Creating electrical contacts between metal particles using directed electrochemical growth

Electrical connections in microelectronics are usually established by means of photolithography to define the conducting channels. But methods that do not involve lithography have been explored, such as the use of electrodeposition1 or electropolymerization2,3,4,5,6 to grow random structures of conducting material between two electrodes. This approach has been used to make diodes, transistors and signal amplifiers based on conducting polymers2,3. Template-based7,8,9,10,11,12 and thermal plating13 strategies have also been used to direct the growth of electrically conducting media. One advantage of these approaches over photolithography is the possibility of forming contacts in three dimensions and so achieving enhanced data-processing densities. Previous electrochemical approaches have required that the electrodes to be connected are physically linked to the external voltage source. Here we show that electrodissolution and electrodeposition processes in an applied electric field can be exploited to create directional growth of copper deposits between copper particles that are not connected to an external circuit. Moreover, the particles distort the electric field in such a way as to focus the diffusion of copper ions and consequently the direction of ‘wire’ growth, enabling the particles to be connected to one another in a directional and controllable manner. This suggests that appropriately directed electric fields may be used to connect an array of such particles into an arbitrary circuit pattern.