Ion Sensing with Solution-Gated Graphene Field-Effect Sensors in the Frequency Domain

Area of Science:

• Materials Science
• Electrical Engineering
• Analytical Chemistry

Background:

• Graphene field-effect transistors (GFETs) offer potential for sensitive electronic detection.
• Frequency domain analysis provides a method to characterize signal modulation in electronic devices.
• Solution-gate configurations are crucial for sensing applications involving ionic solutions.

Purpose of the Study:

• To investigate frequency domain sensing capabilities of solution-gated GFETs.
• To analyze the effect of varying salt concentrations (KCl, CaCl2) on GFET signal modulation.
• To evaluate the impact of different graphene substrates (oxide vs. hexagonal boron nitride) on sensing performance.

Main Methods:

• Applied a primary frequency (1f) sine wave to the gate of GFETs.
• Measured power spectral density (PSD) of drain-source current at 1f, 2f, and 3f.
• Varied concentrations of KCl and CaCl2 in the gate electrolyte.
• Correlated PSD changes with Dirac point shifts.
• Compared device performance using oxide versus hexagonal boron nitride substrates.

Main Results:

• PSD at 1f, 2f, and 3f increased with salt concentration for both KCl and CaCl2.
• The PSD at 1f exhibited the highest sensitivity to concentration changes.
• Device-to-device reproducibility improved, and noise reduced significantly with hexagonal boron nitride substrates.
• Higher signal-to-noise ratio and resolution were achieved using hexagonal boron nitride.
• Signal-to-noise ratio at 1f followed a logarithmic function of salt concentration (0.1–1000 mM).

Conclusions:

• Frequency domain sensing with GFETs is effective for detecting salt concentrations.
• Hexagonal boron nitride substrates enhance GFET sensing performance by reducing noise and improving reproducibility.
• The observed logarithmic relationship enables precise quantification of salt concentrations over a wide range.