Abstract
Ion-sensitive field-effect transistors (ISFETs) have gained a lot of attention in recent times as compact, low-cost biosensors with fast response time and label-free detection. Dual gate ISFETs have been shown to enhance detection sensitivity beyond the Nernst limit of 59 mV pH−1 when the back gate dielectric is much thicker than the top dielectric. However, the thicker back-dielectric limits its application for ultrascaled point-of-care devices. In this work, we introduce and demonstrate a pH sensor, with WSe2(top)/MoS2(bottom) heterostructure based double gated ISFET. The proposed device is capable of surpassing the Nernst detection limit and uses thin high-k hafnium oxide as the gate oxide. The 2D atomic layered structure, combined with nanometer-thick top and bottom oxides, offers excellent scalability and linear response with a maximum sensitivity of 362 mV pH−1. We have also used technology computer-aided (TCAD) simulations to elucidate the underlying physics, namely back gate electric field screening through channel and interface charges due to the heterointerface. The proposed mechanism is independent of the dielectric thickness that makes miniaturization of these devices easier. We also demonstrate super-Nernstian behavior with the flipped MoS2(top)/WSe2(bottom) heterostructure ISFET. The results open up a new pathway of 2D heterostructure engineering as an excellent option for enhancing ISFET sensitivity beyond the Nernst limit, for the next-generation of label-free biosensors for single-molecular detection and point-of-care diagnostics.
Highlights
Measuring the ionic content or pH of an analyte is critical for a wide variety of applications, ranging from medical diagnostics, early disease detection, and genome sequencing to industrial process control, homeland security, and environmental monitoring[1,2]
ion-sensitive field-effect transistors (ISFETs) enable rapid, real-time, low-power, low-cost, and label-free electronic detection in a compact setup that is highly compatible with the standard complementary metal–oxide–semiconductor (CMOS) process[3,4]
Unlike metal–oxide–semiconductor (MOS) field-effect transistors (FETs), the gate metal in ISFETs is removed and replaced by a fluid gate which consists of a reference electrode capacitively coupled to the oxide layer through an electrolyte solution[6]
Summary
Measuring the ionic content or pH of an analyte is critical for a wide variety of applications, ranging from medical diagnostics, early disease detection, and genome sequencing to industrial process control, homeland security, and environmental monitoring[1,2]. The backgated transfer characteristics of the standalone WSe2 FET (Supplementary Fig. 2) show much higher currents, highlighting back gate (VBG) and drain voltage (VDS), respectively. The characteristics of the n-channel region are similar to that of a back-gated MoS2 FET, showing minimal effects of heterostructure on the bottom layer.
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