Modeling of Quasi-Static Floating-Gate Transistor Biosensors

Abstract

Floating-gate transistors (FGTs) are a promising class of electronic sensing architectures that separate the transduction elements from molecular sensing components, but the factors leading to optimum device design are unknown. We developed a model, generalizable to many different semiconductor/dielectric materials and channel dimensions, to predict the sensor response to changes in capacitance and/or charge at the sensing surface upon target binding or other changes in surface chemistry. The model predictions were compared to experimental data obtained using a floating-gate (extended gate) electrochemical transistor, a variant of the generic FGT architecture that facilitates low-voltage operation and rapid, simple fabrication using printing. Self-assembled monolayer (SAM) chemistry and quasi-statically measured resistor-loaded inverters were utilized to obtain experimentally either the capacitance signals (with alkylthiol SAMs) or charge signals (with acid-terminated SAMs) of the FGT. Experiments reveal that the model captures the inverter gain and charge signals over 3 orders of magnitude variation in the size of the sensing area and the capacitance signals over 2 orders of magnitude but deviates from experiments at lower capacitances of the sensing surface (<1 nF). To guide future device design, model predictions for a large range of sensing area capacitances and characteristic voltages are provided, enabling the calculation of the optimum sensing area size for maximum charge and capacitance sensitivity.

Dissecting the Interplay between Organic Charge-Modulated Field-Effect Transistors and Field-Effect Transistors through Interface Control Engineering

“…An OCMFET is a type of transistor device driven by the voltage induced in the FG by the voltage applied to the CG. − It has been attracting considerable attention as a sensing platform device in various applications, such as biomaterials or chemical sensors because it prevents direct stimulations applied to the FET element using an externally extended FG as a sensing component. This is an OCMFET device, when a voltage is applied to the CG as a driving electrode but operates as a general FET device when the FG is set as the drive electrode.…”

“…The operation of the OCMFET principle has different aspects from that of OFETs. The V CG , voltage to the CG, primarily induces polarization inside the gate dielectric, which in turn generates an induced V FG in the FG. − The induced V FG could be significantly influenced by the dielectric surface characteristics owing to the sensitive nature of the induced voltage, where a positive DM surface results in a relatively small V FG due to polarization cancellation effects . Conversely, when the dielectric surface has a negative DM, a relatively high V FG could be induced due to polarization enhancement effects with the gate dielectric surface.…”

“…To address the aforementioned problems, some groups proposed organic charge-modulated field-effect transistors (OCMFETs). ,− The OCMFETs consists of a control gate (CG) and an extended floating gate (FG), separated by a dielectric that acts as a capacitor plate. − The CG receives an actual voltage, while the applied voltage to the CG forms an induced voltage in the FG. Therefore, it has an interesting character that operates as an OCMFET when the device is driven by the charge in the FG, which is induced and accumulated by the voltage applied to the CG.…”

Status and Prospects of Heterojunction-Based HEMT for Next-Generation Biosensors

“…This structure suggests that the performance on semiconductor/dielectric pair can be exploited rather than the stability of the sensing medium [ 159 ]. This structure can also prevent the sensing medium from contaminating the transistor channel [ 160 , 161 , 162 ].…”

Tuning Gate Potential Profiles and Current–Voltage Characteristics of Polymer Electrolyte-Gated Transistors by Capacitance Engineering

“…1−4,25−31 In fact, one of attractive features of EGTs is that the gate electrode can be offset from the sourcedrain channel, which makes fabrication easier in some instances, albeit with a loss in switching speed. [1][2][3]10,[25][26][27]32 Gate electrode materials include metals such as Au, conducting polymers such as PEDOT:PSS as in Figure 1, and conducting porous carbon, for example. 8,10,33−37 Often times, not much attention is paid to the size of the contact area between the gate and the electrolyte, despite a few previous studies indicating that the gate electrode significantly influences charge accumulation and EGT performance.…”