I. Abstract of the Paper’s Core Research

This study employs the Optomec AJ300 aerosol deposition system, coupled with a pulsed xenon‑lamp photopolymerization setup, to fabricate conductive traces and insulating isolation layers on three cellulose‑based substrates using silver nanoparticle conductive ink and UV‑curable insulating adhesive ink. The process enables interconnection of surface‑mount components, followed by comprehensive testing of electrical conductivity, flexural stability, and reliability under high‑humidity conditions. Additionally, a tubular paper‑based multilayer touch‑sensing prototype was fabricated. The key findings are as follows:

• Photon-assisted millisecond‑scale low‑temperature sintering completely prevents high‑temperature carbonization of paper.

Eliminating prolonged oven baking at 100°C, a single‑pulse, millisecond‑scale energy is focused onto the silver film, resulting in an extremely low overall temperature rise of the paper substrate. Optimal flash‑sintering parameters are tailored for chromatographic paper, photographic paper, and rigid cardboard, yielding line resistivities as low as 13.1×10⁻⁸ Ω·m—conductivity comparable to that of traditionally high‑temperature‑sintered silver traces.

• Aerosol-layered printing enables multi-layer, cross-wire hybrid circuits.

The process sequentially prints the bottom-layer silver traces, the UV‑curable insulating isolation layer, and the top-layer interconnects, while the insulating ink simultaneously serves as a bonding substrate for surface‑mount components. A single system accomplishes multi‑layer wiring and component mounting, overcoming the limitations of paper‑based single‑layer electronic circuits.

• Comprehensive characterization of the differentiated forming properties of three types of cellulose-based substrates.

Chromatographic paper: It features large fiber pores and deep penetration of silver ink; when repeatedly bent between 0° and 90°, it remains intact without circuit breaks, making it well-suited for foldable, flexible sensing applications.

Photographic paper: dense surface layer, shallow ink penetration, uniform and smooth lines, compatible with high-precision touch electrodes;

Cardboard: It features substantial thickness and high rigidity, with a thick conductive layer that delivers excellent electrical conductivity, making it well-suited for high-power circuits.

Stable and reliable under both high-humidity and bending conditions.

Within a humidity range of 35%–80%, the line resistance fluctuates by less than 5%; when chromatographic paper is bent to 90°, no significant resistance drift is observed, and cardboard and photographic paper exhibit only slight degradation even after large‑angle bending, thereby meeting the requirements for single‑use devices in diverse application scenarios.

• 3D curved-surface paper-based fully functional smart touch prototype

A four-channel capacitive touch array is fabricated on a paper cylindrical substrate, integrating a Bluetooth module and LEDs. Finger contact increases capacitance by approximately 42%, and the touch signal is transmitted wirelessly, enabling human–machine interaction on curved paper surfaces. Mutual.

II. Complete Preparation Process and Core Advantages of Aerosol + Photon Sintering

• Complete Fabrication Process for Paper-Based Smart Devices

1) Plasma surface cleaning of cellulose paper (chromatography paper / photographic paper / cardboard), etc.;

2) Aerosol‑jet printed silver nanoparticle ink is used to fabricate the underlying conductive traces, followed by a short pre‑drying step at 140°C.

3) Pulsed xenon lamp photon flash transient sintering, with voltage and pulse duration tailored to the paper type;

4) AJP applies NOA81 UV-curable insulating adhesive, which cures in situ under UV light, isolating multilayer circuitry and bonding 0603 surface-mount components.

5) A second aerosol‑based printing step deposits an upper interconnect silver line, connecting the chip pads to the underlying circuitry.

6) Package the flexible battery and integrate touch‑sensing and Bluetooth communication modules to conduct full‑system testing.

• Five Core Process Advantages (Comparison of Screen Printing, Inkjet, and High-Temperature Oven Processes)

Photon-induced instant curing protects the biodegradable paper substrate.

