I. Abstract of the Paper’s Core Research

In this experiment, Cabot’s commercial silver nanoparticle ink was used. On a single 50°C silicon‑substrate platform, we employed Dimatix inkjet printing and Optomec aerosol jet deposition to fabricate isolated ink dots, linear conductive traces, and square thin films. Comprehensive dimensional comparisons were conducted using a profilometer, SEM, and four‑probe electrical measurements. The key findings are as follows:

Formation Mechanism and Differences in Basic Ink Spots

Inkjet printing relies on piezoelectric single-drop ejection, producing well‑defined circular ink spots with no satellite droplets and sharp edges; aerosol deposition, by contrast, yields a continuous mist that forms a central primary spot accompanied by fine peripheral splatter (overspray). The size of the individual spots is comparable to that of inkjet prints, but edge uniformity is poorer. Both techniques exhibit the coffee‑ring morphology resulting from solvent evaporation.

Comparison of Line Morphology and Dimensional Controllability

Inkjet printing offers two distinct directions: same‑direction (IPD) and opposite‑direction (CPD). In the same‑direction mode, line width exhibits significant variation and the lines are relatively thin; in contrast, the opposite‑direction mode results in markedly increased stacking thickness, with a maximum of 5.8 μm, leading to a larger conductive cross‑sectional area and lower resistance. The adjustable line‑width range spans 56–195 μm.

Aerosols are focused and controlled by sheath gas, achieving a minimum line width of just 33 μm and an even thinner single‑layer film thickness (as low as 0.3 μm), making them well suited for ultra‑thin, high‑precision interconnects; however, residual overflow trenches persist on both sides of the lines, resulting in lower edge definition compared to inkjet printing.

Differences in the formation of large-area square thin films

Inkjet grating printing with line-by-line deposition results in uneven film thickness and severe central buildup. Aerosol‑supported contour filling (PFA) and serpentine filling (SFA) are two vector‑based patterning strategies; the serpentine fill approach significantly improves film‑thickness uniformity, yielding an overall film thickness far lower than that achieved by inkjet printing and reducing silver‑ink consumption.

Rules of Electrical Properties

Inkjet reverse printing yields lines with large cross-sectional areas and optimal electrical conductivity after sintering; aerosol‑deposited single‑layer ultra‑thin traces have small current‑carrying cross‑sections and, under identical sintering conditions, exhibit higher resistance. After prolonged annealing at 300°C, the fine aerosol‑deposited traces tend to fracture and fail, whereas the thicker inkjet‑deposited traces retain an intact conductive structure.

The process adaptation boundaries are clearly defined.

Inkjet printing is well-suited for large-area thick films and high‑conductivity circuits, while aerosol jet printing excels at fabricating ultra‑thin, micron‑scale fine lines and small‑size devices on curved or irregularly shaped substrates.

II. Standardized and Comprehensive Experimental Procedure

Raw material standardization: Cabot CSD32 silver nano‑ink (solid content 45–55 wt%), with a 6‑inch silicon dioxide wafer as the standard substrate;

Equipment Parameter Standardization:

Inkjet DMP3000: 10 pL nozzles, printing distance of 1 mm, droplet pitch of 5–150 μm, with IPD/CPD dual‑direction printing;

Aerosol AJ300 CE: 200 μm nozzle, sheath gas 50–100 cm³/min, scan speed 1/3/5 mm/s;

Preparation of three types of standard patterns: Single-point array, 11 mm-long conductive traces, 5 mm square thin film;

Uniform heat treatment: Sintering on a temperature‑gradient hot plate at 100–300°C, followed by gradient‑controlled holding.

Characterization: Optical microscopy for profile observation, Dektak profilometer for line width and film thickness measurement, SEM for microstructural morphology, and four-point probe for measuring sheet resistivity.

III. The Five Core Technological Advantages Unique to Aerosol Jet Printing (Compared with Inkjet)

Stronger capability for ultra-fine wire machining

Sheath‑gas airflow focusing enables ultra‑fine lines as narrow as 33 μm—narrower than the minimum line width achievable with inkjet printing—making it well suited for MEMS microelectrodes and millimeter‑wave micro‑interconnects.

Ultra-thin films with precise controllability

The single-layer deposition thickness can be as low as 0.3 μm, enabling precise, layer-by-layer control of film thickness—ideal for ultra-thin transparent conductive traces and fine‑pitch chip interconnects.

