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Proceedings Paper

Chemical imaging sensor for observation of microscopic pH distribution
Author(s): Motoi Nakao; Satoshi Nomura; Shuji Takamatsu; Katsuhiko Tomita; Tatsuo Yoshinobu; Hiroshi Iwasaki
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Paper Abstract

A novel chemical imaging sensor has been developed using a Si semiconductor. The sensor (Si3N4/SiO2Si) is in contact with the electrolyte solution that serves as an objective sample. The backside of the Si substrate is illuminated by a modulated laser beam. The AC photocurrent flows through the electrolyte-insulator-semiconductor. The intensity of the photocurrent depends on the electrolyte solution pH value on only the illuminated region. A 2D pH distribution can be obtained by scanning the focused laser beam. The sensor visualizes the pH distribution in the gel solution induced by ion exchange resin and microorganisms. The spatial resolution of this sensor is restricted by the Si substrate thickness as well as the laser beam spot size. A practical sensor with a spatial resolution better than 5 micrometers was fabricated using a SOI wafer instead of Si wafer, and anisotropic chemical etching instead of mechanical polishing. Such a high spatial resolution makes it possible to detect the microscopic pH distribution in solution. A reduction of spatial resolution due to the lateral spread of the depletion layer was estimated at approximately 80 nm in the present sensor system. The pH resolution of this sensor was also estimated to be 0.01 pH.

Paper Details

Date Published: 8 September 1998
PDF: 11 pages
Proc. SPIE 3514, Micromachined Devices and Components IV, (8 September 1998); doi: 10.1117/12.323922
Show Author Affiliations
Motoi Nakao, Horiba Ltd. (Japan)
Satoshi Nomura, Horiba Ltd. (Japan)
Shuji Takamatsu, Horiba Ltd. (Japan)
Katsuhiko Tomita, Horiba Ltd. (Japan)
Tatsuo Yoshinobu, Osaka Univ. (Japan)
Hiroshi Iwasaki, Osaka Univ. (Japan)


Published in SPIE Proceedings Vol. 3514:
Micromachined Devices and Components IV
Patrick J. French; Kevin H. Chau, Editor(s)

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