“Sens. Actuators A Phys.” High-Sensitivity Aerosol-Jet-Printed Resistive Temperature Sensor
Product Introduction
Equipment Parameters
I. Abstract of the Paper’s Core Research
- Ultra-high temperature coefficient of resistance, approaching the intrinsic properties of bulk silver.
The single-layer silver thin film exhibits an average TCR of 3.7 × 10⁻³ °C⁻¹, nearly matching that of bulk silver at 3.8 × 10⁻³ °C⁻¹, and significantly exceeding the values reported for commercially available inkjet‑printed silver temperature‑sensing devices (1.0–2.9 × 10⁻³ °C⁻¹), resulting in a substantial improvement in temperature‑sensing sensitivity.
- The number of thin-film layers is controllable, and the sensitivity can be adjusted as needed.
The single-layer film exhibits a sensitivity of 1.33 Ω/°C; as the number of printed layers increases, the baseline resistance decreases, and the six‑layer film achieves a sensitivity of only 0.25 Ω/°C. The film thickness can be customized to meet the accuracy requirements of the temperature‑sensing circuit.
- Ultra-fast thermal response, outperforming commercial thermistors.
The step‑change temperature test time constant is only 0.83 s, whereas that of commercial ceramic thermistors reaches 2.00 s; the ultra‑thin aerosol film exhibits an even lower thermal capacitance, resulting in superior real‑time temperature‑measurement capability.
- Flexible, bend-resistant, and moisture-proof; can be encapsulated.
Thin-film traces exhibit greater resistance drift after bending, whereas thick-film resistors demonstrate superior strain‑induced stability. After spin‑coating a 5‑μm polyimide passivation layer, the device maintains linear performance with no offset across 20–100°C thermal cycling in a 75% relative humidity environment, effectively resolving the issue of silver‑film drift caused by moisture absorption.
- Wide-Temperature-Range Stable Linear Temperature Measurement Range
Resistance across the full range of −20°C to 150°C exhibits excellent temperature linearity, with only minimal hysteresis during heating and cooling cycles, making it well suited for low‑temperature wearable applications and medium‑to‑high‑temperature industrial monitoring scenarios.
II. Complete RTD Preparation Process and Core Advantages of Aerosol Spraying
(1) Complete Fabrication Process of Flexible Temperature Sensors
- Kapton film ultrasonic cleaning with isopropyl alcohol, with the workbench held at 60°C;
- 50 wt% high-solids silver ink, ultrasonic atomization; 200 μm nozzle; printing serpentine temperature-sensing traces at a speed of 6 mm/s.
- Print the 1st, 3rd, and 6th layers of the thin film separately to distinguish the thickness gradient.
- Heat‑sinter in a 260°C oven at constant temperature for 1 hour to completely decompose the organic binder, resulting in tight interconnection of the silver particles.
- Some samples were spin-coated with a PI passivation layer for moisture protection.
- The high- and low-temperature oven, bending fixture, and humidity test chamber have completed full‑range performance calibration.
(II) Five Key Advantages of Aerosol-Based Processes (Comparison with Lithography and Inkjet)
- Highly dense silver thin films, achieving a TCR close to that of bulk silver.
The impact velocity of aerosol droplets is significantly higher than that of inkjet printing, resulting in a greater packing density of silver particles. After sintering, residual impurities are minimal, and temperature‑sensing sensitivity is improved by an order of magnitude.
- Digital precision control of thickness, with sensitivity customizable at will.
Only the printing repetition sequence needs to be adjusted—no ink change is required—enabling a single system to produce both highly sensitive thin‑film and highly stable thick‑film temperature‑sensing devices.
- Maskless serpentine array rapid prototyping
CAD allows for arbitrary adjustments to trace length, trace width, and layout, maximizing resistance per unit area, while the miniature curved‑surface temperature probe undergoes rapid iterative refinement.
- Flexible / Conformal Compatibility with Irregular Curved Surfaces
3–5 mm non-contact nozzle-to-substrate distance, enabling direct printing on PI, mica, and curved metal components; compatible with battery surface curvatures and temperature sensing in soft robots.
- Low consumable usage and low cost, no cleanroom lithography production line required.
Only the temperature‑sensing region is coated with the precious metal silver, eliminating large‑area etching waste and significantly reducing costs for both small‑batch research and mass production.
III. Five Core Technological Innovations of This Study
Innovation 1: High-solid silver ink combined with aerosol-based high-speed deposition, breaking through the bottleneck of low TCR in printed RTDs.
Innovation 2: Number of Thin-Film Layers – A Quantitative Regulation System for Sensitivity
Innovation 3: An ultra-thin, low-thermal-capacitance aerosol thin film enables millisecond‑scale rapid temperature measurement.
Innovative 4-PI Passivation and Moisture-Proof Integrated Process
Innovative Design Approach for Flexible Strain Differentiation, Version 5
IV. Existing Process Challenges and Corresponding Solutions for Overcoming Them
Challenge 1: Inkjet-printed silver films exhibit high porosity and binder residues, resulting in generally low TCR values.
Challenge 2: A single thin film cannot simultaneously achieve both high sensitivity and bendability.
Challenge 3: Silver nanofilm is prone to oxidation in high-humidity environments, leading to shifts in the temperature‑measurement curve.
Challenge 4: Traditional RTD lithography is costly and cannot achieve large-area patterning on curved surfaces.
Challenge 5: Commercial temperature‑sensing components have slow response times, making it impossible to capture instantaneous temperature fluctuations.
V. Future Diversified Industrial Application Scenarios
- Wearable continuous body temperature monitoring patch
- Curved-Surface Thermal Monitoring Array for Power Batteries
- Soft robotics, deformation and temperature sensing for prosthetics
- Distributed Surface Temperature Measurement for Industrial Equipment
Laboratory Flexible Sensing Rapid Development Platform
Figure 1. Aerosol jet‑printed resistive temperature detector (RTD): (a) Schematic illustrating the key steps of the AJP process, including aerosol generation via ultrasonic treatment, aerosol transport, aerodynamic focusing, and substrate impact; (b) Geometric structure of the printed RTD sensor.
Figure 2. RTD devices fabricated by aerosol-jet printing: (a) Digital image of a temperature-sensor array printed on a flexible substrate; (b) Optical micrograph; (c) Scanning electron micrograph of a thin film printed using a silver nanoparticle ink.
Figure 3. Profile measurement results of a typical aerosol-jet-printed temperature sensor: (a) 3D scanning image of the six-layer RTD structure; (b) thickness distribution profile of the structure.
Figure 4. Resistance–temperature measurements of aerosol-jet-printed thermoelectric resistors (RTDs) with varying thicknesses during heating–cooling cycles: (a) single-layer RTD; (b) three-layer RTD; (c) six-layer RTD; (d) average baseline resistance of RTDs with different thicknesses at room temperature; (e) average temperature coefficient of resistance (TCR) for RTDs of different thicknesses; (f) average sensitivity of RTDs of different thicknesses.
Table 1 Comparison of Aerosol-Jet-Printed RTD Performance with Literature Data
Figure 5. Transient response of a printed resistive temperature detector (RTD): (a) in deionized water; (b) inside a freezer at various temperatures.
Figure 6. Effects of electrostatic passivation and bending strain on aerosol‑based temperature sensors fabricated by inkjet printing with silver nanoparticle ink: (a) Temperature cycling tests of sensors printed with a single‑layer patterned structure under 75% relative humidity; (b) Normalized resistance changes of sensors printed with varying pattern thicknesses at different bending radii.
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