I. Abstract of the Paper’s Core Research

This study has developed a dual‑atomization, multi‑material aerosol‑jet printing system to fabricate polyimide (PI) dielectric ink and nickel–zinc ferrite (Ni₀.₅Zn₀.₅Fe₂O₄) magnetic nano‑ink. In the atomization channel, these inks are mixed in situ to form magnetic composite layers, enabling the complete fabrication of three types of microwave devices: inductors, microstrip transmission lines, and ring resonators. The material’s magnetic and dielectric properties, as well as its RF performance, were systematically characterized. The key findings are as follows:

Dual-Channel In-Situ Aerosol Composite Forming System

PI pneumatic atomization and ferrite ultrasonic atomization are employed; the two streams of atomized droplets are thoroughly mixed within the print-head delivery channels. By dynamically adjusting the flow rates of the two carrier gases, the filling ratio of magnetic particles can be varied in real time, eliminating the need to pre‑prepare a composite slurry. At the optimal gas‑flow ratio, the film contains approximately 18 wt.% ferrite, with a relative permeability μᵣ of 1.4–1.6.

Partition border anti-overflow printing process

A 70-μm PI border is pre-printed around the magnetic region to suppress the spreading and overflow of low-viscosity ferrite ink, ensuring micrometer‑scale pattern accuracy and enabling precise partitioned fabrication of magnetic–dielectric heterostructures.

Verification of High-Performance Planar Microwave Inductors

A 4.5‑turn, 1 mm² microstrip inductor on a magnetic composite substrate exhibits an inductance of 4.2 nH at 1 GHz, representing a 40% improvement over the 3.0 nH achieved on a pure PI substrate. The inductance density reaches 4.2 nH/mm², the highest reported to date for additive manufacturing processes, while the quality factor remains stable at 6.6–6.7.

Microwave characteristics of tunable magnetic metamaterials in the external field

A composite thin film subjected to a DC bias magnetic field exhibits a magnetic resonance effect, with the resonant frequency tunable by the magnetic field strength, making it suitable for tunable RF devices and electromagnetic absorption circuits.

End-to-end integrated additive manufacturing

The dielectric substrate layer, magnetic composite layer, silver conductive traces, and bridging PI bridges are all fabricated via aerosol printing—eliminating the need for photolithography or vacuum deposition—and enabling the complete microwave circuit to be realized on a single device.

II. Complete Preparation Procedure for Multi-Material Aerosol Microwave Circuits

1) Ink formulation: PI polyimide acid NMP ink, 20 wt.% nickel–zinc ferrite nanodispersion, and commercial silver conductive ink;

2) Polishing of MoCu composite carrier wafers, with an interfacial adhesion promoter applied; a 1 μm PI underlayer is first printed to enhance adhesion.

3) Multi-material aerosol equipment with dual‑path atomization: PI pneumatic atomization and ferrite ultrasonic atomization, featuring an 85 mm mixing manifold and a focusing ratio of 1.2.

4) First, print a 70 μm PI overflow‑preventing border; then, perform in‑situ mixed deposition of the magnetic composite layer, adjusting the number of printed layers to achieve two thicknesses: 30 μm and 60 μm.

5) High-temperature curing of the magnetic composite film at 295°C under a nitrogen atmosphere;

6) 150 μm nozzle aerosol‑printed silver microstrip coils and bridging PI insulating bridges, with silver traces cured at 180°C.

7) The GSG probe station combined with a vector network analyzer was used to perform RF S‑parameter measurements from 1 to 40 GHz, while SEM and EDS were employed to characterize the compositional distribution.

III. Five Core Process Advantages of Multi-Material Aerosol Technology (Comparison with Screen Printing, Inkjet, and Lithography)

Adjust material proportions in real time during printing.

Two independent airflow paths enable precise gas control, while the magnetic particle loading can be adjusted online—eliminating the need to change inks or re‑prepare the slurry. A single system thus supports the production of multiple types of magnetically assisted composite films.

Partitioned Heterogeneous Integrated Molding

On the same substrate, pure PI dielectric and magnetic composite regions can be printed on demand, with micron‑scale boundary definition, eliminating the need for masking and simplifying multilayer microwave fabrication.

Precision graphical design with an anti-overflow border

Low-viscosity magnetic ink, combined with a PI edge‑encapsulation structure, addresses print spreading and overflow issues, meeting the precision requirements of millimeter‑wave microcircuits.

Full-device, single-equipment manufacturing

Dielectric, magnetic, and conductive layers are sequentially written in a single step, enabling the complete fabrication of inductors and resonators in one go and eliminating the need for multiple coating systems.

