I. Abstract of the Paper’s Core Research

In this study, we prepared both a VO₂‑based semiconductor composite ink and a ferrocyanide‑based solid‑state redox gate ink. Using aerosol jet printing, we fabricated fully vertically stacked transistor devices layer by layer, systematically optimizing nanoparticle dispersion, ink formulation, photonic annealing, and multilayer stacking processes. We then performed comprehensive characterization of the microstructure, crystallographic features, and electrical cycling performance. The key findings are as follows:

A stable colloidal ink system for atomizing VO₂

VO₂ is finely milled to 15–30 nm via planetary wet ball milling, with PSMA polymer serving as a stabilizer and PEG as a crosslinking agent to regulate film formation. DLS confirms that particle agglomeration size is controllable, ensuring the ink remains stable over long periods without delamination and preventing nozzle clogging during printing, while being compatible with aerosol‑based ultrasonic and pneumatic atomization.

Photonic low-temperature annealing process protection VO₂ crystal

Millisecond pulsed photon annealing replaces prolonged high-temperature baking, preventing the reduction of VO to lower-valent vanadium oxides. The resulting thin film fully retains its 67°C metal–insulator transition (MIT) behavior, with a tenfold difference in electrical conductivity between room temperature and elevated temperatures.

Solid-State Redox-Gated Low-Voltage Switching Mechanism

A self-developed PVOH–glycerol cross‑linked redox ink is used to print a solid‑state electrolyte gate layer; with an ultra‑low gate voltage of only ±0.4 V, efficient carrier injection is achieved without the need for a high electric field, and the switching response time is approximately 1 second.

All-aerosol multilayer vertically integrated device

The channel, insulating isolation layer, and redox gate were sequentially fabricated, with gold electrodes deposited via thermal evaporation. X-ray fluorescence analysis revealed a well-defined interlayer interface, with no significant elemental interdiffusion and an intact structural integrity.

Ultra-high cycling durability and electrical performance

After 6,000 consecutive gate‑voltage cycles, the on‑state current exhibits no significant drift, and the redox reactions remain reversible, thereby addressing the issue of cyclic degradation commonly observed in conventional printed transistors.

II. Complete Process Flow for All-Printed Redox Transistors Based on Aerosol Jet Printing

1) Preparation of VO₂ ink: Nanoparticles are refined via wet ball milling, using an ethanol/terpineol mixed solvent, with PSMA stabilizer and PEG crosslinker added for ultrasonic dispersion.

2) Redox‑gate ink: ferrocyanide serves as the active component, formulated as a crosslinked aqueous solution comprising PVOH, glycerol, and glyoxal.

3) Optomec aerosol jet printer, with a 300 μm nozzle and a temperature-controlled platform for PI/silicon substrates, used to print the conductive VO₂ channel;

4) Photonic pulse annealing of VO₂ thin films, with precise control of energy density to preserve the intrinsic phase-transition properties;

5) An aerosol‑printed UV‑insulating isolation layer is applied, followed by the layer‑by‑layer deposition of a solid‑state redox gate film.

6) Sputter-deposit the top and bottom gold electrodes, then mount the device on a probe station to perform transfer‑characterization and cycling‑stability tests.

III. Core Advantages of Aerosol-Based Processes (Comparison with Sputtering, Inkjet, and Lithography)

Digital integrated stacking of multilayer heterogeneous materials

A single system can sequentially print three types of functional inks—semiconductor, insulating, and redox electrolyte—enabling the fabrication of vertically stacked multilayer devices without the need for repeated substrate transfers.

Low-temperature compatible on flexible substrates, with no high-temperature damage.

The entire printing process operates at a mild temperature, and photon‑induced annealing provides millisecond‑scale instantaneous thermal treatment, ensuring that heat‑sensitive flexible substrates such as PET and PI remain undeformed.

High-precision, maskless custom microchannels

CAD enables free-form design of micron-scale transistor channels, eliminating the need for photolithography masks and vacuum chambers, thereby significantly shortening the R&D and prototyping cycle.

Compatible with specialty functional composite inks, with controllable particle size.

Wet ball milling combined with aerosol atomization enables the stable delivery of metal oxide nanoparticles, whereas inkjet printing tends to clog when handling high‑particle‑size slurries.

Non-contact conformal printing, compatible with curved flexible circuits.

A spray distance adjustable from 1 to 5 mm enables the fabrication of low-power switching arrays on curved and irregularly shaped flexible substrates.

