I. Core Research Summary

• Precise, controllable deposition with a dot matrix, offering continuously adjustable dimensions.

Within a single‑point deposition time range of 15–120 ms, the silver nanoparticle array exhibits diameters of 20–144 μm and heights of 1.4–6.25 μm. Compared with commercial inkjet printing, the array height is increased by a factor of 40, completely eliminating coffee‑ring surface defects and significantly enhancing film uniformity.

• Implementation of Analog Grayscale Direct-Write Technology

Without requiring binary halftoning, the image’s 8-bit grayscale values are directly mapped to single-point deposition durations, enabling the simultaneous formation of gradient‑thickness patterns on a single substrate. The resulting image exhibits far greater detail and smoothness than conventional digital dot‑matrix printing.

• Support-free fabrication of complex three-dimensional conductive structures

Multilayer lattice stacking enables the fabrication of vertical micro‑columns; by printing with lateral offset from layer to layer, it is possible to create inclined pillars ranging from 40° to 140°, inverted V‑shaped three‑dimensional bridges, and helical micro‑circuits—entirely without the need for support materials—and to achieve conductive interconnections across substrates of differing heights.

• Stable pneumatic shut-off architecture for the entire machine

Equipped with a built-in split‑flow shutter, the nozzle maintains a constant total airflow whether printing or in the off state, eliminating deposition errors caused by pressure fluctuations in the fluid path. With millisecond‑level switching response, printing is free of droplet splatter and exhibits minimal edge spreading.

• Physical Verification of Heterogeneous Circuits

3D conductive bridges were printed on high‑ and low‑layer substrates, successfully connecting LEDs to resistors; upon power application, the devices emitted stable light, demonstrating that this process can be directly employed for mass production of micro‑heterogeneous chips and 3D interconnections in MEMS.

II. Core Operating Principle and Unique Process Advantages of Dot‑Matrix Aerosol Jetting

(1) Complete Dot-Matrix Printing Process Flow

• High-solid-content silver nano‑ink is fed into a pneumatic atomization chamber, where nitrogen gas breaks it down to produce a micron‑sized, uniformly dispersed aerosol.
• The mist flow enters the built-in pneumatic shut-off unit, where a three-way solenoid valve switches the flow path: during printing, the mist flows through the nozzle for deposition; when the valve is closed, the airflow is diverted to the exhaust channel.

3. Coaxial sheath gas continuously focuses the beam, ensuring stable airflow throughout the nozzle; the three-axis platform of the spray head enables precise positioning and synchronized start/stop operations.

• A single-point controllable deposition lattice; by adjusting Td, the deposition volume can be modulated; multi-layer stacking and lateral offset enable printing of various 3D structures.
• Low-temperature sintering at 240°C yields highly conductive micron-scale three-dimensional metal interconnects.

(II) Five Core Process Advantages (Compared with Inkjet, Direct Writing, and Traditional Continuous Aerosol Technologies)

• Dual capabilities: fixed-point matrix and stereolithography

Conventional aerosol‑based techniques can only produce continuous lines, whereas this device achieves on‑demand, site‑specific printing with millisecond‑scale switching, enables independent thickness control at each point, and allows the fabrication of stackable, support‑free 3D micro‑columns and oblique interconnect bridges, thereby overcoming the limitations of two‑dimensional printing.

• Compatible with high-viscosity inks, featuring a more densely packed three-dimensional structure.

It is compatible with high-solid silver pastes up to 70 cp; inkjet printing supports only low-viscosity, diluted inks. After aerosol dot‑matrix stacking, the aspect ratio of the resulting pillars is significantly enhanced, ensuring continuous, unbroken conductive pathways.

• Completely eliminate coffee-ring defects.

Ultrafine, polydisperse aerosol droplets undergo simultaneous spreading and drying, with no solute‑induced edge enrichment and a uniformly flat array surface, thereby significantly reducing leakage current and contact resistance in microdevices.

• Non-contact wide-distance adaptive curved surface / High-low substrate

The nozzle–substrate gap is adjustable, enabling localized deposition on both textured, multi‑layered surfaces and irregularly shaped substrates, thereby perfectly addressing the challenge of interlayer wiring in heterogeneous chips.

