Frequency modulation-type capacitance sensor using amorphous In-Ga-Zn-O thin-film transistors

We have developed a frequency modulation-type capacitance sensor using amorphous In-Ga-Zn-O (α-IGZO) thin-film transistors (TFTs) for integrated touchpanels. This capacitance sensor consists of a ring oscillator, whose one stage is replaced by a reset transistor, sensing transistor, and sensing electrode. The sensing electrode becomes one terminal when the other terminal is added by finger to form a sensing capacitor. The ring oscillator consists of pseudo CMOS inverters. We confirm that the oscillation output changes when the other terminal is added. This result indicates that this capacitance sensor can be applied to integrated touchpanels on flatpanel displays.