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

Lateral diffusion of photocarriers in substrate causes the crosstalk in light-addressable potentiometric sensor (LAPS), which degrades the performance of LAPS. Surface optical isolation is a useful method to suppress the crosstalk 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. The main idea of this method is to use the trench structure to narrow the diffusion scope of photocarriers and then irradiate the trench bottom by isolation light to locally suppress crosstalk. According to the experimental analysis, when using 400-
$\mu \text{m}$
-thick substrate, 240-
$\mu \text{m}$
-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 crosstalk and reduce the loss of detection signal.