Soldering of solution-processed organic vertical transistor and light-emitting diode on separate glass substrates by tin micro-balls

The vertical organic space-charge-limited transistor made of P3HT and small-molecule phosphorescent organic light-emitting diode (OLED) are made on two separate glass substrate by blade coating, then soldered vertically together by tin balls with 40 μm diameter. The soldering is done by hot wind of 150 °C for 5 min Contact resistance is only 10 Ω. The vertical transistor is annealed at 150 °C for 5 min before soldering to enhance the output current up to 25 mA/cm² and give high thermal stability. Both OLED and the annealed vertical transistor are not affected by the soldering process. The vertical transistor has 1/4 of the OLED area and turns on the bottom-emission white OLED up to 300 cd/m² and orange OLED up to 600 cd/m². The entire operation is within 8 V. OLED and transistor array can therefore be made on separate glass substrates then soldered together to form the display.     

Additive-free organic solar cells with enhanced efficiency enabled by unidirectional printing flow of high shear rate

High-performance OSCs prepared by scalable techniques without additives are highly desirable because residual additives may cause gradual deterioration of the photoactive-layer morphology and device performance. Printing flows with high shear rate have the potential to replace additives by inducing higher degree of ordered stacking and crystallinity of organic molecules, as well as favorable phase separation. Here, PTQ10:Y6 organic solar cells (OSCs) without any additives were fabricated by a scalable and robust processing approach termed as soft porous blade printing (SPBP). The fluid flow and drying process of the wet films made by SPBP, blade coating and spin coating are visualized by high speed imaging, which reveals that the blade coating and SPBP introduce unidirectional flow while the wet film interference pattern of spin coating is irregular and random. The simplified flow model of SPBP suggests that the shear rate could be as high as ~1000 s⁻¹. The additive-free SPBP produces photoactive-layer with adequate morphology, which could be attributed to three intrinsic properties of SPBP: very high shear rate, flow assisted crystallizations induced by microstructures of the soft porous blade, and numerous nucleation sites generated as the liquid contact line follows the motion of the blade. The additive-free SPBP device demonstrates weaker charge recombination, higher and more balanced charge transport, and consequently better device performance than the spin-coated and blade-coated devices with 0.25 vol% 1,8-diioctane (DIO). SPBP achieved power conversion efficiency (PCE) of 16.45%, which is higher than those of spin-coated and blade-coated counterparts doped with DIO.     

Efficiency enhancement of organic light-emitting devices by using honeycomb metallic electrodes and two-dimensional photonic crystal arrays

In this paper, a facile fabrication technique called nanosphere lithography combining with two-step reactive ion etching method for patterning honeycomb metallic electrode with high transparency and excellent uniformity is demonstrated. The patterning silver electrode with 15-nm film thickness and 68.6% fill-factor was used as the organic light-emitting diode (OLED) anode, which showed an average transmittance of 77.4% and sheet resistance of 30.7 Ω/□. The current efficiency is 8.35 cd/A for the OLED with patterned silver anode under 100 cd/m² operation brightness, which was 47% higher than the device with indium tin oxide (ITO) anode. After applying the polystyrene nanosphere to form a photonic crystal array onto the device, the extracted light from organic mode can be further coupled out from device substrate mode. The overall luminous enhancement of the device with the combination of internal honeycomb metallic anode and external photonic crystal array is 115% higher than the traditional ITO-based OLED.     

Fabrication of periodic square arrays by angle-resolved nanosphere lithography

We investigate the fabrication of periodic square arrays of solid gold islands by angle-resolved nanosphere lithography (ARNSL) in conjunction with thermal evaporation and etching. By varying θ (the tilt angle between the direction of gold deposition beam and the substrate surface normal) and ? (the substrate rotation angle about the beam axis), adjacent islands on a deposited hexagonal gold array will have a constant and periodic difference in height. Upon etching, this height bias will result in the shorter structures being removed to produce an array with a different symmetry from the original hexagonal symmetry of the parent mask. By depositing at three directions of ? = 0°, 120° and −120° with a constant θ = 20°, experimental results show that deposited two-dimensional gold periodic arrays will have a measurable difference in height between adjacent islands. Etching of the resulting patterns produced periodic near-square arrays with triangular nanostructures. Thus the combination of ARNSL and etching can allow selective periodic nanostructures to be removed, increasing the diversity of array symmetries available through nanosphere lithography.     

