A High Gain Low-Noise Amplifier Based on ITO-Stabilized ZnO Thin-Film Transistors

A novel high gain low-noise analog amplifier based on n-type indium tin oxide (ITO)-stabilized ZnO thin-film transistors (TFTs) was studied in this work. Amplifiers with capacitor bootstrap structure are proposed. The effect of unequal numbers of bootstrap structure, various capacitance, and different circuit topology on the gain and noise of circuits were investigated. The input referred noise of five kinds of amplifier circuits, Amp1, Amp2 (C444, C333, C422), and Amp3 were measured to be 101.1, 44, 47.3, 43.5, and $38.3~\mu \text{V}_{rms}$ , respectively, and the gains are 19.5, 28.8, 26.8, 25.7, and 32 dB, respectively. It is found that as the numbers of bootstrap structure increase in a small range, the input referred noise decreases, and the circuit gain increases. The effects of the capacitance on the gain or noise can be negligible. And also, the gain of the circuit with cascode structure is higher than that with common source. Results show that the noise is much lower than that of a-InGaZnO (IGZO) TFTs technology, which is widely used in TFT circuits design. The proposed high gain and low-noise analog amplifier with the ITO-stabilized ZnO TFTs technology has great potential in the biomedical fields like electro cardiogram (ECG) and pulse detection, as well as wearable electronic applications.