Temperature coefficient of diode-connected LTPS poly-Si TFTs and its application on the bandgap reference circuit

Abstract

The temperature coefficient (TC) of n-type diode-connected polycrystalline silicon thin-film transistors (poly-Si TFTs) is investigated. The relationship between TC and the activation energy is observed and explained. It is also found that TC is not sensitive to the deviation of the laser crystallization energy. On the contrary, channel width can effectively modulate TC. By using the diode-connected poly-Si TFTs with different channel widths, a new bandgap reference circuit for precise analog circuit design on glass substrate is proposed and realized. From the experimental results in a LTPS process, the output voltage reference exhibits a very low TC of 195 ppm/degrees C, between 25 degrees C and 125 degrees C.