Coaxial-structured ZnO/silicon nanowires extended-gate field-effect transistor as pH sensor

Hung Hsien Li*, Chi En Yang, Chi Chung Kei, Chung Yi Su, Wei Syuan Dai, Jung Kuei Tseng, Po Yu Yang, Jung Chuan Chou, Huang-Chung Cheng

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


An extended-gate field-effect transistor (EGFET) of coaxial-structured ZnO/silicon nanowires as pH sensor was demonstrated in this paper. The oriented 1-μm-long silicon nanowires with the diameter of about 50 nm were vertically synthesized by the electroless metal deposition method at room temperature and were sequentially capped with the ZnO films using atomic layer deposition at 50 C. The transfer characteristics (IDS-VREF) of such ZnO/silicon nanowire EGFET sensor exhibited the sensitivity and linearity of 46.25 mV/pH and 0.9902, respectively for the different pH solutions (pH 1-pH 13). In contrast to the ZnO thin-film ones, the ZnO/silicon nanowire EGFET sensor achieved much better sensitivity and superior linearity. It was attributed to a high surface-to-volume ratio of the nanowire structures, reflecting a larger effective sensing area. The output voltage and time characteristics were also measured to indicate good reliability and durability for the ZnO/silicon nanowires sensor. Furthermore, the hysteresis was 9.74 mV after the solution was changed as pH 7 → pH 3 → pH 7 → pH 11 → pH 7.

Original languageEnglish
Pages (from-to)173-176
Number of pages4
JournalThin Solid Films
StatePublished - 1 Feb 2013


  • Atomic layer deposition (ALD)
  • Electroless metal deposition (EMD)
  • Extended-Gate Field-Effect Transistors (EGFET)
  • Low temperature
  • pH sensor
  • Zinc oxide (ZnO)

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