I. Core Research Abstract

• Direct Writing of Micrometer-Scale Ultra-High-Precision THz Passive Devices

Aerosol-based techniques enable the stable fabrication of 10-μm ultra‑fine metal gratings, significantly outperforming conventional printing processes. For a 40-μm standard polarization grating, the extinction ratio reaches 30 dB; for a 10-μm ultra‑fine polarization grating, the 200-GHz extinction ratio is boosted to 45 dB, with polarization‑separation performance far surpassing that of traditional photolithography‑based 40-μm structures.

• Stable Fabrication of Multi-Band THz Filters

Band-stop filters operating at 250 GHz and 550 GHz, as well as a band-pass filter at 250 GHz, were fabricated. The resonant frequency, insertion loss, and etched copper‑based device dimensions of the silver‑based aerosol structure are closely matched. The 250‑GHz band‑stop filter achieves a resonance suppression of up to −27 dB, thereby meeting the requirements for terahertz signal filtering.

• Flexible ultra-thin LCP substrate compatible with low-temperature processes.

The entire printing and curing process is controlled at 180°C, which is below the deformation temperature of LCP. The substrate is only 25.4 μm thick—ultrathin and flexible—overcoming the limitations of conventional quartz‑based rigid substrates and enabling the fabrication of curved terahertz devices.

• Composite Enhancement Process for Electroless Plating of Aerosol Seed Layers

The single-layer silver aerosol film is only 600 nm thick, resulting in relatively high high-frequency losses. By using silver as a seed layer and chemically plating copper to increase the thickness by 2.5 μm, the metal thickness reaches five times the skin depth, thereby more than doubling the attenuation performance of the 550 GHz filter.

• Maskless Digital Rapid Iteration

No photolithography mask is required; CAD can directly adjust the grating line width and unit dimensions, enabling rapid prototyping of novel THz devices within hours and significantly shortening the development cycle of terahertz systems.

II. Complete Preparation Process Flow and Core Process Advantages of Aerosol Spraying

(1) Complete fabrication process of terahertz quasi-optical devices

• The ultra-thin LCP copper-clad laminate is etched with sodium persulfate to remove the double-sided copper layer, then rinsed and dried for later use.
• Commercial silver‑nanoparticle ink can be diluted with deionized water and is compatible with ultrasonic atomization; Optomec’s aerosol‑jet printing system, equipped with a 200‑μm nozzle, enables the fabrication of various THz grating structures.
• Cure in a 180°C constant-temperature oven for 3 hours to form an approximately 600 nm-thick silver conductive film.
• An optional post‑plating chemical copper‑plating step is employed to deposit a 2.5 μm‑thick copper layer on the silver seed layer, thereby increasing the metal thickness.
• A 9-mm-aperture optical window was fabricated, and frequency-domain terahertz measurement was performed to obtain a sweep‑frequency characterization over the 100–1700 GHz range.

(II) Five Core Processes (Photolithography / Micromachining / Inkjet Comparison)

• Compatible with inks ranging from 1 to 1000 cP viscosity, enabling ultra-fine 10 μm high-precision printing.

Inkjet printing is suitable only for low-viscosity inks, with a minimum line width starting at 40 μm; aerosol jetting enables stable atomization of silver‑ink formulations, allowing single‑pass direct writing of ultra‑fine 10‑μm polarization gratings to meet the requirements of terahertz subwavelength structures.

• 4 mm ultra-large print safety clearance, with outstanding conformability to curved surfaces.

The nozzle is maintained at a few millimeters from the substrate, enabling the deposition of metallic grids on curved and irregular flexible substrates—something that conventional lithography on rigid planar surfaces such as quartz cannot achieve for curved‑surface devices.

• Low-temperature processing compatible with flexible, low-loss LCP films

Lithographic sputtering and multi‑step high‑temperature processes can easily induce LCP warpage; in contrast, aerosol‑based curing at a low temperature of 180°C throughout the entire process ensures that ultra‑thin substrates remain deformation‑free, enabling the realization of lightweight, flexible terahertz components.

