The ability to measure subtle changes in arterial pressure using devices mounted on the skin can be valuable for monitoring vital signs in emergency care, detecting the early onset of cardiovascular disease and continuously assessing health status. Conventional technologies are well suited for use in traditional clinical settings, but cannot be easily adapted for sustained use during daily activities. Here we introduce a conformal device that avoids these limitations. Ultrathin inorganic piezoelectric and semiconductor materials on elastomer substrates enable amplified, low hysteresis measurements of pressure on the skin, with high levels of sensitivity (~0.005 Pa) and fast response times (~0.1 ms). Experimental and theoretical studies reveal enhanced piezoelectric responses in lead zirconate titanate that follow from integration on soft supports as well as engineering behaviours of the associated devices. Calibrated measurements of pressure variations of blood flow in near-surface arteries demonstrate capabilities for measuring radial artery augmentation index and pulse pressure velocity.

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Conformable amplified lead zirconate titanate sensors with enhanced piezoelectric response for cutaneous pressure monitoring

Transparent ceramics: Processing, materials and applications

The accumulation of various contaminants in air, soil and water is threatening the natural environment. The remediation of the environmental contaminations is today an urge. Among the remediation methods employed, advanced oxidation processes (AOPs) are a class of techniques based on the in situ generation of highly reactive and oxidizing radical species which can destroy most of the organic pollutants. AOPs driven by light are found to be the most popular for wastewater treatment due to the abundance of solar light in some regions. The removal of organic contaminants using semiconductor-based photocatalysts has been extensively investigated. However, low charge carrier mobility and rapid electron-hole pair recombination are the common problems that limit the semiconductor-based photocatalysis. Although a large number of alternative systems have been investigated, electron–hole pair separation is still too low in photocatalytic systems. A new concept was introduced recently in which the built-in electric field by ferroelectric, pyroelectric and piezoelectric effects in photocatalytic particles was exploited to enhance the separation of photoinduced charge carriers. Among these new systems that are still under investigation, the use of piezoelectric materials in the photodegradation of pollutants recently drew a lot of attention for environmental remediation. Due to the non-centrosymmetric nature, the piezoelectric materials demonstrate unique catalytic properties as a result of the creation of the built-in electric field by the dipole polarization. This latter provides a driving force for the transport of the photoinduced charge carriers enabling their separation. This review covers the use of piezoelectric materials in photocatalysis and catalysis, especially piezoelectric-catalysis, for environmental remediation. The paper details the fundamentals and basic properties of ferroelectric, pyroelectric and piezoelectric materials. The effect of the built-in electric field in these materials on the photocatalysis/catalysis charge carrier separation is discussed. Possible applications of piezoelectric materials in environmental remediation are reviewed and discussed taking into account several different aspects such as the kinetics of the degradation of the organic pollutants and water splitting. Finally, the current research trends and future prospects of piezocatalysis and piezophotocatalysis are discussed.

Piezoelectric materials for catalytic/photocatalytic removal of pollutants: Recent advances and outlook

In this review article, new systems being investigated for application in solid oxide fuel cells are discussed. For the electrode materials, materials with the perovskite or related structures continue to dominate the field, due to the need for high electronic conductivity. Research in this field is being directed toward compositions allowing high ionic conductivity in addition to their electronic contribution. In contrast, research on new electrolyte materials has shown a diverse range of structure-types, with an apparent tendency toward structures containing cations in lower coordination environments, particularly tetrahedral. In both the electrode and electrolyte area, materials allowing the incorporation of oxygen excess into interstitial sites have shown promising results, warranting further investigations of materials that will allow this type of defect chemistry.

New Chemical Systems for Solid Oxide Fuel Cells

Phase structure and properties of sodium bismuth titanate lead-free piezoelectric ceramics

Low Temperature Co-fired Ceramics (LTCC) is one of the microelectronic techniques. This technology was initially developed as an alternative to Printed Circuit Boards (PCB) and classical thick-film technology, and it has found application in the fabrication of multilayer ceramic boards for electronic devices. Fast and wide development of this technology permitted the fabrication of 3D mechanical structures and integration with various different processes. Thanks to this, LTCC has found application in the manufacturing of various microelectronic devices. This paper presents an overview on LTCC technology and gives a detailed summary on physical quantity sensors fabricated using LTCC technique.

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Overview on low temperature co-fired ceramic sensors

The attachment of the silicon piezoresistive pressure-sensor die to the ceramic substrate is one of the most critical steps in the production of highly accurate low-pressure sensor modules. In this paper process-induced residual stresses that adversely influence the sensor’s performance are analysed. The effect of the process parameters was first estimated using a virtual prototyping approach. A finite-element analysis (FEA) was performed in order to reveal the distribution of residual stresses in the silicon sensor die introduced by the polymer adhesive during the curing and to identify the construction and material parameters that influence the variability of the sensor’s output characteristics. The most significant factors that have an influence on the sensor’s characteristics were determined using the design-of-experiment (DOE) procedure. Optimum levels as well as the worst-case selection of the chosen main factors were chosen for the preparation of the real prototypes designed for further experimental analysis and verification of the obtained numerical results. The experimental case study confirmed the adequacy of the applied numerical approach. As a result, optimum process parameters were determined.

Residual stresses in a pressure-sensor package induced by adhesive material during curing: a case study

The oscillation test methodology is presented for active RC filters. The authors develop general guidelines for the design of the oscillation-based test structures and describe in more detail test transformations of filter configurations which are most frequently used in practice. Frequency measurements performed on some implemented test structures and fault detection experimental results are included. The oscillation-based test described in the paper is primarily intended for field testing. In some cases, it can also be used as a functional go no-go test in production. The presented test structures can also be employed for stimulus generation in a built-in self-test.

Design of oscillation-based test structures for active RC filters

Summary form only given. We apply the oscillation-based test strategy to test active RC filters. We develop general guidelines for the design of the oscillation-based test structures and describe in more details the resonator active filler (biquad filter) configuration. It can be shown that some of the derived structures are achieved by simple circuit modification while for the more general case additional feedback loop network is required.

Laminated 3D structures made using low-temperature co-fired ceramic (LTCC) technology are practical for ceramic micro-electro-mechanical systems (C-MEMS). The sensors for mechanical quantities, and/or actuators, are fundamental parts of MEMS. Thick-film resistors can be used to sense the mechanical deformations, and thick-film piezoelectric materials can be used as electro-mechanical transducers in a C-MEMS structure. The integration of these thick-film materials on LTCC substrates is in some cases difficult to realise due to interactions with the rather glassy LTCC substrates. The subject of our work is an investigation of thick-film materials for electro-mechanical transducers (sensors and actuators) and their compatibility with LTCC substrates. Resistors made with commercial thick-film resistor materials for use as sensors on LTCC substrates have been investigated and evaluated. Ferroelectric ceramic materials based on solid solutions of lead zirconate titanate (PZT) with low firing temperatures around 850°C were developed for thick-film technology and evaluated on LTCC substrates.

Marina Santo Zarnik

Papers

Overview on low temperature co-fired ceramic sensors

Residual stresses in a pressure-sensor package induced by adhesive material during curing: a case study

Design of oscillation-based test structures for active RC filters

Design of oscillation-based test structures for active RC filters

The application of thick-film technology in C-MEMS