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The recent developments in the field of large area, flexible and printed electronics have fueled substantial advancements in Laser Printing and Laser Sintering, which have been attracting interest over the past decade. Resulting applications, ranging from flexible displays and sensors, to biometric devices and healthcare, have already showcased transformational advantages in terms of form factor, weight and durability. In HiperLAM project, Laser-Induced Forward Transfer (LIFT), combined with high speed laser micro-sintering are employed, as digital microfabrication tools for the demonstration of fully functional RFID antennas and fingerprint sensors based on highly viscous Ag and Cu nanoparticle inks. Having previously successfully demonstrated complex structures, this work's focus is on increasing the process throughput and yield by increasing the laser repetition rate (up to 40 kHz) and scanning speed (up to 2 m/s), without compromising reliability and resolution. In order to gain insight into the effects of the incremented repetition rate on the printing procedure, the latter was monitored in real time via a high-speed camera, able to acquire up to 540.000 fps, coupled to the setup. Examples of resulting structures comprise well-defined interdigitated and spiral micro-electrodes with post-sintering electrical resistivity lower than 5 x bulk Ag and 3 x bulk Cu. The aforementioned results validate the compatibility of laser based processing with the field of flexible RFID tags and OTFT based fingerprint sensors and foster the wider adoption of LIFT and laser micro-sintering technology for laboratory and industrial use.

Thin-film transistor technologies have great potential to become the key technology for leafnode Internet of Things by utilizing the NFC protocol as a communication medium. The main requirements are manufacturability on flexible substrates at a low cost while maintaining good device performance characteristics, necessary to be compatible with the NFC specifications. Such low-cost flexible NFC tags can be attached to any object with any form factor, connecting this object to the Internet using a smartphone or tablet as an intermediate node. Among all commercial thin-film transistor technologies, metal oxide transistors is a viable technology for this application. The metal-oxide transistors in this work are based on InGaZnO as semiconductor. Since these are unipolar by nature (i.e., they exhibit only n -type transistors), different options to make logic circuits are studied from static and dynamic points of view. The different topologies are diode-load logic, dual-gate diode-load logic, and pseudo-CMOS logic. The static parameters lead to a comparison of soft yield between those circuit topologies, while the transient analysis provides insight on the power consumption and circuit speed. This is indicative for selecting the logic style matching the data rate requirements of the NFC standards. Moreover, metal-oxide NFC circuits that combine 12-bit code generators to the analog front-end of RFID tags are integrated on a PCB board to evaluate performance of a matched and optimized system. The measured data rates of these integrated NFC tags are compatible with the ISO 15693 specifications. Finally, a fully integrated, flexible NFC tag is realized, which comprises the tuning capacitor, rectifier, load modulator, and code generator.

The integration of flexible integrated circuits (FlexICs) on flexible plastic substrates to deliver smart flexible electronic solutions has enormous potential across a range of consumer markets, including wearable devices, healthcare devices and smart labels. At present, reliable FlexIC integration for hybrid flexible electronic circuits is mainly based on conductive adhesive packaging which is too slow and/or expensive to address the highest volume products envisioned for consumer markets. In this research we have investigated low-cost bonding processes for FlexICs based on non-conductive adhesive (NCA) and thermosonic-adhesive (TS-A) bonding. Four-wire resistance tests, shear tests and bending tests were used for evaluation during process development. The results confirmed that NCA and TS-A bonding were feasible for FlexIC packaging, and the evaluation tests showed encouraging electrical and mechanical performance. This research is bringing novel bonding techniques that will significantly advance the development of low-cost manufacturing of smart flexible electronics to drive mass market adoption in consumer markets.

We present a QVGA (320x240 with 3 sub-pixel) top-emitting AMOLED display with 250ppi resolution using a self-aligned (SA) IGZO TFT backplane on polyimide-foil with full barrier. The back plane process flow is based on a 7 layer photolithography process. The aperture ratio of the top-emitting OLEDs is approx. 80%. An integrated gate driver is shown that can be driven at operation speed equivalent to a 4k2k display at 100Hz

We describe the device and transport characteristics of amorphous zinc tin oxide thin-film (ZTO) transistors. In samples with a sufficiently high mobility and at a high gate voltage, a crossover occurs from transport governed by thermal excitation of trapped charges to one where the charge carriers reside for a sufficiently long time in extended states. Very few semiconductors exhibit this range of behavior in the same device under different conditions. We also describe the correct methods to extract mobility values and ionization energies from current voltage characteristics.

