I. Abstract of the Paper’s Core Research

• Green, undoped CPA composite conductive ink system

NMP and other highly toxic organic solvents are eliminated, and a water/IPA dual-solvent system is employed. Chitosan is used to in situ polymerize polyaniline, yielding particles with outstanding dispersibility (polydispersity index of only 0.005), and the resulting deposited film exhibits intrinsic conductivity, obviating the need for post‑doping with hydrochloric acid and thereby simplifying the fabrication process.

• Micrometer-scale, high-precision direct-write patterning of memristive channels

Precise aerosol-based fabrication of 10-μm ultra‑short conductive channels; single‑ or double‑layer CPA films with controllable thicknesses ranging from 400 to 1200 nm; significantly fewer pore‑related defects compared to pure polyaniline inks; and well‑defined pattern edges with no material overflow.

• Stable typical memristive hysteresis switching characteristics

Voltage sweep range: 0.4 to +0.6 V, exhibiting a typical counter‑clockwise current hysteresis and rectification behavior; after 40 consecutive cycles, the cyclic voltammograms show virtually no drift, with an on/off switching ratio of three orders of magnitude, and stable operation is maintained across sweep rates from 10 to 100 mV/s.

• Simplify the integrated device manufacturing process

The aerosol directly prints the source–drain conductive channel, requiring only drop-casting of a solid-state polyelectrolyte together with a silver gate electrode, thereby eliminating time-consuming steps such as Langmuir–Blodgett multilayer deposition and repeated acid–base treatments, and significantly reducing the fabrication time for a single device.

• Biocompatible substrate compatibility

Chitosan exhibits excellent natural biocompatibility, and the ink is free of heavy metals and toxic solvents. It can be printed on a variety of substrates, including flexible PI and silicon wafers, making it well-suited for the development of implantable brain–computer interface hardware.

II. Complete Fabrication Process and Core Advantages of the Aerosol-Jet-Printed Memristor Series

(1) Complete Organic Memristor Fabrication Process

• A low-molecular-weight chitosan–glacial acetic acid system was employed to carry out in situ oxidative polymerization of aniline at low temperature, yielding CPA composite powders.
• Prepare a stable aerosol suspension using a 4:1 water/isopropanol ratio, and sonicate to disperse and eliminate agglomerates.
• SiO₂/silicon substrate: UV–ozone treatment combined with plasma activation enhances film adhesion.
• AJP device with a 200 μm nozzle, carrier gas flow of 30 sccm and sheath gas flow of 40 sccm, and a stage temperature maintained at 90°C, was used to print the CPA conductive channel.
• Double-layer stacking enhances film thickness and conductivity; dries at room temperature.
• A three-terminal memristive device was fabricated by drop-casting an AlCl₃-doped PEO solid-state polyelectrolyte and embedding a silver-wire gate.

(II) Five Major Process Advantages (Comparison of LB Film, Lithography, and Inkjet)

• All‑green bio‑based ink, free of highly toxic organic solvents.

It eliminates the need for hazardous reagents such as NMP and xylene; the aqueous system is environmentally friendly and easy to handle, reducing environmental compliance costs in both laboratory and mass-production settings.

• Native conductive thin film, eliminating the acid‑washing and doping steps.

Pure polyaniline films must be doped with hydrochloric acid after printing to achieve conductivity; in contrast, CPA composite films exhibit stable conductivity upon formation, thereby simplifying the post‑processing steps.

• Micrometer-scale microchannels enable high-density memristor arrays.

It enables the stable fabrication of 10-μm ultra-short conductive channels, whereas the Langmuir–Blodgett (LB) film process can only achieve features on the order of hundreds of micrometers, making it well suited for large-scale integration of neural synaptic arrays.

• Digital maskless direct writing, with a significant boost in iteration speed.

Simply modify the CAD channel length and array layout to quickly generate prototypes; a single-layer LB film deposition takes just a few hours per sample, while aerosol-based fabrication can be completed in minutes.

• Biocompatible and flexibly moldable, suitable for implantable electronics.

Chitosan is naturally biocompatible, and its printing process operates at low temperatures without thermal damage, enabling the fabrication of wearable and implantable brain‑inspired devices on flexible polymer films.

