'Living' electrodes breathe new life into traditional silicon electronics

High-speed electronic devices that do not use much power are useful for wireless communication. High-speed operation has traditionally been achieved by making devices smaller, but as devices become smaller, fabrication becomes increasingly difficult.

A research team at Osaka University is exploring another way to improve device performance: placing a patterned metal layer, i.e., a structural metamaterial, on top of a traditional substrate, e.g., silicon, to accelerate electron flow.

The findings are published in the journal ACS Applied Electronic Materials.

This method is promising, but a challenge is to make the structure of the metamaterial controllable, thereby allowing the properties of the metamaterial to be adjusted based on real-word conditions.

In search of a solution, the research team examined vanadium dioxide (VO₂). When heated appropriately, small areas in a VO₂ layer transform from insulating to metallic. These metallic regions can carry charge, thus behaving as tiny dynamic electrodes. The researchers exploited this behavior to produce ‘living’ microelectrodes that selectively enhanced the response of silicon photodetectors to terahertz light.

“We produced a terahertz photodetector containing VO₂ as a metamaterial,” explains lead author Ai Osaka.

“A precise processing method was used to fabricate a high-quality VO₂ layer on a silicon substrate. The size of the metallic domains in the VO₂ layer, tens of times larger than what has been conventionally achieved, was controlled through temperature regulation, which in turn modulated the response of the silicon substrate to terahertz light.”

When the temperature was suitably regulated, the metallic domains in the VO₂ formed a conductive network that controlled the localized electric field in the silicon layer, increasing its sensitivity to terahertz light.

“Heating the photodetector to 56°C led to strong signal enhancement,” adds senior author Azusa Hattori.

“We attributed this enhancement to effective coupling between the silicon layer and a dynamic conductive VO₂ microelectrode network at this temperature. That is, the temperature-controlled structure of the VO₂ metamaterial regulated electric field enhancement and thus impacts ionization in silicon.”

The temperature-regulated behavior of the “living” VO₂ metallic regions enhanced the response of silicon to terahertz light. These results illustrate the potential of metamaterials to spur the development of advanced electronics that overcome the limitations of traditional materials to meet speed and efficiency requirements.