Aging-robust amplifier composed of p-type low voltage OTFT and organic semiconductor load

Abstract

This paper proposes an amplifier circuit design suitable for low-voltage organic thin-film transistors (OTFTs). To overcome the issues common to low-voltage OTFTs, such as the yield, degradation, and performance differences between p-type and n-type TFTs, we design the circuit based on an inverter comprising only p-type transistors. The optimal bias voltage for the amplifier stage is provided through a bias circuit. The transistor performance degradation is compensated for by sharing the gate bias voltage (i.e. the main cause of degradation) between the bias and amplifier stages. In addition, an organic semiconductor is used as a passive load of the amplifier to reduce the area and failure probability. Test chip measurements demonstrate that the organic material operates as a resistor. The gain and cut-off frequencies of the proposed amplifier circuit can be adjusted by changing the size of the dinaphtho[2,3-b:2’,3’-f]thieno[3,2-b]-thiophene resistor, providing a maximum gain of 27 dB. The proposed circuit can operate continuously for over 100 min without significant characteristic changes. The operation of the bias circuit, when applied to a differential amplifier design, is also verified. The differential amplifier achieves a maximum common-mode rejection ratio of 25 dB.