• Digital maskless rapid iteration

CAD‑based customization of dot‑array layouts and single‑point dwell‑time parameters eliminates the need for photolithography and metal molds, enabling rapid prototyping of small‑batch microstructured samples and significantly shortening the R&D cycle.

III. Five Key Technological Innovations

Innovation 1: Built-in pneumatic shunt‑type fast shutter architecture

Innovation 2: Continuous Tuning of Lattice Morphology via Single-Point Deposition Duration

Innovation 3: Simulated grayscale direct writing, eliminating the need for binary image conversion.

Innovative 4‑point lattice‑stacked, support‑free 3D microfabrication process

Innovative 5-layer height-difference 3D interconnect printing solution

IV. Existing Process Challenges and Corresponding Solutions for Overcoming Them

Challenge 1: Traditional external shutters require increasing the nozzle-to‑target distance, leading to beam divergence and reduced precision.

Challenge 2: Fluctuations in airflow pressure caused by switch toggling, coupled with uneven thickness across the front and rear arrays.

Challenge 3: Inkjet‑type single‑point heights are extremely low, making it impossible to establish three‑dimensional interconnections.

Challenge 4: Conventional printing of grayscale images requires halftoning, which results in loss of detail.

Challenge 5: 3D printing generally requires support structures, and post-processing is time-consuming and labor-intensive.

V. Future Diversified Industrial Application Scenarios

1. Heterogeneous Chip 3D Micro-Interconnects

2. MEMS Microsensor Array

3. Flexible Wearable Three-Dimensional Circuitry

4. Microscale biomedical devices

5. RF Antennas and Miniature Passive Components

Figure 1. a) Dot‑plot image generated from Td values (scale bar: 100 μm); b–d) Effects of Td on the following parameters: b) diameter, c) height, and d) volume.

Figure 2. Three-dimensional shape and thickness distribution maps of silver nanoparticle (Ag NPs) droplets printed using a) axial jetting (AP) and b) inkjet printing techniques.

Figure 3. Dot‑modulation printing technology. a–c) Results of the AP process: (a) Microscopic image of the dot‑matrix pattern; (b) Three‑dimensional image of the printed dots; (c) Height distribution curve. d–f) Results of inkjet printing: (d) Microscopic image of the dot‑matrix pattern; (e) Three‑dimensional image of the printed dots; (f) Height distribution curve. g–i) Gradient circular images and their printing outcomes obtained using the continuous dot‑modulation AP process: (g) Sample gradient circle with a pixel size of 30 × 30; (h) Three‑dimensional contour of the printed result; (i) Height distribution curve along the radial direction.

Figure 4. Photographs and micrographs of aerosol samples printed using silver nanoparticle ink: a) Original color image; b) Extracted grayscale image; c) Binary‑image aerosol print obtained via simple thresholding (pixel threshold = 164, Td = 40 ms); d) Binary‑pixel aerosol print processed with an error‑diffusion halftoning algorithm (pixel threshold = 127, Td = 50 ms). The color photograph in (a) was taken by the corresponding author and used with permission; no copyright issues apply.

Figure 5. Aerosol image results printed using the proposed simulated halftoning method (Td = 20–60 ms).

Figure 6. a) Variation of 3D pillar height as a function of the number of stacking points; b) Control of 3D pillar diameter by tuning Td (20–100 ms); c) Realization of multiple relative orientations between the 3D pillars and the substrate through lateral displacement of the deposition point and adjustment of the pillar tilt angle in multiple directions (inset); d) Formation of an inverted V‑shaped 3D structure via the construction of a 3D bridge, along with non‑connected cross‑line printing results (inset); e) Complex 3D helical structures; f) A 3D bridge structure connecting surface electrodes at different heights; g) Demonstration, using an LED light, of the electrical connectivity of the printed 3D bridge.

Figure 7. a) Schematic diagram of the AP technique; b) Experimental photograph

Figure 8. Schematic diagram of the pneumatic shutter mechanism inside the AP system: a) Printing stage; b) Shutter-closing stage.