We report on heterogeneous sensor functionalization of carbon nanotube-based hydrogen sensors by Poly(4-vinylpyridin) (P4VP) polymeric encapsulation combined with (bi-)metallic catalysts. Parametrical studies unfold the influence of different functionalization architectures on the sensor's responsivities and time constants. Moreover, these studies provide fundamental insights on the underlying doping- and charge transport phenomena for repealing the responsivity/selectivity trade-off. In an optimized sensor configuration, we report on highly linear behavior from 2500 ppm down to 10 ppm and a response time below 15 s enabling safety-relevant leak detection within the whole hydrogen value chain.

In this work, we report a stage-controlled wafer level drop casting technique of thin graphene paths from a water based, additive free graphene dispersion. SEM cross sections indicate a strong planar orientation of graphene flake networks. The graphene dispersion was cast onto wafer substrates up to 8 in. in size and annealed at 300 degrees C, achieving 0.14 x 106 S/m with controllable path thicknesses down to 30 nm. The electrical conductivity can be significantly increased to up to 3.5 x 106 S/m by gas-phase doping using AlCl3. We discuss a doping experiment, resulting in a gradual increase of conductivity between 2 and 30 times, underlined by EDX, Raman spectroscopy and profile measurements. Further, we have modelled the graphene paths as an idealized layered system with many flakes per layer, connected all flakes to form a conductor network, and finally solved this network via nodal analysis. These simulations reproduce the experimentally shown thickness-dependence of the conductivity and provide a deeper understanding of the influence of path thickness and microscopic flake properties. The simulations suggest that the doping process not only enhances the in-plane conductivity of the flakes but also the interlayer coupling, indicating that the dopants predominantly act as surface dopants. The reported results surpass previously shown conductivities for dispersion casting of graphene by over an order of magnitude, offering a sustainable alternative to replace metal based conductors in electronic devices.

Carbon nanotube (CNT) based ion-sensitive FETs (ISFETs) and biosensor FETs (BioFETs) provide scalable solutions for liquid electrochemical sensing. We present fab-compatible CNT-ISFETs fabricated on 200 mm wafers and evaluated under electrolyte gating, showing consistent threshold voltage (V-th) (0.45 +/- 0.06) V, low gate leakage (10(-9) A), <10% on-current drift over 7 h, and <20% variation in key electrical parameters such as on-current, transconductance, threshold voltage, and subthreshold swing, demonstrating good deposition uniformity. After 3-Aminopropyltriethoxysilane functionalization, BioFETs exhibit I-on/I-off > 10(4), a narrow V-th (0.31 +/- 0.02) V, and a subthreshold swing of (101 +/- 4) mV/dec, meeting relevant performance criteria. Upon functionalization for DNA sensing, our BioFETs achieve responsivities of >300% for 100 aM target DNA and Delta V-th similar to 80 mV, marking the first instance of such low detection in label-free, non-nanoparticle-assisted CNT-FET biosensors.

There has been an increasing interest in pH sensors based on nanomaterials in environmental and biological sensing. This work addresses persistent challenges in the development of stable and sensitive pH measurements. We present a CNT-FET-based pH sensor with a hybrid encapsulation stack consisting of poly(4-vinylpyridine)/HfO2 layers. The resulting liquid-gated sensors feature an excellent sensitivity of up to 50 mV/pH in an operation regime below 1 V, which is within the electrochemical window of most biological species. Moreover, the P4VP encapsulation results in a 1000× higher on-off-current ratio and nearly 83% smaller drift compared to devices encapsulated in only HfO2.