Compatible with curved surfaces and millimeter-level height‑difference substrates.

Continuous mist‑flow non‑contact deposition, with an adjustable nozzle‑to‑substrate gap; conformal printing of 3D housings and three‑dimensional structures; inkjet printing is suitable only for planar surfaces.

Wider ink compatibility range

Compatible with wide‑viscosity inks ranging from 1 to 1000 cP; both large‑particle‑size, high‑solid‑content nano‑slurries and conventional inks can be atomized; inkjet printing supports only low‑viscosity, dilute inks.

Freehand vector drawing, with flexible shaping of complex, irregular paths.

No raster grid is required; arbitrary curves and custom-shaped contours are defined directly via vector data, enabling higher efficiency in prototyping small‑batch custom devices.

IV. Five Core Technological Innovations of This Study

Innovation 1: A standardized comparison system for inks and substrates

By ensuring complete consistency in ink formulation, substrate material, and sintering conditions, variable‑induced uncertainties are eliminated, enabling quantitative differentiation of AJP‑ and IJP‑derived morphological and electrical characteristics. The resulting data provide direct, actionable guidance for component selection.

Innovative Two-Channel Inkjet Printing Morphology Quantification Mechanism

We clearly define two forming modes—IPD wet stacking and CP semi‑dry stacking—explain the bidirectional differences in line thickness and width, and establish a process window for high‑conductivity inkjet printing.

Innovation 3: Performance Comparison of Dual Aerosol Filling Paths

Distinguish between contour‑fill and serpentine‑fill processes to identify differences in film uniformity, thereby addressing the critical manufacturing challenge of non‑uniform thickness in large‑area aerosol films.

Innovation 4: A Comprehensive Analysis of the Microscopic Origins of Over-Spray and Coffee-Ring Effects

The edge‑spot defect is explained in terms of aerosol‑flow dynamics and solvent‑evaporation fluid dynamics, providing a theoretical basis for optimizing the equipment’s gas‑delivery system.

Innovation 5: Film Thickness – Quantitative Modeling of Electrical Conductivity

Two correlation curves are established, linking film thickness, cross-sectional area, and resistance; based on the device’s conductive requirements, the printing method can be selected in reverse.

V. Current Industry Challenges in the Two Processes and Corresponding Solutions for Overcoming Them

(1) Existing Challenges and Solutions in Aerosol Spraying

Challenge 1: The lines exhibit overspray and speckling, and their edge sharpness is inferior to that of inkjet printing.

✅ Increasing the sheath gas flow rate enhances beam focusing, while employing multi-layer stacking and narrow-channel printing strategies helps minimize material overflow.

Challenge 2: Ultra-thin traces are prone to cracking and exhibit elevated resistance during high-temperature sintering.

✅ Multi-layer stacking increases the conductive cross-sectional area, and when combined with gradient low-temperature photonic sintering, it prevents high-temperature film layer cracking.

Challenge 3: Uneven thickness in large-area thin-film contour filling

✅ Employs a serpentine reciprocating filling algorithm to reduce material buildup at corners and enhance film flatness.

Challenge 4: The production efficiency of single-nozzle inkjet printing is lower than that of multi-channel inkjet printing.

✅ Array‑type aerosol printheads and parallel multi‑device production lines boost batch throughput.

(II) Existing limitations of inkjet printing (aerosols can serve as an alternative)

Challenge 1: Compatible only with low-viscosity inks; high-solids nano‑ink formulations tend to clog the print head.

✅ Aerosol-based wide-viscosity atomization system for stable deposition of high-loading conductive inks.

Challenge 2: It can only process flat substrates; curved or three-dimensional surfaces cannot be machined.

✅ Adjustable aerosol spray distance, conformal direct writing for irregular-shaped and 3D enclosures.

Challenge 3: The lower limit of the minimum line width makes it difficult to fabricate micron-scale microelectrodes.

✅ Aerosol-focused airflow enables ultra-fine, 33-μm precision patterning.

VI. Scenario-Specific Guidelines for Selecting Industrialization Applications in the Future

1 Aerosol spraying prioritized for ground-level scenarios

MEMS, biochip micrometer-scale interdigitated microelectrodes;

In-vehicle / Wearable 3D Shaped Curved RF Antenna;

Mini/Micro LED precision pixel interconnection;

Ultra-thin conductive wiring for miniature photodetectors;

R&D of small-batch, custom prototypes using new materials.

