Control of the Intrinsic Sensor Response to Volatile Organic Compounds with Fringing Electric Fields

Abstract

The ability to control surface-analyte interaction allows tailoring chemical sensor sensitivity to specific target molecules. By adjusting the bias of the shallow p-n junctions in the electrostatically formed nanowire (EFN) chemical sensor, a multiple gate transistor with an exposed top dielectric layer allows tuning of the fringing electric field strength (from 0.5 × 10 to 2.5 × 10 V/m) above the EFN surface. Herein, we report that the magnitude and distribution of this fringing electric field correlate with the intrinsic sensor response to volatile organic compounds. The local variations of the surface electric field influence the analyte-surface interaction affecting the work function of the sensor surface, assessed by Kelvin probe force microscopy on the nanometer scale. We show that the sensitivity to fixed vapor analyte concentrations can be nullified and even reversed by varying the fringing field strength, and demonstrate selectivity between ethanol and n-butylamine at room temperature using a single transistor without any extrinsic chemical modification of the exposed SiO surface. The results imply an electric-field-controlled analyte reaction with a dielectric surface extremely compelling for sensitivity and selectivity enhancement in chemical sensors.

Realization of an Ultrasensitive and Highly Selective OFET NO2 Sensor: The Synergistic Combination of PDVT-10 Polymer and Porphyrin–MOF

“…Several detection techniques exist for gas sensing, such as the electromagnetic spectroscopic method, optical fiber, [2][3][4] electrochemical, [5][6] quartz crystal microbalance (QCM), [7][8] microelectromechanical systems (MEMS), [9][10] resistance changes, [11][12][13] capacitance changes, [14][15][16] mass spectrometry, 17 and surface potential measurement. [18][19] Some of the important drawbacks of the aforementioned techniques are their bulky design, environmental interferrants, high operating temperature, and high power consumption, which impede the growth of widely explored gas sensing strategies. As an alternative to silicon dominated electronics (complementary metal oxide semiconductor, or CMOS), recently many research groups have explored the potential of emerging organic and flexible platforms for electronic devices in environmental sensing applications.…”

Electrostatic Selectivity of Volatile Organic Compounds Using Electrostatically Formed Nanowire Sensor

“…The EFN sensor response is affected by two main factors: (1) the fringing electric fields at the EFN surface and (2) the effective channel diameter . Our hypothesis is that the molecular dipoles orient themselves in the direction of the electric field, generated by the biased p–n junctions of the EFN sensor, resulting in a net molecular dipole moment.…”

“…In our recent work, we have used 3D finite element simulations ( TCAD Sentaurus , Synopsys , Mountain View, USA) to compute the magnitude and distribution of the fringing electric field across the p-n-p regions of the sensor. The resulting fringing electric field strength on the top dielectric layer of the sensor is large for negative V JG , while it becomes significantly smaller for the positive V JG (Figure ), as described in detail in our previous work . Thus, the strength of the fringing electric fields strongly depends on the V JG of the EFN sensor.…”

“…It is clearly observed that the patterns in Figure strongly depend on the adsorbed molecule (analyte). The interaction between the analyte and the randomly distributed Si–OH and Si–O–Si binding sites on the top dielectric SiO 2 surface (molecular gate) is affected by the strong fringing electric fields, generated by the shallow p–n junctions of the EFN device.…”

“…As previously described, ,− the EFN is a multiple gate FET fabricated in a complementary metal–oxide–semiconductor (CMOS) process, where the nanowire is not physically shaped but is electrostatically defined post fabrication. The EFN has already been demonstrated for detection of ethanol, acetone, and several aliphatic hydrocarbons. − Recently, the EFN has been demonstrated for electric-field-controlled sensing, a novel sensing concept . We exploit the above sensing concept and demonstrate highly selective (∼90%) detection of homologous and different functional groups containing VOCs, relying on the use of multiple parameters of the EFN sensor (threshold voltage, V th , and the drain-source on current, I on , for both junction and back gates).…”