Jae-Hyoun Park

Quantum-wired MOSFET photodetector fabricated by conventional photolithography on SOI substrate

NMOSFETs with a sub-30 nm-wide silicon quantum wire were fabricated and its electrical and optical characteristics were investigated. The silicon quantum wire was obtained by conventional photolithography with the help of anisotropic wet etching and reactive ion etching on a silicon-on-insulator substrate. Step-like conductance versus gate voltage, which is an evidence of one-dimensional electron motion, has been observed even at temperatures below 173 K. A maximum photo-responsivity of the quantum MOSFET was larger than 1/spl times/10/sup 2/ A/W at a wavelength of 632.8 nm. These features make this transistor feasible for applications to highly sensitive photodetectors.

Active Pixel Sensor Using a 1?16 Nano-Wire Photodetector Array for Complementary Metal Oxide Semiconductor Imagers

In this paper, a novel photodetector using an N-channel metal oxide semiconductor field effect transistor (NMOSFET) with a 30 nm-wide silicon nano-wire is described. The photodetector was fabricated on silicon-on-insulator (SOI) substrate and its wire was patterned by optical lithography, electron beam lithography and thermal oxidation. At room temperature, the device has similar IDS-VDS characteristics to a general NMOSFET when incident light is supplied instead of the gate voltage. A maximum responsivity of higher than 1×102 A/W and optical transient time of 80 µs have been obtained. Additionally, for the purpose of demonstrating the feasibility of the new device application, a 1×16 complementary metal oxide semiconductor (CMOS) active pixel sensor (APS) connected with the novel photodetector array was also designed and fabricated using 1-poly and 2-metal 1.5 µm CMOS technology. It is confirmed that this photodetector with high sensitivity as well as nano-scaled area could be applied to an image acquisition system for low illumination level.

Design of LED driver using digital up/down counter

A novel digital-controlled switch mode LED driver is presented, consisting of a digital up/down counter, a binary-to-PWM (pulse-width-modulation) converter, a comparator, and switching devices. The digital counter is a substitution of an error amplifier in a normal LED driver or a DC-DC converter. This counter increases or decreases its binary value, according as the output of the comparator is high or low. Then the binary value would be converted to a PWM signal which has a duty ratio proportional to the binary value and controls the switching devices. This is a novel digital-control algorithm for the proposed LED driver. We successfully verify the proposed digital-control algorithm using a test board which consists of a digital controller or a CPLD (complex programmable logic device) and several discrete devices such as a comparator, a transistor, and a Schottky barrier diode. And then, we design the novel LED driver through a 0.35μm 2-poly 4-metal 40V process.

Fabrication of silicon nano-wire MOSFET photodetector for high-sensitivity image sensor

We fabricated Si nano-wire MOSFET by using the conventional photolithography with a resolution. Si nano-wire was fabricated by using reactive ion etching (RIE), anisotropic wet etching and thermal oxidation on a silicon-on-insulator (SOI) substrate, and its width is 30 nm. Logarithmic circuit consisting of a NMOSFET and Si nano-wire MOSFET has been constructed for application to high-sensitivity image sensor. Its sensitivity was 1.12 mV/lux. The output voltage swing was 1.386 V.

Multi-channel LED driver with self-optimized active current regulator

A novel multi-channel LED driver is presented, consisting of an active current regulator and a switch-mode voltage regulator for each channel. This driver is implemented using a 0.35µm 40V high voltage process. The active current regulator directly controls an LED-current without any current-sensing resistor and its operating voltage is self-optimized by the switch-mode voltage regulator. This self-optimization is successfully achieved and the active current regulators have channel-current deviations of a maximum of ±2%. Its power-conversion efficiency is up to 91% at the load power of 7W.

Novel pixel calibration circuit for bolometer-type uncooled infrared image sensor

Lately, research on bolometer type uncooled infrared image sensor has been increasing for industrial applications. But it is hard to remove a Fixed Pattern Noise (FPN) of bolometer sensor. In this paper, a novel average-current calibration algorithm is presented for reducing bolometer resistance offset. A resistor which is produced standard CMOS process, on the average, has a deviation, respectively. We compensate for deviation of each active resistor using average-current calibration algorithm. The algorithm consists of as follows: bolometer pixel array, average current generator, current-to-voltage converters (IVCs), digital-to-analog converter (DAC), and analog-to-digital converters (ADCs). These bolometer-resistor array and readout circuit were designed and manufactured by 0.35μm standard CMOS process.

ADC-free digital-control switch-mode LED driver with high switching frequency

A new ADC-free digital-control switch-mode LED driver with 1MHz switching frequency is presented, which is featured by digital counters, a PWM generator, and current comparators. The digital counter consists of up/down counters with a delay routine. The counter increases or decreases its binary value, depending on comparison result between the output current and the desired current. Then a PWM signal can be generated, which its pulse width is determined by multiplication of the binary value and the clock period. To prevent oscillation of the counter value owing to high frequency clock, a delay routine is added. This designed LED driver is successfully implemented through a 0.35μm 2poly-4metal high voltage process.

Fully digitalized switch-mode LED driver without ADC

A digitalized switch-mode LED driver is implemented using a 0.35μm high voltage process, which featured by no use of any ADCs. The comparison result between the output current and the desired current causes the counter to increase or decrease its binary value which determines the duty ratio of the PWM signal. This PWM signal controls switching devices. A delay routine added in the counter prevents oscillation of the counter value owing to a high speed clock.

Current-to-Voltage Converter Using Current-Mode Multiple Reset and its Application to Photometric Sensors

Abstract Using a current-mode multiple reset, a current-to-voltage(I-V) converter with a wide dynamic range was produced. The converterconsists of a trans-impedance amplifier(TIA), an analog-to-digital converter(ADC), and an N-bit counter. The digital output of the I-Vconverter is composed of higher N bits and lower bits, obtained from the N-bit counter and the ADC, respectively. For an input currentthat has departed from the linear region of the TIA, the counter increases its digital output, this determines a reset current which issubtracted from the input current of the I-V converter. This current-mode reset is repeated until the input current of the TIA lies in thelinear region. This I-V converter is realized using 0.35 ㎛ LSI technology. It is shown that the proposed I-V converter can increase themaximum input current by a factor of 2 N and widen the dynamic range by 6 N . Additionally, the I-V converter is successfully applied to aphotometric sensor. Keywords : Current-to-Voltage Converter, Current-Mode Multiple Reset, Trans-Impedance Amplifier, Dynamic Range

Design of SOI CMOS image sensors using a nano-wire MOSFET-structure photodetector

In order to design SOI CMOS image sensors, SOI MOSFET model parameters were extracted using the equation of bulk MOSFET model parameters and were optimized using SPICE level 2. Simulated I-V characteristics of the SOI NMOSFET using the extracted model parameters were compared to the experimental I-V characteristics of the fabricated SOI NMOSFET. The simulation results agreed well with experimental results. A unit pixel for SOI CMOS image sensors was designed and was simulated for the PPS, APS, and logarithmic circuit using the extracted model parameters. In these CMOS image sensors, a nano-wire MOSFET photodetector was used. The output voltage levels of the PPS and APS are well-defined as the photocurrent varied. It is confirmed that SOI CMOS image sensors are faster than bulk CMOS image sensors.