The development of innovative, miniaturized, and low-cost Radio Frequency Identification (RFID) tags for application in asset monitoring, counterfeit prevention, or personnel tracking requires advancements in materials, fabrication processes, and packaging. Typical RFID tags can be circumvented by tampering, cloning, or spoofing; however, by adding security features to the tag, nefarious actions such as these can be mitigated. Toward this objective, this paper presents the design and fabrication of an Ultra High Frequency (UHF) RFID tag through flexible hybrid electronics (FHE) materials and processes for authentication and anti-tamper /anti-counterfeit applications. The presented UHF RFID tag consists of a passive RF chip and dipole antenna with embedded hardware and software security features. The tag was fabricated using a hybrid of manufacturing techniques including, conventional photolithography and additive aerosol jet printing. The design, materials selection, processing, and tailored FHE fabrication processes, led to achieving a system-level functional RFID tag with a read distance of up to 15 in (0.381 m). The dependency of the read distance on the host surface was studied by attaching tags to different materials including surfaces with various dielectric constants and thicknesses. The performance of the tags was evaluated under realistic use conditions by performing thermal cycling, bending, and wearability tests. The RFID tag’s resistance to different tamper attack vectors (vulnerability assessment) is demonstrated. Overall, the demonstrated UHF RFID tag opens new opportunities for the development of flexible, lightweight, and low-cost RFID tags that leverage FHE fabrication techniques and materials for authentication and anti-tamper applications.

Direct writing methods created a revolution in the electronic industry due to their lower cost, fast processing and lower wasted material. Microstrip line is an important electronic component that transfers the signal and the foundation for the communication between multiple components in any circuit board. Therefore, studying its electromechanical behavior against thermal and mechanical stresses is necessary for real life applications. In this research, novel microstrip lines were printed on “Polyethylene Terephthalate” (PET) and “Polyimide” (PI) flexible substrates using an aerosol jet printer and dispensing system. An advanced post treatment technique was used to enhance the conductivity of the microstrip lines printed on low glass transition flexible PET substrate. Different microstrip line designs with various mesh ground planes were tested under mild and harsh mechanical bending and different environmental conditions and their losses were characterized. The results showed that the photonic curing enhanced the microstrip lines conductivity by 65% compared to the convectional curing. The in-situ resistance measurements during harsh bending demonstrated conclusively that the robustness of the printed microstrip lines increased as the filling percentage of the ground plane became lower. The aging at 85°C/85% RH had a significantly stronger effect on the microstrip lines conductivity compared to the aging at 85°C without humidity due to the changes in the printed ink’s microstructure and the increment in ionic conductivity. Thermal aging led to a reduction in the microstrip line’s ductility and the cracking became easier in the microstructure of the printed films. The resistance of a sample aged at 85°C increased by 81.7% after 10000 bending cycles compared to only 20.5% for a sample without thermal aging. Such findings provide important guidelines for those designing flexible hybrid electronics and for manufacturers who seek the assurance of these technologies for both maturing and reliable products.

Water-based carbon inks provide a cost-effective and sustainable alternative to organic-solvent-based metal conductive inks, making them attractive for wearable sensor applications. However, poor adhesion on non-porous polymer substrates and susceptibility to temperature and humidity fluctuations raise concerns on printability and reliability, hindering their widespread commercial adoption. This study focuses on screen-printing defect-free multilayer structures on flexible and stretchable polymer substrates using a commercial water-based conductive carbon black ink and evaluating their reliability. A robust printing process was developed by modifying the fabrication flow, optimizing printing parameters, and maintaining atmospheric relative humidity between 70% and 75%. Multilayer sweat-rate electrodes (SREs) with conductors and resistors were successfully screen-printed using a solvent-based silver ink and a water-based carbon black ink, respectively, and their environmental and mechanical reliability was comprehensively investigated. The water-based carbon resistors printed on polyimide substrate demonstrated promising results. Ambient-dried resistors on polyimide exhibited satisfactory electrical performance and reliability, while thermal curing further reduced their electrical resistance by 18% without compromising reliability. Moreover, these resistors demonstrated excellent environmental and mechanical reliability by withstanding thermal exposure at 125 °C, relative humidity of 15%, and 500 tensile bending cycles at a 1 cm bend radius, suggesting their suitability for wearable sensors. Failure analysis revealed the development of crater-like morphological structures during the drying process, which later acted as stress concentration points. Resistors printed on polyester, high-density polyethylene, and thermoplastic polyurethane substrates failed due to cracking, delamination, ink-to-ink interactions, or out-of-plane deformation. Cracking and delamination patterns provided useful insights into failure mechanisms.

Direct-Write printing enables the selective deposition and patterning of dielectric and conductive materials in a multi-layer fashion to create high-resolution 3D circuit elements. An embedded PIN diode limiter circuit was demonstrated as an example of a millimeter wave radio frequency circuit element with aerosol jet printed interconnections in place of wire bonding. A hybrid circuit fabrication approach was chosen using conventional low dielectric constant substrates and copper foil circuitry with active die embedded in the substrate. Printed radio frequency elements were placed in the circuit where there was a realizable size-weight-power-cost advantage in terms of better performance, size reduction, or faster build time. Aerosol jet was used because of its micron-sized printed features and its use of digitally driven data from CAD files for multi-axis control of the deposition tool and use with different print materials. DC resistance, return loss and insertion loss were measured and compared to wire bonded samples up to 20 GHz frequency. The PIN diodes circuit limiter was evaluated after exposure to military standard tests including thermal cycling and salt fog testing. Comparing aerosol jet printed connections to wire bonding showed equal radio frequency performance at high frequency without the need for wire tuning and with printed connections being more robust and reliable.

Changes in the morphology and profile of the printed electronic traces affect the radio frequency (RF) performance, especially when compared to the simulated designs, which are primarily rectangular and smooth. The shape and morphology of the printed traces depend on the printing system, a combination of ink and substrate properties, and the printed technology used for fabrication. This paper investigates the significance of printing parameters like roughness, height, width, and profile shape on the RF performance of screen-printed traces statistically. This paper also derives a model based on actual profile shape and roughness measurements from incorporating these effects into the simulations. From the statistical study, we found that the role of surface roughness becomes more significant as the frequency increases. Thus, modeling surface roughness in flexible hybrid electronics simulations is fundamental for accurate results. Different simulated profile shapes also showed their effect on the RF performance, when combined with roughness, showed better correlation with experimental data. Our proposed model combines the modified Morgan and Hammerstad equation with the compound conductor model. Our proposed model uniquely integrates the modified Morgan and Hammerstad equation with the compound conductor model, leveraging a comprehensive approach focused on the quality and uniformity of printed electronics trace. This integration is aimed at constructing a model that is firmly grounded in actual roughness data, resulting in a solution that is both straightforward to implement and exceptionally accurate in its outcomes. The model agreed well with experimental measurement data over 7 GHz–40 GHz with a root-mean-square error average of 5.7%.