Study on Silicon Color Sensor with Double PN Junction and Its Application
|Course||Microelectronics and Solid State Electronics|
|Keywords||Jilin University Doctoral Dissertation The width of the base Peak wavelength Incident Current ratio Semiconductor Photocurrent Absorption coefficient Current distribution|
The fast development of information technology makes color detection an important field in information science. Because of the difficulty in color calibration, less attention has been paid in color detection compared with radiative intensity detection. Thus, researches on color detection are valuable and in great need. Based on the strong dependence of light absorption coefficient in silicon on the incident light’s wavelength, silicon color sensor with double PN-junction can detect color information of the incident light, and it has been successfully used in detecting the wavelength of homogeneous light. Meanwhile, researches on identification of color difference and the measurements of both color-temperature and peak wavelength of polychromatic light are being carried out. With the advantages of low in cost, small in size, simple in structure, and being easily realized in online testing with a high reliability, this kind of silicon color sensor can be applied in many different fields. Thus researches carried out on silicon color sensor with double PN-junction are of great importance.In this thesis, we adopt the numerical simulation method to analyze the relationships among base current distributions color optical wavelength, base width, base doping concentration, and etc. The structure of the device and technical parameters also go through a series of optimal design in this paper. Purple-blue sensitivity of Silicon color sensor with double PN-junction is gained through appropriate selection from different structures of devices and technology conditions, on the base of which a device for panchromatic wave band has been fabricated. Based on the chromatism identifying ability of this kind of silicon color sensor, a color measurement system which can be used in tooth color identification has been designed.According to the absorption and transmission features of light in the semiconductors, as well as photovoltaic effect principles, we analyze the working principles of light in the semiconductor, establish one-dimensional model, and make assumptions on the distribution of photocurrents in the base region as follows. Assume that minority carrier in the upper section [xj1 to (xj1+xj2)/2] can only be spread to xj1 position, while the minority carrier in the lower section [(xj1+xj2)/2 to xj2] can only be directed towards xj2 under which condition base current distribution and transportation situation towards the two PN junctions have been theoretically analyzed, and two short-circuit current formulas （2.11） and （2.12） of PD1 and PD2 have been obtained. Two corresponding spectral response curves have been obtained from these formulas, and the working principles of silicon color sensor with double PN-junction have been stated by analyzing the relationship between short circuit current ratio and incident light wavelength.In this thesis, taken the function of self building electric field into account, we analyze and calculate how photocurrents in the base region are distributed to deep junction and shallow junction as shown in formulas （3.12）, （3.13） and （3.14）. Based on the former calculation, short circuit formula ISC1 and ISC2 have been revised. The results are analyzed by using the software MATLAB, and numerical analysis results can be well confirmed by the experiment. More accurate and reliable results have been obtained from our research which accords with the practical current distribution. Theoretic analysis results show that the doping concentration and junction depth are main factors for the range of spectrum response of Si color sensor with double PN junction. So that silicon color sensors fabricated by different technology will have distinctive identifying features. To fulfill the practical needs, we have to design different technology parameters so as to produce the finest color sensor.Considering the silicon material its own unique optical quality, within the bluish violet light to the ultraviolet wave band, devices responsiveness reduces along with the light wave length reducing rapidly and the effective detectability of color devices will be affected. Since lights within this wave band have widespread use in health, chemical industry, material, environmental protection, fanning and forestry domains, therefore to enhance the responding ability of the silicon color sensor with double PN-junction to the bluish violet light wave has become an important aspect in the color device research.The fine color sensor for panchromatic wave band with larger utility is gained through different matches of the structures of devices and technology conditions. When the color sensor instruments are working, those two PN junctions are both at the condition of short-circuit, and the correspondent short circuit currents of those two PN junctions are ISC1 and ISC2. Since the photo carriers excited by the incident light with different wavelength have different distribution, the ratio ISC2/ISC1 is closely related to the wavelength.Based on the chromatism identifying ability of this kind of silicon color sensor with double PN-junction, a new color measurement system which can be used in tooth color identification is designed, with the assistance of well-designed signal process circuit, control software and singlechip management. From the experiment we can get the conclusion that the precision and repetition properties of the instrument are much better than that of the direct naked eyes observation. With the advantages of small in size, convenient for use, high reliability and high accuracy, this new color sensor will be a promising short-cut for the tooth color identification, prosthodontics and tooth fabrication field.