104 research outputs found
Fabrication and AC performance of flexible Indium-Gallium-Zinc-Oxide thin-film transistors
The internet of things or foldable phones call for a variety of flexible sensor conditioning and transceiver circuits. However, the realization of high-performance, large-area, and deformable analog circuits is limited by the materials and the processes compatible with mechanically flexible substrates. Among the different semiconductors, InGaZnO is one of the most promising materials to realize high-frequency flexible thin-film transistors (TFTs) and circuits. In this work, the effect of different geometries, including self-aligned, vertical, and double-gate structures on the AC behaviour of flexible IGZO TFTs is presented. All TFTs are based on Al2O3 insulating layers, InGaZnO semiconductor, and polyimide substrates. The presented TFTs exhibit state-of-the-art performance including a field-effect mobility up to 15 cm2 /Vs and a mechanical bendability down to radii of 3.5 mm. Due to different trade-offs required in the fabrication, flexible IGZO TFTs with the shortest channel length of 160 nm do not exhibit the highest measured frequency, whereas exceptional maximum oscillation and transit frequencies of 304 MHz and 135 MHz are demonstrated for 500 nm long self-aligned TFTs. Such optimized transistors can be used to realize entirely flexible analog circuits leading towards imperceptible electronic systems
Flexible In-Ga-Zn-O thin-film transistors with sub-300-nm channel lengths defined by two-photon direct laser writing
In this work, the low-temperature (≤ 150 °C) fabrication and characterization of flexible Indium-Gallium-ZincOxide (IGZO) top-gate thin-film transistors (TFTs) with channel lengths down to 280 nm is presented. Such extremely short channel lengths in flexible IGZO TFTs were realized with a novel manufacturing process combining two-photon direct laser writing (DLW) photolithography with Ti/Au/Ti source/drain e-beam evaporation and lift-off. The resulting flexible IGZO TFTs exhibit a saturation field-effect mobility of 1.1 cm2V -1 s -1 and a threshold voltage of 3 V. Thanks to the short channel lengths (280 nm) and the small gate to source/drain overlap (5.2 µm), the TFTs yield a transit frequency of 80 MHz (at 8.5 V gate-source voltage) extracted from the measured S-parameters. Furthermore, the devices are fully functional when wrapped around a cylindrical rod with 6 mm radius, corresponding to 0.4 % tensile strain in the TFT channel. These results demonstrate a new methodology to realize entirely flexible nano-structures, and prove its suitability for the fabrication of short-channel transistors on polymer substrates for future wearable communication electronics
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Gain-tunable complementary common-source amplifier based on a flexible hybrid thin-film transistor technology
In this letter, we report a flexible complementary common-source (CS) amplifier comprising one p-type spray-coated single walled carbon nanotube and one n-type sputtered InGaZnO4 thin-film transistor (TFT). Bottom-gate TFTs were realized on a free-standing flexible polyimide foil using a maximum process temperature of 150 °C. The resulting CS amplifier operates at 10 V supply voltage and exhibits a gain bandwidth product of 60 kHz. Thanks to the use of a p-type TFT acting as a tunable current source load, the amplifier gain can be programmed from 3.5 V/V up to 27.2 V/V (28.7 dB). To the best of our knowledge, this is the highest gain ever obtained for a flexible single-stage CS amplifiers
Influence of uniaxial bending on IGZO TFTs: A study of materials and device
In recent years flexible electronics have gained relevance with applications such as displays, sensors and wearables. In that regard, studying how flexible transistors behave under bending has become of major importance. This work aims to fabricate indium gallium zinc oxide (IGZO) Thin Film Transistors (TFT) with the best bendability possible, without any major changes in the production techniques already used in the industry.
To understand the influence of the substrate on flexible devices, TFTs were fabricated on polyimide substrates using different thicknesses, down to 25 μm, with and without parylene encapsulation layers on top of the device stack. To determine the position of the neutral strain plane, nanoindentation measurements were performed on different device layers at IKTS-Fraunhofer, within BET-EU project.
The delamination of the substrates is a critical step, especially for thinner substrates. The concept of “paper blade” was used in this project to improve the yield of the delamination process.
Initial bending measurements, using a 75 μm thick substrate, showed that bending radii of 45, 25 and 15 mm do not permanently change the performance of the TFTs. Tensile bending measurements with a radius of 1.25 mm were also performed, revealing that the 75 μm thick substrate achieves critical failure in <500 cycles, while the thinner substrate (25 μm) could withstand almost 1000 cycles.
The most common failure mechanism observed under tensile bending was the appearance of cracks in the oxide dielectric when in direct contact with the polyimide substrate. These cracks do not appear in regions where molybdenum gates were in contact with the substrate, hence the mismatch between the coefficient of thermal expansion of the substrate and the dielectric thin film were identified as the reason for failure.
