I. Core Research Summary

Three commercial silver inks: quantitative comparison across all operating conditions.

Three well-established silver inks—ANP Silverjet, Clariant Prelect, and UT Dots—were employed, with standardized aerosol‑printing parameters used to fabricate four‑point probe conductivity test pads and coplanar waveguide (CPW) RF devices. The experiments spanned five temperature levels (145°C, 165°C, 185°C, 205°C, and 225°C) and three sintering atmospheres (air, nitrogen, and vacuum), enabling the establishment of a comprehensive lateral performance comparison framework.

• The sintering atmosphere significantly determines the upper limit of thin-film conductivity.

Sintering under a nitrogen atmosphere yields the best overall electrical conductivity; ANP ink achieves a conductivity of 188,655 S/cm at 225°C in a nitrogen environment, significantly higher than that obtained via air or vacuum sintering. In contrast, Clariant and UT Dots inks exhibit a specific temperature‑compatibility window, and low‑temperature air sintering readily leads to film open‑circuits and a sharp increase in RF losses.

• The storage environment of unsintered samples affects their forming and electrical properties.

ANP samples stored under vacuum for 8 days exhibit the best conductivity after sintering; Clariant inks demonstrate superior performance when stored in air; UT Dots must be sintered immediately after printing, as long-term storage leads to nanoparticle oxidation and a sharp decline in electrical conductivity. Corresponding storage guidelines are provided for each ink type.

• X-band microwave RF loss quantification benchmark

S21 insertion loss data were collected across the entire frequency band. Silver‑film RF components sintered at high temperature in nitrogen exhibit the lowest RF losses, making them well suited for 5G and high‑frequency microwave devices such as radar systems. In contrast, samples sintered at low temperature in air show RF losses exceeding −50 dB at high frequencies, which fails to meet the performance requirements of RF circuits.

• Standardized aerosol printing + reusable testing workflow

We are making publicly available the complete ACSPL printing process, sintering temperature‑control curves, profile‑thickness scans, and the LRRM RF calibration method, enabling enterprises and laboratories to directly reproduce the tests for benchmarking in‑house ink performance and for quality control of production‑line processes.

II. Complete Process Flow and Core Technological Advantages of Aerosol Jet Printing

(1) Complete Sample Preparation and Testing Procedure

• Plasma cleaning of silicon and glass substrates removes contaminants, enhancing the adhesion of silver films.
• Optomec AJ300 ultrasonic atomization silver ink, with dual-nozzle partitioned printing: a 300-μm nozzle is used to fabricate conductive test pads, while a 100-μm nozzle prints coplanar waveguide RF traces with a 100-μm line width.
• The samples were divided into three groups: immediate sintering, air storage for 8 days, and vacuum storage for 8 days.
• The programmable furnace performs stepwise temperature‑ramp sintering under controlled atmospheres (air, N₂, or vacuum), maintains a constant temperature for 30 minutes, and then cools passively at a slow rate over 5 hours.
• A profilometer measures film thickness, while a four‑probe technique is used to determine sheet resistance and calculate electrical conductivity; a probe station combined with a vector network analyzer enables the acquisition of RF S‑parameters in the 10–40 GHz range.

(II) Five Core Advantages of Aerosol-Based Processes (Compared with Screen Printing, Lithography, and Inkjet)

• Micrometer-scale, high-precision direct writing of RF circuits

Minimum 10 μm fine RF transmission lines, precise fabrication of narrow‑gap coplanar waveguides, and screen‑printed trace widths as low as hundreds of micrometers—none of these can meet the impedance‑matching requirements at high microwave frequencies.

• Multi-ink rapid switching with a unified printing standard

The same device and a single set of operating procedures can rapidly switch among three commercial silver inks, eliminating inter‑device variability and ensuring fair performance comparisons—making it ideal for ink screening and evaluation.

• Digital printing parameters are precisely controllable.

Atomization flow rate, sheath‑gas ratio, printing speed, and layer‑stacking count can be saved as fixed settings; a standardized ACSPL file is generated, enabling full experimental reproducibility across different laboratories and facilitating horizontal benchmarking within the industry.

