Programmable Hard‐Wiring of Circuitry Using Spatially Coupled Bipolar Electrochemistry

2016

We describe electrolyte design for bipolar electrochemical growth and patterning of a range of materials on an electrically floating substrate using the scanning bipolar cell (SBC). In the SBC, bipolar electrodeposition is driven by local potential variation generated beneath a rastering microjet anode connected to a far-field cathode. Metal reduction occurs beneath the microjet when the substrate is approached, provided the electrolyte possesses a suitable reducing agent that undergoes oxidation across the substrate far-field. We use a series of metal reduction reactions (Ni, Cu, Au, Ag) that cover a wide range of nobility, and couple them to the oxidation of ascorbic acid or ferrous ion, depending upon the metal used. The reversibility or irreversibility of the local metal reduction reaction dictates details of the required electrolyte thermodynamics. For irreversible deposits (Ni, Au), there is a wide thermodynamic operating window for the bipolar counter reaction. Reversible deposits that are easily etched (Cu, Ag) have tight thermodynamic windows; deposit stability requires the use of metastable electrolytes. We provide a simple scaling relationship that incorporates the electrolyte thermodynamics, interfacial charge transfer kinetics, and SBC operating conditions, then demonstrate its use through a 10X reduction in the spatial dimensions of local nickel reduction chemistry. Bipolar electrochemistry enables remote control of an electrochemical system without any direct electrical connection to the conducting substrate.1-13 Bipolar electrochemical systems involve spatially segregated, equal and opposite reduction and oxidation on an electrically floating substrate. The driving force for bipolar electrochemistry is the ohmic potential variation in an electrolyte that forms during the passage of current. When there is an appreciable 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 electrochemical reactions occurring on different regions of the conductor. To achieve remote control materials patterning, the electrolyte chemistry and electrochemical cell must be tailored to work together.In recent years, bipolar electrochemical systems have been used for new kinds of electrochemical applications ranging from electrodeposition to electroanalytical chemistry. For example, bipolar electrochemistry can be used to grow interconnects between electrically isolated conducting posts in an electrolyte.1,2 Bipolar electrochemistry has also been successfully used for screening electrocatalysts where a hard to detect reaction rate is readily visualized by an equal and opposite electrochemical indicator.3-5 Typical bipolar systems have used resistive electrolyte solutions and macroscopic electrochemical cells to produce the electrolyte potential gradients needed to drive bipolar reactions on small conductors. Here, we demonstrate and generalize a microscopic electrochemical cell configuration (termed ...

Section: Methodsmentioning

confidence: 99%

Remote Control Electrodeposition: Principles for Bipolar Patterning of Substrates without an Electrical Connection

2016

“…The boundary condition for the feeder anode is defined by Eq. 7 and the feeder cathode boundary condition is − κn · ∇φ = −I app A cathode [9] where A cathode is the area of the outer ring cathode. The most general form for the reaction rates at the conductive substrate are given by a modified Butler-Volmer kinetic approximation…”

Section: Simulation Methodsmentioning

confidence: 99%

“…Eliminating the need for direct electrical connections to the substrate has generated several new bipolar electrochemical applications ranging from electroanalytical chemistry to electrodeposition. [1][2][3][4][5][6][7][8][9][10][11][12][13] For example, bipolar electrochemistry has been used for screening electrocatalysts, where the hard to detect electrocatalytic rate is visualized by an equal and opposite indicator chemistry such as electrochemiluminescence 1,2 or metal etching. [3][4][5] Bipolar electrochemistry has also proven useful for electrodeposition of material gradients 6,7 and to grow interconnects between electrically isolated conducting posts.…”

mentioning

confidence: 99%

Analytical and Computational Scaling Relationships for the Coupled Phenomena that Control Local Bipolar Electrochemical Behavior

2016

Bipolar electrochemistry involves intricate coupling of ionic migration in the electrolyte, charge transfer kinetics of the equal and opposite oxidation and reduction chemistries, and the thermodynamic relationship of the bipolar couple. Finite element method simulations are used to explore these coupled phenomena in the scanning bipolar cell (SBC), an experimental system we recently introduced. We generalize simulation results through the development of scaling relationships based on a linearized equivalent circuit model comprised of resistors and a transistor. Accurate analytical expressions are presented for the SBC electrolyte ohmic resistance. Secondary current distribution simulations for two thermodynamically distinct bipolar couples identify the most appropriate linearizations for the charge transfer resistance. In our model, the bipolar redox couple can have a thermodynamic barrier that serves as a gate voltage for switching the transistor that enables or blocks bipolar current flow through the substrate. The resulting resistortransistor network provides an analytical expression for the bipolar current efficiency, the fraction of applied current participating in bipolar electrochemistry. Simplification of coupled (nonlinear) phenomenon into circuit elements has inevitable inaccuracies, and we explore the origins and size of these systematic errors. The implications of the scaling ideas presented here are generalizable for other purpose-driven bipolar electrochemical systems.

“…[1][2][3][4][5][6][7][8][9][10][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.…”

mentioning

confidence: 99%

“…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.…”

mentioning

confidence: 99%

Localized Electrodeposition and Patterning Using Bipolar Electrochemistry

2015

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...