Flavio Giacomozzi

Bio: Flavio Giacomozzi is an academic researcher from fondazione bruno kessler. The author has contributed to research in topics: Surface micromachining & Capacitive sensing. The author has an hindex of 19, co-authored 120 publications receiving 1147 citations.

Symmetric toggle switch—a new type of rf MEMS switch for telecommunication applications: Design and fabrication

Abstract: In this paper, we present a new type of rf MEMS switch with low actuation voltage and high isolation, for high rf power and reliability applications in telecommunication. ‘Symmetric toggle switch’ (STS) is based on push–pull mechanism and utilizes torsion springs and levers, placed symmetrically and transverse to CPW line. The switches designed for 8–14 GHz applications have analytically calculated and FEM simulated actuation voltages in the range of 8–10 V. The simulated insertion loss and isolation for the devices are 0.25 and 35 dB, respectively, at 10 GHz. The fabrication process and preliminary experimental results are also presented.

Stress characterization of electroplated gold layers for low temperature surface micromachining

Abstract: In this work, the stress of electroplated gold films has been analyzed versus plating current density and bath temperature. Two different plating solutions have been adopted, one being based on cyanide-gold salt, the other on sulfite-gold. Gold surface quality was investigated in the experimented range of plating temperature and current density, in order to control the limit conditions for plating: surface roughness and non-uniformity appear whenever deposition parameters are brought to the limit (typically below 2 mA/cm/sup 2/ and above 5 mA/cm/sup 2/). Plated gold stress measurement was carried out by wafer curvature comparison, before and after deposition, using Stoney's formula for thin films/sup 1,2/. A current density range between 1.5 and 6 mA/cm/sup 2/ and temperature range between 50 and 70/spl deg/C was investigated. Stress analysis was also carried out on a Cr-Au multilayer, which actually is the structural layer employed for gold microstructures: the multilayer consists of a chromium adhesion layer, a PVD gold seed layer and a plated gold layer, with thickness respectively 10 nm, 150 nm and 1500 nm. A range of stress was obtained, varying from tensile to compressive: cyanide bath yielded stress from -30 MPa to about 0 MPa, and sulfite bath showed stress between -90 MPa and 110 MPa. Stress variation induced by thermal treatments after deposition was also investigated, by examining the effect of photoresist sacrificial etching on the internal stress of chromium-gold structural layers: the final stress was about 180 MPa tensile for all samples, regardless the as-deposited stress, with a variation ranging from about 80 MPa to more than 200 MPa.

Controlling stress and stress gradient during the release process in gold suspended micro-structures

Abstract: In this paper it will be demonstrated that the conditions of the final release process in oxygen plasma strongly influence the shape of suspended gold micro-structures. Both single-clamped and double-clamped cantilever test devices have been examined. The structures have typically a thickness of 1.8 μm, and are produced by patterned gold electrodeposition above a sacrificial photoresist layer which is then removed by oxygen plasma ashing. In general, deformations are strongly reduced lowering the temperature, but the release time increases abruptly. A simple model is presented to explain the experimental observation, and from it can be deduced that yield and inelastic relaxation are critical phenomena responsible for most of the deviations from the ideal planar shape of MEMS structures. To overcome these unwanted effects, the parameters to be optimized are mainly the initial stress value, the release temperature and the vertical structural homogeneity of the gold layer.

Development of a low-power thick-film gas sensor deposited by screen-printing technique onto a micromachined hotplate

Abstract: We report on the design, implementation and characterisation of a thick-film gas sensor deposited for the first time by screen-printing technique onto a micromachined hotplate, the microheater maintains a film temperature as high as 400°C with 2 was achieved by computer-aided screen-printing. The films were then fired through the microheater itself to guarantee thermodynamic stability for long time exploitation. The response of the device to CO, CH 4 and NO 2 at concentrations typical for indoor and outdoor applications was recorded by measuring the film resistance through ultra high impedance CMOS circuit.