• Ultra-thin, uniform silver film formation with reduced RF loss.

Multi-layer thin films are stacked, with film thickness controllable in the range of 0.5–2 μm, low surface roughness, and significant scattering loss for high-frequency electromagnetic waves—achieved through a thick-film printing process.

• Universal for both flexible and rigid substrates; rapid prototyping of RF devices.

Silicon, glass, and PI films can all be printed simultaneously without the need for custom masks, enabling rapid prototyping of novel microwave antennas and flexible RF sensors with sample validation completed on the same day.

III. Five Key Technological Innovations

Innovation 1: The industry’s first multi-brand, silver‑ink, full‑dimensional AJP performance benchmark database.

Innovation 2: Identifying the optimal sintering process parameters for different inks

Innovation 3: Quantitative Validation of the Oxidation Failure Mechanism of Unsintered Wet Films

Innovative 4-Way Broadband RF and DC Performance Coupled Analysis Model

Innovation 5: Fully Open-Source Standardized Testing and Process Pipeline

IV. Existing Process Challenges in the Industry and Corresponding Solutions for Overcoming Them

Challenge 1: The market offers a wide variety of silver inks, with no unified performance benchmark, resulting in high costs associated with trial-and-error selection.

Challenge 2: Improper control of the sintering atmosphere and temperature leads to a sharp degradation in the electrical conductivity and RF performance of the silver film.

Challenge 3: After batch printing, immediate sintering is not possible, and the wet film exhibits unstable performance when stored.

Challenge 4: Measuring only the sheet resistance cannot assess the usability of high-frequency RF devices.

Challenge 5: The aerosol printing protocols vary across laboratories, making it impossible to compare experimental results across different labs.

V. Future Diversified Industrial Application Scenarios

• Development of Mass-Production Processes for 5G/Millimeter-Wave RF Antennas

• Research and Development of Aerospace Microwave Sensor Devices

• Flexible Wearable Wireless Sensor Circuit

• Aerosol Process Teaching and New Material Development in University Laboratories

• Production Line Quality Control Standards for Electronics Manufacturing Enterprises

Figure 1. Schematic diagram of the sample layout for sintering studies. One sub‑sample was taken from each ink type, and a total of three sub‑samples were deposited on each sample substrate (a). Each sub‑sample comprises five coplanar waveguides and a four‑point probe pad. The sample substrates were fabricated from intrinsic silicon (resistivity >10,000 Ω·cm) by dicing 2‑inch (50.8 mm) wafers (as indicated by the dashed lines in (c)). The target coplanar waveguide geometry is shown in (d).

Figure 2 shows the relationship between average DC conductivity and four-point probe pad thickness and sintering temperature for each ink under different sintering atmospheres. Standard deviation values were calculated based on three sheet resistance measurements per sample, as well as the z‑height deviations measured at the probe pad surface (see Figure 11). The samples were subjected to the following sintering protocol: ramped to the target temperature over 1 hour, held at that temperature for 30 minutes, and then passively cooled to below 75°C over approximately 5 hours (see Figure 10).

Figure 3. Example of the average S21 (insertion loss) spectra for coplanar waveguides printed with three different inks and sintered at 225°C. The shaded regions indicate the standard deviations of five coplanar waveguides per sample.

Figure 4 presents box plots that graphically depict the distribution of insertion loss for each ink across different sintering conditions in the 10 MHz to 40 GHz frequency range. This visualization clearly highlights five key statistical measures for each sintering condition: the minimum value, the first quartile, the mean, the third quartile, and the maximum value. In Figures (b) and (c), additional blue secondary vertical axes have been included to more intuitively illustrate the differences in insertion‑loss distributions under two distinct operating states. Some coplanar waveguide (CPW) samples exhibited scratching or interlayer delamination during RF testing; these samples were labeled as “unmeasurable.”

Figure 5 shows a subset of the insertion loss data (mean ± standard deviation, n = 5), with insertion loss values averaged over the X-band frequency range (7 GHz–11.2 GHz) and plotted as a function of sintering temperature.