Fabrication of antireflection nanostructures by hybrid nano-patterning lithography

Antireflection (AR) nanostructures are fabricated on a glass substrate using hybrid nano-patterning lithography (H-NPL) consisting of nanosphere lithography (NSL) and UV-nanoimprint lithography (UV-NIL). The shape and diameter of the AR nanostructures were controlled by fabricating Si masters with different RIE conditions. The shapes of the AR nanostructures were a pillar-type and a corn-type. The diameters of the AR nanostructures were about 350 and 250 nm, respectively. AR nanostructures were successfully nanoimprinted on glass in accordance with Si master prepared by NSL. The pillar-type AR nanostructure with diameter of 350 nm exhibited the transmittance of over 98% in the wavelength range from 1100 to 2200 nm. From the results, the fabricated AR nanostructures demonstrate the possibility to improve the efficiency of optoelectronic devices such as a photo-detector and an IR-LED.     

Unmodified small-molecule organic light-emitting diodes by blade coating

Blade coating with substrate heating and hot wind is demonstrated to be a general platform for multi-layer deposition of unmodified small-molecule organic semiconductors. Most unmodified small molecules, originally designed for vacuum evaporation, can be blade coated while the solubility is above 0.5 wt.%. High uniformity is achieved for scale over 5 cm. Orange devices by evaporation and blade coating are compared with 4,4′-bis(carbazol-9-yl)biphenyl (CBP) as the host, iridium(III) bis(4-(4-t-butylphenyl)thieno[3,2-c]pyridinato-N,C²′)acetylacetonate (PO-01-TB) as the emitter. The efficiency difference is within 10%. When 2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine (26DCzPPy) is used as the host, the current efficiencies are 40 cd/A for orange, 32 cd/A for green, and 20 cd/A for blue. The optimized organic light-emitting diodes (OLED) structure developed for vacuum deposition can therefore be exactly copied by the low cost blade coating method in solution.     

Flexible thin-film transistors using multistep UV nanoimprint lithography

A multistep imprinting process is presented for the fabrication of a bottom-contact, bottom-gate thin-film transistor (TFT) on poly(ethylene naphthalate) (PEN) foil by patterning all layers of the metal–insulator–metal stack by UV nanoimprint lithography (UV NIL). The flexible TFTs were fabricated on a planarization layer, patterned in a novel way by UV NIL, on a foil reversibly glued to a Si carrier. This planarization step enhances the dimensional stability and flatness of the foil and thus results in a thinner and more homogeneous residual layer. The fabricated TFTs have been electrically characterized as demonstrators of the here developed fully UV NIL-based patterning process on PEN foil, and compared to TFTs made on Si with the same process. TFTs with channel lengths from 5 μm down to 250 nm have been fabricated on Si and PEN foil, showing channel length-dependent charge carrier mobilities, μ, in the range of 0.06–0.92 cm² V⁻¹ s⁻¹ on Si and of 0.16–0.56 cm² V⁻¹ s⁻¹ on PEN foil.     

Fabrication of submicron photon sieve using E-beam lithography and X-ray lithography

In this paper, a new hybrid method to fabricate submicron photon sieve is proposed, where the E-beam lithography and the X-ray lithography are used. It is found that 2.8 μm thickness of the polyimide film, 400 nm thickness of the ZEP-520 and 280 μC/cm² exposure dose are good for E-beam lithography, while 500 nm thickness of the PMMA and 30 s developing time are good for X-ray lithography. We have successfully fabricated the photon sieve with these parameters (the diameter of photon sieve: 250 μm, the focal length: 150 μm, the diameter of the outmost pinhole: 420 nm). Some key techniques of this method are analyzed respectively, and the error analysis are done at the end of this paper. It provides a direction of nanoscale optical element fabrication with higher resolution and lower cost.     

Electron beam nanolithography in AZnLOF 2020

We present a lithography process using electron beam lithography with an optical resist AZnLOF 2020 for pattern transfer. High-resolution 100 keV electron beam lithography in 400 nm layers of negative resist AZnLOF 2020 diluted 10:4 with PMGEA is realized. After the electron beam lithography process, the resist is used as a mask for reactive ion etching. We performed the transfer of patterns by RIE etching of the substrate allowing a final resolution of 100 nm. We demonstrate the patterning in an insulating layer, thus simplifying the fabrication process of various multilayer devices; proximity correction has been applied to improve pattern quality and also to obtain lines width according to their spacing. This negative resist is removed by wet etching or dry etching, could allow combining pattern for smallest size down to 100 nm by EBL techniques and for larger sizes by traditional lithography using photomask.     

