Trench Bottom Optical Isolation for Suppressing Lateral Diffusion of Photocarriers in LAPS

Abstract

Lateral diffusion of photocarriers in substrate causes the cross-talk in light-addressable potentiometric sensor (LAPS), which degrades the performance of LAPS. Surface optical isolation is a useful method to suppress the cross-talk in LAPS of backside irradiation manner, but the remarkable reduction of detection signal is a defect. In this study, a method of trench bottom optical isolation is developed. Main idea of this method is using the trench structure to narrow the diffusion scope of photocarriers, then irradiating the trench bottom by isolation light to locally suppress cross-talk. According to experimental analysis, when using 400 μm thick substrate, 240 μm deep trench and 100 mA drive current of isolation laser, the suppressing ability of trench bottom optical isolation is 1.38 times as strong as surface optical isolation, and 3.14 times as strong as having no isolation. Besides, the detection signal intensity of trench bottom optical isolation is 1.4 times as great as surface optical isolation. Thus, the method of trench bottom optical isolation can effectively suppress the cross-talk and reduce the loss of detection signal.