Transfer Printing Research Articles

Micro‐Engraving UV‐Sensitive Thin‐Film Transistor from Metal–Metal Oxide Nanoparticles with Band‐Gap Engineering

AbstractAs known, n‐type inorganic semiconductor nanoparticles such as zinc oxide nanoparticles have been explored in various sensing applications, which demand high‐density electronic elements placement for rapid operation. Herein, high‐resolution designs of conductive channels of noble metal‐doped zinc oxide nanoparticles is demonstrated using an engraving transfer printing process and silver metal doping approach. Such thin‐film transistors with reduced feature size to 2 µm fabricated exhibited significantly enhanced electron mobility up 3.46 × 10−2 cm2 V−1 s−1 and light sensitivity. Furthermore, the integration of this micropatterning technology and metal doping in thin‐film transistors is utilized for control of current–voltage characteristics under the ultraviolet radiation with high sensitivity. It is suggested that this approach to design of doped inorganic nanoparticle channels paves the way for high‐density thin‐film transistors suitable for optoelectronic circuit, UV photodetectors and neuromorphic computing systems.

Direct‐Write Printing of Multicolor Electroluminescent Films for Stretchable Display

AbstractElectroluminescent (EL) films are promising light sources for flexible displays, wearable electronics, and soft machines. Traditional fabrication methods like thermal lamination, transfer printing, and screen printing are often labor‐intensive. To address these challenges, a mask‐free, fully printable alternating‐current electroluminescent (PACE) film using a direct‐write printing strategy is presented. This method simplifies fabrication, enhances design flexibility, and allows precise, layer‐by‐layer deposition without alignment issues. The multicolor PACE film, available in blue, green, and orange, reaches a thickness of ≈150 µm and achieves 180 cd m⁻2 at 6 V µm⁻¹. It stretches up to 180% and withstands 10 000 bending/stretching cycles without significant luminance loss. Compared to conventional EL devices, the approach offers similar brightness with thinner films, avoids UV‐curable elastomers, and reduces equipment needs. This innovation broadens design possibilities, especially for stretchable displays, making it ideal for rapid prototyping with computer‐aided design (CAD) tools.

A Portable LIFT Printer to Enable the Fast On‐Site Optimization of Inks Toward Special Customer Needs

ABSTRACTLaser‐induced forward transfer (LIFT) printing uniquely enables localized deposition of nanoparticle pastes onto target substrates. The extent of its versatility hinges upon the availability of nanoparticle inks that align with the capabilities of the printing device. Given the inherent distinctions among various devices attributed to differences in laser types (continuous‐wave or pulsed), laser energy profiles, and adaptable wavelengths, ink formulation and the LIFT printing processes are frequently disjointed, which results in a lengthy optimization cycle. Significantly expedited optimization cycles could be achieved if LIFT performance of an ink could be tested on‐site of the ink developer. This localization empowers ink developers to tailor inks precisely to specific usage scenarios by promptly adjusting parameters such as particle size, viscosity, and surface properties. This paper presents a dedicated LIFT device that focuses on fine‐tuning ink characteristics and provides insights into the construction to allow other interested researchers to build similar low‐cost, user‐friendly setups.

Electrically tunable InAs/GaAs QD in a nanocavity with a transfer-printed ITO electrode

We demonstrate the electrical tuning of InAs/GaAs quantum dots (QDs) embedded in a photonic-crystal (PhC) cavity with transparent indium tin oxide (ITO) electrodes hybrid-integrated by transfer printing. The design includes spacer layers between the cavity and the electrodes to reduce absorption loss while still maintaining a significant bias field. The bottom electrode, PhC cavity, and top electrode were fabricated independently and integrated by transfer printing, and an electrical connection was made by inkjet printing, both implemented locally without affecting the entire chip. We observed the electrical tuning of QD emissions into the cavity mode and Purcell enhancement. This work paves the way for utilizing multiple hybrid-integrated QDs on the same chip.

Advancing cellular transfer printing: achieving bioadhesion-free deposition via vibration microstreaming.

