Integrated sensors for process monitoring and health monitoring in microsystems

This thesis presents the development of integrated sensors for health monitoring in Microsystems, which is an emerging method for early diagnostics of status or “health” of electronic systems and devices under operation based on embedded tests. Thin film meander temperature sensors have been designed with a minimum footprint of 240 m × 250 m. A microsensor array has been used successfully for accurate temperature monitoring of laser assisted polymer bonding for MEMS packaging. Using a frame-shaped beam, the temperature at centre of bottom substrate was obtained to be ~50 ºC lower than that obtained using a top-hat beam. This is highly beneficial for packaging of temperature sensitive MEMS devices. Polymer based surface acoustic wave humidity sensors were designed and successfully fabricated on 128° cut lithium niobate substrates. Based on reflection signals, a sensitivity of 0.26 dB/RH% was achieved between 8.6 %RH and 90.6 %RH. Fabricated piezoresistive pressure sensors have also been hybrid integrated and electrically contacted using a wire bonding method. Integrated sensors based on both LiNbO3 and ZnO/Si substrates are proposed. Integrated sensors were successfully fabricated on a LiNbO3 substrate with a footprint of 13 mm × 12 mm, having multi monitoring functions for simultaneous temperature, measurement of humidity and pressure in the health monitoring applications

Flexible pressure sensors for integration into karate body protector

The increasing interest in karate has also attracted the attention of researchers, especially in combining the equipment used by practitioners with technology to prevent injuries, improve technical skills and provide appropriate scoring. Contrary to the sport of taekwondo, the development of a smart body protector in the sport of karate is still a niche field to be researched. This study focused on developing piezoresistive, textile-based pressure sensors using piezoresistive film, conductive fabric as well as different bonding materials and methods. Primarily, small-scale sensors were produced using ultrasonic welding, hot press welding and oven curing. These were characterized using a universal testing machine and specific conditioning and data-acquisition hardware combined with custom processing software. Large-scale sensors were then manufactured to be placed inside the karate body protector and characterized using cyclic testing. The conditioning circuit allows flexible gain adjustment, and it was possible to obtain a stable signal with an output of up to 0.03 V/N, an adequate signal for the tested force range. The transfer function shows some drift over the cycles, in addition to the expected hysteresis and slight nonlinearity, which can be compensated for. Finally, the configuration with the best results was tested in real practice tests; during these tests the body protector was placed on a dummy as well as on a person. The results showed that the piezoresistive textile-based pressure sensor produced is able to detect and quantify the impact of even light punches, providing an unobtrusive means for performance monitoring and score calculation for competitive practice of this sport.This research was funded by National Founds through FCT/MCTES, grant number UID/CTM/00264/2019 of 2C2T—Centro de Ciência e Tecnologia Têxtil—and by European Cooperation in Science and Technology as a Short-Term Scientific Mission regarding the COST Action: CA17107–European Network to connect research and innovation efforts on advanced Smart Textiles, grant number 44750, Grant period: AGA-CA17107-2: 1 May 2019–30 April 2020, Dates: 8 July 2019–6 August 2019

Development of MEMS Sensors for Measurements of Pressure, Relative Humidity, and Temperature

Continued demands for better control of the operating conditions of structures and processes have led to the need for better means of measuring temperature (T), pressure (P), and relative humidity (RH). One way to satisfy this need is to use MEMS technology to develop a sensor that will contain, in a single package, capabilities to simultaneously measure T, P, and RH of its environment. Because of the advantages of MEMS technology, which include small size, low power, very high precision, and low cost, it was selected for use in this thesis. Although MEMS sensors that individually measure T, P, and RH exist, there are no sensors that combine all three measurements in a single package. In this thesis, a piezoresistive pressure sensor and capacitive humidity sensor were developed to operate in the range, of 0 to 2 atm and 0% to 100%, respectively. Finally, a polysilicon resistor temperature sensor, which can work in the range of -50ºC to 150ºC, was analyzed. Multimeasurement capability will make this sensor particularly applicable for point-wise mapping of environmental conditions for advanced process control. In this thesis, the development of sensors for such an integrated device is outlined. Selected results, based on the use of analytical, computational, and experimental solutions (ACES) methodology, particularly suited for the development of MEMS sensors, are presented for the pressure, relative humidity, and temperature sensors

