Si Thin-film Transistors Research Articles

Retina-Inspired X-Ray Optoelectronic Synapse Using Amorphous Ga2O3 Thin Film.

Machine vision techniques are widely applied for object identification in daily life and industrial production, where images are captured and processed by sensors, memories, and processing units sequentially. Neuromorphic optoelectronic synapses, as a preferable option to promote the efficiency of image recognition, are hotly pursued in non-ionizing radiation range, but rarely in ionizing radiation including X-rays. Here, the study proposes an X-ray optoelectronic synapse using amorphous Ga2O3 (a-Ga2O3) thin film. Boosted by the interfacial VO 2+ defects and its slow neutralization rate, the enhanced electron tunneling process at metal/a-Ga2O3 interface produces remarkable X-ray-induced post-synaptic current, contributing to a sensitivity of 20.5, 64.3, 164.1 µC mGy-1 cm-2 for the 1st, 5th, and 10th excitation periods, respectively. Further, a 64×64 imaging sensor is constructed on a commercial amorphous Si (a-Si) thin film transistor (TFT) array. The image contrast can be apparently improved under a series of X-ray pulses due to an outstanding long-term plasticity of the single pixel, which is beneficial to the subsequent image recognition and classification based on artificial neural network. The merits of large-scale production ability and good compatibility with modern microelectronic techniques belonging to amorphous oxide semiconductors may promote the development of neuro-inspired X-ray imagers and corresponding machine vision systems.

Organosilicon-Based Thin Film Formation in Very High-Frequency Plasma Under Atmospheric Pressure

Owing to recent interest in the production of flexible devices, it is necessary to develop a more convenient approach in which silicon (Si) thin film transistors (TFTs) are fabricated directly onto the flexible substrates at low substrate temperatures. Unfortunately, the physical limitations of conventional plasma-enhanced chemical vapor deposition (PECVD) under low pressures becomes a critical obstacle. In this study, Si film deposition using PECVD under atmospheric pressure excited by very high-frequency electrical power was investigated to overcome this issue. Tetramethylsilane [Si(CH3)4] is used as a source gas that is much safer than silane (SiH4) gas. We investigated the effects of the reactive gas concentration and specific energy (the ratio of input power to unit volume of the reaction gas) on carbon incorporation into the resultant films. Based on the results, we discuss the possibility of forming Si films with sufficiently low carbon content, which is applicable to Si TFTs.

(Invited) Industrial Face of Nanotechnology

Ever since the proposal and demonstration of quantum dots in 1980 by Drs. A. Efros, Al. Efros and A. Ekimov, the relentless progress of nanotechnology has been unstoppable. And nowhere this progress is more evident than in the Si Very Large Scale Integrated Circuits (VLSI) and Thin Film Transistor (TFT) technologies. The minimum feature size of the Si VLSI with up to 2.6 trillion transistors on a chip was reduced to 3 nm in 2022 with plans for the 2 nm technology. TFTs fabricated on glass or even on cloth or paper enable integrated circuits with 50 nm tolerances over square meter sizes. These technologies have become disruptive with applications ranging from 5G and Beyond 5G communications to robotics, driverless cars, and electronic warfare. This talk will focus on the new counter-intuitive physics of ballistic transport required to support the design, characterization, and parameter extraction for nanoscale Si VLSI and TFT integrated circuits. Figure 1

Total-Ionizing-Dose Effects in IGZO Thin-Film Transistors

Total-ionizing-dose (TID) effects are evaluated in back-gated IGZO thin-film transistors irradiated under different gate biases. Negative-bias irradiation leads to worst-case degradation of TID response in these devices, primarily as a result of enhanced charge trapping in the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> overlayer. The relatively small peak transconductance decrease after irradiation illustrates that IGZO transistors are much less sensitive to interface-trap buildup and other instabilities due to hydrogen release and transport than amorphous Si thin film transistors examined previously. The TID response of devices with different gate sizes is also investigated. No significant geometry dependence is observed, which is promising for future scaling down of the technology.

