Ultra-Thin Chips for High-Performance Semi-Transparent Flexible Electronics

Silicon-based ultra-thin chips (UTCs), with thickness below $50\ \mu\mathrm{m}$, are needed to meet high-performance (fast communication, computing etc.) requirements of several emerging applications such as robotics, internet of things etc. Below $10\ \mu\mathrm{m}$ thickness the UTCs are translucent and can offer new solutions for flexible opto-electronics applications. In this work, we present semi-transparent (44% to 67% transmittance under the visible spectrum) UTCs obtained from bulk silicon wafers, using a combination of mechanical lapping and chemical etching. The optimised thinning process leads to UTCs with extremely low thickness (as low as $\sim 2\mu\mathrm{m})$. To demonstrate the reliability of the proposed work, the optimised process has been adopted to realise UTCs with Metal Oxide Semiconductor Field Effect Transistors. The systematic electrical characterisation shows negligible changes between devices before and after thinning the Si wafer substrate. This study can potentially open avenues for manufacturing high performance semi-transparent flexible electronics.