A maskless laser-write lithography processing of thin-film transistors on a hemispherical surface

We report on the design and fabrication methods for a hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) on a non-planar substrate using laser-write lithography (LWL). Level-to-level alignment with a high accuracy is demonstrated using LWL method. The fabricated a-Si:H TFT exhibits a field-effect mobility of 0.27 cm²/V s, threshold voltage of 4.9 V and on/off current ratio of ∼6 × 10⁶ in a saturation regime. The obtained results demonstrate that it is possible to fabricate the a-Si:H TFTs and complex circuitry on a curved surface, using a well-established a-Si:H TFT technology in combination with the maskless lithography, for hemispherical or non-planar sensor arrays.     

Gold Nanoparticle–Colloidal Carbon Nanosphere Hybrid Material: Preparation,Characterization, and Application for an Amplified Electrochemical Immunoassay

A rapid microwave‐hydrothermal method has been developed to prepare monodisperse colloidal carbon nanospheres from glucose solution, and gold nanoparticles (AuNPs) are successfully assembled on the surface of the colloidal carbon nanospheres by a self‐assembly approach. The resulting AuNP/colloidal carbon nanosphere hybrid material (AuNP/C) has been characterized and is expected to offer a promising template for biomolecule immobilization and biosensor fabrication because of its satisfactory chemical stability and the good biocompatibility of AuNPs. Herein, as an example, it is demonstrated that the as‐prepared AuNP/C hybrid material can be conjugated with horseradish peroxidase‐labeled antibody (HRP‐Ab₂) to fabricate HRP‐Ab₂‐AuNP/C bioconjugates, which can then be used as a label for the sensitive detection of protein. The amperometric immunosensor fabricated on a carbon nanotube‐modified glass carbon electrode was very effective for antibody immobilization. The approach provided a linear response range between 0.01 and 250 ng mL^?1 with a detection limit of 5.6 pg mL^?1. The developed assay method was versatile, offered enhanced performances, and could be easily extended to other protein detection as well as DNA analysis.     

Sub-100 nm ALD-assisted nanoimprint lithography for realizing vertical organic transistors with high ON/OFF ratio and high output current

We introduced a conformal atomic-layer-deposited aluminum oxide layer to cover the imprint mold to reduce the feature size and to strengthen the mold durability. A nano-hole array pattern with diameter down to 85 nm was successfully transferred to sample substrate to fabricate a vertical organic transistor. The Imprint vertical organic transistor exhibited high output current density as 4.35 cm²/V s and high ON/OFF current ratio as 11,000 at a low operation voltage as 1.5 V.     

Solution processed inverter based on zinc oxide nanoparticle thin-film transistors with poly(4-vinylphenol) gate dielectric

An enhancement-load inverter using bottom-gated ZnO nanoparticle thin-film transistors and a polymer gate dielectric is demonstrated. The deposition of the ZnO active layer is done by spin coating of a colloidal dispersion and is hence cost-effective. Since the maximum process temperature is 200 °C, the presented device is furthermore suitable for plastic substrates. Although hysteresis is observed, the inverter shows reasonable transfer characteristics with a gain of up to 5.5 V/V at a supply voltage between 10 V and 15 V, whereas the static power dissipation is lower than 6 μW.     

Laser-assisted patterning of solution-processed oxide semiconductor thin film using a metal absorption layer

We present a method to pattern solution-processed oxide semiconductor thin films by all laser process. A metal thin film is first photoetched by a spatially-modulated pulsed Nd-YAG laser beam and this layer is then covered with a semiconductor film. Uniform irradiation by the same laser generates a thermo-elastic force on the underlying metal layer and this force serves to detach it from the substrate, leaving only a patterned semiconductor structure. Sharp-edged zinc-tin oxide (ZTO) patterns at the micrometer scales could be fabricated over a few square centimeters by a single pulse of 850 mJ. A mobility of 7.6 × 10⁻² cm² V⁻¹ s⁻¹, an on/off ratio higher than 10⁶, and an off-current of 1.91 × 10⁻¹¹ A were achieved from a thin film transistor (TFT) with the patterned ZTO channel. These values were similar to those from a reference TFT, demonstrating the feasibility of this patterning process for electronic devices.     

Vacuum-free lamination of low work function cathode for efficient solution-processed organic light-emitting diodes

The low work function cathode of blade-coated organic light-emitting diode is transferred from a soft polydimethylsiloxane (PDMS) mold by lamination without vacuum. The cathode is a bilayer of polyethylene glycol (PEG) (<10 nm) and Al (100 nm). A sacrificial layer of polystyrene with low Mw 1500 and melting point of 120 °C is inserted between the cathode and PDMS for the subsequent mold removal at 150 °C by melting polystyrene. Current efficiency of 3 cd/A (1.1%) and luminance of 2500 cd/m² are achieved for green polyfluorene fluorescent emitter. 25 cd/A (8.2%) and 3200 cd/m² are achieved for green phosphorescent tris[2-(p-tolyl)pyridine]iridium(III) (Ir(mppy)₃) emitter in polymer blend host. The efficiency is about 70% of the devices with thermally evaporated cathode. The turn-on voltage is about 5 V higher.     

