Continuous Tunable Optical Detectors with a-Si:H Bias Sensitive Photodiodes
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Continuous Tunable Optical Detectors with a-Si:H Bias Sensitive Photodiodes Christian Merfort1, Konstantin Seibel1, Andreas Bablich1, Krystian Watty1 and Markus Boehm1 1 Institute for Microsystem Technologies (IMT), Siegen University, Hoelderlinstr. 3, 57076, Germany
ABSTRACT Today's image-based systems in civil security rely on sensors based either on CMOS or CCD technology, and they do not analyze color with sufficient equivalence to the human eye. The main reason for this is that the function of the fundamental color matching curves of the cones in the human eye can hardly be reproduced by technical systems [1]. Common color sensors are optimized for the three-area method in accordance with the standard DIN 5033-6. In civil security applications, for example, color sensors are used to identify the potential danger of whitish powder samples. Colorimetric classification based on the three-area method only provides suboptimal results [2], but not an unequivocal optical description. A series of tests performed at the IMT with more than 30 types of whitish powder samples were carried out with a spectrophotometer. These measurements showed that specimens with similar or different chemical compositions cannot be distinguished by the human eye, using the three-area method, exhibit characteristic differences in the CIE-L*a*b* measurement system under spectral method conditions. Until now, the realization of the spectral method on chip has been impossible with common color sensors. In this paper, we present a-Si:H-based bias-sensitive ni³p photodiodes, which have been fabricated successfully in a low temperature PECVD process. Present research focuses on the optimization of the continuous tunability of a-Si:H multispectral photodiodes, to increase the number of spectral stimulus specifications.
INTRODUCTION A fast and reliable detection of potentially dangerous substances has become very important in ensuring civilian safety in the recent past. Increased strict security checks at airports represent only one of many examples. For matters of time and money, it is a desirable solution to shorten the time required for these checks and ensure that they cause to passengers as little stress as possible. Modern security systems are only able to identify objects carried on the human body, in clothes or in bags. These systems could be considerably more effective if such objects could be properly characterized and identified. For instance, chemical tests are used to identify samples of whitish powder suspected of being dangerous or illegal. In these tests, however, a sample of the substance needs to be examined with the help of a swab analysis in a test tube. A color change in the sample show whether the result is positive or not. These tests are conducted very quickly, however they are relatively expensive. They can be used only once. In addition, most chemical tests recognize only a few substances. In a worst case scenario, many tests must be performed to identify a sample without doubt. To carry out such chemical analyses, a par
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