Using Amorphous Silicon Gap-Type Thin Film Transistor as Ambient Light Sensors and Proximity Sensors for Smartphones

Abstract

In the smartphone industry, there is a clear trend of developing high screen-to-body ratio display. In order to achieve this demand, we proposed the idea of integrating photo sensing devices into display panels. The photosensitive characteristic of amorphous silicon (a-Si) gap-type thin-film transistors is reviewed and the applicability is examined from the viewpoints of ambient light sensor and proximity sensor. The advantages and feasibility of this idea are fully investigated.

Light-Controlled Gap-Type TFT Used for Large-Area Under-Screen Fingerprint Sensor

“…The size of the device is 10µm in both channel width (W) and length (L), and the gap length (Li) is 4µm. Its process is identical to that of the conventional amorphous silicon TFT [10]. As the transfer curves shown in Fig.…”

“…There are several photosensitive devices can be made on the same substrate of TFT, including PIN diode [4], phototransistor [5][6][7], gap-type TFTs [8][9]. We consider that gap-type TFT is the best optical device in the under-screen fingerprint sensor for its good sensitivity and low cost owing to the high photocurrent and fully TFT-compatible process [10][11]. In this paper, a system with the gap-type TFT for the optical sensing array, the array under OLED panel with collimator in between, and the readout circuit is built to demonstrate the good performance in fingerprint image capture.…”

47‐1: Ambipolar Gap‐type a‐Si‐TFT Circuit Applied for a Color Ambient Light Sensor

“…Another way is shown in Fig. 1, where we propose ALS circuit designed around the LCD panel and located in the narrow margin of TFT array layer [2]. It avoids the problems of placing ALS under the screen.…”

Optical properties of a‐Si:H thin‐film transistors by illumination by white light with different colour temperatures

“…Unlike infrared or projected capacitive (Pcap) touch panels, TFT-based optical sensors can be directly fabricated on a glass substrate, realising a compact product without additional sensing modules [5][6][7][8][9]. Since hydrogenated amorphous silicon (a-Si:H) TFTs have good optical responses to visible light and have a uniform structure on large substrates, several optical sensors that are based on a-Si:H TFTs have been proposed for integration into LCDs and to support an optical input function and remote control for multiuser applications [10][11][12][13].…”