• Integrated Efficiency-Enhancing Solution for Seed Layer Composite Electroplating

First, aerosol‑based low‑cost printing is used to fabricate fine patterns, followed by electroless plating to build up a thick metal layer, achieving both high pattern resolution and low RF loss in thick metallization. However, it is challenging to simultaneously realize fine lines and a thick conductive film using a single process.

• Maskless digital manufacturing, low-cost prototyping for small batches.

By eliminating high‑cost investments such as photomasks and cleanrooms, we enable same‑day prototyping of design revisions during the R&D phase, thereby lowering the barrier to entry for terahertz device development.

III. Five Key Technological Innovations

Innovation 1: Aerosol jetting enables a 10 μm ultrafine terahertz polarization grating.

Innovative Additive Manufacturing Solution for a Flexible, Ultra-Thin LCP-Substrate THz Filter

Innovative Three-Step Aerosol Silver Seed Layer Chemical Plating Composite Enhancement Process

Innovation in a Multi-Band Standardized Design Framework for THz Aerosol Components

Innovative 5‑band wideband 100–1.7 THz stable printing process

IV. Existing Process Challenges and Corresponding Solutions for Overcoming Them

Challenge 1: Conventional lithography is limited to planar rigid substrates and cannot fabricate flexible, curved THz devices.

Challenge 2: The minimum line width in conventional printing is 40 μm, and the machining precision for ultra-fine polarization gratings is inadequate.

Challenge 3: The thickness of the single-layer printed silver film is insufficient, resulting in significant skin-effect losses at terahertz high frequencies.

Challenge 4: Long lithography mask‑making cycle and extremely high costs for small batches.

Challenge 5: The high-temperature coating process can cause deformation and failure of the LCP flexible substrate.

V. Future Diversified Industrial Application Scenarios

• Portable Terahertz Security Screening Imaging Device

• Terahertz Nondestructive Testing in Biomedicine

• Nondestructive Testing of Industrial Composite Materials

• Automotive millimeter-wave/terahertz radar front-end

• Terahertz Laboratory Rapid Prototyping Platform for Universities

Figure 1. Concept of an Aerosol Jet System

Figure 2. Schematic diagram of the components. Left: Structure of the band‑stop and band‑pass filter units; Right: Structure of the polarizer unit. A: Filter linewidth; B: Filter line length; C: Width and length of the filter unit structure; D: Polarizer linewidth; E: Polarizer line spacing; F: Width and length of the polarizer unit structure.

Figure 3. Simulated transmission coefficient of the 250 GHz band-stop filter

Figure 4. Simulated transmission coefficient of the 550 GHz band-stop filter

Figure 5. Simulated transmission coefficients of 550 GHz band-stop filters with different line widths.

Table I Filter Dimensions

Figure 6. Simulated transmission coefficient of the 250 GHz bandpass filter

Figure 7. Extinction Ratio of the Simulated Polarizer

Figure 8. Measurement Setup Configuration

Figure 9. Unit-cell structure of the fabricated 250 GHz band-stop filter. Left: Copper metal patterned by photolithography; right: Components produced via aerosol jet printing.

Figure 10. Measured transmission coefficient of the 250 GHz band-stop filter

Figure 11. Structure of the fabricated 550 GHz band-stop filter unit. Left: Copper metal patterned by photolithography; right: Components fabricated via aerosol jet printing.

Figure 12. Measured transmission coefficient of the 550 GHz band-stop filter

Figure 13. Unit-cell structure of the fabricated 250 GHz bandpass filter. Left: Copper metal patterned by photolithography; right: Components produced via aerosol jet printing.

Figure 14. Measured transmission coefficient of the 250 GHz bandpass filter

Figure 15. Unit-cell structure of the fabricated 40-μm polarization‑grid. Left: Copper metal patterned by photolithography; right: Component produced via aerosol jet printing.

Figure 16. Unit cell structure of the prepared 10 μm aerosol-jet-printed polarizer grid.

Figure 17. Simulated and Measured Polarizer Suppression Ratio

Figure 18. Unit structure of an electrolytic copper-plated layer for a 550 GHz band-stop filter

Figure 19. Measured transmission coefficients of the 550 GHz band-stop filter (before and after electroless copper plating).