Modern society is striving for digital connectivity that demands information security. As an emerging technology, printed electronics is a key enabler for novel device types with free form factors, customizability, and the potential for large-area fabrication while being seamlessly integrated into our everyday environment. At present, information security is mainly based on software algorithms that use pseudo random numbers. In this regard, hardware-intrinsic security primitives, such as physical unclonable functions, are very promising to provide inherent security features comparable to biometrical data. Device-specific, random intrinsic variations are exploited to generate unique secure identifiers. Here, we introduce a hybrid physical unclonable function, combining silicon and printed electronics technologies, based on metal oxide thin film devices. Our system exploits the inherent randomness of printed materials due to surface roughness, film morphology and the resulting electrical characteristics. The security primitive provides high intrinsic variation, is non-volatile, scalable and exhibits nearly ideal uniqueness.

There is increasing interest in the utilisation of medical gases, such as ozone, for the treatment of herniated disks, peripheral artery diseases, and chronic wounds, and for dentistry. Currently, the in situ measurement of the dissolved ozone concentration during the medical procedures in human bodily liquids and tissues is not possible. Further research is necessary to enable the integration of ozone sensors in medical and bioanalytical devices. In the present review, we report selected recent developments in ozone sensor technology (2016–2020). The sensors are subdivided into ozone gas sensors and dissolved ozone sensors. The focus thereby lies upon amperometric and impedimetric as well as optical measurement methods. The progress made in various areas—such as measurement temperature, measurement range, response time, and recovery time—is presented. As inkjet-printing is a new promising technology for embedding sensors in medical and bioanalytical devices, the present review includes a brief overview of the current approaches of inkjet-printed ozone sensors.

Functional inks enable manufacturing of flexible electronic devices by means of printing technology. Silver nanoparticle (Ag NP) ink is widely used for printing conductive components. A sintering process is required to obtain sufficient conductivity. Thermal sintering is the most commonly used method, but the heat must be carefully applied to avoid damaging low‐temperature substrates such as polymer films. In this work, two alternative sintering methods, damp heat sintering and water sintering are systematically investigated for inkjet‐printed Ag tracks on polymer substrates. Both methods allow sintering polyvinyl pyrrolidone (PVP) capped Ag NPs at 85°C. In this way, the resistance is significantly reduced to only 1.7 times that of the samples on polyimide sintered in an oven at 250°C. The microstructure of sintered Ag NPs is analyzed. Taking the states of the capping layer under different conditions into account, the explanation of the sintering mechanism of Ag NPs at low temperatures is presented. Overall, both damp heat sintering and water sintering are viable options for achieving high conductivity of printed Ag tracks. They can broaden the range of substrates available for flexible electronic device fabrication while mitigating substrate damage risks. The choice between them depends on the specific application and the substrate used.

The biocompatibility of medical sensors is of great importance. In order to prevent harm of the patient during measurement, this aspect must be considered throughout the entire design process. Biocompatibility can be achieved by various methods. For example, the sensor can be encapsulated, only biocompatible materials can be used for the sensor, or anti-inflammatory agents can be applied to the surface of the sensor. In this paper the focus is on sensors fully fabricated from biocompatible materials. Two exemplary inkjet-printed amperometric and impedimetric sensors are systematically assessed regarding their biocompatibility. Both sensors can be used for the measurement of dissolved ozone during oxygen-ozone injection therapy. For the sensors each material is evaluated with respect to the international standard ISO 10993. Overall, many amperometric and impedimetric sensors are fabricated from a small set of materials. The assessment reveals that for this specific application an amperometric sensor consisting of gold and silver nanoparticle inks, inkjet-printed on a polydimethylsiloxane membrane, and passivated with SU-8 ink offers the highest biocompatibility and reaches a good compliance with other important requirements. In addition, biological characterization tests are required for the specific medical application to validate the biocompatibility. From this study, it can be concluded that the findings on biocompatibility can also be transferred to other sensors that are made of the same set of materials but are for other applications. This applies to oxygen, glucose, pH, hydrogen peroxide, sweat lactate, and acetone sensors.

Functional printing shows a huge potential for fabrication of flexible electronics on polymer films. However, not all electronic functionality can be realized by functional printing yet. The combination of functional printing and mounting of silicon electronic components is a pragmatic approach to realize new functionalities. This paper presents an integrated, automated workflow to derive fabrication data for a flexible hybrid printed circuit from a CAD-layout. These CAD data and prior knowledge from empirical process data are used to create motion programmes for subsequent fabrication and inspection steps. On the example of a demonstrator circuit, circuit layout and assignment of different functionalities to different CAD layers are illustrated. The exported CAD data are the input for a generator tool, which first verifies and then optimises the layout for the subsequent fabrication processes. Thereafter the tool automatically generates motion commands for a vector single nozzle ink-jet printing module, an optical inspection module and a SMT component placement module. The automated data and fabrication workflow is explained in detail, finally leading to the functional printed demonstrator circuit.

Printing technology and mounting technology enable the novel field of hybrid printed electronics. To establish a hybrid printed system, one challenge is that the applied mounting process meets the requirements of functional inks and substrates. One of the most common requirements is low process temperature. Many functional inks and substrates cannot withstand the high temperatures required by traditional mounting processes. In this work, a standardized interconnection and an automated bump-less flip-chip mounting process using a room temperature curing conductive adhesive are realised. With the proposed process, the conductive adhesive selected for the standardized interconnection can be dispensed uniformly, despite its increase of viscosity already during pot time. Electrical and mechanical performance of the interconnection are characterized by four terminal resistance measurement and shear test. The herein proposed automated process allows for fabrication of hybrid printed devices in larger batch sizes than manual assembly processes used beforehand and thus, more comprehensive evaluation of device parameters. This is successfully demonstrated in a first application, a novel hybrid printed security device. The room temperature mounting process eliminates any potentially damaging thermal influence on the performance of the printed circuits that might result from other assembly techniques like soldering.