High-Linearity In-Pixel Thermal Sensor Using Low-Temperature Poly-Si Thin-Film Transistors

A novel highly linear thermal sensing scheme with thin-film transistor (TFT) reuse in a pixel circuit is presented for accurately extracting thermal information of each pixel in a display panel. Since the proposed sensor reuses existing TFTs of display pixels, the sensor can be easily embedded on the pixel, resulting in high compatibility and low cost. High conversion linearity of the proposed sensor is achievable by detecting the voltage difference between two driving TFTs of adjacent pixels operating at unequal current densities; this is based on experimental concept that the I-V transfer characteristic of an low-temperature polycrystalline-silicon (LTPS)-TFT in a subthreshold region can be modeled as an Arrhenius-like equation. Trimming methods for pixel-to-pixel spread on sensor inaccuracy are suggested, as well. The proposed thermal sensor was fabricated by using LTPS-TFT process to test the feasibility of its structure. With one-end-point calibration, the proposed thermal sensor achieves a measured inaccuracy of ±6 °C (±3σ) from 30 °C to 70 °C. After a spatial averaging with 16 sensors, the measured inaccuracy of maximum ±0.6 °C was achieved.