Traditional ovens can cause paper to yellow and become brittle after just a few tens of minutes at high temperatures; in contrast, FLA’s millisecond‑scale pulses heat only the silver thin film, keeping the substrate temperature low, so various cellulose‑based substrates neither carbonize nor deform.

Dual-ink integrated multi-layer additive manufacturing

An AJP system switches between conductive silver ink and UV‑curable insulating adhesive ink, simultaneously performing wiring, interlayer insulation, and chip mounting—eliminating the need for auxiliary processes such as lamination or transfer printing.

High-precision non-contact adaptation for flat surfaces / 3D curved paper materials

Aerosol‑based beam‑focusing technology enables the fabrication of 250‑μm‑scale fine conductive traces, allowing uniform deposition on irregular curved surfaces such as flat panels and paper cylinders, thereby facilitating curved‑surface touch interfaces and packaging electronics with ease.

Digital Maskless Rapid Iteration Touch-Array

With CAD, you can instantly modify finger‑type and multilayer circuit layouts without the need for tooling, while simultaneously conducting parallel comparative tests across multiple substrate materials, significantly shortening the R&D cycle.

End-to-end green and low‑consumption, with components that are naturally biodegradable.

The substrate is made of renewable cellulose, generates no photoresist etching waste, and allows discarded circuits to be directly incinerated or biodegraded in soil, significantly reducing e‑waste pollution.

III. Five Core Technological Innovations of This Study

Innovation 1: A complete process integrating aerosol-assisted and photonic sintering tailored for cellulose-based substrates.

A systematic paper-based electronic low-temperature manufacturing process has been established, with standardized flash sintering parameters developed for three commonly used types of paper, thereby addressing the industry’s longstanding challenge of paper materials’ poor high-temperature resistance.

Innovation 2: A Dual-Function Composite Architecture for Insulating Ink and Adhesive

NOA81 UV‑curable polymer serves both as a multilayer circuit insulating dielectric and as an adhesive for SMD component mounting, eliminating the need for conductive adhesives and insulating films and thereby simplifying multilayer circuit structures.

Innovative Three-Layer Interconnected Paper-Based Hybrid Integrated Circuit Manufacturing Paradigm

It enables three-dimensional wiring on a paper substrate, with bottom-layer traces, an insulating layer, and top-layer interconnects, allowing direct soldering of surface-mount components and Bluetooth modules, thereby overcoming the limitation of paper-based electronics to simple single-layer circuits.

Innovation: A Differentiated Design System for Substrate Performance

The three substrate types—chromatographic paper (high bend durability), photographic paper (high-precision touch control), and rigid cardboard (high conductivity, high power)—are clearly defined in terms of their respective application scenarios, providing a quantitative basis for material selection in paper-based devices.

Innovative 5-in-1 3D curved all-paper wireless touch-enabled smart device

Integrating a multi-channel capacitive sensor array with paper‑based cylindrical curved‑surface printing and wireless communication, this approach enables power‑free touch interaction on curved surfaces, thereby expanding the boundaries of paper‑based electronics.

IV. Current Industry Challenges in the Process and Corresponding Breakthrough Solutions

Challenge 1: Cellulose fibers in paper have poor thermal stability and are prone to embrittlement and breakage under prolonged high-temperature sintering.

✅ Millisecond photon flashes selectively heat the silver layer, with minimal temperature rise in the substrate and no prolonged thermal baking throughout the process, leaving the paper intact and flexible.

Challenge 2: Traditional printing can only support single-layer wiring and cannot accommodate cross‑layer multi‑layer circuits.

✅ Aerosol-based stepwise printing of conductive and insulating layers, followed by UV‑curable adhesive curing to isolate the upper and lower silver traces, enabling multi‑layer, cross‑wire complex circuits.

Challenge 3: The paper substrate makes it difficult to securely attach the chip, leading to easy detachment and open circuits in the interconnections.

