Inkjet-printed graphene Hall mobility measurements and low-frequency noise characterization

We report room-temperature Hall mobility measurements, low-temperature magnetoresistance analysis, and low-frequency noise characterization of inkjet-printed graphene films on fused quartz and SiO2/Si substrates. We found that thermal annealing in vacuum at 450 ◦C is a necessary step in order to stabilize the Hall voltage across the devices, allowing their electrical characterization. The printed films present a minimum sheet resistance of 23.3 Ω/sq after annealing, and are n-type doped, with carrier concentrations in the low 1020 cm−3 range. The charge carrier mobility is found to increase with increasing film thickness, reaching a maximum value of 33 cm2 V−1 s−1 for a 480 nm-thick film printed on SiO2/Si. Low-frequency noise characterization shows a 1/f noise behavior and a Hooge parameter in the range of 0.1 – 1. These results represent the first in-depth electrical and noise characterization of transport in inkjet-printed graphene films, able to provide physical insights on the mechanisms at play

Fabrication and characterization of electronic devices based on inkjet-printed two-dimensional materials

Thanks to their electrical, mechanical and optical properties, two-dimensional materials are promising candidates for the next generation of flexible and wearable electronic systems. The liquid phase exfoliation technique enables the production, on a large scale and at low cost, of a wide variety of two-dimensional materials in solution. Inkjet printing offers a fast and low-cost method for the deposition of two-dimensional materials in solution. However, several issues need to be addressed to achieve high performance electronic devices using this technology. In this thesis, water-based inks of two-dimensional materials have been used for the fabrication of inkjet printed electronic devices. First, the electrical properties of printed films of two-dimensional materials have been studied, in particular graphene and hexagonal boron nitride. The following part is based on the fabrication of field-effect transistors on paper substrate, initially by means of fully inkjet printed solutions, using graphene as channel material. Secondly, a hybrid approach has been adopted, in which the channel is molybdenum disulfide synthesized by chemical vapor deposition and then transferred on paper, while the other components of the device are printed. A detailed analysis of electrical low-frequency noise has also been carried out on these latter devices

Caratterizzazione e simulazione di sensori di velocità delle particelle acustiche CMOS compatibili

In questa tesi verranno descritti ed analizzati dei sensori di velocità delle particelle acustiche CMOS compatibili, basati su un principio di trasduzione termica. Particolare attenzione sarà rivolta alla caratterizzazione del rumore elettrico del sensore, che costituisce un aspetto di fondamentale importanza perché concorre a determinare il minimo segnale rilevabile dal sensore stesso. I sensori di velocità acustica CMOS compatibili fin qui realizzati hanno mostrato una bassa sensibilità; in questo lavoro verrà analizzata l’influenza dei vari parametri di progetto sul comportamento del sensore, con l’obiettivo di massimizzare la sensibilità e la risposta in frequenza, caratteristiche fondamentali per rendere il sensore effettivamente utilizzabile. Questa tesi è strutturata in quattro capitoli. Nel capitolo 1, dopo una breve introduzione all’acustica, verrà fornita una panoramica dei sensori acustici, con particolare attenzione all’unico sensore di velocità acustiche ad oggi commercialmente disponibile: il Microflown. Verranno inoltre discussi gli ambiti applicativi nei quali i sensori di velocità acustiche possono essere impiegati. Nel capitolo 2 si introdurranno i sensori di velocità acustica CMOS compatibili: saranno descritti il loro principio di funzionamento, la loro realizzazione tecnologica e le diverse versioni realizzate fino ad oggi. Nel capitolo 3 verranno documentate le misure di rumore effettuate sull’ultima versione del sensore. Nel capitolo 4 verranno infine descritte le simulazioni numeriche sviluppate per analizzare la dipendenza delle caratteristiche del sensore dai parametri di progetto e saranno forniti i risultati ottenuti

Water-based 2-dimensional anatase TiO 2 inks for printed diodes and transistors

2-Dimensional (2D) materials are attracting strong interest in printed electronics because of their unique properties and easy processability, enabling the fabrication of devices with low cost and mass scalable methods such as inkjet printing. For the fabrication of fully printed devices, it is of fundamental importance to develop a printable dielectric ink, providing good insulation and the ability to withstand large electric fields. Hexagonal boron nitride (h-BN) is typically used as a dielectric in printed devices. However, the h-BN film thickness is usually above 1 μm, hence limiting the use of h-BN in low-voltage applications. Furthermore, the h-BN ink is composed of nanosheets with broad lateral size and thickness distributions, due to the use of liquid-phase exfoliation (LPE). In this work, we investigate anatase TiO2 nanosheets (TiO2-NS), produced by a mass scalable bottom-up approach. We formulate the TiO2-NS into a water-based and printable solvent and demonstrate the use of the material with sub-micron thickness in printed diodes and transistors, hence validating the strong potential of TiO2-NS as a dielectric for printed electronics

All-2D Material Inkjet-Printed Capacitors: Toward Fully Printed Integrated Circuits

A well-defined insulating layer is of primary importance in the fabrication of passive ( e.g., capacitors) and active ( e.g., transistors) components in integrated circuits. One of the most widely known two-dimensional (2D) dielectric materials is hexagonal boron nitride (hBN). Solution-based techniques are cost-effective and allow simple methods to be used for device fabrication. In particular, inkjet printing is a low-cost, noncontact approach, which also allows for device design flexibility, produces no material wastage, and offers compatibility with almost any surface of interest, including flexible substrates. In this work, we use water-based and biocompatible graphene and hBN inks to fabricate all-2D material and inkjet-printed capacitors. We demonstrate an areal capacitance of 2.0 ± 0.3 nF cm-2 for a dielectric thickness of ∼3 μm and negligible leakage currents, averaged across more than 100 devices. This gives rise to a derived dielectric constant of 6.1 ± 1.7. The inkjet printed hBN dielectric has a breakdown field of 1.9 ± 0.3 MV cm-1. Fully printed capacitors with sub-micrometer hBN layer thicknesses have also been demonstrated. The capacitors are then exploited in two fully printed demonstrators: a resistor-capacitor (RC) low-pass filter and a graphene-based field effect transistor