Development of Multifunctional E-skin Sensors

Electronic skin (e-skin) is a hot topic due to its enormous potential for health monitoring, functional prosthesis, robotics, and human-machine-interfaces (HMI). For these applications, pressure and temperature sensors and energy harvesters are essential. Their performance may be tuned by their films micro-structuring, either through expensive and time-consuming photolithography techniques or low-cost yet low-tunability approaches. This PhD thesis aimed to introduce and explore a new micro-structuring technique to the field of e-skin – laser engraving – to produce multifunctional e-skin devices able to sense pressure and temperature while being self-powered. This technique was employed to produce moulds for soft lithography, in a low-cost, fast, and highly customizable way. Several parameters of the technique were studied to evaluate their impact in the performance of the devices, such as moulds materials, laser power and speed, and design variables. Amongst the piezoresistive sensors produced, sensors suitable for blood pressure wave detection at the wrist [sensitivity of – 3.2 kPa-1 below 119 Pa, limit of detection (LOD) of 15 Pa], general health monitoring (sensitivity of 4.5 kPa-1 below 10 kPa, relaxation time of 1.4 ms, micro-structured film thickness of only 133 µm), and robotics and functional prosthesis (sensitivity of – 6.4 × 10-3 kPa-1 between 1.2 kPa and 100 kPa, stable output over 27 500 cycles) were obtained. Temperature sensors with micro-cones were achieved with a temperature coefficient of resistance (TCR) of 2.3 %/°C. Energy harvesters based on micro-structured composites of polydimethylsiloxane (PDMS) and zinc tin oxide (ZnSnO3) nanowires (NWs; 120 V and 13 µA at > 100 N) or zinc oxide (ZnO) nanorods (NRs; 6 V at 2.3 N) were produced as well. The work described herein unveils the tremendous potential of the laser engraving technique to produce different e-skin devices with adjustable performance to suit distinct applications, with a high benefit/cost ratio

Relative contributions of packaging elements to the thermal hysteresis of a MEMS pressure sensor

Piezoresistive silicon pressure sensor samples were thermally cycled after being consecutively packaged to three different levels. These started with the absolute minimum to allow measurement of the output and with each subsequent level incorporating additional packaging elements within the build. Fitting the data to a mathematical function was necessary both to correct for any testing uncertainties within the pressure and temperature controllers, and to enable the identification and quantification of any hysteresis. Without being subjected to any previous thermal preconditioning, the sensors were characterized over three different temperature ranges and for multiple cycles, in order to determine the relative contributions of each packaging level toward thermal hysteresis. After reaching a stabilised hysteretic behaviour, 88.5% of the thermal hysteresis was determined to be related to the bond pads and wire bonds, which is likely to be due to the large thermal mismatch between the silicon and bond pad metallisation. The fluid-fill and isolation membrane contributed just 7.2% of the total hysteresis and the remaining 4.3% was related to the adhesive used for attachment of the sensing element to the housing. This novel sequential packaging evaluation methodology is independent of sensor design and is useful in identifying those packaging elements contributing the most to hysteresis

Nanoelectromechanical Sensors based on Suspended 2D Materials

The unique properties and atomic thickness of two-dimensional (2D) materials enable smaller and better nanoelectromechanical sensors with novel functionalities. During the last decade, many studies have successfully shown the feasibility of using suspended membranes of 2D materials in pressure sensors, microphones, accelerometers, and mass and gas sensors. In this review, we explain the different sensing concepts and give an overview of the relevant material properties, fabrication routes, and device operation principles. Finally, we discuss sensor readout and integration methods and provide comparisons against the state of the art to show both the challenges and promises of 2D material-based nanoelectromechanical sensing.Comment: Review pape

Multifunctional photocurable advanced materials for electronics and sensing applications

276 p.Photocurable multifunctional polymer composites have been obtained and characterized according totheir photopolymerization capability, physico-chemical and functional properties. Polyurethane acrylate(PUA) has been selected as polymer matrix combined with multi-walled carbon nanotubes (MWCNT),barium titante (BaTiO3), indium tin oxide (ITO), magnetite (Fe3O4), cobalt ferrite (CFO), neodymiumiron boron alloy (NdFeB) and 1-buthyl-3-methylimidazolium tetracholonickelate ([Bmim]2NiCl4) ionicliquid (IL) to obtain different functional and multifunctional responses.Different functional and multifunctional responses have been added to the UV curable polymer,depending on the filler type and content. The inclusion of MWCNTs induce a piezoresistive responsecharacterized by GF values between 0.8 and 2.6. BaTiO3 and ITO, strongly increase the dielectricconstant from 7.5 to 25 and up to 33, respectively. In the case of Fe3O4, CFO and NdFeB, magneticcomposites with tailored magnetic properties (from hard to soft magnetic ones) are obtained. Saturationmagnetization values up to 63.86 emu/g, remanence up to 44.95 emu/g and coercivity up to 7000 Oe havebeen obtained depending on filler type and content. Finally, IL allows the preparation of temperatureactivated thermochromic humidity sensing materials with a colour change from blue to colourless,depending on relative humidity.Thus, this work successfully demonstrated the development of UV photocurable functional andmultifunctional materials, compatible with printing technologies, for electronic and sensing applications.BcMaterials: Basque Center for materials applications & nanostructure

Multifunctional photocurable advanced materials for electronics and sensing applications

