An-Thung Cho

Silicon nanocrystal-based photosensor on low-temperature polycrystalline-silicon panels

A photodetector, comprising a layer of silicon nanocrystals that is sandwiched between two electrodes, is proposed and demonstrated in a photosensing application on low-temperature polysilicon panels. Laser annealing of silicon-rich oxide films can form nanocrystals that respond optimally to a certain absorption spectrum of a light source. These silicon nanocrystals are smaller than 10nm in diameter, which size determines the effectiveness of their quantum confinement, and promote electron-hole pair generation in the photosensing region because of their direct band gap. Besides obtaining a photosensitivity that is comparable to that of a p‐i‐n diode, which is currently used in low-temperature polysilicon technology, the sensor maximizes the photosensing area of a pixel by its stacked structure.

Integrated Ambient Light Sensor With Nanocrystalline Silicon on a Low-Temperature Polysilicon Display Panel

A novel integrated ambient light sensor using nanocrystalline silicon fabricated using low-temperature polysilicon technology has been developed on a display panel. The photosensing structure of the silicon nanocrystals embedded in a dielectric film sandwiched between the bottom metal and top indium-thin-oxide electrodes perfectly eliminates backlight noise, which is a problem typical of conventional p-i-n photodiodes integrated into a liquid-crystal display. Experimental results indicate that the Si-nanocrystal photosensor has better performances in dark current and quantum efficiency than those of the p-i-n diode. The Si-nanocrystal photosensor also exhibited response linearity and speed comparable to the p-i-n diode. In terms of long-term operation and reliability, the lifetime of the Si-nanocrystal photosensor is roughly two orders longer than that of the p-i-n diode. The Si-nanocrystal ambient light sensor has considerable flexibility in the design of spectrum, geometry, and the readout circuit, which is achieved by adjusting the nanocrystal size and applying a vertical stacking structure. The Si-nanocrystal photosensor can be a promising low-cost PMOS-only solution for various photosensing applications on display panels.

Silicon-nanocrystal-based photosensor integrated on low-temperature polysilicon panels

— A photodetector using a silicon-nanocrystal layer sandwiched between two electrodes is proposed and demonstrated on a glass substrate fabricated by low-temperature poly-silicon (LTPS) technology. Through post excimer-laser annealing (ELA) of silicon-rich oxide films, silicon nanocrystals formed between the bottom metal and top indium thin oxide (ITO) layers exhibit good uniformity, reliable optical response, and tunable absorption spectrum. Due to the quantum confinement effect leading to enhanced phonon-assisted excitation, these silicon nanocrystals, less than 10 nm in diameter, promote electron-hole-pair generation in the photo-sensing region as a result resembling a direct-gap transition. The desired optical absorption spectrum can be obtained by determining the thickness and silicon concentration of the deposited silicon-rich oxide films as well as the power of post laser annealing. In addition to obtaining a photosensitivity comparable to that of the p-i-n photodiode currently used in LTPS technology, the silicon-nanocrystal-based photosensor provides an effective backlight shielding by the bottom electrode made of molybdenum (Mo). Having a higher temperature tolerance for both the dark current and optical responsibility and maximizing the photosensing area in a pixel circuit by adopting a stack structure, this novel photosensor can be a promising candidate for realizing an optical touch function on a LTPS panel.

Flat panel fingerprint optical sensor using TFT technology

A 3.2×3.0 inch2 optical type fingerprint scanning flat panel is designed and implemented. The driving system is based on the passive pixel sensor (PPS) array with amorphous silicon (a-Si) TFT technology. The sensing layer of the optical sensor is composed of the Si-nanocrystals (Si-NCs) embedded in the dielectric material. The pixel density is over 500 PPI and the gray levels are up to 256 with excellent linearity.

Sensitivity enhancement of ion sensors by charge trapping on Extended Gate Field Effect Transistors

Electrolyte-insulator-semiconductor (EIS) and Extended-gate Field Effect Transistor (EGFET) devices with programmable HfO2/Si3N4/SiO2 structures are demonstrated for pH detection. The proposed programmable EIS and EGFET sensors with pH sensing membranes exhibit a high pH sensitivity (larger than the ideal Nernstain response, 59.16 mV/pH at 25°C) owing to the hydrogen ions attraction by electrons trapped within the embedded trapping layer(Si3N4) after programming. When compared with the conventional devices, the programmable sensors with programming provide the possibility for the small pH fluctuation detection and can be used in future pH sensor applications owing to its high pH sensing response.

P-191: Embedded Nano-Si Optical Sensor in TFT-LCDs Technology and Integrated as Touch-Input Display

We report the controllable UV-Visible-to-NIR Si-nanocrystals photonic sensor, photo-spectrum band-gap engineering technology, and integrated in TFT-LCD as multi-function intelligent display. Photonic Sensor using Si-nanocrystals as sensitizer sandwiched between two electrodes structure is proposed to integrate optical input function for new application in next generation mobile devices. The optical input function, used for image scanner, fingerprint recognition, and touch-input application, are achieved by integrating these image sensor elements within each display pixel. A 2-transistor (2T) active pixel sensor (APS) is used to integrate a VGA (> 250 dpi) image sensor within an LCD panel.

22.4: In‐Cell Multiple Ambient Light Sensor (ALSs) LCD Integration Using Si‐based Photonic Sensor by a‐Si TFT Technology

We have developed a new AMLCD with multiple ambient light sensors (ALSs) for reducing backlight (BL) power consumption, and false sensing of ambient illuminance. ALSs perform well in showing BL control for power-saving, even though one of the sensors is covered by a finger shadow. Architecture of integrated ALS with a-Si and LTPS technologies are presented. We fabricate the in-cell, and wide-dynamic-sensing ALSs display using new light sensor technology. Photo-electrical characteristics with well linearity and reliability under long-term operation were observed.

P-199L: Late-News Poster: Silicon Nanocrystals Photo Sensor Integrated on Low-Temperature Polycrystalline-Silicon Panels

A photo-detector using silicon nanocrystal layer sandwiched between two electrodes is first time proposed and demonstrated for photo-sensing application on LTPS panels. Through post-annealing of silicon rich oxide films, Si nanocrystals can be formed with good uniformity and high temperature tolerance to respond best to certain absorption spectrum of the corresponding light source. These silicon nanocrystals, less than 10nm in diameter, exhibit better quantum confinement effect, which promote electron-hole pair generation in photo-sensing region as a result of its direct bandgap. In addition to obtaining photo sensitivity superior to that of a P-I-N diode currently used in LTPS technology, the new sensor can maximize the fill factor in a pixel circuit by adapting a stacked structure.