Flexible and Transparent BEOL Monolithic 3DIC Technology for Human Skin Adaptable Internet of Things Chips

For the first time, below 400°C-fabricated poly-Si MOSFETs and 6T -SRAM fabrication process was demonstrated on polyimide (PI) substrate for flexible and transparent monolithic 3DIC. Key enablers are 400–900 nm transparent laser-stop layer (LsL), laser-crystallized/CMP-thinned poly Si channel and pulse UV-laser S/D activation. These advanced low thermal budget fabrication technologies enable stackable polySi MOSFETs on flexible 6” -wafer-scale PI substrate with high device uniformity $(\mathrm{V}_{\mathrm{th}}$ ‘SS~16.2%/16.6%) and bending stability $(\mathrm{V}_{\mathrm{th}}/\mathrm{SS}\sim 4.2\%/9.8\%)$ after cycle-bending at radius of 10mm. Such CMOS compatible technologies envision flexible 3D heterogeneous integration of circuits/optical sensors for human-skin adaptable Internet of Things (IoT) chips.