This work shows that, even with intrinsically rigid materials as oxides and metals, it is possible to obtain reliable flexible TFTs, provided that proper stack engineering is considered for their fabrication
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Buckled Thin-Film Transistors and circuits on soft elastomers for stretchable electronics
Although recent progress in the field of flexible electronics has allowed the realization of biocompatible and conformable electronics, systematic approaches which combine high bendability ( 3-4 %) and low complexity in the fabrication process are still missing. Here, we show a technique to induce randomly-oriented and customized wrinkles on the surface of a biocompatible elastomeric substrate, where Thin-Film Transistors (TFTs) and circuits (inverter and logic NAND gates) based on Amorphous-IGZO are fabricated. By tuning the wavelength and the amplitude of the wrinkles, the devices are fully operational while bent to 13 µm bending radii as well as while stretched up to 5%, keeping unchanged electrical properties. Moreover, a flexible rectifier is also realized, showing no degradation in the performances while flat or wrapped on an artificial human wrist. As proof of concept, transparent TFTs are also fabricated, presenting comparable electrical performances to the non-transparent ones. The extension of the buckling approach from our TFTs to circuits demonstrates the scalability of the process, prospecting applications in wireless stretchable electronics to be worn or implanted
Metal oxide semiconductor thin-film transistors for flexible electronics
The field of flexible electronics has rapidly expanded over the last decades, pioneering novel applications, such as wearable and textile integrated devices, seamless and embedded patch-like systems, soft electronic skins, as well as imperceptible and transient implants. The possibility to revolutionize our daily life with such disruptive appliances has fueled the quest for electronic devices which yield good electrical and mechanical performance and are at the same time light-weight, transparent, conformable, stretchable, and even biodegradable. Flexible metal oxide semiconductor thin-film transistors (TFTs) can fulfill all these requirements and are therefore considered the most promising technology for tomorrow's electronics. This review reflects the establishment of flexible metal oxide semiconductor TFTs, from the development of single devices, large-area circuits, up to entirely integrated systems. First, an introduction on metal oxide semiconductor TFTs is given, where the history of the field is revisited, the TFT configurations and operating principles are presented, and the main issues and technological challenges faced in the area are analyzed. Then, the recent advances achieved for flexible n-type metal oxide semiconductor TFTs manufactured by physical vapor deposition methods and solution-processing techniques are summarized. In particular, the ability of flexible metal oxide semiconductor TFTs to combine low temperature fabrication, high carrier mobility, large frequency operation, extreme mechanical bendability, together with transparency, conformability, stretchability, and water dissolubility is shown. Afterward, a detailed analysis of the most promising metal oxide semiconducting materials developed to realize the state-of-the-art flexible p-type TFTs is given. Next, the recent progresses obtained for flexible metal oxide semiconductor-based electronic circuits, realized with both unipolar and complementary technology, are reported. In particular, the realization of large-area digital circuitry like flexible near field communication tags and analog integrated circuits such as bendable operational amplifiers is presented. The last topic of this review is devoted for emerging flexible electronic systems, from foldable displays, power transmission elements to integrated systems for large-area sensing and data storage and transmission. Finally, the conclusions are drawn and an outlook over the field with a prediction for the future is provided
Flexible a-IGZO phototransistor for instantaneous and cumulative UV-exposure monitoring for skin health
Flexible thin‐film phototransistors based on amorphous indium‐gallium‐zinc‐oxide semiconductor and a novel read‐out scheme allow for both real time and cumulative measurement of the ultraviolet
light intensity. Furthermore, encapsulation in polydimethylsiloxane and lamination to human skin, as well as mechanical stability of the device is presented
Radio frequency electronics on plastic
In this paper the recent progress of active high frequency electronics on plastic is discussed. This technology is mechanically flexible, bendable, stretchable and does not need any rigid chips. Indium Gallium Zinc Oxide (IGZO) technology is applied. At 2 V supply and gate length of 0.5 μm, the thin-film transistors (TFTs) yield a measured transit frequency of 138 MHz. Our scalable TFT compact simulation model shows good agreement with measurements. To achieve a sufficiently high yield, TFTs with gate lengths of around 5 μm are used for the circuit design. A Cherry Hopper amplifier with 3.5 MHz bandwidth, 10 dB gain and 5 mW dc power is presented. The fully integrated receiver covering a plastic foil area of 3 × 9 mm2 includes a four stage cascode amplifier, an amplitude detector, a baseband amplifier and a filter. At a dc current of 7.2 mA and a supply of 5 V, a bandwidth of 2 - 20 MHz and a gain beyond 15 dB were measured. Finally, an outlook regarding future advancements of high frequency electronics on plastic is given
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Device-circuit interactions and impact on TFT circuit-system design
This paper reviews the importance of device-circuit interactions (DCI) and its consideration when designing thin film transistor circuits and systems. We examine temperature- and process-induced variations and propose a way to evaluate the maximum achievable intrinsic performance of the TFT. This is aimed at determining when DCI becomes crucial for a specific application. Compensation methods are then reviewed to show examples of how DCI is considered in the design of AMOLED displays. Other designs such as analog front-end and image sensors are also discussed, where alternate circuits should be designed to overcome the limitations of the intrinsic device properties
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Flexible In-Ga-Zn-O based circuits with two and three metal layers: simulation and fabrication study
The quest for high-performance flexible circuits call for scaling of the minimum feature size in Thin-Film Transistors (TFTs). Although reduced channel lengths can guarantee an improvement in the electrical properties of the devices, proper design rules also play a crucial role to minimize parasitics when designing fast circuits. In this letter, systematic Computer-Aided Design (CAD) simulations have guided the fabrication of highperformance flexible operational amplifiers (opamps) and logic circuits based on Indium-Gallium-Zinc-Oxide (IGZO) TFTs. In particular, the performance improvements due to the use of an additional third metal layer for the interconnections has been estimated for the first time. Encouraged by the simulated enhancements resulting by the decreased parasitic resistances and capacitances, both TFTs and circuits have been realized on a free-standing 50μm thick polymide foil using three metal layers. Despite the thicker layer stack, the TFTs have shown mechanical stability down to 5mm bending radii. Moreover, the opamps and the logic circuits have yielded improved electrical performance with respect to the architecture with two metal layers: gainbandwidth- product (GBWP) increased by 16:9%, for the first one, and propagation delay (tpd) decreased by 43%, for the latter one
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