Luca Maiolo

Flexible pH sensors based on polysilicon thin film transistors and ZnO nanowalls

A fully flexible pH sensor using nanoporous ZnO on extended gate thin film transistor (EGTFT) fabricated on polymeric substrate is demonstrated. The sensor adopts the Low Temperature Polycrystalline Silicon (LTPS) TFT technology for the active device, since it allows excellent electrical characteristics and good stability and opens the way towards the possibility of exploiting CMOS architectures in the future. The nanoporous ZnO sensitive film, consisting of very thin (20 nm) crystalline ZnO walls with a large surface-to-volume ratio, was chemically deposited at 90 °C, allowing simple process integration with conventional TFT micro-fabrication processes compatible with wide range of polymeric substrates. The pH sensor showed a near-ideal Nernstian response (∼59 mV/pH), indicating an ideality factor α ∼ 1 according to the conventional site binding model. The present results can pave the way to advanced flexible sensing systems, where sensors and local signal conditioning circuits will be integrated on the same flexible substrate.

PEDOT-CNT-Coated Low-Impedance, Ultra-Flexible, and Brain-Conformable Micro-ECoG Arrays

Electrocorticography (ECoG) is becoming a common tool for clinical applications, such as preparing patients for epilepsy surgery or localizing tumor boundaries, as it successfully balances invasiveness and information quality. Clinical ECoG arrays use millimeter-scale electrodes and centimeter-scale pitch and cannot precisely map neural activity. Higher-resolution electrodes are of interest for both current clinical applications, providing access to more precise neural activity localization and novel applications, such as neural prosthetics, where current information density and spatial resolution is insufficient to suitably decode signals for a chronic brain-machine interface. Developing such electrodes is not trivial because their small contact area increases the electrode impedance, which seriously affects the signal-to-noise ratio, and adhering such an electrode to the brain surface becomes critical. The most straightforward approach requires increasing the array conformability with flexible substrates while improving the electrode performance using materials with superior electrochemical properties. In this paper, we propose an ultra-flexible and conformable polyimide-based micro-ECoG array of submillimeter recording sites electrochemically coated with high surface area conductive polymer-carbon nanotube composites to improve their brain-electrical coupling capabilities. We characterized our devices both electrochemically and by recording from rat somatosensory cortex in vivo. The performance of the coated and uncoated electrodes was directly compared by simultaneously recording the same neuronal activity during multiwhisker deflection stimulation. Finally, we assessed the effect of electrode size on the extraction of somatosensory evoked potentials and found that in contrast to the normal high-impedance microelectrodes, the recording capabilities of our low-impedance microelectrodes improved upon reducing their size from 0.2 to 0.1 mm.

Ultraflexible Tactile Piezoelectric Sensor Based on Low-Temperature Polycrystalline Silicon Thin-Film Transistor Technology

In this paper, we present an ultraflexible tactile sensor, in a piezo-eletricoxide-semiconductor FET configuration, composed by a poly[vinylidenefluoride-co-trifluoroethylene] capacitor with an embedded readout circuitry, based on nMOS polysilicon electronics, integrated directly on polyimide. The ultraflexible device is designed according to an extended gate configuration. The sensor exhibits enhanced piezoelectric properties, thanks to the optimization of the poling procedure (with electric field up to 3 MV/cm), reaching a final piezoelectric coefficient d33 of 47 pC/N. The device has been electromechanically tested by applying perpendicular forces with a minishaker. The tactile sensor, biased in a common-source arrangement, shows a linear response to increasing sinusoidal stimuli (up to 2 N) and increasing operating frequencies (up to 1200 Hz), obtaining a response up to 430 mV/N at 200 Hz for the sensor with the highest value of d33. The sensor performances were also tested after several cycles of controlled bending in different amount of humidity with the intent to investigate the device behavior in real conditions.

Wearable band for hand gesture recognition based on strain sensors

A novel fully wearable system based on a smart wristband equipped with stretchable strain gauge sensors and readout electronics have been assembled and tested to detect a set of movements of a hand crucial in rehabilitation procedures. The high sensitivity of the active devices embedded on the wristband do not need a direct contact with the skin, thus maximizing the comfort on the arm of the tester. The gestures done with the device have been auto-labeled by comparing the signals detected in real-time by the sensors with a commercial infrared device (Leap motion). Finally, the system has been evaluated with two machine-learning algorithms Linear Discriminant Analysis (LDA) and Support Vector Machine (SVM), reaching a reproducibility of 98% and 94%, respectively.