276 p.Photocurable multifunctional polymer composites have been obtained and characterized according totheir photopolymerization capability, physico-chemical and functional properties. Polyurethane acrylate(PUA) has been selected as polymer matrix combined with multi-walled carbon nanotubes (MWCNT),barium titante (BaTiO3), indium tin oxide (ITO), magnetite (Fe3O4), cobalt ferrite (CFO), neodymiumiron boron alloy (NdFeB) and 1-buthyl-3-methylimidazolium tetracholonickelate ([Bmim]2NiCl4) ionicliquid (IL) to obtain different functional and multifunctional responses.Different functional and multifunctional responses have been added to the UV curable polymer,depending on the filler type and content. The inclusion of MWCNTs induce a piezoresistive responsecharacterized by GF values between 0.8 and 2.6. BaTiO3 and ITO, strongly increase the dielectricconstant from 7.5 to 25 and up to 33, respectively. In the case of Fe3O4, CFO and NdFeB, magneticcomposites with tailored magnetic properties (from hard to soft magnetic ones) are obtained. Saturationmagnetization values up to 63.86 emu/g, remanence up to 44.95 emu/g and coercivity up to 7000 Oe havebeen obtained depending on filler type and content. Finally, IL allows the preparation of temperatureactivated thermochromic humidity sensing materials with a colour change from blue to colourless,depending on relative humidity.Thus, this work successfully demonstrated the development of UV photocurable functional andmultifunctional materials, compatible with printing technologies, for electronic and sensing applications.BcMaterials: Basque Center for materials applications & nanostructure

Design and development of microcantilever as a platform for moisture sensing

Ultra-sensitive and selective moisture sensors are needed in various industries for processing control or environmental monitoring. As an outstanding sensor platform, microcantilevers have potential application in moisture detection due to their advantages, such as low-level moisture detection limits, high accuracy, quick response time, high reproducibility, good recovery rate and low in cost. Our research results will lead to the first of its kind for the commercialization of a microcantilever-based moisture sensor used for industrial and household applications. The novelty of the present work is the development of SiO2 and Si cantilevers, which were fabricated using developed processes and modified with Al2O3, for detecting moisture as low as ppm level. To increase the deflection of the microcantilever under surface stress induced by specific reactions, a new SiO2 microcantilever, which consists of two SiO2 cantilever beams as the sensing and reference elements, two connecting wings and three guard arms, has been developed which features a much lower Young\u27s modulus than conventional Si or SiNx microcantilevers. For comparing SiO2 cantilever with Si cantilevers, a model of the cantilever sensor is reported by using both analysis and simulation, resulting in good agreement with the experimental data. The results demonstrate that the SiO2 cantilever can achieve a much higher sensitivity than the Si cantilever due to its lower Young\u27s modulus. In order to fabricate this device, a new fabrication process using isotropic combined with anisotropic dry etching to release the SiO2 microcantilever beam by Inductively Coupled Plasma (ICP) was developed and investigated. This new process not only obtains a high etch rate at 9.1 μm per minute, but also provides good etch profile controllability, and a flexibility of device design. Attributed to its high sensitivity, Al2O3 coated SiO2 microcantilevers demonstrated the capability of detecting moisture concentration levels down to 30 ppm using optical detection methods. It can be seen that the SiO2microcantilevers, with appropriate sensing material, can be utilized as ultra sensitive moisture sensors and are potentially able to detect the moisture concentration level as low as 1 to 10 ppm. Although optical readout systems are most extensively used for measurement of cantilever deflections in labs, they have some disadvantages, such as its alignment system is expensive and involves great precision. Piezoresistive, capacitive, MOSFET-embedded and frequency readout methods, which are all fit for commercial application, have been investigated both in simulation and experiment. It is found that the Al2O3 modified microcantilever operating in frequency mode is able to meet the requirements of detecting low moisture levels. To make this device compatible with IC technology, the piezoelectric microcantilever is chosen as the platform for moisture sensing. A piezoelectric microcantilever vibrates at its resonant frequency upon applying an appropriate AC voltage and provides an electrical signal at the output via piezoelectric coupling, which can be fed back through the phase shift loop to determine the change in resonant frequency caused by any change in mass. In order to fabricate the piezoelectric microcantilever, the sputtering parameters for ZnO were reported and investigated. The piezoelectric microcantilevers, which consists of bottom electrode, ZnO piezoelectric layer, and two separate top electrodes as sensing and actuation elements, were designed and fabricated using a standard lithography process. Its resonant frequency shift is measured at 1.25 Hz/ppm, based on an optical detection method. Although both SiO 2 and Si piezoelectric cantilevers were fabricated successfully, the latter are more likely to be used in dynamic mode because of the higher fragility of SiO2. The developed cantilever sensor platform operating in dynamic mode, which can be integrated with on-chip electronic circuitry, is able to provide ultra-sensitive detection, not only for moisture sensing, but also for chemical and biological sensing with appropriate surface modification