Graphite based conductors are promising low cost and light -weight alternatives to copper but current challenges are among others the improvement of the conductivity of graphite films (GF). Therefore, in this work the influence of copper(II) chloride and nickel(II) chloride on the graphitization of graphene oxide and the electrical conductivity of the resulting GF was studied. The electrical conductivity was measured at different scales by contactless eddy current method and four point probe scanning tunneling microscopy transport measurements. The macroscopic and nanoscopic transport measurements were complemented by network -based simulations, which allowed us to estimate the microscopic material properties of the GF with and without additives. Annealing temperatures between 1600 degrees C to 2850 degrees C and varying metal chloride concentrations revealed an optimum at 2850 degrees C and a concentration of 8.8 mmol/l NiCl 2 in the aqueous dispersion. These GFs displayed an electrical conductivity of 609 kS/m, around 30 % higher than the GFs without any metal chloride addition. The graphitization morphology was analyzed by x-ray diffraction and scanning electron microscopy respectively. The precipitation effect of carbon from Ni supports the growth of graphitic structures, whereas the catalytic activity of Cu known from chemical vapor deposition does not promote graphitic structures. Rather, the annealing temperature is the crucial parameter for achieving highly conductive films. Furthermore, the influence of applied pressure during compression was studied. High pressures of at least 250 MPa are needed to obtain compact GFs with an electrical conductivity 3 times larger than before compression.

Physical Unclonable Functions (PUFs) are increasingly used in the process of securing applications. For this purpose, it is crucial that the PUF satisfies all the required properties adequately, including Unpredictability. An important aspect of Unpredictability is Randomness, which includes being free of spatial correlation effects. However, most methods for assessing randomness are not capable of detecting correlation, such that this aspect is often ignored. This work summarises the current literature to shed more light on the topic of analysing spatial correlation in weak PUFs, and evaluates the various methods proposed in the literature for detecting such effects. Additionally, the spatial correlation of a Dynamic Random Access Memory (DRAM) decay-based PUF implemented on the DRAM of a Raspberry Pi board, as well as that of a Carbon-NanoTube-based PUF (CNT-PUF), are examined, using, for the first time in the context of PUFs, not only other well-known metrics proposed in the relevant literature, but also the Getis-Ord G metric. Finally, a mitigation technique against attacks based on spatial auto-correlation is proposed and its effective application to PUF responses is discussed.

As the number of devices being interconnected increases, so does also the demand for (lightweight) security. To this end, Physical Unclonable Functions (PUFs) have been proposed as hardware primitives that can act as roots of trust and security. Recently, a new type of PUF based on Carbon NanoTubes (CNTs) has been proposed. At the same time, attacks and testing based on direct electrical probing appear to be moving towards non-invasive techniques. In this context, this work attempts to examine the potential for practical non-invasive probing attacks against the CNT-PUF, a novel PUF based on CNTs. Our results indicate that direct probing might potentially compromise the security of this PUF. Nevertheless, we note that this holds true only in the case that the attacker can directly probe the wire corresponding to the secret value of each CNT-PUF cell. Thus, we can conclude that the examined CNT-PUFs are rather resilient to direct probing attacks, that non-invasive probing methods appear to be promising for testing such PUFs, and that, in order for the attacker to gain the full-length value of the secret, all the relevant channels would need to be probed. Nevertheless, as our work proves, practical non-invasive attacks against the CNT-PUF are feasible and adequate countermeasures need to be employed in order to address this issue.

Carbon nanotubes (CNTs) offer great potential for both high-integration digital and high-frequency applications due to their unique 1-D carrier transport properties. However, the typically large contact resistance between the source/drain metal and the metal-covered CNT prevents the advantages of CNTs from being exploited. For supporting process development toward lowering the contact resistance and also compact modeling of CNT field-effect transistors (CNTFETs), a method for extracting the contact resistance is proposed. By measuring at sufficiently high gate voltages and subsequent suitable extrapolation toward infinite gate voltage, the bias-dependent components of the total channel resistance can be eliminated to extract the contact resistance. The accuracy of the proposed method was first verified using device simulation and subsequently applied to fabricated CNTFETs. The proposed method is suitable for both single- and multitube CNTFETs as well as for capturing the statistical variation of the contact resistance across the wafer.

