Cristian Collini

Towards Tactile Sensing System on Chip for Robotic Applications

This paper presents the research on tactile sensing system on chip. The tactile sensing chips comprise of 5 × 5 array of Piezoelectric Oxide Semiconductor Field Effect Transistor (POSFET) devices and temperature sensors. The POSFET devices are obtained by spin coating piezoelectric polymer, poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), films directly on to the gate area of Metal Oxide Semiconductor (MOS) transistors. The tactile sensing chips are able to measure dynamic contact forces and temperatures. The readout and the data acquisition system to acquire the tactile signals are also presented. The chips have been extensively tested over wide range of dynamic contact forces and temperatures and the experimental results are presented. The paper also reports the research on tactile sensing chips with POSFET array and the integrated electronics.

Tactile Sensing Chips With POSFET Array and Integrated Interface Electronics

PThis paper presents the advanced version of novel piezoelectric oxide semiconductor field effect transistor (POSFET) devices-based tactile sensing chip. The new version of the tactile sensing chip presented here comprises of a 4 × 4 array of POSFET touch sensing devices and integrated interface electronics (i.e., multiplexers, high compliance current sinks, and voltage output buffers). The chip also includes four temperature diodes for the measurement of contact temperature. Various components on the chip have been characterized systematically and the overall operation of the tactile sensing system has been evaluated. With new design, the POSFET devices have improved performance [i.e., linear response in the dynamic contact forces range of 0.01-3 N and sensitivity (without amplification) of 102.4 mV/N], which is more than twice the performance of their previous implementations. The integrated interface electronics result in reduced interconnections which otherwise would be needed to connect the POSFET array with off-chip interface electronic circuitry. This paper paves the way for CMOS implementation of full on-chip tactile sensing systems based on POSFETs.

Planar Silicon-Polydimethylsiloxane Optofluidic Ring Resonator Sensors

We report an optofluidic ring resonator sensor based on liquid-core hybrid silicon-polymer waveguides. The device features a planar layout that combines optical and fluidic functions on the same platform. A high quality factor of 1.44 × 104 is achieved. The device resonant wavelength shift has been measured as a function of the water-core temperature, obtaining a temperature sensitivity of 0.0633 nm/°C. Based on the thermo-optic effect of water, this corresponds to a bulk refractive index (RI) sensitivity of ~700 nm per RI unit (RIU), resulting in the RI limit of detection of ~1.57 × 10-6 RIU. The planar architecture combined with an optofluidic design concept holds the promise of high functionality and compactness toward a complete on-chip integrated sensing system.

Bendable ultra-thin silicon chips on foil

This work presents research towards obtaining ultra-thin silicon chips (flex-chips) on flexible foils through post-processing steps. The flex-chips are obtained by chemically thinning down the silicon and then transferring the chips to polyimide foils. The transfer printing approach that has thus far been used to transfer quasi 1-D structures such as wires and ribbons, has been adapted in this work to transfer various large sized (width of chips ranging from 4.5mm to 1.5cm and the length ranging from 8mm to 3.6cm) and ultra-thin (thickness ≈ 15μm) chips. The flex-chips contain passive devices, whose resistances do not show any appreciable change on bending, at least in the testing range of radius of curvature 9mm and above. The distinct advantages of the work presented here are attaining bendability through postprocessing of chips, low-cost of fabrication, and east transferring of chips to the flexible substrates without using conventional and sophisticated equipment such as pick-an-place set up.

Super-Hydrophilic PDMS and PET Surfaces for Microfluidic Devices

In this work the effect of air plasmas on wettability of Polydimethylsiloxane (PDMS) and polyethylene terephthalate (PET) was studied. These polymers are widely used materials in the fabrication of microfluidic devices. The microfluidic system fabricated from native PET and PDMS requires active pumping mechanism, due to a low hydrophilic surface behavior. To render hydrophilic and increase the capillary flow into the device, plasma treatments can be used. Air plasma treatment is an interesting technology for microfluidic fields due to simplicity of use and low cost. This study describes the effect of the working plasma pressure on wettability of polymers. The polymers were treated by RF plasma and the wettability was studied by means of sessile contact angle. The results established that the air plasma can increase the wettability of both polymers. Moreover we demonstrated that by optimizing the working pressure a superhydrophilic surface (with a contact angle less than 5°) can be obtained. The findings suggest that air plasma treatments are a suitable technology to enhance polymers surface wetting performance for microfluidic devices.