We demonstrated self-aligned amorphous-Indium-Gallium-Zinc-Oxide (a-IGZO) thin-film transistors (TFTs) where the source–drain (S/D) regions were made conductive via chemical reduction of the a-IGZO via metallic calcium (Ca). Due to the higher chemical reactivity of Ca, the process can be operated at lower temperatures. The Ca process has the additional benefit of the reaction byproduct calcium oxide being removable through a water rinse step, thus simplifying the device integration. The Ca-reduced a-IGZO showed a sheet resistance (RSHEET) value of 0.7 kΩ/sq., with molybdenum as the S/D metal. The corresponding a-IGZO TFTs exhibited good electrical properties, such as a field-effect mobility (μFE) of 12.0 cm2/(V s), a subthreshold slope (SS−1) of 0.4 V/decade, and an on/off current ratio (ION/OFF) above 108. Cop. 2015 The Korean Information Display Society.

A process to make self-aligned top-gate amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) on polyimide foil is presented. The source/drain (S/D) region's parasitic resistance reduced during the SiN interlayer deposition step. The sheet resistivity of S/D region after exposure to SiN interlayer deposition decreased to 1.5 kΩ/□. TFTs show field-effect mobility of 12.0 cm2/(V.s), sub-threshold slope of 0.5 V/decade, and current ratio (I ON/OFF) of >107. The threshold voltage shifts of the TFTs were 0.5 V in positive (+1.0 MV/cm) bias direction and 1.5 V in negative (-1.0 MV/cm) bias direction after extended stressing time of 104 s. We achieve a stage-delay of ~19.6 ns at V-DD = 20 V measured in a 41-stage ring oscillator. A top-emitting quarter-quarter-video-graphics-array active-matrix organic light-emitting diode display with 85 ppi (pixels per inch) resolution has been realized using only five lithographic mask steps. For operation at 6 V supply voltage (V-DD), the brightness of the display exceeds 150 cd/m2. A process to make self-aligned top-gate amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) is presented. TFTs show field-effect mobility of 12.0 cm2/(V.s), sub-threshold slope of 0.5 V/decade, and current ratio (I ON/OFF) of over 107. In applications, a 41-stage ring oscillator with a stage-delay of ~19.6 ns (at V-DD = 20 V) and a top-emitting quarter-quarter-video-graphics-array (QQVGA) active-matrix organic light-emitting diode (AMOLED) display with 85 ppi (pixels per inch) resolution using five lithographic mask steps have been realized on a polyimide foil. Copyright 2015 Society for Information Display.

We present a QQVGA (160times120 with 3 sub-pixel) top-emitting AMOLED display with 85ppi resolution using a self-aligned (SA) IGZO TFT backplane on polyimide-foil. The back plane process flow is based on a 5 layer photolithography process. The aperture ratio of the top-emitting OLEDs is approx. 25%. For operation at 6 V supply voltage (VDD), the brightness of the display exceeds 150cd/m2. On the same substrate a 160 stage gate-driver was measured at FHD rate. cop. 2014 Society for Information Display.

We report on charge transport and density of trap states (trap DOS) in ambipolar diketopyrrolopyrrole-benzothiadiazole copolymer thin-film transistors. This semiconductor possesses high electron and hole field-effect mobilities of up to 0.6 cm 2/V-s. Temperature and gate-bias dependent field-effect mobility measurements are employed to extract the activation energies and trap DOS to understand its unique high mobility balanced ambipolar charge transport properties. The symmetry between the electron and hole transport characteristics, parameters and activation energies is remarkable. We believe that our work is the first charge transport study of an ambipolar organic/polymer based field-effect transistor with room temperature mobility higher than 0.1 cm 2/V-s in both electrons and holes.

While much of the OTFT activity has been display-centric there is no doubt that as the OTFT technology matures the number of applications will continue to increase. Using our most recent flexible X-ray detectors we will discuss the prospect and challenges of organic transistors in sensor backplanes. For these application, the current mobility of ~0.1-2 cm2/Vs of OTFTs is currently not a problem. Their low leakage currents give them a distinct advantage over competing technologies, such as amorphous silicon TFT. Yet, challenges remain and these will be discussed.