Figure 6 shows a schematic of the experimental protocol used to print and compare the storage stability of the samples prior to sintering. For each of the three inks, we printed a total of 15 rectangular samples measuring 8 mm × 3 mm on three clean 2-inch × 3-inch glass substrates, following the scanning paths indicated by the red dashed lines. Immediately after deposition, substrate “A” was subjected to sintering, and its electrode pads were evaluated for DC electrical conductivity; substrates “B” and “C,” meanwhile, were stored in ambient air and under vacuum, respectively, for eight days before undergoing sintering and subsequent DC conductivity analysis.

Figure 7 illustrates the effect of storage conditions on the electrical conductivity of sintered samples. (a) shows the conductivity measurements and thickness data for samples printed with ANP ink and sintered at approximately 165°C for 60 minutes; among them, the sample stored in a vacuum for 8 days exhibits the best performance. (b) presents the results for samples printed with Clariant ink and sintered at about 190°C for 60 minutes, with the highest conductivity observed in those sintered after being stored in air for 8 days. (c) displays data for UT Dots samples: these were sintered at 175°C for 60 minutes, and the samples sintered immediately after printing demonstrated the best conductivity.

Figure 8. (a) shows an optical micrograph of the complete sample, mounted on a glass substrate. The sample comprises five coplanar waveguides and an 8 mm × 3 mm pad for four‑point probe conductivity measurements; (b) presents an optical micrograph of a single coplanar waveguide, fabricated on a silicon substrate. Each waveguide has a width of 1 mm, with a central conductor width of 100 μm and a gap width of 100 μm.

Figure 9. Schematic diagram of the graphical layout for the sintering protocol. Each substrate comprises sub‑samples printed with three different inks, with each sub‑sample distinguished by a distinct color.

Figure 10. Shows an example of a customized sintering program: (a) illustrates the parameters set to a target temperature of 225°C for 30 minutes, while (b) presents the actual sintering temperature profiles for all fifteen substrates. During this process, the samples are allowed to cool passively for approximately five hours before being removed from the furnace.

Figure 11 shows typical profilometry data. (a) presents a single two-dimensional profile along the width of the four‑point probe pad; (b) displays the three‑dimensional distribution map of the four‑point probe pad. Here, ten two-dimensional profiles are combined and presented from a top-down perspective, with height values annotated using the calibrated color scale shown on the right.

Table 1 Summary of Data for Aerosol Jet‑Printed Samples Prepared Using ANP SilverJet DGP 40LT‑15C Ink under Various Sintering Conditions

Table 2 Summary data for aerosol jet‑printed samples using Clariant Prelect TPS 50‑G2 ink under different sintering conditions

Table 3 Summary data of aerosol jet‑printed samples using UT Dots UTDAg40x ink under different sintering conditions

Table 4 Summary Data of Aerosol-Jet-Printed Samples Sintered Using ANP SilverJet DGP 40LT-15C Ink Under Different Storage Conditions

Table 5: Summary Data of Aerosol Jet-Printed Samples Sintered Under Different Storage Conditions Using Clariant Prelect TPS 50-G2 Ink

Table 6 Summary Data of Aerosol-Jet-Printed Samples Sintered with UT Dots UTDAg40x Ink under Different Storage Conditions

Table 7 presents a summary of the general printing parameters used when fabricating each feature with three different inks. Nozzle size refers to the nominal inner diameter of the nozzle; pressure stabilization time is the duration required for the atomizer and sheath‑flow pressures to reach steady state after gas flow is initiated; we determined the nominal trace width by adjusting the sheath‑flow rate, atomizer flow rate, and printing speed, and by measuring the trace using calibrated machine‑vision video signals; print pitch denotes the spacing between raster patterns used to arrange the various shapes that comprise the printed feature: for single‑layer features, a horizontal (i.e., longitudinal) raster pattern is employed; for double‑layer features, a horizontal raster pattern is first applied, followed by a vertical raster pattern; the estimated printing time does not include the pressure stabilization period.