✅AJP’s precision spot‑printing UV‑curable insulating ink cures in situ, securely locking components in place; the upper‑layer silver traces connect directly to the pads for stable electrical contact.

Challenge 4: Significant differences in porosity among various papers lead to uneven ink penetration and poor electrical conductivity consistency.

✅ Customized atomization and flash‑sintering parameters are tailored to the substrate, enabling precise control of ink penetration depth through paper porosity and ensuring consistent resistivity levels.

Challenge 5: Paper-based devices are prone to significant resistance drift when exposed to moisture or subjected to bending.

✅ A dense silver aerosol film combined with a fibrous permeation structure ensures minimal resistance variation even in high-humidity environments; the chromatographic paper substrate can withstand repeated 90° bending.

V. Future Diversified Industrial Application Scenarios

1 Smart Food Label for Disposable Paper Packaging

Biodegradable paper NFC touch‑sensing tags for fresh‑food preservation monitoring and traceability, which degrade completely upon disposal—no electronic waste.

2 Medical disposable paper-based biochemical sensor test strips

Electrochemical/capacitive sensing array on a chromatographic paper substrate, enabling rapid non-invasive detection of bodily fluids; disposed of by incineration after use, with no need for disinfection or recycling.

3 Eco-friendly paper-based human-machine interaction control panel

Curved paper-based touch panels, simple interactive buttons for courier boxes and cultural‑creative products, and low‑cost disposable interactive devices.

4 Agricultural Environmental Paper-Based Monitoring Strips

Field soil and greenhouse temperature–humidity sensing paper, enabling large‑scale, low‑cost deployment with natural degradation and zero pollution.

5 University-Based Electronic R&D Platform for Green Printing

Desktop aerosol + compact photonic sintering equipment, eliminating the need for high‑temperature furnaces or lithography production lines, enables rapid prototyping of biodegradable paper‑based circuits.

Image and Text Guide

Figure 1. Block diagram of the circuit manufacturing process: A complete process flow for fabricating hybrid smart circuits on cellulose substrates, employing “aerosol jet printing (AJP) + photonic curing (FLA).”

• a)   Bare paper substrate;
• b)   Silver (Ag) conductive traces are deposited using AJP and then cured by FLA photopolymerization.
• c)   Surface-mount devices (SMD, QFN/DFN leadless packages, with pads facing upward);
• d)   AJP is used to selectively print NOA 81 photocurable adhesive as the insulating/bonding layer, with simultaneous UV curing during printing to secure the SMDs.
• e)   Printed silver traces enable device interconnection and multilayer structures (d and e can be repeated to create additional circuit layers), ultimately yielding a ready-to-use device (the lower-right corner shows the finished product).

Table 1. AJP printing process parameters for silver conductive ink (HPS 108-AE1, Novacentrix): Sheath gas flow rate: 500 SCCM; atomizing gas flow rate: 1350 SCCM; exhaust gas flow rate: 1000 SCCM; substrate temperature: 35 °C; process speed: 1 mm/s (using the Optomec AJ300 aerosol jet printer). This water-based silver‑flake ink is specifically formulated for AJP and, when combined with FLA photoinitiated curing, enables the fabrication of low‑resistance conductive traces on paper substrates.

Figure 2. AJP-printed test sample:

• a)   Printed pattern and geometric dimensions: The total length of the U-shaped trace is approximately 44.55 mm (with a straight segment L = 22.5 mm, port spacing D = 1 mm, and trace width W = 1 mm);
• b), c), d)   These are the printed physical samples on chromatographic paper, cardboard, and photographic paper—10 layers were deposited on both the chromatographic paper and the cardboard, and 5 layers on the photographic paper—followed by pre‑drying in an oven at 140 °C as recommended by the ink manufacturer.