IV. Five Core Technological Innovations of This Study

Innovation 1: Two sets of multi-component functional inks specially formulated for aerosols.

A complete formulation comprising VO₂ semiconductor colloidal ink and solid redox electrolyte ink addresses, respectively, the challenges of particle agglomeration, film cracking, and ion conduction.

Innovation 2: A complete process for VO₂ thin films combining wet ball milling and photonic annealing.

Wet‑process fine grinding reduces particle size, and photon‑induced instantaneous thermal treatment perfectly preserves the reversible metal–insulator phase transition of VO₂ while preventing high‑temperature lattice damage.

Innovative 3-Aerosol All-Vertical Stacked Redox Transistor Architecture

The channel, insulator, and gate layers are fully integrated via additive manufacturing, eliminating the limitations of vacuum‑deposited multilayer composites.

Innovation: 4.0 V Ultra-Low Gate-Voltage Solid-State Redox Regulation Mechanism

Leveraging the reversible redox reaction of ferrocyanide, substantial carrier modulation can be achieved at extremely low voltages, thereby significantly reducing device power consumption.

Innovative 50,000‑cycle long‑life printed transistor solution

Solid-state cross-linked electrolytes eliminate liquid leakage and maintain stable performance over 6,000 switching cycles, addressing the critical drawback of liquid electrolytes—prone to failure.

V. Current Industry Challenges and Corresponding Solutions

Challenge 1: VO₂ nanoparticles are highly prone to agglomeration, and conventional ink atomization can clog the print head.

✅ Wet ball milling for particle size reduction; PSMA polymer provides spatial stabilization, enabling continuous aerosol printing without agglomeration or nozzle clogging.

Challenge 2: Conventional high-temperature annealing reduces VO₂, leading to the loss of its phase-transition switching properties.

✅ Low-energy pulsed photon annealing, with instantaneous thermal treatment, completely eliminates secondary reactions during prolonged thermal reduction.

Challenge 3: Conventional field-effect transistors have high drive voltages and high power consumption.

✅ Solid-state redox gate, enabling conductance modulation at an ultra-low voltage of 0.4 V, ideal for ultra-low-power devices.

Challenge 4: Multilayer microelectronics require multiple vacuum deposition systems, resulting in a lengthy process flow.

✅ A single aerosol printer enables layer-by-layer fabrication of semiconductor, insulator, and electrolyte layers, streamlining the manufacturing process.

Challenge 5: Liquid redox electrolytes are prone to leakage, resulting in a short cycle life.

✅PVOH cross-linked solid-state film, with no liquid electrolyte, enabling stable operation over thousands of cycles.

VI. Future Diversified Industrial Application Scenarios

1 Flexible, Low-Power Neuromorphic Computing Devices

Large-area aerosol‑printed VO₂ transistor arrays, enabling low‑power synaptic switching and lightweight edge‑computing chips.

2 Wearable Physiological Sensing Microcircuits

PI flexible substrate ultra-low-power switch, reducing standby power consumption in wearable devices and extending battery life.

3 Micro MEMS Temperature-Control Switch Chip

Leveraging the dual characteristics of VO₂’s thermal phase transition and electrical modulation, this compact device provides automatic circuit‑breaking protection against overheating.

4 Curved-Surface Smart Window Control Microcircuit

A switch array is printed on a curved, flexible substrate, enabling on-demand tuning of the VO₂ thin film’s optical transmittance and thermal insulation properties.

5 Laboratory Rapid R&D Platform for Printed Electronics

Rapidly iterate prototypes of various miniature transistors, including oxide‑semiconductor and redox‑gate types.

Image and Text Guide

Figure 1. VO ₂  Schematic of the semiconductor channel ink formulation and the AJP process flow

From the high-energy planetary ball mill to commercial VO ₂  Starting with particles reduced to the nanoscale, the particles are dispersed in an ethanol/terpineol mixed solvent, and a PSMA polymer stabilizer is added. After probe‑assisted ultrasonic dispersion, a PEG‑400 crosslinking agent is further incorporated to obtain a low‑viscosity ink suitable for AJP. Subsequently, the channel ink is printed onto Au electrodes using an Optomec Aerosol Jet 5X (pneumatic atomizer, 300 μm nozzle). The wet film is first subjected to rapid photothermal annealing to crosslink the PSMA into a continuous film, followed by thermal curing to complete the channel layer.

