Stretchable interconnections for flexible electronic systems.

Sensors, actuators and integrated circuits (IC) can be encapsulated together on an elastic substrate, which makes a flexible electronic system. In this system, electrical interconnections that can sustain large and reversible stretching are in great need. This paper is devoted to the fabrication of highly stretchable metal interconnections. Transfer printing technology is utilized, which mainly involves the transfer of 100-nm-thick gold ribbons from silicon wafers to pre-stretched elastic substrates. After the elastic substrates relax from the pre-strain, the gold ribbons buckle and form wavy geometries. These wavy geometries change in shapes to accommodate the applied strain and can be reversely stretched without cracks or fractures occurring, which will greatly raise the stretchability of the gold ribbons. As an application example, some of these wavy ribbons can accommodate high levels of stretching (up to 100%) and bending (with curvature radius down to 1.20 mm). Moreover, the efficiency and reliability of the transfer, especially for slender ribbons, have been increased due to the improvement of the technology. All the characteristics above will permit making stretchable gold conductors as interconnections for flexible electronic systems such as implantable medical systems and smart clothes.

Impedance spectroscopy analysis of cell-electrode interface.

Many chronically implanted electrodes suffer sensitivity loss in their applications in brain computer interface systems. It is hard to diagnose the cause of the problem because few measures are available to analyze directly what happened on the cell-electrode interface. In this paper, the impedance characterization of the cell-electrode interface was discussed in detail using equivalent circuit approach, which was used to evaluate the cause of the electrode sensitivity loss. The impedance spectroscopy of the cell-electrode interface acts as a function of several parameters, such as the sealing resistance and the shunt capacitance between the microelectrode and the electrolyte. Changes of the impedance spectroscopy can be traced to the parameter changes of the equivalent circuit, which reflect the status of the cell-electrode interface, such as the cell-electrode gap change, the erosion of microelectrodes, and so on. The circuit impedance simulation results give an important reference for the monitor of the cell-electrode connection, and are also helpful for the improvement of the microelectrode design.