(Invited) Oxide TFT Applications: Principles and Challenges

The main advantage of the thin film transistor (TFT) is that it can be fabricated on non-wafer substrate independent of the size, flexibility, and morphology. All composing films of the TFT are deposited at the low temperature. Therefore, TFTs can be applied to a broad range of consumer, biological, chemical, and optical products that are difficult to fabricate with the wafer based MOSFETs.There are many reports on a-Si:H and poly-Si TFT applications in displays, imagers, sensors, drivers, flexible electronics, and circuits (1,2). In principle, oxide TFTs can be applied to similar products. However, since the device characteristics and compositing materials of the oxide TFT are different from those of the a-Si:H and poly- Si TFTs, as shown in Figure 1 and Table 1, there are advantages and disadvantages in former’s applications. In this presentation, oxide TFT applications in the following three areas will be discussed. Control of the attached device, such as pixel-driving in displays,Integrated circuits, such as drivers or inverters, andChanging of characteristics with environment, such as pH, optical, and temperature sensors. L. Antonuk, Chapt. 10, and Y. Kuo, Chapt. 11, Amorphous Silicon Thin Film Transistors, pp. 395-505, Kluwer Academic Publishers, 2004.B.-D. Choi, et al., Chapt. 11-13, Polycrystalline Silicon Thin Film Transistors, Y. Kuo Editor, pp. 360-495, Kluwer Academic Publishers, 2004.Kuo and G. W. Chang, ECS Trans, 64(10), 145-153 (2014). Figure 1

(Invited, Digital Presentation) Nondegenerate Hydrogen-Doped Polycrystalline Indium Oxide (InOx:H) Thin Films for High-Mobility Thin Film Transistors

Transparent metal oxide semiconductors (OSs) have been extensively investigated for use as the active channel layer of thin film transistors (TFTs) for next-generation flat-panel displays, nonvolatile memories, image sensors, and pH sensors, to name a few. Among OSs, the amorphous In–Ga–Zn–O (IGZO) has attracted particular attention for TFT applications owing to its high field effect mobility (μFE) of more than 10 cm2V−1s−1, steep subthreshold swing (S.S.), extremely low off-state current, large-area uniformity, and good bias stress stability. Although the μFE of an IGZO TFT is approximately one order of magnitude higher than that of an amorphous Si TFT, further improvement of the μFE of OS TFTs is required to expand their range of applications as an alternative to polycrystalline Si TFT.Single-crystalline In2O3 has a Hall mobility as high as 160 cm2V−1s−1, which makes amorphous (a-) or polycrystalline (poly-) InOx a potential material for enhancing the μFE of OS TFTs. However, undoped InOx thin films is known as a degenerate semiconductor with high background electron density of over 1020 cm-3, which is attributed to the presence of native defects, such as oxygen vacancies, making them unsuitable for a channel material of OS TFTs. In this presentation, nondegenerate hydrogen-doped polycrystalline InOx (poly-InOx:H) thin films were successfully prepared by low-temperature solid phase crystallization (SPC). A degenerate amorphous InOx:H thin film was deposited by sputtering in Ar, O2, and H2 gases, and an amorphous to polycrystalline phase transition (SPC) of the film was achieved after PDA at more than 175 °C. By PDA at 250 °C in air, a nondegenerate poly-InOx:H film could be obtained with a carrier density as low as 2.4 × 1017 cm−3, which is approximately three orders of magnitude lower than that of the initial a-InOx:H film. The TFTs with a 50 nm thick nondegenerate poly-InOx:H channel could be fully depleted by a gate electric field. A maximum μFE of 125.7 cm2V−1s−1 was exhibited by the TFT with the poly-InOx:H channel. The use of a nondegenerate poly-InOx:H film is a promising approach to boost the μFE of OS TFTs.

