Wen-Jen Chiang

Electromagnetic Energy Harvesting Circuit With Feedforward and Feedback DC–DC PWM Boost Converter for Vibration Power Generator System

This paper presents an integrated vibration power generator system. The system consists of a mini electromagnetic vibration power generator and a highly efficient energy harvesting circuit implemented on a minute printed circuit board and a 0.35-mum CMOS integrated chip. By introducing a feedback control into the dc-dc pulsewidth modulation (PWM) boost converter with feedforward control, the energy harvesting circuit can adjust the duty ratio of the converter following the variation of the input voltage and the voltage of energy storage element to get high energy conversion efficiency. The energy harvesting circuit rectifies the input ac voltage, steps up the dc output of the rectifier by the dc-dc PWM boost converter with feedforward and feedback control and stores the electric energy into a super capacitor, which can be used as a small electrical power supply for an intelligent micro sensor network

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.

Embedded Optical Sensor Using Gate-Body-Tied Thin-Film Transistor on Low-Temperature Poly-Silicon Display Panel

An embedded photosensor using a gate-body-tied (GBT) thin-film transistor is investigated on a low-temperature poly-silicon display panel. The GBT photosensor is formed by connection of the floating gate and body in a metal-oxide-semiconductor field-effect transistor (MOSFET). The intrinsic body region without gate metal on top is the photosensing area where the photogenerated electron-hole pairs are excited and separated. The GBT structure leads to photogenerated carrier accumulation on the floating gate and results in positive feedback of gate potential and increase of MOSFET current. Thus, the photocurrent is amplified. The photoresponse is enhanced to two to three times that of the conventional p-i-n photodiode.

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.

A New Photodiode Model for SPICE Simulation of Complementary Metal?Oxide?Semiconductor Image Sensors

In this paper, a novel photodiode model that better describes the electro optical behavior of a complementary metal–oxide–semiconductor (CMOS) image sensor has been developed. The conventional diode model adopted by Berkeley short-channel insulated-gate field-effect transistor model 3 (BSIM3) suffers from a large discrepancy between simulation and measurement results for CMOS image sensors (CISs). The simulated response exceedingly overestimates the dark signal and is unable to provide the optical response of a CIS pixel circuit. A closed-form photodiode model is proposed in our work. The experimental results demonstrate that this photodiode model can accurately predict the relationship between the diode current and the operation voltage, temperature, incident light intensity and wavelength. Using the novel photodiode model, a more precise environment can be established for performance optimization and system-on-chip simulations in various CIS applications.

A logarithmic response complementary metal oxide semiconductor image sensor with parasitic P-N-P bipolar junction transistor

Logarithmic-response complementary metal oxide semiconductor (CMOS) active pixel sensors provide a desirable attribute of wide dynamic range even with low supply voltages. In this paper, a log-mode pixel with employing parasitic P–N–P bipolar junction transistor (BJT) to amplify photo-current is investigated and optimized. A new log-mode cell with a calibration transistor is proposed to increase the output voltage swing as well as to reduce the fixed pattern noise. The measurement results demonstrate that, the output voltage swing of this new cell is enhanced by 4× and fixed pattern noise (FPN) of a pixel array can be reduced by 10× comparing to that of a conventional log-mode CMOS active pixel sensor.

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.

Optimization of The Ultra-Low Dark Current Complementary MOS Image Sensor Cell Using n+ Ring Reset

An ultra low dark current pixel has been developed for embedded active-pixel complementary metal oxide semiconductor (CMOS) image sensors using a standard CMOS logic process. Conventional CMOS image sensors suffer from high dark current as a result of the high interface state density at the field oxide edge. In the proposed novel pixel, the photo-sensing diode is surrounded by a ring-shaped poly-silicon reset gate which isolates the photo-sensing area from the field oxide edge. Hence, the dark current level can be effectively reduced. However, in the novel pixel, the large overlap capacitance between the reset poly-gate ring and the sensing node can severely affect the output swing. To optimize this novel pixel, the poly-silicon gate is limited to isolate the photo-sensing area from the field oxide edge. Furthermore, a constant bias voltage applied to the poly-silicon gate provides an additional advantage of extended dynamic range. The effects of technology scaling on the pixel performance are investigated as well.