A Light Shield Temperature Sensor for a Display Backplane

Abstract

Liquid Crystal Display (LCD) and Organic Light Emitting Diode (OLED) display are operated by voltage or current driving. Several types of Thin-Film Transistor (TFT) are used in the backplane of a display, LTPS and a-IGZO TFTs are those. As the applied voltage increases to increase the brightness of the display, heat generation also increases at the channel of the TFT. Such heat generation increase the temperature, which degrades the characteristics of the TFT, and decrease the lifetime of the organic device. Therefore, in order to keep the quality of the display, it is necessary to monitor the temperature of the display and control related signals to implement optimal image quality. There are various temperature sensors which can be used to detect such a temperature change in a display. In the case of using a discrete temperature sensor, the process and cost are increased by attaching the temperature sensor additionally. However, in the case of a temperature sensor integrated into the display, an process for the temperature sensor is not necessary. One way to integrate is using resistance changing material with a reference resistor outside. In this case, temperature accuracy can be reduced when the reference resistance changes due to the influence of the external temperature. To solve the problem, external reference resistance is removed in this proposed sensor scheme. Figure 1 shows the developed thin-film temperature sensor, which consists of two wires connected in series. The temperature coefficients of Molybdenum (Mo) and Indium Tin Oxide (ITO) are different from each other, and that of ITO is about 1.2 times or more than that of Mo. In this scheme, no external resistance is required. In addition, to reduce the process steps, a thin film temperature sensor is designed to replace a light shield layer which is formed at the bottom of the active layer to prevent the input of light. The two thin film materials are connected in series and the voltages at a connecting point are measured. The generated heat transferred to the temperature sensor was tested for repeatability and accuracy. The thin-film temperature sensor was designed to be located at the bottom of a-IGZO Top Gate TFT structure to check the heating during the operation of TFT. an interlayer insulation film was deposited on the temperature sensor before deposition of the active layer. The temperature of the TFT was measured by a temperature sensor Figure 1. shows the schematic cross-sectional structure of the developed oxide TFT with an integrated temperature sensor. Figure 1