Resistive switching characteristics of CMOS embedded HfO2-based 1T1R cells

This work addresses a 1T1R RRAM architecture, which allows for the precise and reliable control of the forming/set current by using an access transistor. The 1T1R devices were fabricated in a modified 0.25 μm CMOS technology. The memory cells show stable resistive switching in dc as well as pulse-induced mode with an endurance of 10³ and 10² cycles, respectively. The variation of pulse widths as a function of amplitudes in 1R devices confirmed the set process distribution over a wide range of pulse widths (300 ns-100 μA), whereas the reset process variation is confined (1-3 μs).     

Design of self-bias tail transistor technique for low phase noise CMOS VCO with harmonic suppression using capacitance ground

This paper presents a low phase noise wideband CMOS VCO based on the self-bias tail transistor technique and harmonic suppression using a capacitance ground. This VCO utilizes switching capacitor arrays in which four channels are able to be selected for multi-band application. Moreover, the design of CMOS VCO makes good use of the self-bias tail transistor and capacitance ground filter technique to reduce the phase noise. The MOS varactors are used as fine tuning for wideband operating application. The fully integrated VCO provides excellent performance with high FOM −193 dBc/Hz. The bandwidth of the frequency is 1.1 GHz and the tuning range is 13.8%. The power dissipation of the core circuit is 8.28 mW under a 1.8 V supply and phase noise is measured as low as −123.6 dBc/Hz at 1 MHz offset under 8.5 GHz oscillation frequencies. This VCO was made by the TSMC 0.18 μm 1P6M CMOS standard process and the chip area is 0.75×0.69 (mm²).     

Patterning of SiO2 nanoparticle-PMMA polymer composite microstructures based on soft lithographic techniques

Soft lithography and self-assembly provide powerful means of organizing colloidal solution of synthesized nanoparticles (NPs) for a wide variety of application. Pattern transfer of silicon dioxide (SiO₂) nanoparticles-polymethylmethacylate (PMMA) nanocomposite was investigated using two such soft lithographic techniques, micro molding in capillaries (MIMIC) and micro transfer molding (μTM) using an elastomeric stamp in Polydimethyl siloxane (PDMS). Nanocomposite periodic arrays of 20 μm wide and 10 μm deep lines with 10 μm spacing were obtained over approximately 1 cm² area on silicon substrates by μTM and MIMIC using a 3 wt.% monodisperse silica nanoparticles (∼338 ± 2 nm) in polymethyl methacrylate (PMMA) solution. In addition, free standing nanocomposite self-standing films of centimeter size were also manufactured by μTM. Single line of nanocomposite could also be obtained using MIMIC with a lower concentration of silica NPs (0.25 wt.%) in PMMA.     

Electrical responses of short-channel organic transistor prepared by solution-processed organic crystal wire mask

We report a formation of a solution-grown single crystal wire mask for the fabrication of short-channel organic field-effect transistor with enhanced dynamic response time. The various channel length, ranging from submicrometer to a few micrometers, were obtained by controlling the concentration of solution and processing conditions. We fabricated p- and n-channel bottom-contact organic field-effect transistors using pentacene and PTCDI-C₁₃, respectively, and static and dynamic electrical characteristics of the devices were investigated. The highest and average field-effect hole mobility values were found to be 0.892 cm²/V s and 0.192 cm²/V s, respectively. The load type inverter based on the short-channel transistor connected with a 2 MΩ resistor showed a clear switching response when square wave input signals up to 1 kHz were applied at V_DD = −60 V.     

High-mobility pentacene phototransistor with nanostructured SiO2 gate dielectric synthesized by sol-gel method

We have fabricated a pentacene based phototransistor by employing a modified nanostructured SiO₂ gate dielectric. The photosensing properties of the pentacene thin film transistor fabricated on n-Si substrate with nanostructured SiO₂ as gate dielectric have been investigated. The photocurrent of the transistor increases with an increase in illumination intensity. This suggests that the pentacene thin film transistor behaves as a phototransistor with p-channel characteristics. The photosensitivity and responsivity values of the transistor are 630.4 and 0.10 A/W, respectively at the off state under AM 1.5 light illumination. The field effect mobility of the pentacene phototransistor was also found to be 2.96 cm²/Vs. The nanostructured surface of the gate possibly is the cause of the high-mobility value of the phototransistor due to light scattering from the increased surface area.