Cell transfer printing plays an essential role in biomedical research and clinical diagnostics. Traditional bioadhesion-based methods often necessitate complex surface modifications and offer limited control over the quantity of transferred cells. There is a critical need for a modification-free, non-labeling, and high-throughput cell transfer printing technique. In this study, an adhesion-free cellular transfer printing method based on vibration-induced microstreaming is introduced. By adjusting the volume of the microcavity, the number of cells transferred per microtiter well can be realized to the level of a single cell. Additionally, it allows for precise control of large-scale cellular spatial distribution, leading to the formation of biomimetic patterns. Moreover, the demonstrated biocompatibility and high throughput of this cell transfer printing method highlight its potential utility. The correspondence of the transferred cell amount to the vibration and frequencies allows the system to exhibit excellent tunability of the transferred cell amount and pattern. This bioadhesion-free cell transfer printing method holds promise for advancing cell manipulation in biomedical research and analysis.

Improvement of device performance of solution-processed multilayered LEDs with QD/polymer blend as the emission layer

Abstract We fabricated the solution-processed multilayered light-emitting diodes having the colloidal quantum dots/ polymer blend as an emitting layer (QD-LEDs) with the inverted organic LED structure. We proposed the multilayered electron injection layers consisting of 4,7-Dimethoxy-1,10-phenanthroline (p-MeO-Phen) on ZnO nanoparticles, and the multilayers of ZnO:p-MeO-Phen blend (1st EIL) and the heat-treated Zr (IV) acetylacetonate (Zr(acac)4) as a 2nd EIL. We achieved a higher material utilization rate and multilayered structure by combining the meniscus coating and transfer printing techniques. We then fabricated the QD-LEDs consisting of ITO/ZnO or ZnO:p-MeO-Phen blend (1st EIL)/2nd EIL/QD: polymer blend/polyvinylcarbazole (PVCz)/Poly(9,9-dioctylfluorene-alt-N-(4-sec-butylphenyl)-diphenylamine) (TFB)/hole injection layer/Anode (Al or Ag). We compared the device performance of QD blended with PVCz and polymethylmethacrylate (PMMA). The thickness of the QD layer was controlled between 1 and 3 QD layers by repeating the meniscus coating and transfer printing. The work function of ZnO was reduced by p-MeO-Phen and the threshold voltage was reduced from 4.9 V to 2.95 V. The peak value of EQE was improved from 1.14% to 3.1% by insertion of Zr(acac)4 probably owing to the reduction of leakage current and exciton quenching.

III-V Photonic Crystal Nanobeam Lasers Side-Coupled to Silicon Waveguide by Transfer Printing

III-V Photonic Crystal Nanobeam Lasers Side-Coupled to Silicon Waveguide by Transfer Printing

Patterning technologies of quantum dots for color-conversion micro-LED display applications.

Quantum dot (QD) materials and their patterning technologies play a pivotal role in the full colorization of next-generation Micro-LED display technology. This article reviews the latest development in QD materials, including II-VI group, III-V group, and perovskite QDs, along with the state of the art in optimizing QD performance through techniques such as ligand engineering, surface coating, and core-shell structure construction. Additionally, it comprehensively covers the progress in QD patterning methods, such as inkjet printing, photolithography, electrophoretic deposition, transfer printing, microfluidics, and micropore filling method, and emphasizes their crucial role in achieving high precision, density, and uniformity in QD deposition. This review delineates the impact of these technologies on the luminance of QD color-conversion layers and devices, providing a detailed understanding of their application in enhancing Micro-LED display technology. Finally, it explores future research directions, offering valuable insights and references for the continued innovation of full-color Micro-LED displays, thereby providing a comprehensive overview of the potential and scope of QD materials and patterning technologies in this field.

High-Brightness Color-Tunable AC-Driven Quantum Dot Light-Emitting Diodes for Integrated Passive High-Electric-Field Contactless Detection.

This work explores the carrier recombination dynamics of AC-driven quantum dot (QD) light-emitting diodes (AC-QLEDs) and proposes their application in the field of electric field contactless detection. Different sequences of green QD (GQD)/red QD (RQD) bilayer thin films as the emission layer of AC-QLEDs were fabricated via film transfer printing to ensure the complete morphology of each layer. AC-QLEDs with the emission layer as the sequence of GQD + RQD (GR-QLEDs) show a significantly enhanced carrier recombination efficiency due to its stable energy level structure, achieving the highest peak brightness ever recorded for vertically emitting brightness of 1648.2 cd/m2 depending on the carriers generated inside the device under AC bias. Owing to an imbalance in the carrier concentration generated by two sides of the emission layer, the proportion of emitted green light changes with the electric field strength, resulting in a macroscopic color shift of GR-QLEDs. The results indicate that although no carriers are injected directly from two electrodes, the equilibrium-induced carrier concentration under the AC electric field remains important. We utilized this unique device structure and color shift of GR-QLEDs for on-site inspection of large-scale communications power consumption. The patterned detector displays a significant color change from 9 × 106 to 6 × 107 V/m. True noncontact direct visualization detection was conducted under variable electric fields from 1 × 107 to 2 × 107 V/m in the vicinity of the running cable by emitting bright light. The proposed passive electric field detector is well-suited for investigating air gap discharge and monitoring spatial electric fields, featuring high integration, transparency, lightweight characteristics, high sensitivity, and broad bandwidth.

