This paper presents the first successful implementation of fully printed electronics for flexible and wearable smart multi-pad stimulation electrodes intended for use in medical, sports and lifestyle applications. The smart multi-pad electrodes with the electronic circuits based on organic electrochemical transistor (OECT)-based electronic circuits comprising the 3–8 decoder for active pad selection and high current throughput transistors for switching were produced by multi-layer screen printing. Devices with different architectures of switching transistors were tested in relevant conditions for electrical stimulation applications. An automated testbed with a configurable stimulation source and an adjustable human model equivalent circuit was developed for this purpose. Three of the proposed architectures successfully routed electrical currents of up to 15 mA at an output voltage of 30 V, while one was reliably performing even at 40 V. The presented results demonstrate feasibility of the concept in a range of conditions relevant to several applications of electrical stimulation.

Printed organic thin-film transistor (OTFT) technology has the potential to enable ubiquitous, inexpensive, flexible electronic systems. Realization of this vision requires circuit design techniques sensitive to the constraints of the technology, as well as integration with components such as memory, sensors, and displays. The OTFT fabrication process is much less mature than silicon technologies, and direct implementation of conventional complementary designs is challenging due to the relatively low yield, high variability, and drift instability of printed OTFTs. Here we demonstrate an OTFT-specific approach to design with a pulse generator circuit for writing non-volatile thin-film ferroelectric (FE) memory. The approach takes into account the constraints of existing OTFT processes and can be extended to other circuits. The new circuit, and a more conventional complementary pulse-generator, are designed, fabricated, and tested in an additive ink-jet OTFT process.

Scalable circuits of organic logic and memory are realized using all-additive printing processes. A 3-bit organic complementary decoder is fabricated and used to read and write non-volatile, rewritable ferroelectric memory. The decoder-memory array is patterned by inkjet and gravure printing on flexible plastics. Simulation models for the organic transistors are developed, enabling circuit designs tolerant of the variations in printed devices. We explain the key design rules in fabrication of complex printed circuits and elucidate the performance requirements of materials and devices for reliable organic digital logic.

Low-voltage organic field-effect transistors (OFETs) promise for low power consumption logic circuits. To enhance the efficiency of the logic circuits, the control of the threshold voltage of the transistors are based on is crucial. We report the systematic control of the threshold voltage of electrolyte-gated OFETs by using various gate metals. The influence of the work function of the metal is investigated in metal-electrolyte-organic semiconductor diodes and electrolyte-gated OFETs. A good correlation is found between the flat-band potential and the threshold voltage. The possibility to tune the threshold voltage over half the potential range applied and to obtain depletion-like (positive threshold voltage) and enhancement (negative threshold voltage) transistors is of great interest when integrating these transistors in logic circuits. The combination of a depletion-like and enhancement transistor leads to a clear improvement of the noise margins in depleted-load unipolar inverters.

There has been a remarkable progress in the development of organic electronic materials since the discovery of conducting polymers more than three decades ago. Many of these materials can be proces ...

We present a dc model to simulate the static performance of electrolyte-gated organic field-effect transistors. The channel current is expressed as charge drift transport under electric field. The charges accumulated in the channel are considered being contributed from voltage-dependent electric-double-layer capacitance. The voltage-dependent contact effect and short-channel effect are also taken into account in this model. A straightforward and efficient methodology is presented to extract the model parameters. The versatility of this model is discussed as well. The model is verified by the good agreement between simulation and experimental data.

Organic complementary inverters and ring oscillators based on polyelectrolyte-gated thin-film transistors are demonstrated. Detrimental electrochemical doping is suppressed by using polyanionic and polycationic gate insulators in the p- and n-channel transistors, respectively. The circuits operate at supply voltages between 0.2 V and 1.5 V, have a static power consumption of less than 2.5 nW per logic gate and show propagation delays down to 0.26 ms per stage.

