Buried Double P-n Junction Research Articles

Quality monitoring of flowing water using colorimetric method based on a semiconductor optical wavelength sensor

Chroma and turbidity of flowing water were measured by using a colorimetric method that requires no conventional spectrophotometer, colorimeter or turbidimeter. A dual-wavelength light-source and a BDJ (buried double p–n junction) optical wavelength sensor were employed in the measurement. The intensity–insensitive photocurrent ratio of the two p–n junctions in the sensor is monotonously related to chroma and turbidity of water. The potential applications of this method of monitoring water chroma and turbidity, two important physics indexes to describe the quality of water, have been demonstrated. The results show that this simple method is sensitive and accurate, and not affected by fluctuation of flowing water.

CMOS absorbance detection system for capillary electrophoresis

This paper presents a cost-effective portable photodetection system for capillary electrophoresis absorptiometry. By using a CMOS BDJ (buried double p–n junction) detector, a dual-wavelength method for absorbance measurement is implemented. This system includes associated electronics for low-noise pre-amplification and A/D conversion, followed by digital signal acquisition and processing. Two signal processing approaches are adopted to enhance the signal to noise ratio. One is variable time synchronous detection, which optimizes the sensitivity and measuring rate compared to a conventional synchronous detection technique. The other is a statistical approach based on principal component analysis, which allows optimal estimation of detected signal. This system has been designed and tested in capillary electrophoresis conditions. Its operation has been verified with performances comparable to those of a commercialized spectrophotometric system (HP-3D CE). With potential on-chip integration of associated electronics, it may be operated as an integrable detection module for microchip electrophoresis and other microanalysis systems.

Design and testing of a CMOS BDJ detector for integrated micro-analysis systems

This paper reports the design and testing of a CMOS BDJ (Buried Double p–n Junction) detector for developing integrated microanalysis systems. The device is an optical detector producing two photocurrents (I1 and I2) when it receives an incident flux. It can be operated either as a photodetector by using its output current I1+I2, or as a colour detector if the photocurrent ratio I2/I1 is considered as the detector response. For photometric detection, the device has a sensitive response covering the visible and near-IR regions, and for colour detection, the photocurrent ratio I2/I1 versus wavelength is monotonic increasing when wavelengths are larger than 430nm. A statistical method is employed for sensitivity testing, and noise analysis is performed. At low signal levels, a minimum intensity-independent noise level, mainly due to noise contributions of the coupled amplifiers, sets a detectivity of about 0.7×1012cmHz1/2W−1. On-chip integration of low-noise preamplifiers may further improve sensitivity performance.

A dual-wavelength method using the BDJ detector and itsapplication to iron concentration measurement

A new and uncomplicated method for absorption detection is presented that requires no optical instrument such as a spectrophotometer or colorimeter. It makes use of a two-wavelength light source and a BDJ (buried double p-n junction) detector operating as wavelength-sensitive device. The intensity-insensitive photocurrent ratio rdual=I2/I1 is used as the detector response and is related to the absorbing species. A reference curve rdual(C) obtained by calibration serves to determine concentrations of the component. It has been theoretically shown and experimentally verified that the curve rdual(C) becomes linear at low concentrations. Through an investigation in the case of iron concentration measurements, the suggested method has proved to be sensitive and reliable. Keywords: BDJ detector, dual-wavelength method, absorption detection, concentration measurements

A colorimetric method with the use of BDJ detector for seawater pH measurement

By using a recently developed, wavelength-sensitive BDJ (buried double p-n junction) detector, a reliable and inexpensive method for colorimetric determination of seawater pH is suggested. A BDJ detector is a silicon photodetector providing two photocurrents proportional to the incident radiation, and the ratio of photocurrents is wavelength-dependent. In the visible range, the ratio of the deep junction photocurrent to the shallow junction one is monotonic increasing with the wavelength. This characteristic allows the BDJ detector to be applied to the detection of colours or spectral changes. For colorimetric seawater pH measurement with the use of tymol blue (TB) as pH-indicator dye, we propose a simple and reliable method based on the concept of the photocurrent ratio. By determining the concentration of the acidic form and that of the alkaline form in a dye solution, the pH can be deduced. The presented method has experimentally been verified, with a more stable dye, bromo phenol blue (BPB), which has very similar absorption spectra to those of the TB dye. As the design and fabrication of the BDJ detector requires only a standard CMOS process, a miniaturised pH-measuring system can be developed, thanks to the potential of on-chip integration of BDJ detector and electronic circuitry.

A seawater pH determination method using a BDJ detector

A novel colorimetric method using a new optical detector for seawater pH determination is presented. The used detector is a buried double p-n junction (BDJ) structure which provides two photocurrents whose ratio is sensitive to spectral changes. The BDJ detector directly picks up the transmitted signal for the determination of the solution pH. Both measurements and simulations have been performed to validate the suggested method which requires no spectrophotometer or colorimeter. The method, based on the concept of intensity-independent photocurrent ratio seems to provide a solution to the problems in development of compact, low cost, robust and reliable pH measuring systems. Such systems may be cost effective and miniaturized since the required BDJ detector can be monolithically integrated with electronic circuitry on the same chip in conventional CMOS technology.

Colour detection using a buried double p - n junction structure implemented in the CMOS process

The authors present a novel technique for monochromatic colour detection. By using a buried double p-n junction (BDJ) structure, wavelength-dependent photocurrents I1 and I2 can be measured. And the incident light wavelength can be identified from the ratio I2/I1. The device operation was verified with a test circuit implemented in CMOS process.