cause a free floating conductor of the active material to etch on one side and deposits an equal amount on the other side, resulting in a propagating chemical wave that moves in the direction of the solution potential gradient. 4 Applications for surface modification and electroanalytics have also recently been explored using bipolar electrochemistry. For example, bipolar electrochemistry induced by the solution potential gradient across a conductive subs...

Economic CO2 conversion to CO or syngas production requires product-selective, high-throughput, and durable electrolyzers. High-surface-area nanocatalysts combined with gas-diffusion layers (GDLs) enable high CO2 flux and conversion but can suffer from ineffective catalyst utilization, premature degradation, and flooding of the GDL that limit electrolyzer operation. Herein, a catalyst layer (CL) composed of a highly conductive catalyst bed of high-aspect-ratio Ag nanowire (Ag NW) electrocatalysts is integrated with a nonconductive porous polytetrafluorethylene (PTFE) GDL to enable more durable and selective electrolyzer performance. This platform enables exploration of CL thickness effects on catalyst utilization efficiency and selectivity. Combined with a 1-D computational model of the Ag NW-PTFE GDL, optimized CL thickness was found to be limited by significant depletion of local aqueous CO2 concentration, resulting in an optimal performance of 250 A/g (15× improvement) and a suppression of the hydrogen evolution reaction up to 20×. Furthermore, the local pH within the catalyst microenvironment indicates that local speciation of the bicarbonate electrolyte influences the selectivity between H2 and CO. Additional experimental measurements indicate that proton dissociation from bicarbonate contributes significantly to hydrogen evolution at intermediate overpotentials. The combination of a conductive and mechanically stable nanowire catalytic network with a hydrophobic PTFE porous support structure provides an effective platform for tuning the microenvironment of mesoscale catalysts for improved performance and durability during CO2 electroreduction.