Single Grain Si TFTs for RF and 3D ICs

Abstract

Single-grain Si TFTs have been fabricated using accurate 2D location control of large Si grain with the μ-Czochralski process. TFTs fabricated inside the crystalline islands of 6 μm show a mobility (600cm2/Vs) as high as that of the SOI counterpart, despite of the low-temperature (<350oC) process. By applying a tensile stress into the grain, the mobility surpass even the SOI counterparts. We have succeeded in controlling crystallographic orientation of the location-controlled Si grains as well, by combination of metal induced lateral crystallization and the micro-Czochralski process. Owing to the orientation control, uniformity in device properties approaches to the level of the SOI counterpart. Using the high performance single-grain (SG) Si TFTs, we have fabricated RF amplifier. The cut-off frequency of the RF device is 5.5 GHz with a channel length of 1.5 μm. We have even succeeded to stack two SG-TFT layers with which CMOS inverters were fabricated. This will open several new applications in TFTs of RF wireless communication, 3D-ICs with device level integration, and flexible electronics.