The improvement of a filter-less fluorescence sensor, by suppressing forward scattering in silicon by surface planarization is presented. A fluorescence microscope has been widely used in biochemical fields. However, it is difficult to miniaturize because optical filters and other parts are necessary. We previously developed a filter-less fluorescence sensor. The separation ability of excitation light and fluorescence in the previous device was 550:1. It is necessary to improve the separation ability. This study focuses on the suppression of forward-scattered incident light in silicon, through the enhanced surface planarization of polysilicon, which is the gate electrode material. The separation ability of the filter-less fluorescence sensor was increased from 550:1 to 1250:1 by the suppression of forward-scattered light.
Although fluorescence microscopy is an important technique in biomedical fields, the bulky equipment is disadvantageous in some situations. We have previously proposed a filter-less fluorescence sensor whose operation is based on the light absorption coefficient, which depends on the wavelength in a silicon substrate. In this sensor, the ratio of the excitation light intensity to the fluorescence intensity is as high as 400 : 1 upon optimizing the impurity concentration and the depth of the p-well region. To improve the dynamic range, herein we use a body-biasing technique to optimize the potential distribution of the sensing area to acquire sufficient photocurrent. Consequently, the dynamic range of the filter-less fluorescence sensor is improved to 800 : 1 with an 8 V substrate voltage.
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