Electrolyte-gated Field-effect Transistors Research Articles

Tailoring Threshold Voltages of Printed Electrolyte-Gated Field-Effect Transistors by Chromium Doping of Indium Oxide Channels.

Printed systems spark immense interest in industry, and for several parts such as solar cells or radio frequency identification antennas, printed products are already available on the market. This has led to intense research; however, printed field-effect transistors (FETs) and logics derived thereof still have not been sufficiently developed to be adapted by industry. Among others, one of the reasons for this is the lack of control of the threshold voltage during production. In this work, we show an approach to adjust the threshold voltage (Vth) in printed electrolyte-gated FETs (EGFETs) with high accuracy by doping indium-oxide semiconducting channels with chromium. Despite high doping concentrations achieved by a wet chemical process during precursor ink preparation, good on/off-ratios of more than five orders of magnitude could be demonstrated. The synthesis process is simple, inexpensive, and easily scalable and leads to depletion-mode EGFETs, which are fully functional at operation potentials below 2 V and allows us to increase Vth by approximately 0.5 V.

Design and Evaluation of a Printed Analog-Based Differential Physical Unclonable Function

A physical unclonable function (PUF) is a hardware circuit that produces a random sequence based on its manufacturing-induced intrinsic characteristics. In the past decade, silicon-based PUFs have been extensively studied as a security primitive for identification and authentication. The emerging field of printed electronics (PE) enables novel application fields in the scope of the Internet of Things (IoT) and smart sensors. In this paper, we design and evaluate a printed differential circuit PUF (DiffC-PUF). The simulation data are verified by Monte Carlo analysis. Our design is highly scalable while consisting of a low number of printed transistors. Furthermore, we investigate the best operating point by varying the PUF challenge configuration and analyzing the PUF security metrics in order to achieve high robustness. At the best operating point, the results show areliability of 98.37% and a uniqueness of 50.02%, respectively. This analysis also provides useful and comprehensive insights into the design of hybrid or fully printed PUF circuits. In addition, the proposed printed DiffC-PUF core has been fabricated with electrolyte-gated field-effect transistor technology to verify our design in hardware.

Impact of Intrinsic Capacitances on the Dynamic Performance of Printed Electrolyte-Gated Inorganic Field Effect Transistors

Electrolyte-gated, printed field-effect transistors exhibit high charge carrier densities in the channel and thus high on-currents at low operating voltages, allowing for the low-power operation of such devices. This behavior is due to the high area-specific capacitance of the device, in which the electrolyte takes the role of the dielectric layer of classical architectures. In this paper, we investigate intrinsic double-layer capacitances of ink-jet printed electrolyte-gated inorganic field-effect transistors in both in-plane and top-gate architectures by means of voltage-dependent impedance spectroscopy. By comparison with deembedding structures, we separate the intrinsic properties of the double-layer capacitance at the transistor channel from parasitic effects and deduce accurate estimates for the double-layer capacitance based on an equivalent circuit fitting. Based on these results, we have performed simulations of the electrolyte cutoff frequency as a function of electrolyte and gate resistances, showing that the top-gate architecture has the potential to reach the kilohertz regime with proper optimization of materials and printing process. Our findings additionally enable accurate modeling of the frequency-dependent capacitance of electrolyte/ion gel-gated devices as required in the small-signal analysis in the circuit simulation.

Influence of Humidity on the Performance of Composite Polymer Electrolyte-Gated Field-Effect Transistors and Circuits

In the domain of printed electronics (PE), field-effect transistors (FETs) with an oxide semiconductor channel are very promising. In particular, the use of high gate-capacitance of the composite solid polymer electrolytes (CSPEs) as a gate-insulator ensures extremely low voltage requirements. Besides high gate capacitance, such CSPEs are proven to be easily printable, stable in air over wide temperature ranges, and possess high ion conductivity. These CSPEs can be sensitive to moisture, especially for high surface-to-volume ratio printed thin films. In this paper, we provide a comprehensive experimental study on the effect of humidity on CSPE-gated single transistors. At the circuit level, the performance of ring oscillators (ROs) has been compared for various humidity conditions. The experimental results of the electrolyte-gated FETs (EGFETs) demonstrate rather comparable currents between 30%–90% humidity levels. However, the shifted transistor parameters lead to a significant performance change of the RO frequency behavior. The study in this paper shows the need of an impermeable encapsulation for the CSPE-gated FETs to ensure identical performance at all humidity conditions.