Nanocavity-based quantum-dot single-photon source on a SiN waveguide integrated by transfer printing.

Silicon nitride (SiN) integrated photonics is a highly promising platform for photonic quantum information processing. However, the efficient generation of single photons remains a significant challenge. Epitaxial InAs/GaAs quantum dots (QDs) embedded in wavelength-scale nanocavities offer a promising solution as single-photon sources (SPSs), but their integration with SiN has not yet been demonstrated. In this work, we employed a photonic crystal (PhC) nanobeam cavity to realize a QD SPS on a SiN waveguide. We found that the second-order mode of a period-modulated PhC nanobeam cavity is located close to the waveguide mode in the momentum space and could present a way to efficiently couple photons from the QD SPS into the waveguide. We fabricated the SiN circuitry and QD SPSs separately and integrated the SPS onto the waveguide by transfer printing. We observed Purcell enhancement by the cavity and confirmed the coupling of single photons into the waveguide.

Bioinspired balloon catheter integrated with stretchable "flounder" electrodes under high voltage for uniform pulsed field ablation.

Atrial fibrillation leads to severe diseases such as heart failure and strokes. While catheter ablation is prevalent for the treatment, existing techniques hardly can achieve both tissue selectivity and ablation uniformity. Here, we propose a bioinspired strategy for balloon-based pulsed field ablation (PFA) systems based on "flounder" electrodes. Inspired by a flounder skeleton and citrus peels, the microfabricated electrodes are ultrathin, stretchable, and have a scattered configuration, withstanding large balloon deformation (87% compression), high voltage (1200 volts), and owning exceptional tissue conformability (720° twists). Mechanical-electrical coupled stimulation optimizes balloon electrodes with hemispherical electric field uniformity. A water lily-inspired transfer printing method enables one-step integration of multielectrodes with the balloon. A comprehensive PFA system is complemented, achieving ablation depths of 3.8 millimeters (potato), 3.1 millimeters (rabbit), and 2.3 millimeters (swine) with good uniformity and electrophysiological isolation. These results shed light on the quantitative design of PFA systems, with high potential for more precise, safe, and effective catheter ablation therapies.

Laser-induced adhesives with excellent adhesion enhancement and reduction capabilities for transfer printing of microchips.

Transfer printing based on tunable and reversible adhesive that enables the heterogeneous integration of materials is essential for developing envisioned electronic systems. An adhesive with both adhesion enhancement and reduction capabilities in a rapid and selective manner is challenging. Here, we report a laser-induced adhesive, featuring a geometrically simple shape memory polymer layer on a glass backing, with excellent adhesion modulation capability for programmable pickup and noncontact printing of microchips. Selective and rapid laser heating substantially enhances the adhesive's adhesion strength from kilopascal to megapascal within 10 ms due to the shape fixing effect, allowing for precise and programmable pickup. Conversely, the enhanced adhesion can be quickly reduced and eliminated within 3 ms through the shape recovery effect, enabling noncontact printing. Demonstrations of transfer printing microlight-emitting diodes (LEDs) and mini-LEDs onto various low-adhesive flat, rough, and curved surfaces highlight the unusual capabilities of this adhesive for deterministic assembly.

High-Fidelity Pick-and-Place Transfer Printing of Colloidal Quantum Dot Pixel Arrays via a Composite Stamp.