Bottom gate single crystal Si thin-film transistors fabricated by all sputtering processes

Single-crystal Si (c-Si) bottom-gate thin-film transistors (BG-TFTs) were fabricated using all sputtering processes. Laser doping from sputter-deposited Sb-doped amorphous Si film was proposed, by which n+ c-Si with resistivity and contact resistivities of 1.5 × 10−3 Ωcm and 2.1 × 10−5 Ωcm2, respectively, were fabricated. In addition, thin (50 nm) and low-heat conductive titanium was proposed for BG to realize continuous lateral crystal growth in Si film above the edge of BG. The fabricated n-channel c-Si BG-TFTs exhibited a field-effect mobility of 75 ± 21 cm2 V−1s−1, subthreshold swing of 0.612 ± 0.110 Vdec−1, and threshold voltage of 4.9 ± 1.38 V. Lack of bottom Si/SiO2 interface quality was indicated to be the origin of insufficient mobility.

9‐2: Oxide TFT behavior Under X‐Ray Irradiation in DXD Backplane

Recently, the digital X‐ray detector (DXD) technology requires high quality and high frame rate dynamic images, so efforts are being made to apply an oxide semiconductor (OS) thin film transistor (TFT) to the DXD backplane as a switching device instead of an amorphous Si (a‐Si) TFT. In order for the OS TFT to be used as a switching device of the X‐ray detector, it is necessary to study about the degradation parameters of the OS TFT under X‐ray irradiation. We confirmed that the threshold voltage (Vth) of the InGaZnO (IGZO) TFTs shifted negatively without s‐factor degradation according to X‐ray exposure. To understand these characteristics, we evaluated the X‐ray degradation characteristics of various methods.

Compact Integration of Hydrogen–Resistant a–InGaZnO and Poly–Si Thin–Film Transistors

The low–temperature poly–Si oxide (LTPO) backplane is realized by monolithically integrating low–temperature poly–Si (LTPS) and amorphous oxide semiconductor (AOS) thin–film transistors (TFTs) in the same display backplane. The LTPO–enabled dynamic refreshing rate can significantly reduce the display’s power consumption. However, the essential hydrogenation of LTPS would seriously deteriorate AOS TFTs by increasing the population of channel defects and carriers. Hydrogen (H) diffusion barriers were comparatively investigated to reduce the H content in amorphous indium–gallium–zinc oxide (a–IGZO). Moreover, the intrinsic H–resistance of a–IGZO was impressively enhanced by plasma treatments, such as fluorine and nitrous oxide. Enabled by the suppressed H conflict, a novel AOS/LTPS integration structure was tested by directly stacking the H–resistant a–IGZO on poly–Si TFT, dubbed metal–oxide–on–Si (MOOS). The noticeably shrunken layout footprint could support much higher resolution and pixel density for next–generation displays, especially AR and VR displays. Compared to the conventional LTPO circuits, the more compact MOOS circuits exhibited similar characteristics.

