Microwave Flexible Electronics Directly Transformed from Foundry-Produced, Multilayered Monolithic Integrated Circuits

Monolithic microwave integrated circuits hold a dominant position in telecom applications, especially in mobile devices with capabilities for wireless connectivity, due to high and repeatable performance, compact form factor, and low cost. With flexible electronic technologies forming the foundation for a rapidly growing wearable and implantable device segment, the need for flexible microwave electronics with levels of performance that match those of rigid counterparts has increased to unprecedented levels. Here, the fabrication processes for transforming a rigid form of foundry-produced, multilayered monolithic microwave integrated circuit into a flexible format for amplification of radio frequency signals in the gigahertz level are described. The strategy involves a complete replacement of all rigid materials in the integrated circuit that do not provide any active electronic functionality with a soft, silicone elastomer to yield an overall structure that is mechanically compliant. Experimental studies indicate that the transformation process leads to a flexible silicon-germanium-based heterojunction bipolar transistor with a maximum oscillation frequency of 49 GHz and a 24 GHz amplifier with a small-signal gain of 13.2 dB. This approach has potential uses across a diverse set of microwave devices and circuits, in a manner that could enable wireless connectivity using entirely flexible electronics.