For decades, the electronics industry has been accurately described by Moore’s Law, where the march towards increasing density and smaller feature sizes has enabled continuous cost reductions and performance improvements. With flexible electronics, this perpetual scaling is not foreseen to occur. Instead, the industry will be dominated by Wright’s Law, first proposed in 1936, where increasing demand for high volumes of product will drive costs down. We have demonstrated thin film based circuitry compatible with flexible substrates with high levels of functionality designed for such a high volume industry. This includes a generic 8-bit microprocessor totaling more than 3.5k TFTs operating at 2.1 kHz. We have also developed a post fabrication programming technique via inkjet printing of conductive spots to form a one-time programmable instruction generator, allowing customization of the processor for a specific task. The combination demonstrates the possibility to achieve the high volume production of identical products necessary to reap the benefits promised by Wright’s Law, while still retaining the individualization necessary for application differentiation. This is of particular importance in the area of item level identification via RFID, where low cost and individualized identification are necessary. Remotely powered RFID tags have been fabricated using an oxide semiconductor based TFT process. This process is compatible with the post-fabrication printing process to detail individual identification codes, with the goal of producing low cost, high volume flexible tags. The goal is to produce tags compatible with existing NFC communication protocols in order to communicate with readers that are already ubiquitous in the market.

In this paper we describe three methods that can be used to measure the transient response of organic and polymer field-effect transistors (FETs) and also how such measurements can be used to determine the drift mobility and velocity. The first method measures the response of a FET to a step voltage applied to the source with the gate grounded and the drain held at close to ground, while the second uses a ramp input to the source. The third technique evaluates the frequency response of the FET, connected as a diode, to a large-signal alternating voltage. We show that important information can be obtained from such measurements which can be quantitatively interpreted with the help of models that we are developing. In general, there is good agreement between the drift mobility measured with these approaches and the field-effect mobility calculated from transistor output and transfer characteristics. The specific results we present in this paper are for pentacene devices; however, other recent work by our group indicates that these results are more general.

In this paper, the design of a low-voltage line driver in a complementary organic technology on foil is presented. The behavior and the variability of circuits are predicted by means of transistor modeling and statistical characterization. The comparison of measurements and simulations of simple digital blocks verifies the effectiveness of the design approach. A transmission-gate based 32-stage line driver and a fully-static one are shown. It is also shown that, based on the statistical organic thin-film transistor (OTFT) characterization, the fully-static logic style is a more suitable choice for implementing line drivers in this technology. The implemented fully-static line driver, which is comprised of 1216 transistors, has the highest transistor count reported for a complementary organic circuit to date. It works at supply voltages from 10 V to as low as 3.3 V, reaching a 1 kHz clock frequency, and occupying an area of 25 $\times$ 4.7 mm $^{2}$ . The drivers are implemented in a technology compatible with that of flat-panel display backplanes and are tested with a QQVGA AMOLED display.

Our goal is to create thin low-cost flexible NFC tags to allow everyday objects to communicate to smartphones and computers and thus participate in the Internet of Things. We employ amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) thin-film transistor circuits processed at low temperatures, less than 250C, directly on thin polyester substrates. Reaching NFC standards with a-IGZO circuits is challenging because the technology is n-type only and the electron mobility (∼15cm7Vs) is lower compared to silicon. As the main result, we show that the most important NFC regulatory standards are met, even with relaxed 5 micron design rules, using optimized design topologies.

Ferroelectric polarization switching of poly(vinylidene difluoride-trifluoroethylene) is investigated in different thin-film device structures, ranging from simple capacitors to dual-gate thin-film transistors (TFT). Indium gallium zinc oxide, a high mobility amorphous oxide material, is used as semiconductor. We find that the ferroelectric can be polarized in both directions in the metal-ferroelectric-semiconductor (MFS) structure and in the dual-gate TFT under certain biasing conditions, but not in the single-gate thin-film transistors. These results disprove the common belief that MFS structures serve as a good model system for ferroelectric polarization switching in thin-film transistors. cop. 2015 AIP Publishing LLC.

