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A pH sensor with a double-gate silicon nanowire field-effect transistor
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10.1063/1.4793655
/content/aip/journal/apl/102/8/10.1063/1.4793655
http://aip.metastore.ingenta.com/content/aip/journal/apl/102/8/10.1063/1.4793655
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Figures

Image of FIG. 1.
FIG. 1.

Images of the fabricated device. (a) Schematic of the double-gate nanowire FET for pH sensing. A silicon nanowire is formed on a buried oxide. The current flowing from the drain (D) to the source (S) is controlled by the voltages applied to gate 1 and gate 2. The hydroxyl groups (−OH) of the sensing oxide react with H+ ions in the solution and then generate the surface potential. Therefore, the VT value of the FET is changed. (b) Cross-sectional schematic of the double-gate nanowire FET along the gate direction. (c) A magnified SEM image of the fabricated double-gate nanowire FET. The nanowire sidewall is covered by the two gates, and the top surface of the nanowire is opened in order to react with the ionic solution. (d) A SEM image of the fabricated device. The nanowire device is seen inside the passivation layer. The passivation layer is formed in order to protect the metal lines from the ionic solution and to block the leakage current. (e) A microscopic image of the fabricated device. The arrow indicates the area of (d). The remaining area is covered by the passivation layer. (f) A microscopic image of the fabricated devices in an array form. Two gates per nanowire are assigned, which lead to individual access and elaborate control capabilities. The metal lines are extended out for the electrical measurement.

Image of FIG. 2.
FIG. 2.

Dependence of the pH response on the gate bias conditions. (a) Schematic showing the DG mode. Gate 1 and gate 2 are swept at the same voltage. (b) Schematic showing the IDG mode. Gate 1 is swept and a fixed voltage is applied to gate 2. (c) ID -VG characteristics according to various pH values under the DG mode. (d) ID -VG characteristics according to various pH values under the IDG mode. (e) The VT shift versus pH. The two methods (DG and IDG modes) are compared. (f) Dependence of the VT shift on the voltage of gate 2. After a constant voltage is applied to gate 2, the change in the value of VT is measured while the pH value of the solution is changed from 4 to 10. This experiment is repeated with various conditions of gate 2.

Image of FIG. 3.
FIG. 3.

Dependence of the pH response on the gate oxide thicknesses. (a) Dependence of the VT shift on the gate oxide thickness. Two different thicknesses of the gate oxide which forms on the nanowire sidewall are used: 5 nm and 30 nm. The measured data are fitted with simulation data using a semiconductor device simulator. (b) Simulated result of the VT shift depending on the oxide thicknesses of gate 1 and gate 2 under the DG mode (VG 1 = VG 2). (c) Simulated result of the VT shift depending on the oxide thicknesses of gate 1 and gate 2 under the IDG mode in which gate 1 is swept and a fixed voltage is applied to gate 2. In all simulations, the VT shift is extracted after a test charge of −1 × 1011 cm−2 is set on the top surface of the nanowire. The test charge is obtained by fitting with measured data in (a).

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/content/aip/journal/apl/102/8/10.1063/1.4793655
2013-02-26
2014-04-20
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: A pH sensor with a double-gate silicon nanowire field-effect transistor
http://aip.metastore.ingenta.com/content/aip/journal/apl/102/8/10.1063/1.4793655
10.1063/1.4793655
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