High-performance vertically stacked bottom-gate and top-gate polycrystalline silicon thin-film transistors for three-dimensional integrated circuits

The three-dimensional CMOS inverter with top-gate (TG) poly-Si thin film transistors (TFTs) vertically stacked on the bottom-gate (BG) poly-Si TFTs have been proposed to achieve high-performance characteristics via excimer laser crystallization (ELC) for the first time. Under an appropriate laser irradiation energy density, the silicon grain growth could be controlled from the sidewalls of the bottom-gate structure and thus the high-quality laterally grown poly-Si film with single perpendicular grain boundary in the channel would be formed for the BG TFTs. In addition, a simple ELC method was also utilized to the top-layered poly-Si film for TG TFTs as compared with solid-state-crystallized (SPC) ones. As a result, the field-effect mobilities of the proposed n-type BG and p-type TG TFTs could be significantly increased to be 390 and 131 cm2/V s, respectively, in contrast to 32.3 and 14.7 cm2/V s for the SPC ones, accordingly. Furthermore, such three-dimensional (3-D) TFT have also been employed to demonstrate the inverter devices and is suitable for future 3-D ICs as well as system-on-panel applications.

► A novel structure for three-dimensional integrated circuits.
► The CMOS inverter with a top-gate TFT vertically stacking on a bottom-gate TFT.
► Single perpendicular grain boundary formed in the channel for the bottom-gate TFTs.