Ferroelectric polymers and amorphous metal oxide semiconductors have emerged as important materials for re-programmable non-volatile memories and high-performance, flexible thin-film transistors, respectively. However, realizing sophisticated transistor memory arrays has proven to be a challenge, and demonstrating reliable writing to and reading from such a large scale memory has thus far not been demonstrated. Here, we report an integration of ferroelectric, P(VDF-TrFE), transistor memory arrays with thin-film circuitry that can address each individual memory element in that array. n-type indium gallium zinc oxide is used as the active channel material in both the memory and logic thin-film transistors. The maximum process temperature is 200 °C, allowing plastic films to be used as substrate material. The technology was scaled up to 150 mm wafer size, and offers good reproducibility, high device yield and low device variation. This forms the basis for successful demonstration of memory arrays, read and write circuitry, and the integration of these. cop. 2015 IOP Publishing Ltd.

The Internet of Things is driving extensive efforts to develop intelligent everyday objects. This requires seamless integration of relatively simple electronics, for example through `stick-on' electronics labels. We believe the future evolution of this technology will be governed by Wright's Law, which was first proposed in 1936 and states that the cost of a product decreases with cumulative production. This implies that a generic electronic device that can be tailored for application-specific requirements during downstream integration would be a cornerstone in the development of the Internet of Things. We present an 8-bit thin-film microprocessor with a write-once, read-many (WORM) instruction generator that can be programmed after manufacture via inkjet printing. The processor combines organic p-type and soluble oxide n-type thin-film transistors in a new flavor of the familiar complementary transistor technology with the potential to be manufactured on a very thin polyimide film, enabling low-cost flexible electronics. It operates at 6.5 V and reaches clock frequencies up to 2.1 kHz. An instruction set of 16 code lines, each line providing a 9 bit instruction, is defined by means of inkjet printing of conductive silver inks. ispartof: Scientific Reports vol:4 issue:1 ispartof: location:England status: published

We present an 8b general-purpose microprocessor realized in a hybrid oxide-organic complementary thin-film technology. The n-type transistors are based on a solution-processed n-type metal-oxide semiconductor, and the p-type transistors use an organic semiconductor. As compared to previous work utilizing unipolar logic gates [1], the higher mobility n-type semiconductor and the use of complementary logic allow for a >50x speed improvement. It also adds robustness to the design, which allowed for a more complex and complete standard cell library. The microprocessor consists of two parts, a processor core chip and an instruction generator. The instructions are stored in a Write-Once-Read-Many (WORM) memory formatted by a post-fabrication inkjet printing step, called Print-Programmable Read-Only Memory (P2ROM). The entire processing was performed at temperatures compatible with plastic foil substrates, i.e., at or below 250°C [2].

Carbon-nanotube top-gate transistors with fluorinated dielectrics are presented. With PTrFE as the dielectric, the devices have absent or small hysteresis at different sweep rates and excellent bias-stress stability under ambient conditions. Ambipolar single-walled carbon nanotube (SWNT) transistors are observed when P(VDF-TrFE-CTFE) is utilized as a topgate dielectric. Furthermore, continuous tuning of the threshold voltages of both unipolar and ambipolar SWNT thin-film transistors (TFTs) is demonstrated for the first time. cop. 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In this paper, we successfully fabricated and operated passive matrix P(VDF-TrFE) transistor arrays, i.e. memory arrays in which no pass-transistors or other additional electronic components are used. Because of the smaller cell, a higher integration density is possible. We demonstrate arrays up to a size of 16 × 16, processed on thin (25 μm) poly(ethylene naphthalate) substrates, using Indium-Gallium-Zinc-Oxide (IGZO) as the semiconductor and 200 nm-thick P(VDF-TrFE) as a ferroelectric gate dielectric. The memory transistors have remnant current modulations of ∼105 with a retention time of more than 12 days. They can be switched in less than 1 μs at operating voltages of 25 V. Switching speed is strongly decreased with decreasing voltage: at ∼10 V the transistors do not switch within 10 s. This difference in switching speed of more than 4 orders in magnitude when changing the electric field by a factor of only 2.5 makes these memories robust towards disturb voltages, and forms the basis of integration of these transistors in passive matrix-addressable transistor arrays that contains only one (memory) transistor per cell. It is shown that with current technology and memory characteristics it is possible to scale up the array size in the future. © 2013 Elsevier B.V. All rights reserved.