A MEMS-Reconfigurable Power Divider on High Resistivity Silicon Substrate

Abstract: This paper presents a MEMS-reconfigurable power divider on high resistivity silicon substrate with variable power ratio. The circuit is based on two cascaded hybrid couplers connected through a tunable phase shifter that produces the required power ratio. A 5 state prototype has been fabricated on a 525 m high resistivity silicon substrate employing two 3 dB branch line couplers and a reflection-line MEMS phase shifter. The latter is reconfigured through two MEMS-switched open ended lines, whose lengths can be varied through the actuation of eight ohmic contact MEMS switches. Measurements of the MEMS switch show an isolation and an insertion loss better than 15 dB and 0.2 dB, respectively, with a contact resistance lower than 1 Ohm in the entire power divider bandwidth. RF measurements of the power divider exhibit a return loss better than 16 dB and an isolation better than 17 dB in the bandwidth [11.8-12.2] GHz with nominal power ratios of 1:0, 6:1,1:1,1:6, and 0:1.

Hydrogen Sensors - A review

Abstract: Hydrogen sensors are of increasing importance in connection with the development and expanded use of hydrogen gas as an energy carrier and as a chemical reactant. There are an immense number of sensors reported in the literature for hydrogen detection and in this work these sensors are classified into eight different operating principles. Characteristic performance parameters of these sensor types, such as measuring range, sensitivity, selectivity and response time are reviewed and the latest technology developments are reported. Testing and validation of sensor performance are described in relation to standardisation and use in potentially explosive atmospheres so as to identify the requirements on hydrogen sensors for practical applications.

Instability of metal oxide-based conductometric gas sensors and approaches to stability improvement (short survey)

Abstract: In the present brief review modern views on the reasons of time instability of gas sensors parameters, as well as approaches, which could be used for the improvement of this important sensor's parameter, are summarized. In particular, the influence of factors such as structure transformation, phase transformation, poisoning, degradation of contacts and heaters, bulk diffusion, errors in design, change of humidity, fluctuations of temperature in the surrounding atmosphere, and interference effect was analyzed. It was shown that while designing devices such as solid-state gas sensors, there are no secondary issues or tasks—all are important. Sensors work in extreme temperatures in the presence of active gases, and therefore every element of the sensor could be responsible for its long-term stability. The conclusions, regarding the efficiency of approaches such as optimization of technological processes and optimization of exploitation processes used for improvement of stability of conductometric metal oxide gas sensors, were made as well.

Materials as Machines

Abstract: Machines are systems that harness input power to extend or advance function. Fundamentally, machines are based on the integration of materials with mechanisms to accomplish tasks-such as generating motion or lifting an object. An emerging research paradigm is the design, synthesis, and integration of responsive materials within or as machines. Herein, a particular focus is the integration of responsive materials to enable robotic (machine) functions such as gripping, lifting, or motility (walking, crawling, swimming, and flying). Key functional considerations of responsive materials in machine implementations are response time, cyclability (frequency and ruggedness), sizing, payload capacity, amenability to mechanical programming, performance in extreme environments, and autonomy. This review summarizes the material transformation mechanisms, mechanical design, and robotic integration of responsive materials including shape memory alloys (SMAs), piezoelectrics, dielectric elastomer actuators (DEAs), ionic electroactive polymers (IEAPs), pneumatics and hydraulics systems, shape memory polymers (SMPs), hydrogels, and liquid crystalline elastomers (LCEs) and networks (LCNs). Structural and geometrical fabrication of these materials as wires, coils, films, tubes, cones, unimorphs, bimorphs, and printed elements enables differentiated mechanical responses and consistently enables and extends functional use.

Piezoelectric Polymer and Paper Substrates: A Review

Abstract: Polymers and papers, which exhibit piezoelectricity, find a wide range of applications in the industry. Ever since the discovery of PVDF, piezo polymers and papers have been widely used for sensor and actuator design. The direct piezoelectric effect has been used for sensor design, whereas the inverse piezoelectric effect has been applied for actuator design. Piezo polymers and papers have the advantages of mechanical flexibility, lower fabrication cost and faster processing over commonly used piezoelectric materials, such as PZT, BaTiO3. In addition, many polymer and paper materials are considered biocompatible and can be used in bio applications. In the last 20 years, heterostructural materials, such as polymer composites and hybrid paper, have received a lot of attention since they combine the flexibility of polymer or paper, and excellent pyroelectric and piezoelectric properties of ceramics. This paper gives an overview of piezoelectric polymers and papers based on their operating principle. Main categories of piezoelectric polymers and papers are discussed with a focus on their materials and fabrication techniques. Applications of piezoelectric polymers and papers in different areas are also presented.