CMOS-Based Ion Image Sensor Enabling pH Measurement Under Light Irradiation

• Published in: IEEE sensors journal 2024-12, Vol.24 (24), p.40196-40203
• Main Authors: Noda, Toshihiko, Honjo, Runa, Noda, Yoshiko, Akai, Daisuke, Hizawa, Takeshi, Kimura, Yasuyuki, Choi, Yong-Joon, Takahashi, Kazuhiro, Sawada, Kazuaki
• Format: Article
• Language: English
• Subjects: Electric potential; Electrodes; Image sensors; Ion image sensor; Ions; light signal contamination; pH measurement; Sensor phenomena and characterization; Sensors
• ISSN: 1530-437X; 1558-1748
• DOI: 10.1109/JSEN.2024.3396573

The use of conventionally developed pH image sensors under light irradiation is challenging owing to the strong influence of light signal contamination. Thus, this study developed a pH image sensor that achieves pH measurement without light signal contamination. We propose a method to separate light and pH information by combining and arraying two types of pixels with different characteristics. A proof-of-concept sensor was designed as a 32\times 32 -pixel image sensor. The characterization results of the fabricated sensor demonstrated its capability to simultaneously measure two types of information with a pH and light intensity measurement error of 10%. The proposed method enabled pH imaging under light irradiation, which was previously only possible under dark environments. Consequently, the applications in smart agriculture, wherein the sensor must operate under light irradiation, were rendered possible. The proposed method is expected to be deployed for real-time monitoring of ion information in plants, which was not previously possible.