Progress Report on "From Printed Electrolyte-Gated Metal-Oxide Devices to Circuits".

Printed electrolyte-gated oxide electronics is an emerging electronic technology in the low voltage regime (≤1 V). Whereas in the past mainly dielectrics have been used for gating the transistors, many recent approaches employ the advantages of solution processable, solid polymer electrolytes, or ion gels that provide high gate capacitances produced by a Helmholtz double layer, allowing for low-voltage operation. Herein, with special focus on work performed at KIT recent advances in building electronic circuits based on indium oxide, n-type electrolyte-gated field-effect transistors (EGFETs) are reviewed. When integrated into ring oscillator circuits a digital performance ranging from 250 Hz at 1 V up to 1 kHz is achieved. Sequential circuits such as memory cells are also demonstrated. More complex circuits are feasible but remain challenging also because of the high variability of the printed devices. However, the device inherent variability can be even exploited in security circuits such as physically unclonable functions (PUFs), which output a reliable and unique, device specific, digital response signal. As an overall advantage of the technology all the presented circuits can operate at very low supply voltages (0.6 V), which is crucial for low-power printed electronics applications.

Attomolar Label-Free Detection of DNA Hybridization with Electrolyte-Gated Graphene Field-Effect Transistors.

In this work, we develop a field-effect transistor with a two-dimensional channel made of a single graphene layer to achieve label-free detection of DNA hybridization down to attomolar concentration, while being able to discriminate a single nucleotide polymorphism (SNP). The SNP-level target specificity is achieved by immobilization of probe DNA on the graphene surface through a pyrene-derivative heterobifunctional linker. Biorecognition events result in a positive gate voltage shift of the graphene charge neutrality point. The graphene transistor biosensor displays a sensitivity of 24 mV/dec with a detection limit of 25 aM: the lowest target DNA concentration for which the sensor can discriminate between a perfect-match target sequence and SNP-containing one.

Solution-sheared thin films of a donor-acceptor random copolymer/polystyrene blend as active material in field-effect transistors

Organic semiconductor (OSC):polymer blends are recently increasing their popularity due to the impressive performances they offer once employed as active layer in organic field-effect transistors (OFETs). Here a novel blend formulation composed by the donor-acceptor random copolymer PDPP-TT(1)-SVS(9) and polystyrene has been processed by a solution shearing technique and employed as active material in a thin film transistor. The molecular weight of the polymer binder has revealed to be fundamental for controlling the vertical phase separation and, in turn, for determining the morphological properties of the upper surface which is critical in terms of device stability. The bi-component active layer has been tested as OFET and by using a top gate as electrolyte-gated field-effect transistor (EGOFET). Our strategy based on an OSC:polymer blend processed through a solution shearing technique has demonstrated to be efficient for improving the final device performance in ambient conditions.

Variability Modeling for Printed Inorganic Electrolyte-Gated Transistors and Circuits

Electrolyte-gated field-effect transistor technology is an attractive candidate for printed low-power electronics due to its high field-effect mobility and extremely low-voltage operation. Relying on an additive process, inkjet-printed devices display large process variations due to ink-substrate interactions, sensitivity to environmental conditions, such as temperature and humidity, as well as intrinsic variations of the ink. All of these sources of variations may display themselves in non-Gaussian distributions as suggested by our experiments. In this paper, we therefore propose a generic methodology for variability modeling of printed transistors, based on the Gaussian mixture model, which can be used to model any arbitrary distribution of the transistor model parameters. The proposed methodology was tested on two different data sets and has been used to predict the behavior of a measured printed security circuit as well as transistor dc characteristics.