Transfer printing can pattern emissive colloidal quantum dot (CQD) arrays with ultrahigh pixel density. However, the most used pick-and-place method has difficulty in achieving high pattern fidelity. Here, we report that the regularly used single-composite stamps cannot combine a low deformation rate and conformal contact, leading to the challenge. In response, we propose a composite stamp for the CQD transfer. Stacked with PDMS of different mechanical parameters, the composite stamp outperforms the single-component stamp composed of soft PDMS (Sylgard184) in deformation resistance and exhibits substantially higher contact conformality than that composed of harder PDMS. As a result, the composite stamp exhibits a 3.21-fold enhancement in transfer yield, delivering a pattern fidelity of 94.0% with a pixel diameter of 1.78 μm and a pixel density of 6350 per inch. The pick-and-place process also produces quantum dot light-emitting diode arrays with the same pattern and reasonable electroluminescence performance. This method provides insight into improving CQD arrays' pattern quality.

Lawn-inspired porous protection layers consisting of super-lithiophilic Ag arrays for high-performance Li metal anodes

A lawn-inspired porous and super-lithiophilic protection layer which consists of leaf-like Ag arrays has been successfully constructed on the metallic Li foil surface through a facile and scalable transfer printing method assisted by the mechanical rolling process. Benefited from the superior merits of these lawn-inspired Ag protection layers (L-Ag), Li dendrite growth and structure collapse have been effectively prohibited by the L-Ag@Li composite anodes. Therefore, the L-Ag@Li anodes exhibit outstanding cycling stability with extremely low overpotential (10 mV at 1 mA cm−2 after 500 cycles (1000h)) in symmetric cells and high discharge capacity (147 mAh g−1 at 1C after 200 cycles) in coin-type NCM811||L-Ag@Li full cells. The encouraging results suggest the enormous potential of Li metal anodes protected by lawn-inspired porous Ag array layers for energy-storage applications.

Controlled Formation of Porous Cross-Bar Arrays Using Nano-Transfer Printing.

Nano-transfer printing (nTP) has emerged as an effective method for fabricating three-dimensional (3D) nanopatterns on both flat and non-planar substrates. However, most transfer-printed 3D patterns tend to exhibit non-discrete and/or non-porous structures, limiting their application in high-precision nanofabrication. In this study, we introduce a simple and versatile approach to produce highly ordered, porous 3D cross-bar arrays through precise control of the nTP process parameters. By selectively adjusting the polymer solution concentration and spin-coating conditions, we successfully generated discrete, periodic line patterns, which were then stacked at a 90-degree angle to form a porous 3D cross-bar structure. This technique enabled the direct transfer printing of PMMA line patterns with well-defined, square-arrayed holes, without requiring additional deposition of functional materials. This method was applied across diverse substrates, including planar Si wafers, flexible PET, metallic copper foil, and transparent glass, demonstrating its adaptability. These well-defined 3D cross-bar patterns enhance the versatility of nTP and are anticipated to find broad applicability in various nano-to-microscale electronic devices, offering high surface area and structural precision to support enhanced functionality and performance.

Transferrable GaN-based Micro-LED heterostructures grown on h-BN for optogenetic applications

Individually transferrable GaN-based MQWs micro-LED structures grown on two-dimensional (2D) hexagonal boron nitride (h-BN) have been demonstrated. Different sizes (60 × 30 µm, 60 × 60 µm, 90 × 60 µm and 90 × 90 µm) of GaN-based LED heterostructures on layered h-BN were grown on dielectric SiN patterned sapphire substrates using Metal Organic Vapor Phase Epitaxy (MOVPE). Scanning electron microscope (SEM) images show micro-LEDs were grown with high selectivity within the mask opening areas. Consistent MQWs emission from micro-LEDs was observed at 452 ± 2 nm by cathodoluminescence (CL) spectroscopy for all micro-LED sizes. The structural and optical quality were similar to the GaN-based-LEDs grown on unpatterned substrates. In addition, we have successfully demonstrated the lift-off and transfer of individual micro-LEDs to arbitrary flexible templates using a transfer printing machine, which can be addressed by full front-end process. These studies highlight the role of combination of van der Waals (vdW) epitaxy and selective area growth (SAG) in facilitating the direct realization of dimensionally defined III-Nitride micro-LED structures and the mechanical release and transfer of these micro-LEDs to templates suitable for flexible display and optogenetics applications.

3D Wetting Gradient Janus Sports Bras for Efficient Sweat Removal: A Strategy to Improve Women's Sports Comfort and Health.