(Invited) Flexible and Stretchable Microwave Electronics

he development of microwave electronics has greatly advanced applications including communication, sensing, detection, and so on. The recently emerging markets like wearable devices, biomedical sensors, and foldable large-area microwave systems impose new requirements on microwave electronics, including flexibility, low weight, small size, and even stretchability. The unique mechanical properties of flexible and/or stretchable electronics renders them perfect candidates for applications like biomedical sensors and wearable devices, where the device needs to be attached or wrapped on nonplanar surfaces. Microwave electronics in flexible and/or stretchable form can substantially expand the application of these devices by eliminating lengthy connection wires and implementing modern wireless techniques. Therefore, flexible/stretchable electronics including fundamental components, functional circuits, and complete systems have attracted great interest from both academia and industry. The development of flexible microwave electronics has focused on fundamental flexible components like transistors and passive components in the past decades. As the heart of modern electronics, conventional semiconductor-based transistors have transformed into the flexible form through various mechanisms including substrate removal and exfoliation of the active layer on the surface. Silicon (Si), the most widely studied semiconductor material, has been extensively investigated for flexible microwave transistors. By employing technologies like strained channel and nanoimprinting, flexible Si thin-film transistors (TFTs) with excellent high-frequency performance were obtained. In addition, to extend the application of flexible transistors toward higher frequency and higher power, compound semiconductor-based flexible microwave transistors attracted increasing attention due to their superior material properties like high electron mobility, wide bandgap, and so on. The flexible GaInP/GaAs heterojunction bipolar transistor (HBT) and flexible AlGaN/GaN high electron mobility transistor (HEMT) have shown higher operating frequency than flexible Si TFTs. Besides superior high-frequency performance, flexible GaN HEMTs also show great potential for high-power flexible microwave electronics due to their wide bandgap and excellent thermal stability. The demonstrated flexible GaN HEMT can sustain a dissipation power of 0.5 W while achieving maximum oscillation frequency of 115 GHz. Besides the flexible transistors, flexible passive components operating at the GHz range, i.e. necessary parts of microwave circuits, are demonstrated as well. The operating frequency of inductors and capacitors have been pushed to beyond 10 GHz with optimization in device design. As the flexible microwave fundamental components continue to improve, flexible integrated circuits (ICs) consisting of fundamental components are being developed as well. Simple flexible circuits like switches and filters have been demonstrated by integrating Si or Ge diodes and passive components like inductors and capacitors. Flexible rectifiers, the critical component of wireless power transferring, are demonstrated using membrane GaAs Schottky diodes and flexible capacitors, which can harvest electromagnetic energy at WLAN band. Recently, a flexible power amplifier operating at 5.5 GHz with output power around 10 dBm has been reported. A reliable fabrication process flow has been developed to integrate small membrane GaN HEMT and flexible inductors and capacitors on polyimide thin film. Due to the excellent thermal reliability of GaN HEMT and heat spreader based on large coplanar copper ground plane, the amplifier can retain reliable operation with GaN membrane size as small as 0.5 mm by 0.5 mm. Compared to the rapid advancement of flexible microwave electronics, the development of stretchable microwave components is quite restricted due to the increased fabrication complexity and degraded device performance. The existing stretchable microwave components focus on passive components, especially the interconnect transmission lines. Due to the rigidness and fragility of semiconductor materials, stretchable microwave devices are typically made by connecting compact high-performance rigid/flexible semiconductor devices with stretchable interconnects. We have demonstrated a stretchable transmission line using a twisted structure, which can operate up to 50 GHz with minimized electromagnetic leakage. Recently, we successfully fabricated stretchable inductors operating at the GHz range. By connecting polyimide encapsulated compact spiral inductors with serpentine interconnects, the stretchable inductors inherit the high performance of a spiral inductor as well as the stretchability of serpentine lines. Although several key issues, including effective thermal management and enhanced reliability of the devices, require further research, flexible and stretchable microwave electronics have shown great promise in reshaping the existing electronics.

Origin of Spontaneous Degradation of Flexible Poly-Si TFTs After Dynamic Bending

The origin of an abnormal spontaneous degradation of low-temperature polycrystalline Si (LTPS) thin-film transistors (TFTs) is investigated. After being subjected to dynamic bending stress, LTPS TFTs will continuously degrade when stored in a normal condition. Studies have shown that the interaction between the sensitive area of the TFTs and the O2 in ambient environment causes the spontaneous degradation. Defects at the gate oxide/channel interface generated by mechanical stress continuously capturing electrons with the help of oxygen is regarded as the origin of spontaneous degradation. In contrast, moisture in air can effectively suppress spontaneous degradation by reacting with the above defects to form relatively stable atom groups.

