A method to control subthreshold swing (SS) in transistors by engineering Sn concentration through atomic layer deposition (ALD) subcycles was demonstrated. By increasing the number of Sn ALD cycles, the channel trap density (Nₜ) increased, resulting in SS modulation within the range of 0.161 to 0.231 V/decade. While SS increased, mobility improved, and threshold voltage (VTH) remained stable, indicating that the device's performance was not compromised. Sn concentration adjustment via ALD provides a more efficient approach for SS control, offering advantages in power efficiency and integration, particularly for AMOLED and OLED applications.