Research On The New Structure Of Light-Addressable Potentiometric Sensor

Light-Addressable Potentiometric Sensor (LAPS) has many advantages, such as high sensitivity, good potential stability, fast response, simple manufacturing process, 'light-addressable', so it has been studied widely by reserchers all over the world since it was proposed.Firstly, this thesis will introduce the present status of LAPS from the view of the theory of LAPS, the structure of LAPS, the research of LAPS array, and the measurement of LAPS. It will give you a total understanding about the development of LAPS.Secondly, the thesis will introduce the principle of LAPS mainly from the solid-liquid interface potential theory of sensitive-membrane/electrolyte, the optical characteristics of semiconductor, the surface field effect of semicondutor. At the same time, the thesis will summarize and analyse the equivalent circuit model of EIS-LAPS, especially the composition of photocurrent.In the part of device design, the thesis will propose a new structure of LAPS array. LAPS array usually uses LED array as stimulative light source. LED has a large divergence angle, so it is difficult to avoid some light irradiating on the non-sensitive area between sensitive areas. The signal from the non-sensitive area is regarded as a kind of noise. And it is necessary to reduce the impact of the noise in design and application of LAPS array. In the existing literatures, it is mainly through covering dielectric layer such as polyimide, photosensitive resist, or growing thick oxide layer to solve the problem. But both of them have some limitations. The proposed new structure of LAPS array in this thesis has made some progress. We dope impurity heavily in the non-sensitive area and grow thick oxide layer on the surface during the manufacturing process. These methods can suppress the noise of non-sensitive area effectively. In the experiment, we use laser-beam with a few dozen microns in diameter to irradiate the sensitive area and the non-sensitive area of the chip from the front side, and then compare the two photocurrent corresponding the point of maximum slope of the characteristics curves. The result shows that the photocurrent of the non-sensitive area is much smaller than the sensitive area, less than -20dB. The new structure has good performance in niose suppression.In addition, the thesis will study some characteristics of LAPS, including the position of electrode, the intensity of light source, the thickness of oxide and the modulating frequency of light source. The thesis will give some advices to optimize the design of LAPS by analysing the above factors.