Programmable ion-sensitive transistor interfaces. I. Electrochemical gating

Abstract

Electrochemical gating is the process by which an electric field normal to the insulator electrolyte interface shifts the surface chemical equilibrium and further affects the charge in solution [Jiang and Stein, Langmuir 26, 8161 (2010)]. The surface chemical reactivity and double-layer charging at the interface of electrolyte-oxide-semiconductor (EOS) capacitors is investigated. We find a strong pH-dependent hysteresis upon dc potential cycling. Varying salinity at a constant pH does not change the hysteretic window, implying that field-induced surface pH regulation is the dominant cause of hysteresis. We propose and investigate this mechanism in foundry-made floating-gate ion-sensitive field-effect transistors, which can serve as both an ionic sensor and an actuator. Termed the chemoreceptive neuron metal-oxide-semiconductor (CνMOS) transistor, it features independently driven control gates (CGs) and sensing gates (SGs) that are capacitively coupled to an extended floating gate (FG). The SG is exposed to fluid, the CG is independently driven, and the FG is capable of storing charge Q(FG) of either polarity. Asymmetric capacitive coupling between the CG and SG to FG results in intrinsic amplification of the measured surface potential shifts and influences the FG charge injection mechanism. This modified SG surface condition was monitored through transient recordings of the output current, performed under alternate positive and negative CG pulses. Transient recordings revealed a hysteresis where the current was enhanced under negative pulsing and reduced after positive pulsing. This hysteresis effect is similar to that observed with EOS capacitors, suggesting a field-dependent surface charge regulation mechanism at play. At high CG biases, nonvolatile charge Q(FG) tunneling into the FG occurs, which creates a larger field and tunes the pH response and the point of zero charge. This mechanism gives rise to surface programmability. In this paper we describe the operational principles, tunneling mechanism, and role of electrolyte composition under field modulation. The experimental findings are then modeled by a Poisson-Boltzmann formulation with surface pH regulation. We find that surface ionization constants play a dominant role in determining the pH tuning effect. In the following paper [K. Jayant et al., Phys. Rev. E 88, 012802 (2013)] we extend the dual-gate operation to molecular sensing and demonstrate the use of Q(FG) to achieve manipulation of surface-adsorbed DNA.

Field-effect sensors – from pH sensing to biosensing: sensitivity enhancement using streptavidin–biotin as a model system

“…Assuming electrostatic gating, the shift in the threshold voltage (ΔV T ) is related to the shift in surface potential at the oxide-electrolyte interface (Δψ o ) (discussed in ESI section 2 †). The precise relationship between the addition of biomolecular charge and the change in surface potential remains one of the most important modelling problems in this field, 20,[140][141][142][149][150][151][152][153][154][155][156][157][158] however an appealing model, due to its simplicity, is to approximate the oxide-electrolyte interface as a parallel plate capacitor (Helmholtz-Perrin Theory). 159 The change in charge on the surfaces of the capacitor, ΔQ, with capacitance C 0 can give the voltage shift simply as:…”

An Ion-Sensitive Floating Gate FET Model: Operating Principles and Electrofluidic Gating

“…The gate of the ISFET is replaced by a floating node that is capacitively coupled to two inputs: 1) a sensing gate (SG) and 2) a CG, both of which can be used to modulate the current flow through the transistor. A recent study by Jayant et al [7] is closely related to this paper. A similar sensor concept and a surface programming is elucidated by considering the electric field of the sensing oxide.…”

“…The first ISFET exploiting the FG structure with a control gate (CG) was proposed in [3]. Similar structures have since been described by our group [4] and by several others [5]- [7]. The gate of the ISFET is replaced by a floating node that is capacitively coupled to two inputs: 1) a sensing gate (SG) and 2) a CG, both of which can be used to modulate the current flow through the transistor.…”

A real-time spike classification method based on dynamic time warping for extracellular enteric neural recording with large waveform variability

“…We used a non-amperimetric C υ MOS sensor (Jayant et al (2013)) for the experimental EAP recording of mouse ENS neurons in the jejunum tissues. As large ambient variability is expected from motility and frequent vesicle release, C υ MOS can use its control gate to pin the transistor operating point for less waveform distortion and reduce reliance on the large reference electrode which is impractical for future in vivo monitoring.…”