The authors fabricated diamond solution-gate field-effect transistors (SGFETs) with miniaturization of the channel length to 5 μm by photolithography. The channel surface was directly functionalized with amine by ultraviolet irradiation in an ammonia gas for 4 h and aminated diamond SGFETs were sensitive to pH by 40 mVpH. Urease was immobilized on the amine-modified channel surface, which was sensitive to urea by 27 μA /decade from 10-5 M to 10-2 M. The authors fabricated submicron-sized (500 nm) diamond SGFETs using electron-beam lithography. The transconductance (gm) was 56 mSmm, which was 930-fold greater than that of the 500 μm channel length.
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