III. Five Core Technological Innovations of This Study

Innovation 1: Chitosan–Polyaniline (CPA) Bio‑Composite Ink for Aerosol Applications

Innovation 2: Aerosol Direct Writing of a 10 μm Microscale Organic Memristor Channel

Innovation 3: A native conductive thin-film system that eliminates the need for post‑deposition acidification.

Innovative Architecture for Long-Cycle-Stable Organic Memristive Devices

Innovation: A Low-Cost, Green, and Organic Additive Manufacturing Paradigm for Neuromorphic Devices

IV. Existing Process Challenges and Corresponding Solutions for Overcoming Them

Challenge 1: Pure polyaniline ink exhibits poor solubility, requiring highly toxic solvents such as NMP, and the printed films tend to have numerous pores.

Challenge 2: The LB film‑deposition process can only fabricate millimeter‑scale, wide channels and cannot be scaled down to miniaturize the array.

Challenge 3: Traditional organic memristors suffer from a limited number of cycles and severe performance drift upon repeated scanning.

Challenge 4: Lithography and vacuum processes are costly and involve lengthy workflows, making them unsuitable for rapid prototyping.

Challenge 5: Most conductive polymer inks exhibit poor biocompatibility, making them unsuitable for implantable devices.

V. Future Diversified Industrial Application Scenarios

• Lightweight Neuromorphic Computing Hardware Array

• Implantable brain–computer interface sensing element

• Flexible Bionic Sensing Electronic Skin

• Portable Low-Power Memory Sensor Tag

• Brain-inspired Electronics Rapid Experiment Platform for Universities

Figure 1. Printing line characteristics under different process parameters: (a) ShGF = 40 sscm, CGF = 30 sscm (FR = 1.33), sample stage speed = 0.5 mm/s (for channel deposition); (b) ShGF = 40 sscm, CGF = 30 sscm (FR = 1.33), stage speed = 2.0 mm/s; (c) ShGF = 35 sscm, CGF = 23 sscm (FR = 1.52), stage speed = 0.5 mm/s; (d) Characterization of printing‑process drift and line‑feature stability. During the first 20 minutes of the stable phase, the printed lines are predominantly governed by excess solvent, with very limited material atomization, resulting in broadened lines and blurred feature outlines—sharp edges but a hollow core. As gas flow stabilizes and material atomization increases, line definition becomes more uniform; after approximately 40 minutes, the line width reaches a plateau with only minor fluctuations.

Figure 2. (a) SEM images of pure Pani‑EB (10 layers) without surface pretreatment, (b) pure Pani‑EB (4 layers) after O₂/Ar plasma treatment, and (c) CPA (single layer) AJP‑printed films fabricated on Si/silica substrates, with pinholes highlighted in red; (d) thickness distribution profiles, obtained by profilometry, for printed films consisting of one and two layers (different samples).

Figure 3. (a) FTIR spectrum of the synthesized CPA composite material (potassium bromide precipitate). (b) DLS analysis results for a 0.1 mg/mL CPA aqueous suspension; the sample was sonicated for 5 minutes prior to measurement. (c) MALDI‑TOF mass spectrum of the synthesized CPA composite deposited on a substrate as an aqueous/ACN (1:1 v/v) dispersion; (d) mass spectrum obtained when deposited in an aqueous/HFIP (1:1 v/v) solution. Baseline has been subtracted, and the error margin is 1000 ppm.

Figure 4. (a) Schematic of a memristive microdevice with an AJP‑printed conductive layer. (b) An example of an OMD fabricated with a printed CPA layer. (c, d) In an OMD employing two printed CPA layers as conductive channels and Au electrodes deposited on a Si/SiO₂ substrate with dSD = 10 μm, 40 consecutive I–V cycles were measured at a scan rate of 10 mV/s. Upon switching between the OFF and ON states, the conductance decreased from 7.53 × 10⁻³ S/cm to 0.22 S/cm. The inset in (c) shows that the deposited CPA layer exhibits nearly ideal ohmic behavior. (e) I–V characteristics of the device at higher scan rates. (f) Reference measurements for a standard OMD fabricated by LS deposition of pure Pani (15 cycles).