A monolithically integrated micro-LED display based on GaN-on-silicon substrate

A monolithic micro-LED display technology is proposed using a gallium-nitride-on-silicon substrate. An active matrix (AM) display was realized by interconnecting nitride-based LEDs as display pixels with Si thin-film transistors (TFTs) as driving circuitries. MOS TFTs were fabricated on a Si surface which had been exposed after dry etching of the LED epitaxial layer. The mobility and sub-threshold slope were measured as 354.3 cm2 V−1 s−1 and 0.64 V dec−1, respectively. A 150 pixel-per-inch 0.6 inch monolithic display was demonstrated with a 60 × 60 pixel array AM display by an integration technology on the same substrate.

Inhibiting the Kink Effect and Hot-Carrier Stress Degradation Using Dual-Gate Low-Temperature Poly-Si TFTs

This study examines the appearance of a kink effect phenomenon in the I $_{\mathbf {D}}$ -V $_{\mathbf {D}}$ electrical characteristics of low-temperature polycrystalline Si thin-film transistors (LTPS TFTs) after high-current-induced hot-carrier stress (HCS). During HCS, electron–hole pairs were generated in the channel near the drain terminal owing to impact ionization. Next, the electrons were repelled towar the source by the drain electric field, thereby inducing the floating body effect, which lowered the source barrier. In addition, a dual-gate-structured LTPS was found to inhibit the electrical degradation caused by HCS. The COMSOL simulation indicated that in the dual-gate structure, holes at the upper and lower margins of the channel were inverted and inhibited the degradation caused by the floating body effect. Therefore, the use of dual-gate LTPS TFTs could facilitate high-current gate-on-array circuit applications in display panels.

Highly efficient formation process for functional silicon oxide layers at low temperatures (≤ 120 °C) using very high-frequency plasma under atmospheric pressure

SiO2-like films are deposited with high rates at substrate temperatures in the range of ≤120 °C by means of the developed atmospheric-pressure (AP) plasma-enhanced chemical vapor deposition (PECVD) technology. The AP plasma is excited by using a novel parallel-plate-type electrode system under supplying a 150 MHz very high frequency (VHF) electric power. As the process gases, oxygen (O2) and hexamethyldisiloxane (HMDSO) diluted with helium (He) are used. The electrode system is capable of forming one-dimensional flow of the process gases without any turbulence both inside and outside the plasma zone, which achieves the deposition conditions with no contamination of substrate surface with dust particles. The microstructure and surface roughness of the films are discussed by controlling O2 flow rate (O2/HMDSO source ratio) and VHF power density (PVHF), aiming at the use of the films as the gate insulators of low-temperature thin film transistors (TFTs). Irrespective of the substrate materials (Si wafers or polyethylene naphthalate (PEN) sheets), the films deposited with an appropriate O2 flow rate condition show smooth surface and cross sectional morphologies with no particles being incorporated during the deposition, which lead to the sufficiently good quality to be used as the gate insulator of low-temperature Si TFTs. The capability of forming functional thin films on temperature sensitive substrates will also lead to various applications of AP-VHF plasma as an efficient coating tool for polymer substrates.

High signal-to-noise ratio HgI2 X-ray detector assisted with ultraviolet radiation

Abstract A direct-conversion active matrix flat panel X-ray imaging detector was fabricated with an HgI2 photoconductor. The HgI2 photoconductive layer was coated on an amorphous Si thin film transistor panel with a particle-in-binder process. The micro-morphological properties of the HgI2 photoconductive layer were characterized by micro-computed tomography, X-ray diffraction, and scanning electron microscopy. The volume density of HgI2 in the layer was 40.9%. The effect of the bias voltage on the sensitivity of the HgI2 photoconductor was investigated with different photon irradiations such as ultraviolet and visible light as one of reset processes. The sensitivity of the HgI2 photoconductor was increased with the help of ultraviolet radiation before X-ray radiation, which released trapped carriers inside the photoconductor and increased the sensitivity of the HgI2 photoconductor. Moreover, ultraviolet irradiation with a DC bias stabilized the sensitivity variation. An X-ray imaging detector in conjunction with anHgI2 photoconductor shows a very high signal-to-noise ratio.