The use of 1D and 2D nanomaterials in emerging electronics and sensor technologies is becoming increasingly important due to their unique properties. Here we would like to highlight a scalable process for suspended nanomaterials that provides additional scope for the development of device properties that can be used in advanced concepts ranging from molecular sensing to quantum applications [1]. For example those applications benefit from arrangements as CNT-based nanoresonators with extremely high quality factors [2] usable for quantum bits with long coherence time [3] or suspended sensing nanomaterials for ultra-low power and extremely sensitive gas sensors [4]. Moreover, straining allows to tune intrinsic physical properties of nanomaterials. Thus, the strain-dependence of the band gap (e.g. CNTs <100meV/% [5], MoS 2 ~60meV/% [6],) paves the way for integrated-, highly-efficient-, and tunable light sources for on-chip spectrometry in the context of photonic integrated circuits (PICs), as recently reviewed in [7]. Our technological solution to manufacture suspended nanomaterials is aligned with established semiconductor processing chains on 200 mm wafer level and is developed to be modular integrable and compatible with MEMS, MEOMS or CMOS technologies [8]. Along the process chain, we demonstrate wafer-validated deposition processes for semiconducting CNT films which properties can be adjusted with respect to density and even alignment. In particular, for straining aligned CNTs as well as any transferable 2D nanomaterial, we implemented a stressed functional SiO 2 /SiN layer stack arranged on embedded sacrificial Cu-structures on the wafer surface. After contacting of the nanomaterial and release of sacrificial elements, stressed layers relax, strain and suspend the nanomaterial. This surface engineering approach greatly simplifies the introduction of strain into nanomaterials and makes it accessible for arbitrary device numbers on wafers as well as for monolithic 3D electronic concepts. Unique features include in-plane strains that are applicable in multiaxial directions and can be controlled by designing only two lithography planes. We show that devices with CNTs strained up to 1% determined from Raman spectral analysis, have a positive impact on sensor operation. We show application examples such as a mechanical stress sensor with extremely low on-set sensitivity. References [1] A. Baydin, F. Tay, J. Fan, M. Manjappa, W. Gao, and J. Kono, “Carbon Nanotube Devices for Quantum Technology,” Materials (Basel, Switzerland) , vol. 15, no. 4, 2022. [2] J. Moser, A. Eichler, J. Güttinger, M. I. Dykman, and A. Bachtold, “Nanotube mechanical resonators with quality factors of up to 5 million,” Nature Nanotechnology , vol. 9, no. 12, pp. 1007–1011, 2014. [3] I. Khivrich and S. Ilani, “Nanotubes resound better,” Nature Nanotech , vol. 9, no. 12, pp. 963–964, 2014. [4] D.-H. Baek, J. Choi, and J. Kim, “Fabrication of suspended nanowires for highly sensitive gas sensing,” Sensors and Actuators B: Chemical , vol. 284, pp. 362–368, 2019. [5] L. Yang and J. Han, “Electronic structure of deformed carbon nanotubes,” Physical review letters , vol. 85, no. 1, pp. 154–157, 2000. [6] C. R. Zhu et al., “Strain tuning of optical emission energy and polarization in monolayer and bilayer MoS${}_{2}$,” Phys. Rev. B , vol. 88, no. 12, p. 121301, 2013. [7] M. Pandey, C. Pandey, R. Ahuja, and R. Kumar, “Straining techniques for strain engineering of 2D materials towards flexible straintronic applications,” Nano Energy , vol. 109, p. 108278, 2023. [8] S. Bottger, F. Dietz, M. Hartmann, N. Dahra, E. Kaulfersch, and S. Hermann, “Functional CMOS extension with integrated carbon nano devices,” in 2022 Smart Systems Integration (SSI): 27-28 April 2022 , Grenoble, France, 2022, pp. 1–4.

In this work, we explored a highly robust and unique Physical Unclonable Function (PUF) based on the stochastic assembly of single-walled Carbon NanoTubes (CNTs) integrated within a wafer-level technology. Our work demonstrated that the proposed CNT-based PUFs are exceptionally robust with an average fractional intra-device Hamming distance well below 0.01 both at room temperature and under varying temperatures in the range from 23 ∘C to 120 ∘C. We attributed the excellent heat tolerance to comparatively low activation energies of less than 40 meV extracted from an Arrhenius plot. As the number of unstable bits in the examined implementation is extremely low, our devices allow for a lightweight and simple error correction, just by selecting stable cells, thereby diminishing the need for complex error correction. Through a significant number of tests, we demonstrated the capability of novel nanomaterial devices to serve as highly efficient hardware security primitives.

