Infrared sensors using poly‐Si thin‐film transistors for proximity sensors integrated in smartphone displays

Abstract

We have developed infrared sensors using poly‐Si thin‐film transistors (TFTs) for proximity sensors integrated in smartphone displays. Initially, we evaluate the infrared sensitivities of the poly‐Si TFTs, and it is found that a pin‐type TFT is suitable for the infrared sensors. Next, we propose three types of the infrared sensors. First, an analog current detection‐type sensor has a simple structure, and it is found that it can detect presence of a hand. Second, a lock‐in detection‐type sensor has tolerance against ambient light, and it is found that it can detect a target signal under noise signals. Third, a frequency detection‐type sensor has an advantage that only a digital circuit is necessary for detection, and it is found that it can detect the infrared intensity because the oscillation frequency increases monotonically with the intensity. We can utilize these infrared sensors on demand.

Sensor applications of thin‐film devices originating in display technologies

“…We are also investigating the infrared sensors composed of the thin‐film devices. Proximity sensors are practical application examples of the infrared sensors . Proximity sensors using infrared sensors are shown in Figure .…”

“…49,50 Proximity sensors using infrared sensors are shown in Figure 17. 50 We have developed infrared sensors using LTPS TFTs for proximity sensors integrated in smartphone displays. Initially, we evaluate the infrared sensitivities of the LTPS TFTs, and it is found that a p/i/ n transistor is suitable also for the infrared sensors.…”

“…Proximity sensors are practical application examples of the infrared sensors . Proximity sensors using infrared sensors are shown in Figure . We have developed infrared sensors using LTPS TFTs for proximity sensors integrated in smartphone displays.…”

50.1: Invited Paper: Sensor Applications of Thin‐Film Devices

“…The infrared-light sensor is also operated based on the working principle that the free carriers are generated when the infrared irradiation is done [10]. It can be applied to proximity sensors, etc [11].…”

Vertical integration: a key concept for future flexible and printed electronics

“…TFTs have recently seen a dramatic increase in their technological relevance mainly due to the global market expansion of flat-panel display products since the 1970's (e.g. liquid-crystal displays, organic lightemitting diode displays) which rely on TFT-based pixel driving, and which have obviously become an indispensable part of our daily lives [10][11][12][13][14][15][16]. It is worth recognizing that TFTs also serve as an excellent testbed for fundamental studies on charge transport and injection properties of new semiconductor materials [17][18][19][20][21][22].…”