POSFET touch sensor with on-chip electronic module for signal conditioning

This paper presents the design, fabrication and evaluation of the new version of POSFET (Piezoelectric Oxide Semiconductor Field Effect Transistor) touch sensing device based tactile sensing chip. Implemented using CMOS (Complementary Metal Oxide Semiconductor) technology, the chip consists of POSFET device and the integrated bias (a high compliance current sink) circuitry. The high compliance current sink provides the current IDS for the POSFET devices. The performance of tactile sensing chip has been evaluated in the dynamic contact forces range of 0.01–3 N and the sensitivity of POSFET devices (without amplification) is 102.4 mV/N.

The development of sol–gel derived TiO2 thin films and corresponding memristor architectures

We report the development of sol–gel derived TiO2 thin films with adjustable and defined properties suitable for memristive cell fabrication. Memristive cells were developed by the sol–gel deposition of titania onto SiO2/Ti/Pt engineered electrodes via spin coating, followed by diverse curing and annealing procedures. The influence of the processing conditions and the sols chemical composition on the film properties, and therefore on the memristive response, was studied by micro-Raman and transmission spectroscopies, profilometry, ellipsometry, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and X-ray absorption and diffraction spectroscopies (XAS and XRD). A memristive response was acquired from a number of these cells, revealing a dependence of the electrical behavior on minor changes in the TiO2 structure, electroforming parameters, and architecture. Thus, these properties provide a handle for fine-tuning electrical performance.

Development of an integrated electrochemical system for in vitro yeast viability testing

This work describes the development and testing of a microfabricated sensor for rapid cell growth monitoring, especially focused on yeast quality assessment for wine applications. The device consists of a NMOS ISFET sensor with Si(3)N(4) gate, able to indirectly monitor extracellular metabolism through pH variation of the medium, and a solid-state reference electrode implemented with PVC membranes doped with lipophilic salts (tetrabutylammonium-tetrabutylborate (TBA-TBB) and Potassium tetrakis(4-chlorphenyl)borate (KTClpB)). The use of a solid state reference electrode enables the implementation of a large number of cell assays in parallel, without the need of external conventional reference electrodes. Microbial growth testing has been performed both in standard culture conditions and on chip at different concentrations of ethanol in order to carry out a commonly used screening of wine yeast strains. Cell growth tests can be performed in few hours, providing a fast, sensitive and low cost analysis with respect to the conventional procedures.

Sol-gel synthesis and characterization of undoped and Al-doped ZnO thin films for memristive application

The Sol-gel route is a versatile method to fabricate multi-layer, dense and homogeneous ZnO thin films with a controlled thickness and defects for a memristive application. In this work, sol-gel derived multi-layer undoped and Al-doped ZnO thin films were prepared by a spin-coating technique on SiO2/Ti/Pt and silica glass substrates. The effect of both Al doping and curing conditions on the structural and morphological features of ZnO films was investigated by complementary techniques, including electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, micro-Raman spectroscopy, and X-ray diffraction analysis. Electrical measurements were performed on SiO2/Ti/Pt/ZnO/Pt(dishes) and SiO2/Ti/Pt/ZnO(Al)/Pt(dishes) fabricated memristive cells and preliminary current-voltage curves were acquired.

Smart contact lens using passive structures

The surface of our eye is an interesting chemical interface, which acts like a window into the human body. For example, intraocular pressure is a surrogate marker of cardiovascular health. Just like the blood, the eye tear contains many health parameters which could be used to diagnose. Therefore, a contact lens with integrated biosensors could provide health professionals with a new tool for research studies and for diagnosing diseases in a novel way without traditional lab works. For this reason, the smart multi-purpose contact lenses have recently attracted attention. Motivated by this fact, we aim to integrate biosensors on contact lens to sense the eye tear film solution. In this work we aim to report the patterning of gold electrodes on PDMS. The micro-fabrication techniques are discussed together with various characterization techniques performed on the electrode patterns.