Developing Janus fabrics with excellent one-way sweat transport capacity is an attractive way for providing comfort sensation and protecting the health during exercise. In this work, a 3D wetting gradient Janus fabric (3DWGJF) is first proposed to address the issue of excessive sweat accumulation in women's breasts, followed by integration with a sponge pad to form a 3D wetting gradient Janus sports bra (3DWGJSB). The 3D wetting gradient enables the prepared fabric to control the horizontal migration of sweat in one-way mode (x/y directions) and then unidirectionally penetrate downward (z direction), finally keeping the water content on the inner side of 3DWGJF (skin side) at ≈0%. In addition, the prepared 3DWGJF has good water vapor transmittance rate (WVTR: 0.0409gcm-2h-1) and an excellent water evaporation rate (0.4704gh-1). Due to the high adhesion of transfer prints to the fabrics and their excellent mechanical properties, the 3DWGJF is remarkably durable and capable of withstanding over 500 laundering cycles and 400 abrasion cycles. This work may inspire the design and fabrication of next-generation moisture management fabrics with an effective sweat-removal function for women's health.

Femtosecond laser-induced plasma-assisted backward deposition of robustly adherent porous carbon films on glass substrates

The simple and rapid production and transfer of high-quality carbon materials are crucial for the flexible and efficient fabrication of carbon-based electronic devices. Recently, a laser-assisted transfer method combining laser-induced carbonization and transfer printing was demonstrated for the one-step preparation and transfer of patterned laser-induced carbon films to transparent substrates. However, this method is limited by insufficient robustness and weak adhesion of the carbon film post-transfer. Herein, we developed a non-contact laser-induced plasma-assisted deposition method to deposit robustly adherent porous carbon films on glass substrates. By well-adjusting the laser parameters and inserting spacers with adjustable thickness, laser-induced plasma ablation replaced direct laser ablation during femtosecond laser scanning of the substrate-polyimide-carrier sandwich structure, resulting in micro-channels with a carbon-glass recast layer instead of easily peelable flakes on the glass substrate. This hierarchical structure significantly enhances the adhesion between the laser-induced carbon film and the glass substrate, ensuring outstanding stability of the deposited carbon film under various adhesion tests. Furthermore, compared to carbon films prepared by the laser-assisted transfer method, the obtained carbon films are hydrophilic, low-resistance, and porous, facilitating the fabrication of energy storage devices. To demonstrate its practical application, a planar carbon-based micro-supercapacitor was fabricated on glass, exhibiting excellent electrochemical and cycling performance.

Liquid Metal-Based Elastomer Composite with Selective Switchable Adhesion to Solids.

Selective switchable adhesion has recently attracted much attention due to its wide applications in transfer printing, information transfer, and flexible electronics. However, selective adhesive materials often have a complex adhesion or preparation process, which limits their use. To overcome this problem, this study prepares a composite of liquid metal foam and polydimethylsiloxane (PDMS) with selective photocontrolled adhesion, which can directly adhere to solids at room temperature. Utilizing the photoinduced phase transition of liquid metals, solid adhesion can be regulated by changing the backing layer modulus of the adhesive layer. Since the phase transition process is gradually completed by heat transfer from the illuminated side to the backlight side that adheres to the solid, the melting area on the backlight side can be regulated by controlling the light time, which determines the adhesion regulation area. Therefore, the accuracy of the adhesion regulation can reach less than 0.9 mm without relying on the accuracy of the infrared light. Moreover, based on the selective switchable adhesion, the selective transfer of solids with different scales can be achieved at room temperature. The findings of this study may provide strategies for the simple preparation of selective adhesive materials and the improvement of control accuracy.

Active interface characteristics of heterogeneously integrated GaAsSb/Si photodiodes

There is increased interest in the heterogeneous integration of various compound semiconductors with Si for a variety of electronic and photonic applications. This paper focuses on integrating GaAsSb (with absorption in the C-band at 1550 nm) with silicon to fabricate photodiodes, leveraging epitaxial layer transfer (ELT) methods. Two ELT techniques—nanomembrane transfer printing and macro-transfer printing—are compared for transferring GaAsSb films from InP substrates to Si, forming PIN diodes. Characterization through atomic force microscopy and transmission electron microscopy exhibits a high-quality, defect-free interface. Current–voltage (IV) measurements and capacitance–voltage analysis validate the quality and functionality of the heterostructures. Photocurrent measurements at room temperature and 200 K demonstrate the device's photo-response at 1.55 μm, highlighting the presence of an active interface.