Summary form only given.Thin films of ordered organic semiconductors are being investigated as channel materials in field-effect transistors for a variety of applications. A detailed understanding of charge transport in such organic thin- film semiconductors used in field-effect transistors is of fundamental interest and is also essential to improve device performance. Our work examines the dynamic response of organic transistors in detail and extracts the drift velocity and mobility directly. The drift mobility and field-effect mobility are compared for pentacene and a liquid crystalline polymer with high mobility. The switching speed of FETs with channel length in the 2-8 micron range and scaling behavior of organic transistors (with channel lengths from 10 nm to 5 microns) are described. Frequency domain measurements have been made on diode connected transistors. Comparisons between frequency domain and time domain measurements will be presented. Finally, two important applications of organic transistors: RFID Tags and display drivers are discussed with regard to speed/mobility requirements and future trends.

Pentacene based organic thin-film transistors were used to study the effects of polar analytes on charge transport and trapping behavior during vapor sensing. Three sets of devices with differing morphology and mobility (0.001−0.5 cm2/V s) were employed. All devices show enhanced trapping upon exposure to analyte molecules. The organic field effect transistors with different mobilities also provide evidence for morphology dependent partition coefficients. This study helps provide a physical basis for many reports on organic transistor based sensor response.

The measurement of the distribution of charge carrier velocities in a field-effect transistor can provide considerable insight into charge transport mechanisms and structure-property relationships. We have developed such a method and have applied it to study temperature-dependent velocity distributions in solution-processed zinc-tin oxide thin-film transistors. Two distinct transport pathways, each with a different activation energy, have been observed, in contrast to a single activation energy yielded by steady-state measurements. Our results show that more insight into charge transport behavior and phenomena can be obtained with such time-resolved transport measurements.

We report on charge transport phenomena in high-mobility solution-deposited amorphous zinc-tin oxide based thin-film transistors. At low carrier concentrations, the dominant transport mechanism is multiple trap and release, with the activation energy steadily decreasing with increasing carrier density. The activation energy decreases to zero and beyond a threshold carrier density, the mobility decreases with increasing temperature. This temperature dependence as well as the value of the mobility clearly indicates that transport is bandlike. Also observed is a clear mobility edge in accordance with the prediction of Mott’s model, which are normally observed in crystalline semiconductors.

We report on the realization of dual-channel organic field-effect transistors (FETs). These devices have a four-terminal configuration with a polymeric semiconductor p-channel, a small molecule semiconductor n-channel, and a polymeric gate dielectric. The polymeric p-channel and the small molecule n-channel are coupled across the gate dielectric. Both the p-FET and the n-FET exhibit acceptable device characteristics at ∣VDS∣⩽50V and ∣VG∣⩽50V, in which the performances of the p-FET and the n-FET are comparable. The p-FET and n-FET respond to isopropyl alcohol and ethanol vapors with significant sensitivities.

A method to characterize the frequency response of an organic field effect transistor (FET) is presented. Analysis then shows a method to calculate the average drift mobility from the frequency at which a pole appears in the response. This pole is believed to appear at the point where charge carriers can no longer fully traverse the channel in one period of the input signal. The dc output characteristics of the device are also described, and saturation mobility values are derived. This saturation mobility and the drift mobility calculated from the frequency response are comparable. This method can be used in determining the drift mobility in other materials such as single nanowires in the FET configuration.

Recent advances in flexible electronics have highlighted the importance of high throughput, digital additive microfabrication techniques. In this work, we demonstrate the combination of laser printing and laser sintering of a novel copper nanoparticle ink onto flexible substrates in order to produce oxide free conductive copper patterns in ambient atmospheric conditions. The printed patterns exhibit high reproducibility, very low resistivity (about 2x bulk), and negligible oxidation according to Raman spectroscopy. The process has been employed for the fabrication of an on-chip antenna on a flexible substrate for use in combination with a flexible circuit, in applications where a small form factor and simplicity of integration are required alongside ultra-low cost, e.g. consumable tagging.