Figure 2. Dynamic Light Scattering (DLS) Study of Nanoparticle Processing and Ink Dispersion Assembly

a) 10% VO under three processing conditions ₂  a) Correlation coefficient curves for aggregates, with the solid line representing a single- or double‑stretch exponential fit; b) Corresponding particle size distributions—ball milling combined with PSMA colloidal dispersion reduces aggregate sizes to around 200 nm, whereas dry‑milled samples exhibit a peak shifted to approximately 350 nm; c) With 0.5% PSMA held constant and VO varied… ₂  Content (5/10/15 wt%), the particle size distribution remains consistently narrow and unimodal; d) Schematic showing that the PSMA polymer first adsorbs onto VO. ₂  The particle surfaces are further confined to assemble into confined aggregates measuring 100–300 nm, thereby stabilizing the ink viscosity at approximately 1 mPa·s.

Figure 3. Thermal and electrical transport properties of semiconductor nanocomposite thin films

a) DSC specific heat curves of films prepared via different processing routes—original/dry-milled VO ₂  A broadened bimodal peak emerges at 60–80 °C, whereas the colloidal ball-milling + PSMA sample exhibits a single sharp MIT peak near 67 °C, indicating that the PSMA stabilizer narrows the aggregate particle size and sharpens the phase transition; b) TGA reveals decomposition of the polymer matrix between 200 and 550 °C, VO ₂  The particles ultimately account for 79–83% of the dry film; c) Arrhenius plot: 0% VO ₂  Pure PSMA membrane insulation (<10 ^-10   S·cm ^-1 ), 5% VO ₂  Increase the electrical conductivity by five orders of magnitude, 10% VO ₂  Further increase, with VO determined by slope fitting. ₂  In the monoclinic phase, the band gap is approximately 0.6 eV.

Figure 4. Morphology and electrical properties of printed semiconductor channel thin films

a) AJP-printed VO on the Au electrode ₂  a) Optical image of the channel structure (electrode gap 600 μm, channel width 1 mm, thickness 3 μm); b) SEM image of the printed composite film, showing that PSMA encapsulates VO. ₂  Particles bond to form a dense, porous film; c) Under three different light‑intensity annealing energy densities, the I–V curves are linear and symmetric, with lower resistance at higher energy densities; d) Resistance–temperature curves upon cooling from above the MIT: the resistance exhibits a sharp increase of more than tenfold at ~65 °C, and the room‑temperature resistance of the 0.75 J/cm² sample is approximately 2×10 ⁴  Ω, 1.00 J/cm² can be reduced to ~3×10 ³  Ω; Excessive energy density will damage the VO ₂  Convert to V ₂ O ₃ , therefore the optimal fluence is strictly limited to <1 J/cm².

Figure 6. Stacked structure of all-printed redox-gated transistors and XFM elemental mapping.

a) Cross-sectional schematic: from SiO ₂  The substrate is printed with VO layers in sequence, starting from the bottom. ₂  Channel, NEA121 UV‑curable insulating layer, PHCF (potassium ferrocyanide) redox gate; the gate source and gate drain are encapsulated by insulating layers on both sides. The two lower images show a stepwise optical micrograph—starting with VO deposition. ₂  Channel, followed by the deposition of an insulating layer, and finally the PHCF gate; b) X-ray fluorescence microscopy (XFM), which superimposes the three elemental layers—V (red), Fe (green), and K (blue)—demonstrates that the K/Fe active layer in the PHCF is closely associated with VO. ₂  The channels are precisely aligned at the micrometer scale with no crosstalk, providing a structural foundation for low-voltage redox gate control.

Figure 7. Electrical performance of AJP-printed redox-gated devices

a) V _gs   Scanning transfer curve (500 mV·s) ^-1 ): When the gate voltage is swept from negative to +0.5 V, I _ds   It increases from approximately 1.1 μA to approximately 1.55 μA (about 150% of the zero-bias value), with nearly no hysteresis upon reverse sweep; gate leakage current I _gs   Always <0.05 μA, amplification ratio I _ds /I _gs   Approximately 5; b) The time response to a ±0.5 V step gate voltage exhibits switching time constants of about 0.9/1.0 s; c, d) Under a ±0.5 V gate voltage, after 6,000 repeated cycling cycles, I _ds   Two stable platforms exhibit virtually no drift, I _gs   It consistently remains at the nA–sub-μA level, demonstrating that the all-printed redox-gated VO ₂  The transistor can operate stably at a gate voltage of 0.4–0.5 V.