Ultra‐Thin Chips with Printed Interconnects on Flexible Foils
Sihang Ma, Yogeenth Kumaresan, Abhishek Singh Dahiya, Ravinder Dahiya
Abstract
Abstract “Heterogeneous Integration” is a promising approach for high‐performance hybrid flexible electronics that combine printed electronics and silicon technology. Despite significant progresses made by integrating rigid silicon chips on flexible substrates, the integration of flexible ultra‐thin chips (UTCs) on flexible foils remains a challenge as they are too fragile for conventional bonding methods. Reliable interconnects (low‐resistivity and mechanical robustness) and bonding of UTCs are critical to the realization of hybrid flexible systems. Herein, using a non‐contact printing approach, an easy and cost‐effective method for accessing UTCs on flexible foils is demonstrated. The high‐viscosity conductive paste, extruded from a high‐resolution printer (1–10 µm line width), is used here to connect the metal oxide semiconductor field effect transistors (MOSFETs) on UTCs with the extended pads on flexible printed circuit boards (PCBs). The electrical characterization of MOSFETs, before and after printing the interconnects, reveals an acceptable level of variation in device mobility (change from 780 to 630 cm 2 V −1 s −1 ). This is due to the drop in effective drain bias voltage as a marginally small electrical resistance (≈30 Ω) is added by the printed interconnects. The bonded UTCs show robust device performance under bending conditions, indicating high reliability of both the chip thinning and bonding methods.