Disordered array of Au covered Silicon nanowires for SERS biosensing combined with electrochemical detection

We report on highly disordered array of Au coated silicon nanowires (Au/SiNWs) as surface enhanced Raman scattering (SERS) probe combined with electrochemical detection for biosensing applications. SiNWs, few microns long, were grown by plasma enhanced chemical vapor deposition on common microscope slides and covered by Au evaporated film, 150 nm thick. The capability of the resulting composite structure to act as SERS biosensor was studied via the biotin-avidin interaction: the Raman signal obtained from this structure allowed to follow each surface modification step as well as to detect efficiently avidin molecules over a broad range of concentrations from micromolar down to the nanomolar values. The metallic coverage wrapping SiNWs was exploited also to obtain a dual detection of the same bioanalyte by electrochemical impedance spectroscopy (EIS). Indeed, the SERS signal and impedance modifications induced by the biomolecule perturbations on the metalized surface of the NWs were monitored on the very same three-electrode device with the Au/SiNWs acting as both working electrode and SERS probe.

AlN texturing and piezoelectricity on flexible substrates for sensor applications

We show that AlN-based piezocapacitors with relatively high piezoelectric coefficient (d33) values (3–4 pC/N) can be fabricated on polyimide (PI) substrates at 160 °C or even at room temperature by sputtering processes. With respect to PI, a reduction of the piezoelectric performances was observed on polyethylene naphthalate (PEN). With the same approach, a d33 value as high as 8 pC/N was achieved on rigid substrates (SiO2/Si). In all cases, a thin Al buffer layer was deposited, immediately before AlN, without breaking the vacuum in the deposition chamber, in order to preserve the interface from contaminations that would obstruct the optimal atomic stratification with the desired [0001] growth axis. The piezoelectric behavior was thus correlated to the degree of texturing of the AlN layer through the evaluation of the XRD texturing coefficients and to the morphology by means of AFM analyses. We show that a high level of roughness introduced by the PEN substrate, coupled with the effect of the substrate fl...

Role of gate oxide thickness in controlling short channel effects in polycrystalline silicon thin film transistors

The drain bias induced threshold voltage variation in short channel (L=0.4 μm) polycrystalline silicon thin-film transistors (TFTs), with different gate oxide thicknesses, is investigated with combined experimental measurements and numerical simulations. Drain-induced barrier lowering (DIBL) and floating body effects (FBEs), triggered by impact ionization, are the main causes of such variations. However, the effects are counterbalancing, with a reducing oxide thickness reducing DIBL, while, at the same time, increasing the relative impact of the FBE. Hence, drain bias induced threshold voltage changes, when normalized by oxide thickness, are independent of the gate oxide thickness in these TFTs.

Analysis of Kink Effect and Short Channel Effects in Fully Self-Aligned Gate Overlapped Lightly Doped Drain Polysilicon TFTs

Electrical characteristics of fully self-aligned gate overlapped lightly doped drain (FSA-GOLDD) polysilicon TFTs, fabricated with a spacer technology providing submicron (0.35 μm) LDD regions, have been analyzed by using two-dimensional numerical simulations. The numerical analysis was used to explain the observed reduced kink effect and short channel effects presented by FSA GOLDD devices, compared to SA devices. The reduction of the kink effect has been attributed to the reduced impact ionization rate, and related to reduced electric fields at the channel/LDD junction. In addition, the role of the LDD dose on the kink effect has been also investigated, clarifying the observed current inflection occurring in the kink effect regime and the LDD dose dependence of the breakdown. Reduced short channel effects were attributed to reduced floating body effects, since drain induced barrier lowering was apparently not affected by the SA GOLDD structure, when compared to SA devices.

Wireless sensor networks and safe protocols for user tracking in human-robot cooperative workspaces

Workers protection in collaborative industrial robotics application represents the predominant aspect of robot safety in production systems. Flexible production systems and multimodal human-robot interactions often encompass cooperative tasks that are performed in fenceless configurations. Collaborative open workspaces enable, in fact, a workflow of continuously interchangeable tasks done by operators or by robot at close distance or using hand-guided modes. Layout and workflow optimization may, in fact, require a co-presence in some shared spaces whose safeguarding (e.g. robot speed limitations, distances) is conservatively restricted by the current standards. In such scenarios, the tracking of operators is mandatory for the overall assessment of the system safety. In this work, a combination of wireless sensing technologies, highly robust wireless protocols and safe computation over a standard ethernet IP (black channel) concur to improve the functional safety of a cooperative robotic system. The system architecture and data framework are in particular discussed with reference to the properties of the communication protocols implementing the safety layer.

Ultra-flexible and brain-conformable micro-electrocorticography device with low impedance PEDOT-carbon nanotube coated microelectrodes

Electrocorticography, thanks to its low degree of invasiveness, has received in recent years an increasing attention for chronic brain-machine interface applications. To be up to the task, electrocorticography electrode arrays can benefit from several improvements. Better recording abilities can be obtained through smaller, low impedance and high density electrodes, while conformability can provide superior adhesion to the cortex surface and lower biological impact. In this work we present an ultra-flexible and brain-conformable polyimide-based micro-ECoG array with low-impedance poly(3,4-ethylenedioxythiophene) (PEDOT)-carbon nanotube coated microelectrodes. A first in vivo validation of our device is performed on rat somatosensory cortex.