Spontaneous Degradation of Flexible Poly-Si TFTs Subject to Dynamic Bending Stress

An abnormal spontaneous degradation of polycrystalline Si thin-film transistors (TFTs) subject to dynamic bending stress is reported. Dynamic mechanical bending along either the channel-width or length direction causes degradation in flexible low-temperature polycrystalline Si TFTs, such as on-state current increase and threshold voltage positive shift. However, after the mechanical stress is removed, TFTs stored in a normal ambient continue to degrade spontaneously, with similar degradation behaviors. The amount of spontaneous degradation can be larger than the mechanical bending-induced degradation and is the most significant for a moderate number of bending cycles. The spontaneous degradation is a new challenge to TFT reliability under mechanical stress.

(Invited) Oxide TFT Fabrication with Various Low Temperature Techniques

Oxide thin film transistors (TFTs) have attracted much attention for next-generation electronics because of their superior performance compared with conventional a–Si TFTs such as high mobility and optical transmittance in the visible light.1 Some display manufacturing companies have already manufactured oxide TFTs based products, but there are some issues remained for oxide TFTs to be used for flexible displays. One of the issues is the high-temperature annealing process (> 300°C). Due to low thermal durability, flexible substrates cannot be processed in high temperatures.2-3 In this study, we propose various researches to lower the processing temperatures in oxide TFTs: photocatalytic reactions of titanium dioxide (PRT) and rotating magnetic field (RMF) treatment. In addition, we suggest ethyl cyanoacrylate (ECA) based instant glue (IG) as a new material for the passivation layers of oxide TFTs with low processing temperature. Photocatalytic Reaction of Titanium Dioxide (PRT) In this study, we fabricate indium–zinc oxide (IZO) TFTs using PRT. The hydroxyl radicals are generated by reaction between titanium dioxide (TiO2) and water molecules during UV irradiation. These hydroxyl radicals decompose the 2-methoxyethanol (2ME; one of the representative solvents) into smaller organic molecules. The decomposed 2ME has low boiling points and molar masses compared with non-PRT treated 2ME. Therefore, PRT treatment not only provides superior electronic devices caused by less defect sites in the oxide channel layers, but also allows low temperature process at 230°C. Additionally, since TiO2 particles can generate hydroxyl radicals permanently under UV irradiation, the PRT treated IZO TFTs show improved electrical characteristics even after four times recycling of TiO2. Rotating magnetic field (RMF) treatment In this work, we fabricate indium–gallium–zinc oxide (IGZO) TFTs by RMF treatment at a low temperature of 150°C. For RMF treatment, IGZO films are exposed to periodically rotating magnetic field and thermal energy of 150°C. The magnetic field and thermal energy simultaneously facilitate the interaction and attraction of metal and oxygen atoms leading to formation of M–O bonds in IGZO films. As a result, RMF treated IGZO TFTs exhibited improved electrical performances and positive bias stress (PBS) characteristics compared with those of IGZO TFTs treated by only thermal annealing process at 300°C. Instant Glue (IG) Passivation We introduce IG as a novel material for the passivation layer of IGZO TFTs. The ECA-based IG is a moisture-curing adhesive, which is liquid at room temperature and cures rapidly by reacting with moisture in atmosphere. As it is solidified rapidly at room temperature, it has shorter process time than that of conventional organic materials; the IG passivation layer is prepared successfully just for 1 min at 150°C. The IG passivation layer can modify the chemical stoichiometry of IGZO films and prevent any interaction between the back surface of the IGZO TFT and ambient gas. Therefore, the IGZO TFTs with an IG passivation layer show improved electrical characteristics and reliability compared to those without passivation layer. References Jae Won Na, You Seung Rim, Hee Jun Kim, Jin Hyeok Lee, Seonghwan Hong, and Hyun Jae Kim, ACS Appl. Mater. Interfaces 9, 35, 29849 (2017).Hua Xu, Dongxiang Luo, Min Li, Miao Xu, Jianhua Zou, Hong Tao, Linfeng Lan, Lei Wang, Junbiao Peng, and Yang Cao, J. Mater. Chem. C 2, 7, 1255 (2014).Seonghwan Hong, Sung Pyo Park, Yeong-gyu Kim, Byung Ha Kang, Jae Won Na, and Hyun Jae Kim, Scientific Reports 7, 1, 16265 (2017). Figure. Schematics of various techniques to lower the processing temperatures for oxide TFTs, (a) photocatalytic reaction of titanium dioxide, (b) rotating magnetic field treatment, (c) instant glue passivation. Figure 1