In this work, we present a novel method of increasing the entropy of the CNT-PUF, a Physical Unclonable Function (PUF) based on Carbon-NanoTube Field Effect Transistors (CNT-FETs). The binary responses of this PUF are based on the drain current I D of each CNT-FET under the influence of a particular gate-source voltage V GS, which, through the employment of a single threshold value for I D, can indicate whether each relevant CNT cell of the array is conducting (acting either as a true conductor or as a semiconductor) or not (acting as an insulator). In this work, we propose the adoption of individual threshold values for each such cell as part of the relevant PUF challenge, thereby significantly increasing the overall entropy of this PUF, as well as the security that it can provide. Moreover, this method allows for the realisation of a source of higher entropy in the form of a True Random Number Generator (TRNG). Finally, we note that our work and its results are most probably also relevant for other CNT- based PUFs, structures, and primitives that utilise a single current (or even, voltage) threshold to determine the state of the different CNT cells utilised.

The use of nanomaterials in emerging electronics and sensor technologies is becoming more prevalent due to their unique properties. However, controlling the strain states of these materials in nanodevices remains a persistent challenge. Incorporating mechanical strain in a controllable manner is crucial and is simplified here for suspended nanomaterial assemblies in nano-electro-mechanical system (NEMS) configurations. We discuss a verified CMOS compatible and scalable surface micromachining approach with respect to design capabilities based on FE simulations. It is shown that inplane stress applicable in multi-axial directions can be controlled by only a few geometry factors and by process parameters of strain mediating stress layers.

Deficiencies in software or computer chips cause computers or smartphones to crash and allow hackers to steal passwords. Automated test procedures could avoid these problems. However, the computing power and cooling requirements of conventional computers increase exponentially with the size of the problem, so that the technological limits for solving these problems will soon be reached. The EU project Bio4Comp aims to develop concepts for a bio-computer to help overcome these two main problems. Compared to conventional computers, computers based on biological molecular motors only consume a fraction of the energy per arithmetic operation and scale very well for problems that can be parallelized (“multitasking”). In this article, the topic network-based biocomputation (NBC) i.e. computing with biological molecules as agents that are driven by molecular motors in microfluidic networks, is presented as an alternative approach to computing, data processing, and information technology.

Our work proposes a characterisation and testing methodology, as well as the relevant custom implementation, for measuring novel digital security circuits that use nanomaterial-based Physical Unclonable Functions (PUFs) as their security anchors. Although in this work we focus on PUFs that utilise the electrical characteristics of a crossbar structure of Carbon NanoTube (CNT) cells, the proposed methodology is applicable to most, if not all, PUFs that are based on similar crossbar structures of nanomaterials. Our work describes and discusses in detail the relevant characterisation and testing framework, while also presenting the corresponding mixed-signal circuit implementation, which can be utilised to provide a digital security token in an automated manner. Finally, preliminary results concerning the considered CNT PUFs are also presented, proving in this way the ability of the proposed framework to be utilised for the characterisation and testing of these PUFs, as well as for the implementation of security applications in the context of embedded systems and the Internet of Things (IoT), using nanomaterial-based PUFs in general.

In recent years there has been a steep increase in application and system complexity driven by trends such as Internet of Things (IoT), Industry 4.0 or autonomous driving. Hence, there is a massive demand for cyber-physical systems (CPS) merging sensoric, electronic and communication capabilities. Nanomaterials such as Carbon Nanotubes (CNTs) prospect significant added value for such systems, as they inherently feature low energy consumption, superior sensitivity for bio- , optical-, and mechanical sensing and even high amplification linearity in FETs. However, complemented new functionalities still rely on conventional system architectures requiring complementary metal oxide semiconductor (CMOS) based application-specific integrated circuits (ASICs) with the corresponding front-(FEOL) and back-end-of-line (BEOL). Hence, post-CMOS hetero-integration technologies for upgrading conventional IC’s with nanomaterial based devices is a highly promising path in the context of More than Moore scaling. At the example of condition monitoring, we demonstrate the applicability of CNT strain sensors towards holistic prognostic health monitoring (PHM) approaches of forthcoming electronic systems. Therefore, we develop a CMOS compatible technology platform for integrated CNT field-effect transistors (FETs) serving as the core building block for various system on chip (SOC) applications in analogue high frequency electronics, hardware security, biosensing or condition monitoring.