Figure 3. Optimization of photonic curing parameters—variation of the resistance ratio R/R₀ with flash voltage and pulse duration: The vertical axis shows the ratio (%) of the post‑curing resistance R to the pre‑curing resistance R₀, while the horizontal axis represents the flashlamp voltage (V). The four curves correspond to single‑pulse durations of 1200, 1400, 1600, and 1800 μs, respectively. Each data point was obtained by measuring three samples using the four‑wire method, with a total of 285 samples tested.

• a) Chromatography paper: Average resistance before curing: 11.9 Ω (RSD 38%), optimal parameters   500 V + 1800 μs , the resistance drops to 1.52 Ω (RSD 3%, a reduction of approximately 83%);
• b) Cardboard: Average resistance before curing: 13.02 Ω (RSD 19%), optimal parameters   1200 μs + 580 V , the resistance drops to approximately 1.98 Ω (a reduction of about 85%);
• c) Photographic paper: Average resistance before curing: 6.9 Ω (RSD 39%), optimal parameters   1400 μs + 540 V , the resistance drops to 1.26 Ω (RSD 6%, a reduction of approximately 73%).
• In the high-voltage region of each curve, the resistance increases, corresponding to cracking in the silver traces due to excessive thermal stress.

Figure 5. Optical micrograph of a multilayer circuit region: On the left is a schematic diagram, and on the right is a microscopic image (with a 250 μm scale bar). True multilayer interconnections are achieved through a stack of “insulating layer (NOA 81) – top silver contact – cellulose substrate – bottom silver contact,” demonstrating the feasibility of fabricating multilayer circuits on a cellulose substrate using AJP.

Figure 6. FE-SEM morphology and EDX elemental analysis of silver trace cross-sections on three substrates (red = silver, green = carbon):

• a) Chromatography paper (Ruler: 20 μm): The porous hydrophilic fiber network exhibits strong ink-absorption capacity, with silver ink nearly penetrating the entire paper thickness; therefore, a longer pulse duration is required to ensure thorough penetration of the silver ink.
• b) Cardboard (Ruler: 100 μm): The structure is dense, with silver ink only partially penetrating;
• c) Photographic paper (Ruler: 100 μm): The silver ink occupies only a thin layer on the substrate surface, so a long pulse duration is not required.

Figure 7. Thickness profiles of silver wires on three substrates measured by an optical profiler (white-light interferometry): On the left of each panel is a heat map of single‑line thickness, and on the right is a thickness profile along the width direction.

• a) Chromatography paper: Thickness: 24.9 μm; line width: 274 μm (RSD 15%);
• b) Cardboard: Peak height approximately 51 μm, total width approximately 258 μm (RSD 18% / 10%);
• c) Photographic paper: Thickness: 28.5 μm; line width: 255.5 μm (RSD: 12% / 4%); the number of deposited layers is only half that of other substrates.
• Based on these measurements, the bulk resistivities are as follows: chromatography paper, 26.3 × 10⁻⁸ Ω·m; photographic paper, 22.3 × 10⁻⁸ Ω·m; and cardboard, 13.1 × 10⁻⁸ Ω·m (consistent with Novacentrix’s nominal range of 14–44 × 10⁻⁸ Ω·m).

Figure 11. The Optomec AJ300 uses a photosensitive paper tube during the printing process.

Figure 12. The finally fabricated multilayer smart 3D device: A fully functional prototype integrated onto the 3D surface of a photographic paper tube (including a 10 mm scale), featuring four printed capacitive touch sensors, an LED, and a Bluetooth microcontroller (Cypress CYBLE-222014-01). When a finger touches any of the capacitive sensors, the LED turns off, and the touch data is transmitted via Bluetooth; the device is powered by a flexible 3.7 V / 12 mAh battery. Capacitance measurements show that, upon touch, the capacitance increases by approximately… 42% , thereby demonstrating the feasibility of integrating multilayer circuits, SMD interconnections, and sensors onto a 3D cellulose-based substrate using the AJP + FLA process.