Transfer-printed microscale integrated circuits

Transfer-printing is an emerging technology that enables massively parallel assembly of microscale semiconductor devices onto virtually any target substrate, including glass, plastics, metals or other semiconductors. Transfer-printing is accomplished using a microstructured elastomeric stamp to selectively pick-up devices from a source wafer and then print the devices onto a target substrate. The process is massively parallel as the stamps are designed to transfer hundreds to thousands of discrete devices in a single pick-up and print operation. Previous studies using bare silicon chips [1] demonstrated transfer-print yields in excess of 99% and chip placement accuracy better than plusmn 5 mum. For the first time, foundry-produced CMOS integrated circuits have been designed and transfer-printed. The ICs were designed and built using a commercially available silicon-on-oxide (SOI) CMOS process. The buried oxide (BOx) underneath the device layer is used as a sacrificial layer to ldquoreleaserdquo the ICs from the handle wafer. Microfabricated silicon bridges, or tethers, are used to fasten the ICs to the handle wafer following the sacrificial etch. A process was developed to remove the sacrificial BOx while protecting the interlayer dielectric (ILD) and Aluminum wiring levels present in the ICs. The microscale ICs have been transfer-printed with yields in excess of 99.5% and with placement accuracies better than plusmn 5 mum. Surface topography present on the ICs did not negatively impact the transfer-printing process. Initial studies show that transfer-printing has negligible impact on the I-V characteristics of transistors.