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Description
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Wireless microdevices are going smaller and smaller, at the point that we can talk about devices that are able to flow in our blood stream [1]. Nowadays, it’s possible to find proposals on devices for brain activity recording, for hearth activity registration, or prosthesis monitoring, to mention just a few biomedical applications. However, the power source and radiofrequency (RF) passives and antennas have not being scaling down at the same rate. To solve the problem of limited room for power sources, there is a trend on energy harvesting or scavenging [2], or on wireless powering [3]. Solutions based on energy harvesting may be feasible in some scenarios, but the power available is limited by the harvester volume [2]. And what prevents the use of wireless powering? The challenge is the same that the on-chip integration of RF passives and antennas faces, because, in fact, such solution requires the use of similar front-end passives, as required for wireless communications. They require the use of small, low-loss, and integrated RF passives and antennas. And, despite many proposals, that is still an open issue. The self-folding technology allows the fabrication of extra-small 3D devices [4] from 2D planar layouts, and it is being proposed for many applications. From available results, we were able to conclude that this technology is worthwhile to explore for RF and antenna application. That will allow fabrication of 3D devices, easily mounted on top of RF chips, allowing an unprecedented level of integration, with reduced losses. Moreover, a new degree of freedom is available to tune the properties of RF passives and antennas. It is already possible to fabricate 3D devices but that requires the use of molding techniques, DRIE, bulk or surface micromachining, just o mention a few. However, such technologies are expensive, and, more important, does not offer the possibility to easily fabricate high-aspect ratio structures with a high degree of flexibility on shapes, angles, and geometries. We believe the self-folding fabrication technology may represent a breakthrough in the integration of RF passives and antennas, and will allow the fabrication of RF passives and antennas with unthinkable geometries, at a minimal cost, both on size and system performance. The need for such research is unquestionable when performing a literature review. There is no solution available for efficient on-chip antenna integration that can be used straightforward, as we use a transistor. In this way, there is a current need for solutions that will allow to enable small biomedical devices with an efficient wireless link for powering and communications. And that need will increase in the future, since there is a current trend for placing more and more monitoring devices on-body and inside the body. In this way, the first expectable outcome will be a module that can be integrated with sensors and processing electronics to enable a fully integrated microsystem, with wireless power and communications. Since we already accomplished the design of a structure with less than 1 mm3, we believe that will be possible to release a wireless module, to operate in the 5-10 GHz frequency band with dimensions in that order of magnitude.
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