Triboiontronic Transistor of MoS2

Electric double layers (EDLs) formed in electrolyte-gated field-effect transistors (FETs) induce an extremely large local electric field that gives a highly efficient charge carrier control in the semiconductor channel. To achieve highly efficient triboelectric potential gating on the FET and explore diversified applications of electric double layer FETs (EDL-FETs), a triboiontronic transistor is proposed to bridge triboelectric potential modulation and ion-controlled semiconductor devices. Utilizing the triboelectric potential instead of applying an external gate voltage, the triboiontronic MoS2 transistor is efficiently operated owing to the formation of EDLs in the ion-gel dielectric layer. The operation mechanism of the triboiontronic transistor is proposed, and high current on/off ratio over 107 , low threshold value (75 μm), and steep switching properties (20 µm dec-1 ) are achieved. A triboiontronic logic inverter with desirable gain (8.3 V mm-1 ), low power consumption, and high stability is also demonstrated. This work presents a low-power-consuming, active, and a general approach to efficiently modulate semiconductor devices through mechanical instructions, which has great potential in human-machine interaction, electronic skin, and intelligent wearable devices. The proposed triboiontronics utilize ion migration and arrangement triggered by mechanical stimuli to control electronic properties, which are ready to deliver new interdisciplinary research directions.

Inkjet-Printed EGFET-Based Physical Unclonable Function—Design, Evaluation, and Fabrication

Printed electronics (PE) is a promising technology that provides mechanical flexibility and low-cost fabrication and the key enabler for emerging applications, such as smart sensors, wearables, and Internet of Things. To use printed batteries or printed energy harvesters in the future, electrolyte-gated field-effect transistors (EGFETs) based on inorganic materials enable printed circuits requiring small supply voltage and low power. Since these applications need secure communication and/or authentication, it is imperative to embed security primitives for cryptographic key and identification purposes into the applications. Physical unclonable functions (PUFs) have been adopted widely to provide secure keys. In this paper, we present the design, simulation, fabrication, and measurements of a PUF based on EGFETs using inorganic inkjet PE. A comprehensive framework, including Monte Carlo simulations calibrated on real device measurements, is developed. Moreover, a multibit PE-PUF design is proposed to optimize area usage. Our simulation results show that the PE-PUF has ideal uniqueness (50.1%) and good reliability (89%). In addition, the proposed multibit PE-PUF reduces the area usage around 30%. The proposed PE-PUF was fabricated and the experimental results confirm that the PE-PUF can operate reliably as low as 0.5 V, and hence, it is a remarkable candidate to be utilized in low-power applications.

Understanding the influence of in-plane gate electrode design on electrolyte gated transistor

Present work investigates the influence of gate electrode design in performance of electrolyte-gated carbon nanotube transistors. Electrolyte gated transistors have a huge potential in biological and chemical sensing. Recently, in-plane gate electrode has replaced the earlier used gate electrode wire in these systems. It becomes extremely essential to investigate the impact of gate electrode design on the device properties, and to optimize the electrode design to harness maximum sensitivity and speed. As a part of this work we have investigated the impact of gate electrode area and the distance between the gate electrode and the channel on the transistor characteristics. Area of gate electrode scales almost linearly with the drain to source current. However, the dependence of the gate distance is highly affected by experimental factors. Random network of carbon nanotubes serve as the semicondutor channel for electrolyte gated field effect transistors under study.

Conjugated Polymers in Bioelectronics.

The emerging field of organic bioelectronics bridges the electronic world of organic-semiconductor-based devices with the soft, predominantly ionic world of biology. This crosstalk can occur in both directions. For example, a biochemical reaction may change the doping state of an organic material, generating an electronic readout. Conversely, an electronic signal from a device may stimulate a biological event. Cutting-edge research in this field results in the development of a broad variety of meaningful applications, from biosensors and drug delivery systems to health monitoring devices and brain-machine interfaces. Conjugated polymers share similarities in chemical "nature" with biological molecules and can be engineered on various forms, including hydrogels that have Young's moduli similar to those of soft tissues and are ionically conducting. The structure of organic materials can be tuned through synthetic chemistry, and their biological properties can be controlled using a variety of functionalization strategies. Finally, organic electronic materials can be integrated with a variety of mechanical supports, giving rise to devices with form factors that enable integration with biological systems. While these developments are innovative and promising, it is important to note that the field is still in its infancy, with many unknowns and immense scope for exploration and highly collaborative research. The first part of this Account details the unique properties that render conjugated polymers excellent biointerfacing materials. We then offer an overview of the most common conjugated polymers that have been used as active layers in various organic bioelectronics devices, highlighting the importance of developing new materials. These materials are the most popular ethylenedioxythiophene derivatives as well as conjugated polyelectrolytes and ion-free organic semiconductors functionalized for the biological interface. We then discuss several applications and operation principles of state-of-the-art bioelectronics devices. These devices include electrodes applied to sense/trigger electrophysiological activity of cells as well as electrolyte-gated field-effect and electrochemical transistors used for sensing of biochemical markers. Another prime application example of conjugated polymers is cell actuators. External modulation of the redox state of the underlying conjugated polymer films controls the adhesion behavior and viability of cells. These smart surfaces can be also designed in the form of three-dimensional architectures because of the processability of conjugated polymers. As such, cell-loaded scaffolds based on electroactive polymers enable integrated sensing or stimulation within the engineered tissue itself. A last application example is organic neuromorphic devices, an alternative computing architecture that takes inspiration from biology and, in particular, from the way the brain works. Leveraging ion redistribution inside a conjugated polymer upon application of an electrical field and its coupling with electronic charges, conjugated polymers can be engineered to act as artificial neurons or synapses with complex, history-dependent behavior. We conclude this Account by highlighting main factors that need to be considered for the design of a conjugated polymer for applications in bioelectronics-although there can be various figures of merit given the broad range of applications, as emphasized in this Account.