Electrolyte-gated organic thin-film transistors (OTFTs) can offer a feasible platform for future flexible, large-area and low-cost electronic applications. These transistors can be divided into two groups on the basis of their operation mechanism: (i) field-effect transistors that switch fast but carry much less current than (ii) the electrochemical transistors which, on the contrary, switch slowly. An attractive approach would be to combine the benefits of the field-effect and the electrochemical transistors into one transistor that would both switch fast and carry high current densities. Here we report the development of a polyelectrolyte-gated OTFT based on conjugated polyelectrolytes, and we demonstrate that the OTFTs can be controllably operated either in the field-effect or the electrochemical regime. Moreover, we show that the extent of electrochemical doping can be restricted to a few monolayers of the conjugated polyelectrolyte film, which allows both high current densities and fast switching speeds at the same time. We propose an operation mechanism based on self-doping of the conjugated polyelectrolyte backbone by its ionic side groups.

We present a methodology to extract parameters for an electrolyte-gated organic field effect transistor DC model. The model is based on charge drift/diffusion transport under electric field and covers all regimes. Voltage dependent capacitance, mobility, contact resistance and threshold voltage shift are taken into account in this model. The feature parameters in the model are simply extracted from the transfer or output characteristics of electrolyte-gated organic field effect transistors. The extracted parameters are verified by good agreements between experimental and simulated results.

High-dielectric-constant insulators, organic monolayers, and electrolytes have been successfully used to generate organic field-effect transistors operating at low voltages. Here, we report on a device gated with pure water. By replacing the gate dielectric by a simple water droplet, we produce a transistor that entirely operates in the field-effect mode of operation at voltages lower than 1V. This result creates opportunities for sensor applications using water-gated devices as transducing medium.

Short-channel, vertically structured organic transistors with a polyelectrolyte as gate insulator are demonstrated. The devices are fabricated using low-resolution, self-aligned, and mask-free photolithography. Owing to the use of a polyelectrolyte, our vertical electrolyte-gated organic field-effect transistors (VEGOFETs), with channel lengths of 2.2 and 0.7 μm, operate at voltages below one volt. The VEGOFETs show clear saturation and switch on and off in 200 μs. A vertical geometry to achieve short-transistor channels and the use of an electrolyte makes these transistors promising candidates for printed logics and drivers with low operating voltage.

Electrolyte-gate organic field-effect transistors embedded at the junction of textile microfibers are demonstrated. The fiber transistor operates below I V and delivers large current densities. The transience of the organic thin-film transistor's current and the impedance spectroscopy measurements reveal that the channel is formed in two steps.

A polyanionic electrolyte is used as gate insulator in top-gate p-channel polymer thin-film transistors. The high capacitance of the polyelectrolyte film allows the transistors and integrated circuits to operate below 1.5V. Seven-stage ring oscillators that operate at supply voltages down to 0.9V and exhibit signal propagation delays as low as 300 mu s per stage are reported.

A polyelectrolyte is used as gate insulator material in organic field-effect transistors with self-aligned inkjet printed sub--micrometer channels. The small separation of the charges in the electric double layer at the electrolyte-semiconductor interface, which builds up in tens of microseconds, provides a very high transverse electric field in the channel that: effectively suppresses short-channel effects at low applied gate voltages.

Low operating voltages for p-channel organic field-effect transistors (OFETs) can be achieved by using an electrolyte as the gate insulator. However, mobile anions in the electrolyte can lead to undesired electrochemistry in the channel. In order to avoid this, a polyanionic electrolyte is used as the gate insulator. The resulting OFET has operating voltages of less than 1 V (see figure) and shows fast switching (less than 0.3 ms) in ambient atmosphere.

A polyanionic proton conductor, named poly(styrenesulfonic acid) (PSSH), is used to gate an organic field-effect transistor (OFET) based on poly(3-hexylthiophene) (P3HT). Upon applying a gate bias, large electric double layer capacitors (EDLCs) are formed quickly at the gate-PSSH and P3HT-PSSH interfaces due to proton migration in the polyelectrolyte. This type of robust transistor, called an EDLC-OFET, displays fast response (<1ms) and operates at low voltages (<1V). The results presented are relevant for low-cost printed polymer electronics.