RF CNTFETs are one of the most promising devices for surpassing incumbent RF-CMOS technology in the near future. Experimental proof of concept that outperformed Si CMOS at the 130 nm technology has already been achieved with a vast potential for improvements. This review compiles and compares the different CNT integration technologies, the achieved RF results as well as demonstrated RF circuits. Moreover, it suggests approaches to enhance the RF performance of CNTFETs further to allow more profound CNTFET based systems e.g., on flexible substrates, highly dense 3D stacks, heterogeneously combined with incumbent technologies or an all-CNT system on a chip.

This work demonstrates modular integrability of CNT-based nanodevices on top of the BEOL interconnect stack of a conventional ASIC enabling additional condition monitoring features in the framework of advanced prognostic health monitoring concepts. We highlight in particular a Nanoelectromechanical system (NEMS) technology featuring suspended CNTs with controllable prestrain to ensure detectability of smallest strain variation along with changes in the packing environment. The NEMS is generated by a CMOS-compatible surface micromachining process flow making use of a relaxation of prestrained layer stacks after local removal of a sacrificial-layer. Corresponding critical dimensions and design are derived from FE-simulations. The impressed strain into the nanomaterial is confirmed by Raman spectroscopy. According to this analysis, the CNT specific G-band exhibits a clear blue shift of 6.2 cm-1 upon membrane release indicating on axially acting tensile strain between up to 0.8%. For the piezoresistive sensors this corresponds to a significant reduction of the strain detection limit to 30 MPa and gauge factor of up to 644, which is around 5 times higher than for conventional Si-based strain gauges.

The field of computer hardware stands at the verge of a revolution driven by recent breakthroughs in emerging nanodevices. “Nano Security” is a new Priority Program recently approved by DFG, the German Research Council. This initial-stage project initiative at the crossroads of nano-electronics and hardware-oriented security includes 11 projects with a total of 23 Principal Investigators from 18 German institutions. It considers the interplay between security and nano-electronics, focusing on a dichotomy which emerging nano-devices (and their architectural implications) have on system security. The projects within the Priority Program consider both: potential security threats and vulnerabilities stemming from novel nano-electronics, and innovative approaches to establishing and improving system security based on nano-electronics. This paper provides an overview of the Priority Program's overall philosophy and discusses the scientific objectives of its individual projects.

Next to powders, inks, and microelectronics, many technologies that carry the attribute nano in their name are still waiting for their breakthrough and wide acceptance in engineering and industry. At least nanofabrication technologies are the subject of a vivid track in research and development in a variety of scientific fields but yet most of them are mainly invisible in everyday products. This paper aims to describe three inspiring examples of research work in the area of nanopatterning and systems integration at the micro-nano interface to motivate applications with new and unprecedented functionalities. The application examples comprise the fields of bio-inspired computing, optoelectronic sensing, and spectral imaging. First, network-based biocomputing uses biological agents in a nanopatterned fluidic channel system and opens horizons for energy-efficient solutions to complex mathematical problems. Second, nanoelectronic devices based on carbon nanotubes (CNTs) have emerged because of the outstanding mechanical, electronic, and optical properties of the CNTs. The adaptivity of nanostructures to the world of biological molecules and other nanoscopic building blocks such as quantum dots and nanoparticles enables novel, even personalized, devices and technical solutions. Third, early-on "nano " fame has been devoted to optical effects-the authors here discuss an advanced integrated micro-opto-mechanical system on a micromirror plate forming a Fabry-Perot Interferometer.