Gas sensor made of field effect transistor based on ZnO nanowires
The present invention discloses a gas sensor made of field effect transistor based on ZnO nanowires (ZnO-FET) which operates according to the principle of metal-oxide-semiconductor field effect transistor (MOSFET) and has a charge carrier channel made of ZnO nanowires between source and drain. The gas sensor device disclosed in the present invention has three electrodes-gate, source and drain, so that it is different from the known gas sensor device which has only two electrodes-cathode and anode. The ZnO nanowires as charge channel in the gas sensor device of the present invention is an n-type semiconductor with high specific surface area, and its electric resistance can be controlled by the gate bias, so that the capability of the present device for sensing gas can be largely promoted.
1. A gas sensor device made of ZnO nanowire field effect transistor consisting of:
(a) a Si substrate;
(b) a SiO 2 film grown on Si substrate;
(c) an metal film coated on SiO 2 film;
(d) an insulator film deposited on metal film;
(e) a ZnO nanowire film coated on insulator film;
(f) two metal electrodes deposited on ZnO nanowire film and spaced by a trench; and
(g) an alloy wire coated on the back side of Si substrate.
2. A gas sensor device made of ZnO nanowire field effect transistor according to claim 1 , wherein the SiO 2 film about 1 μm in thickness is directly grown on Si substrate in O 2 atmosphere in a furnace, and is used as the diffusion barrier between Si and metal.
3. A gas sensor device made of ZnO nanowire field effect transistor according to claim 1 , wherein the metal film about 0.5 μm in thickness may be Cu or Al which is formed on SiO 2 film by using electroless plating or vacuum deposition (containing thermal evaporation, electron beam evaporation, and sputtering deposition) and is used as the gate of field effect transistor.
4. A gas sensor device made of ZnO nanowire field effect transistor according to claim 1 , wherein the insulator about 20 nm in thickness may be Si 3 N 4 , SiO 2 , or Al 2 O 3 which is formed on metal film by using sputtering deposition and is used for interrupting the electric connection between metal film (gate) and source, drain and charge carrier channel.
5. A gas sensor device made of ZnO nanowire field effect transistor according to claim 1 , wherein the ZnO nanowire over 10 μm in length is grown on brass (Cu—Zn alloy) substrate in an atmosphere of O 2 or H 2 O under the catalysis of Fe, Co or Ni, and is across the source and drain and is used as the charge carrier channel of field effect transistor.
6. A gas sensor device made of ZnO nanowire field effect transistor according to claim 1 , wherein the two metal electrodes (Cu or Al) about 0.5 μm in thickness as source and drain of field effect transistor is formed by the process in which the metal film is first coated on ZnO nanowire film by vacuum deposition and a trench about 2 μm in width is then formed on the metal film by lithography technology.
7. A gas sensor device made of ZnO nanowire field effect transistor according to claim 1 , wherein the alloy wire for heating the ZnO nanowire field effect transistor may be made of Ni—Cr alloy which is formed by the process in which a Ni—Cr alloy film about 1 μm in thickness is first coated on the back side of Si substrate by sputtering deposition and a curved Ni—Cr wire about 1 μm in width is then formed by lithography technology.