IGZO-based electrolyte-gated field-effect transistor for in situ biological sensing platform

An amorphous indium gallium zinc oxide (IGZO)-based electrolyte-gated field-effect transistor (IGZO-EGFET) was fabricated and its feasibility as a biological sensing platform was evaluated. Herein, a 50-nm-thick IGZO thin film deposited via radio-frequency sputtering was utilized as both the active channel and biological interface of the device. The fabricated IGZO-EGFET operated by inducing a gate voltage directly through the liquid electrolyte at a low bias range (∼±1.5 V) with a subthreshold swing of 185 mV dec−1. The high uniformity of electrical characteristics for the devices were confirmed with 11.4% chip-to-chip deviation by measuring the threshold voltages (Vth), and the shift of Vth was employed as a major parameter to determine the biological interactions. In order to assess IGZO-EGFETs as a biosensing platform, first, pH sensing was conducted with and without amino-silanization on the IGZO surface. The amine-modified device showed steeper slope between Vth shifts and pH variations (68.5 mV pH−1) than that (32.7 mV pH−1) of the bare IGZO-EGFET. Subsequently, IGZO-EGFETs immobilized with a monoclonal antibody were employed for the in situ detection of alpha-synuclein (αS) proteins in concentration ranges from 10 fg mL−1 to 1 ng mL−1. The results showed that IGZO-EGFETs are suitable for the specific recognition of analytes with a linear relationship of 9.35 mV dec−1 between Vth shifts and αS concentrations in a logarithmic scale, verifying its applicability as a sensing device for biological interactions.

Frequency Response of Graphene Electrolyte-Gated Field-Effect Transistors.

This work develops the first frequency-dependent small-signal model for graphene electrolyte-gated field-effect transistors (EGFETs). Graphene EGFETs are microfabricated to measure intrinsic voltage gain, frequency response, and to develop a frequency-dependent small-signal model. The transfer function of the graphene EGFET small-signal model is found to contain a unique pole due to a resistive element, which stems from electrolyte gating. Intrinsic voltage gain, cutoff frequency, and transition frequency for the microfabricated graphene EGFETs are approximately 3.1 V/V, 1.9 kHz, and 6.9 kHz, respectively. This work marks a critical step in the development of high-speed chemical and biological sensors using graphene EGFETs.

A Smooth EKV-Based DC Model for Accurate Simulation of Printed Transistors and Their Process Variations

A printed electronics technology has the advantage of additive and extremely low-cost fabrication compared with the conventional silicon technology. Specifically, printed electrolyte-gated field-effect transistors (EGFETs) are attractive for low-cost applications in the Internet-of-Things domain as they can operate at low supply voltages. In this paper, we propose an empirical dc model for EGFETs, which can describe the behavior of the EGFETs smoothly and accurately over all regimes. The proposed model, built by extending the Enz-Krummenacher-Vittoz model, can also be used to model process variations, which was not possible previously due to fixed parameters for near threshold regime. It offers a single model for all the operating regions of the transistors with only one equation for the drain current. Additionally, it models the transistors with a less number of parameters but higher accuracy compared with existing techniques. Measurement results from several fabricated EGFETs confirm that the proposed model can predict the I-V more accurately compared with the state-of-the-art models in all operating regions. Additionally, the measurements on the frequency of a fabricated ring oscillator are only 4.7% different from the simulation results based on the proposed model using values for the switching capacitances extracted from measurement data, which shows more than 2× improvement compared with the state-of-the-art model.

