Low-Frequency Noise in Electric Double Layer InGaZnO Thin-Film Transistors Gated with Sputtered SiO₂-Based Electrolyte

Using electrolyte as the gate dielectric to form an electric double layer (EDL) is an effective method to reduce the operating voltage of thin-film transistors (TFTs). Such TFTs are typically able to work at a low voltage of 1 V. However, there has been very limited work on the low-frequency noise (LFN) properties of EDL TFTs despite that the nature of EDL means an accumulation of a large number of ions at the channel interface which may well play an important role in device electronic noise. Here, the LFN properties of amorphous indium–gallium–zinc oxide (a-IGZO) EDL TFTs gated with sputtered SiO2-based electrolyte are characterized. The LFN in the EDL TFTs shows two distinctively different dependencies on frequency in different gate bias ranges, i.e., 1/f noise and 1/f2 noise. The 1/f noise generated at low gate voltages VG < 1 V is determined to be flicker noise which follows the carrier mobility fluctuation model. The 1/f2 noise generated at high gate voltages VG > 1 V, on the other hand, is found to be generation–recombination noise. Heat treatment, which reduces ions inside the electrolyte, leads to a dramatic reduction of the 1/f2 noise. Our work shows that the generation–recombination noise might be related to the moisture-induced ions inside the sputtered SiO2-based electrolyte. A larger VG results in a deeper position of the generation–recombination centers at the dielectric/channel interface.