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Single-Grain Si Thin-Film Transistors for Monolithic 3D-ICs and Flexible Electronics
Ryoichi ISHIHARA Jin ZHANG Miki TRIFUNOVIC Jaber DERAKHSHANDEH Negin GOLSHANI Daniel M. R. TAJARI MOFRAD Tao CHEN Kees BEENAKKER Tatsuya SHIMODA
IEICE TRANSACTIONS on Electronics
Publication Date: 2014/04/01
Online ISSN: 1745-1353
Type of Manuscript: INVITED PAPER (Special Section on Solid-State Circuit Design,---,Architecture, Circuit, Device and Design Methodology)
silicon, thin-film transistor, 3D-ICs, excimer-laser, crystallization, SRAM, image sensor, flexible electronics,
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We review our recent achievements in monolithic 3D-ICs and flexible electronics based on single-grain Si TFTs that are fabricated inside a single-grain with a low-temperature process. Based on pulsed-laser crystallization and submicron sized cavities made in the substrate, amorphous-Si precursor film was converted into poly-Si having grains that are formed on predetermined positions. Using the method called µ-Czochralski process and LPCVD a-Si precursor film, two layers of the SG Si TFT layers with the grains having a diameter of 6µm were vertically stacked with a maximum process temperature of 550°C. Mobility for electrons and holes were 600cm2/Vs and 200cm2/Vs, respectively. As a demonstration of monolithic 3D-ICs, the two SG-TFT layers were successfully implemented into CMOS inverter, 3D 6T-SRAM and single-grain lateral PIN photo-diode with in-pixel amplifier. The SG Si TFTs were applied to flexible electronics. In this case, the a-Si precursor was prepared by doctor-blade coating of liquid-Si based on pure cyclopentasilane (CPS) on a polyimide (PI) substrate with maximum process temperature of 350°C. The µ-Czochralski process provided location-controlled Si grains with a diameter of 3µm and mobilities of 460 and 121cm2/Vs for electrons and holes, respectively, were obtained. The devices on PI were transferred to a plastic foil which can operate with a bending diameter of 6mm. Those results indicate that the SG TFTs are attractive for their use in both monolithic 3D-ICs and flexible electronics.