Compatible with hard-metal carrier substrates and high-frequency package substrates.

MoCu and other metals commonly used in microwave applications exhibit stable deposition, and their high-temperature curing processes are compatible with RF packaging production standards.

IV. Five Core Technological Innovations of This Study

Innovation 1: A Novel In-Situ Aerosol Forming Process for Microwave Magnetic Materials Using Multiple Feedstocks

The industry has achieved in‑line mist‑phase mixing of ferrite–polyimide composite films, overcoming the limitation of fixed formulation ratios in pre‑mixed slurries.

Innovative 2-PI border‑less, overflow‑preventing, high‑precision printing structure

A border‑defining process was devised to address the challenge of spreading low‑viscosity magnetic inks, enabling precise patterning of magnetic regions at the micrometer scale.

Innovative Three-Phase High-Inductance-Density RF Inductor Additive Manufacturing Solution

The magnetic composite substrate boosts planar inductors by 40%, and the 4.2 nH/mm² figure sets a new record for inductor density in additive manufacturing.

Innovation 4: An externally magnetic-field-tunable magneto‑dielectric composite microwave material system

The thin film exhibits controllable magnetic resonance characteristics, offering a new material platform for tunable filters and electromagnetic wave-absorbing circuits.

Innovative 5: A Lithography-Free All-Aerosol Microwave Packaging Manufacturing Paradigm

Digital direct writing of all-layer structures for passive RF components, enabling lightweight, rapid prototyping for system‑level packaging (SOP).

V. Current Industry Challenges and Corresponding Solutions

Challenge 1: Traditional magnetic slurries must be pre-mixed, with fixed components that cannot be dynamically adjusted.

✅ In-situ mixing of dual‑path mist streams, with real-time adjustment of the ferrite filling ratio to tailor magnetic permeability films on demand.

Challenge 2: Magnetic ink has low viscosity, making it prone to spreading and bleeding during printing, which results in blurred image edges.

✅ Pre-printed PI overflow‑prevention borders restrict ink flow, ensuring dimensional accuracy for tiny RF components.

Challenge 3: Integrating lithography and screen printing for the monolithic fabrication of magnetic–dielectric–metal multilayer microwave circuits.

✅A single MMAJP device enables layered printing of dielectric, magnetic, and conductive layers, reducing the need for multi‑step transfer and coating processes.

Challenge 4: Conventional printed inductor cores are missing, resulting in low inductance density and a large RF module footprint.

✅ A locally deposited high-permeability composite substrate boosts inductance by 40% at the same footprint, facilitating device miniaturization.

Challenge 5: Conventional magnetic thin films lack field‑tunable resonance characteristics, making the fabrication of tunable RF devices difficult.

✅ Nickel–zinc ferrite composite films exhibit magnetic resonance under an applied DC magnetic field, enabling the development of tunable microwave devices.

VI. Future Diversified Industrial Application Scenarios

1 Millimeter-Wave Radar Miniature Passive Inductor Array

Lightweight RF‑module planar inductors reduce the package footprint of radar front ends, making them well suited for automotive and UAV‑based sensing applications.

2 Tunable microwave filters and resonators

Magnetic-field tuning of the magnetic resonance frequency enables a reconfigurable RF front-end for 5G/6G communications.

3 Satellite Communication System-Level Package (SOP)

An all‑aerosol integrated magnetic‑dielectric circuit reduces satellite payload mass and streamlines the manufacturing process of RF components.

4 Electromagnetic Interference (EMI) Suppression Microcircuits

Magnetic composite thin-film integrated transmission line, which absorbs high-frequency spurious signals, and an anti-interference encapsulation layer for the chip.

5 High-Throughput R&D Platform for RF Device Laboratories

Rapidly fabricate composite circuits with varying magnetic permeabilities, perform batch testing of inductors and resonators’ RF performance, and shorten the iteration cycle for new materials.

Image and Text Guide

Figure 1. Design annotations for three microwave devices (in millimeters; target thicknesses are indicated in parentheses)

Figure 2. Principle of dual-material mixing in multi-material aerosol jet printing (MMAJP)

Figure 3. Physical image of the fully printed device (on a MoCu carrier substrate)

Figure 4. Inductor parameters after de-embedding (≤8 GHz)

Figure 5. S-parameters of the composite layer versus the PI transmission line under DC magnetic biasing

Figure 7. SEM backscattered electron image and EDS spectrum of the composite layer cross-section.