2 Priority Application Scenarios for Inkjet Printing

Large-area flexible photovoltaic conductive grid lines;

Large-size flexible display driver circuit;

Standardized large-area sensing film;

Large‑volume, low‑precision conductive markers and RFID tags.

3 Dual-Process Hybrid Integration Route

Large-area substrates are fabricated using inkjet printing to boost throughput, while localized micron‑scale functional regions are refined via aerosol‑based overprinting, balancing efficiency with precision.

Image and Text Guide

• IJP droplet : Drop distance 150 μm (nozzle 21.5 μm), with a nearly circular shape and well-defined edges, free of satellite droplets.
• AJP spot : Splat distance 150 μm, sheath gas flow rate 70 cm³·min⁻¹ (nozzle diameter 200 μm), with fine overspray particles scattered around the central large splat.
• Size Comparison : IJP droplet diameter 61.5±0.6 μm; AJP central spot diameter 50.1±7.2 μm (including the total length of splatter points 120.9±21 μm) — despite a nearly tenfold difference in nozzle size, the deposited feature sizes are comparable.

• (A,C) IJP droplets : The 2D cross-section exhibits a bimodal distribution, while the 3D surface shows edge elevation.
• (B,D) AJP spot : The morphology is highly similar to that of IJP droplets.
• Key Findings : Both processes produce a typical Coffee ring effect — Convection transports material from the center to the periphery, indicating that the evaporation processes of the two are similar.

• IJP (Raster Type) : The pattern is defined as a pixel grid, with droplets deposited line by line; based on their relationship to the direction of motion, it is classified as IPD (in the printing direction) or CPD (opposite to the printing direction), with CPD requiring additional axis movement.
• AJP (Vector Type) : Define the start/end points and geometry along a mathematical path; the print‑path shutter opens while the transfer‑path shutter remains closed, offering greater flexibility. For square parts, you can use Perimeter Fill (PFA), which fills in a serpentine pattern from the outside inward, or Serpentine Fill (SFA), which uses a bi‑directional snake‑like pattern.

• (A) IJP : Drop distance and printing direction strongly influence the line morphology—IPD yields smooth, continuous lines, whereas CPD exhibits droplet swelling or a scalloped appearance (resembling stacked coins); larger spacing results in narrower lines.
• (B) AJP : As the sheath gas flow rate increases from 50 to 100 cm³·min⁻¹, the line width narrows and focusing improves; spatter points appear on both sides of the line, and at higher sheath gas flow rates, channels form that separate the spatter points from the main line.

• (A) IJP : At a drop distance of 5 μm, the CPD layer thickness is approximately three times that of the IPD; the CPD exhibits no coffee-ring effect, whereas the IPD retains a ring-like pattern; the line width is 194.5 ± 7.7 μm for the IPD versus 66.1 ± 6.6 μm for the CPD.
• (B) AJP : At different speeds and sheath‑gas ratios, the lines become thinner and narrower; AJP preserves the coffee ring under all parameter settings.
• Overall : AJP enables finer lines and smaller cross-sectional areas.

• Sheath gas ratio influence : The higher the sheath gas flow rate, the stronger the airflow focusing, resulting in a narrower line width and a greater layer thickness—when the sheath gas flow rate increases from 50 to 100 cm³·min⁻¹, the line width decreases from 61.5 ± 3.9 μm to 37.5 ± 0.8 μm.
• Impact of process speed : The effect of scanning speed on line height is greater than that of line width; at 5 mm·s⁻¹, the peak height is 3–4 times that at 1 mm·s⁻¹ (higher speed corresponds to a lower deposition amount per unit area).

• IJP block : The surface is relatively uniform, with clear edges.
• AJP PFA (Perimeter Fill) : Visible independent line traces (the previously deposited lines have dried, resembling a stacked‑coin effect); at the corners, silver ink bulging occurs due to reduced speed.
• AJP SFA (Serpentine Fill) : Under the same 20 μm line pitch, there are no isolated lines, resulting in greater uniformity.

• IJP : Appears uniform but is actually concentrated at the center, with a peak height exceeding 7 μm.
• AJP : The deposition amount per unit area is low; the maximum peak height of PFA is 1.2 μm, while that of SFA is only 0.75 μm. Although the PFA layer exhibits higher roughness, the total deposition amounts of the two are identical.
• Conclusion : IJP exhibits sharper edges but lower overall uniformity; AJP yields thinner layers with reduced surface roughness.