Charge transfer doping in functionalized silicon nanosheets/P3HT hybrid material for applications in electrolyte-gated field-effect transistors

This work introduces microwave-assisted thermal hydrosilylation reaction for the functionalization of silicon nanosheets, leading to the successful electronic interaction within SiNS–substrate/P3HT-based hybrid blends.

Correction: Large-scale sensor systems based on graphene electrolyte-gated field-effect transistors.

Correction for 'Large-scale sensor systems based on graphene electrolyte-gated field-effect transistors' by Charles Mackin, et al., Analyst, 2016, 141, 2704-2711.

Low-voltage operated solid-state electrolyte-gated ambipolar organic field-effect transistors

Abstract In this paper, we study the effect of the molecular structure of conjugated polymers on electron and hole transport in organic solid-state electrolyte-gated transistors (SEGTs) using three N,N′-difunctionalized naphthalene diimide (NDI)-based conjugated polymers with (5-methylselenophen-2-yl)vinyl)selenophen-2-yl [P(NDI-SVS)], 2,29-bithiophene [P(NDI2OD-T2)] and 3,3′-dichloro-2,2′-bithiophene [P(NDI2HD-T2Cl2)], respectively. The polymer transistors show electron mobility in the order of 10−2 ∼ 10−3 cm2 V−1 s−1 with very low operating voltage (2 V) using a solution processed solid-state electrolyte gate insulator which is composed of poly (vinylidene fluoride-trifluoroethylene) (99.5 vol%) and ion gel, based on poly (vinylidene fluoride-co-hexafluoropropylene) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ion liquid (0.5 vol%). Interestingly, P(NDI-SVS) SEGTs showed remarkable hole mobility of 0.14 ± 0.02 cm2 V−1 s−1 owing to the large hole accumulation compared to ∼0.03 cm2 V−1 s−1 using the poly (methyl methacrylate) (PMMA) gate dielectric. By controlling the molecular structure, we demonstrate high performance ambipolar SEGTs with P(NDI-SVS) polymer.

Immobilization of glucose oxidase on ZnO nanorods decorated electrolyte-gated field effect transistor for glucose detection

In this paper, we report on growth of ZnO nanorods on the surface of gold interdigital electrodes and its implementation as a conductive n-type channel for the fabrication of a liquid-gated field effect transistor. Glucose oxidase was immobilized on the surface of the ZnO nanorods and the fabricated device was used as a four-electrode glucose biosensor. The resistance of the conductive channel was affected by addition of glucose. The applied bias voltage to the gate in the fabricated device affects the channel resistance in the same manner as the increase of enzymatic products during the glucose oxidation. Large effective area, good conductivity, and biocompatibility properties of ZnO nanorods are the key features in this highly sensitive and stable biosensor. Our measurements showed that the threshold voltage of transistor was about 0.75 V. The current increased in the presence of the glucose and exhibited a dynamic linear range with the logarithm of glucose concentration in the range between 0.01 and 5 mM. The detection limit was about 3.8 μM.

Oxide-based synaptic transistors gated by solution-processed gelatin electrolytes

In human brain, a large number of neurons are connected via synapses. Simulation of the synaptic behaviors using electronic devices is the most important step for neuromorphic systems. In this paper, proton conducting gelatin electrolyte-gated oxide field-effect transistors (FETs) were used for emulating synaptic functions, in which the gate electrode is regarded as pre-synaptic neuron and the channel layer as the post-synaptic neuron. In analogy to the biological synapse, a potential spike can be applied at the gate electrode and trigger ionic motion in the gelatin electrolyte, which in turn generates excitatory post-synaptic current (EPSC) in the channel layer. Basic synaptic behaviors including spike time-dependent EPSC, paired-pulse facilitation (PPF), self-adaptation, and frequency-dependent synaptic transmission were successfully mimicked. Such ionic/electronic hybrid devices are beneficial for synaptic electronics and brain-inspired neuromorphic systems.