Temperature Sensor employing Ring Oscillator composed of Poly-Si Thin-Film Transistors: Comparison between Lightly-Doped and Offset Drain Structures

We propose a temperature sensor employing a ring oscillator composed of poly-Si thin-film transistors (TFTs). Particularly in this research, we compare temperature sensors using TFTs with lightlydoped drain structure (LDD TFTs) and TFTs with offset drain structure (offset TFTs). First, temperature dependences of transistor characteristics are compared between the LDD and offset TFTs. It is confirmed that the offset TFTs have larger temperature dependence of the on current. Next, temperature dependences of oscillation frequencies are compared between ring oscillators using the LDD and offset TFTs. It is clarified that the ring oscillator using the offset TFTs is suitable to detect the temperature. We think that this kind of temperature sensor is available as a digital device. key words: temperature sensor, ring oscillator, poly-Si, thin-film transistor (TFT), lightly-doped drain structure (LDD), offset drain structure