P‐9.2: GaN HEMT‐LED Homogeneous Integration for Micro‐LED Mass Transferring

Mass transfer is transferring a number of Micro‐LED pixels from the original substrate to target backplane, which aims to provide electrical connection and mechanical support for Micro‐LED pixels. Mass transfer technology plays a crucial role in Micro‐LED displays. For Micro‐LED displays larger than 2 inches, such as mobile phone and camera (2∼7 inches), Pad and Laptop (7∼15 inches), television (larger than 15 inches), mass transfer is a significant process in fabrication process. Unfortunately, mass transfer has become a bottleneck restricting the development of the Micro‐LED commercialization. There are many technology routes to solve (or to avoid) the problem of mass transfer. In this experiment, we review several methods of GaN HEMT‐LED monolithic integration to provide better electrical connection and mechanical support of Micro‐LEDs. As the third‐generation semiconductor, then we choose a model to do simulation by using Silvaco. GaN can be used as high‐quality LED and HEMT, especially the mobility of GaN HEMT is more than 2000cm2/V. S, which higher hundreds of times than Si transistor or TFT (Thin Film Transistor). HEMT‐LED monolithic integration can greatly improve the driving performance, save pixel area, improve pixel density, but also can avoid the problem of electrical connection in the mass transfer.

Appearance of the p-channel performance of poly-Si TFTs with a metal S/D electrode using BLDA aiming for low-cost CMOS

ABSTRACTProposed in this study and fabricated on a glass substrate without adopting impurity doping were p-channel polycrystalline silicon (Si) thin-film transistors (TFTs) with a metal source/drain (S/D) electrode. The amorphous 50-nm-thick Si films deposited on a glass substrate via plasma-enhanced chemical vapor deposition were polycrystallized using blue laser diode annealing. Gold (Au), a high-work-function metal, was evaporated for the S/D electrode directly onto the Si channel layer. As a result of the TFT formation, the typical Id–Vg characteristics of the p-channel TFT were successfully obtained. In addition, after hydrogenation at 200°C, the drain current drastically increased. The 14 cm2/Vs effective field effect hole mobility was deduced at the drain voltage of −1 V.

Solution-Based Fabrication of Polycrystalline Si Thin-Film Transistors from Recycled Polysilanes.

Currently, research has been focusing on printing and laser crystallization of cyclosilanes, bringing to life polycrystalline silicon (poly-Si) thin-film transistors (TFTs) with outstanding properties. However, the synthesis of these Si-based inks is generally complex and expensive. Here, we prove that a polysilane ink, obtained as a byproduct of silicon gases and derivatives, can be used successfully for the synthesis of poly-Si by laser annealing, at room temperature, and for n- and p-channel TFTs. The devices, fabricated according to CMOS compatible processes at 350 °C, showed field effect mobilities up to 8 and 2 cm2/(V s) for n- and p-type TFTs, respectively. The presented method combines a low-cost coating technique with the usage of recycled material, opening a route to a convenient and sustainable production of large-area, flexible, and even disposable/single-use electronics.