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Printed electronics, due to its manufacturability using printing technology, allows for fabrication on large areas and the usage of flexible substrates and thus enables novel applications. Non-impact printing technology, such as inkjet-printing, permits for flexible, decentralized manufacturing of electronic devices and systems. This further facilitates split-manufacturing in security-critical electrical components, as well as a maximum in design flexibility in terms of free form factors and non-standardized structures with different geometrical sizes, reaching from a few micrometers up to several millimeters.
Based on the technological benefits printed electronics offers, it provides an interesting counterpart to classical silicon-based electronics, which is usually densely integrated on miniaturized, rigid areas. By utilizing both technologies in a complementary manner, novel systems in the form of hybrid systems can be enabled. Whilst hybrid systems, incorporating passive printed components and electrically conductive wiring concepts, are already commercialized, complex printed systems, which also utilize active components remain rare. To enable more complex (hybrid) systems, various building blocks are required. This includes possibilities for lightweight, printed data storage, the capability to provide sustainable, self-powered printed components and especially circuits for secure, unique identification for holistic printed systems, deployed in the internet of things.
The presented thesis focuses on inkjet-printed electronic devices, circuits and hybrid systems. It investigates solutions for current scientific questions in the area of efficient data storage, sustainable electronics and hardware-based security in printed electronics.
For data storage, an inkjet-printed memristor is developed. The device is fully electrically evaluated with a focus on its data storage capabilities. Furthermore, the printed device is of special interest due to its easy manufacturability and integration capabilities. The experimental analysis reveals that the developed memristor is highly suitable as lightweight non-volatile memory device.
In order to enable sustainable electronic systems, an inkjet-printed full-wave rectifier based on near-zero threshold voltage electrolyte-gated transistors is developed and fully electrically characterized. The circuit is capable for small alternating voltage rectification of low-frequency vibration energy harvesters in the sub-volt region. This provides an important building block in enabling sustainable, self-powered electronic systems. The inkjet-printed full-wave rectifier is evaluated by electrical simulation and experimentally.
To tackle hardware-based security for printed electronics, two implementations for inkjet-printed physically unclonable functions are developed and presented. For unique identification, intrinsic variation in active printed devices are exploited. One implementation is based on a crossbar architecture, incorporating integrable electrolyte-gated transistor cells. The second implementation, the so-called differential circuit physically unclonable function, is based on inverter structures, which provide the basis for unique response generation. Both physically unclonable functions are evaluated using an electrical simulation-based approach and experimentally. The differential circuit approach is furthermore fully integrated within a silicon-based electronic platform environment and serves as intrinsic variation source in a hybrid system. The hybrid system physically unclonable function is fully verified regarding performance metrics and is capable to generate highly unique responses for secure identification.
Hybrid low-voltage physical unclonable function based on inkjet-printed metal-oxide transistors
(2020)
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.
Embedded Analog Physical Unclonable Function System to Extract Reliable and Unique Security Keys
(2020)
Internet of Things (IoT) enabled devices have become more and more pervasive in our everyday lives. Examples include wearables transmitting and processing personal data and smart labels interacting with customers. Due to the sensitive data involved, these devices need to be protected against attackers. In this context, hardware-based security primitives such as Physical Unclonable Functions (PUFs) provide a powerful solution to secure interconnected devices. The main benefit of PUFs, in combination with traditional cryptographic methods, is that security keys are derived from the random intrinsic variations of the underlying core circuit. In this work, we present a holistic analog-based PUF evaluation platform, enabling direct access to a scalable design that can be customized to fit the application requirements in terms of the number of required keys and bit width. The proposed platform covers the full software and hardware implementations and allows for tracing the PUF response generation from the digital level back to the internal analog voltages that are directly involved in the response generation procedure. Our analysis is based on 30 fabricated PUF cores that we evaluated in terms of PUF security metrics and bit errors for various temperatures and biases. With an average reliability of 99.20% and a uniqueness of 48.84%, the proposed system shows values close to ideal.