Thin film transistors (TFT's) on flexible large-area substrates enable large-scale deployment... more Thin film transistors (TFT's) on flexible large-area substrates enable large-scale deployment of form-fitting embedded and tactile sensors. However, the combination of insulating substrates (e.g., glass, plastics), long metal traces for distributed sensors and circuits over large areas, plasma processing and packaging/assembly for hybrid (CMOS-TFT) systems makes anomalous breakdown in TFT gate dielectrics a prominent limiter of yield in complex systems. In this work, we use layout modifications, shielding layers, and temporary “shorting bars” to enable high-yield processing and assembly of distributed sensor-acquisition circuits, in which 161 ZnO TFT's are used per sensor (Fig. 1) to implement compressed sensing (i.e., matrix projection). Although this is a large number of TFT's, compressed sensing greatly enhances critical system metrics, e.g., reduces the number of acquisition cycles and physical interfaces to a readout CMOS IC, as demonstrated in a tactile force-sensing system [1].
2017 75th Annual Device Research Conference (DRC), 2017
Besides traditional RFID [1], an emerging application of large-area electronics is hybrid systems... more Besides traditional RFID [1], an emerging application of large-area electronics is hybrid systems [2], where we need to transfer power and signals from one flexible sheet to another. This is driven by manufacturing considerations: sheets providing different functionality, via different materials and devices, can simply be laminated together. Hard-wired metallurgical bonds between flexible sheets are expected to be problematic, especially for reliability, motivating the use of non-contact inductively-coupled interfaces between adjacent sheets [2-3]. For efficiency of such interfaces, high-frequency thin-film diodes (HF-TFDs) are required, since inductive losses are lower at high frequencies [3].
Damage detection, localization and prognosis are fundamentally important for a comprehensive stru... more Damage detection, localization and prognosis are fundamentally important for a comprehensive structural health monitoring (SHM) process. Damage is often associated with an anomalous strain changes or jumps. These changes are best captured if sensors are in direct contact with the damage. However, one-dimensional direct sensing is often expensive to cover the whole structure. Two-dimensional sensors, on the other hand, show promise to allow direct sensing on a large scale. Researchers at Princeton University have developed a flexible thin-film resistive strain sensor based on the principles on large area electronics (LAE). These two-dimensional sheets are suitable for covering large areas ( 10m2) and, hence, could be used for direct damage detection. In this work, the authors explore the suitability of such sheets for real-life applications. Results of laboratory experiments conducted using an aluminum cantilever beam for evaluation of performance in ideal conditions are presented. T...
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2019, 2019
Damage characterization often requires direct sensing due to the localization of the anomalous be... more Damage characterization often requires direct sensing due to the localization of the anomalous behavior near the cracks. Direct sensing, however, is expensive because of the need to deploy a dense array of individual sensors. Sensing sheets based on Large Area Electronics (LAE) and Integrated Circuits (ICs) are a novel solution to this problem. Such sensing sheets could span several square meters, with a dense array of strain sensors embedded on a polyimide substrate along with the relevant electronics allowing for direct sensing while keeping the costs low. Current studies on LAE based sensing sheets are limited to laboratory experiments. This paper explores the question of suitability of the sensing sheets as a viable option for real-life SHM based on LAE and ICs. Results of laboratory experiments on an aluminum beam are provided to demonstrate the performance of sensing sheets in ideal conditions. Then, the sensing sheets are employed on a pedestrian bridge already equipped with fiber-optic sensors. The strain measurements from the sensing sheets and the fiber-optic sensors are compared and sources of differences are discussed.
IABSE Congress, New York, New York 2019: The Evolving Metropolis, 2019
Damage detection in structures is an important part of structural health monitoring (SHM). Two ap... more Damage detection in structures is an important part of structural health monitoring (SHM). Two approaches for detecting damages are indirect and direct sensing. Indirect sensing uses sparse array of sensors and complex algorithms to determine the extent and localization of damage. Crack initiation can best be captured with direct sensing as it provides resolved information about the anomalous behavior near cracks. Direct sensing, however, is expensive because of the need to install a large array of densely packed sensors. A novel solution developed recently is the use of two-dimensional sensing sheets designed to cover large areas of structures. Such sheets are based on large area electronics (LAE) with flexible thin film resistive strain sensors embedded in polyimide substrate along with the relevant electronics. This paper explores the use of sensing sheets for damage detection using static and dynamic measurement. Laboratory testing on aluminum beam is used to demonstrate the per...
Damage significantly influences response of a strain sensor only if it occurs in the proximity of... more Damage significantly influences response of a strain sensor only if it occurs in the proximity of the sensor. Thus, two-dimensional (2D) sensing sheets covering large areas offer reliable early-stage damage detection for structural health monitoring (SHM) applications. This paper presents a scalable sensing sheet design consisting of a dense array of thin-film resistive strain sensors. The sensing sheet is fabricated using flexible printed circuit board (Flex-PCB) manufacturing process which enables low-cost and high-volume sensors that can cover large areas. The lab tests on an aluminum beam showed the sheet has a gauge factor of 2.1 and has a low drift of 1.5 μ ϵ / d a y . The field test on a pedestrian bridge showed the sheet is sensitive enough to track strain induced by the bridge’s temperature variations. The strain measured by the sheet had a root-mean-square (RMS) error of 7 μ ϵ r m s compared to a reference strain on the surface, extrapolated from fiber-optic sensors embedd...
Sensing sheets based on Large Area Electronics (LAE) and Integrated Circuits (ICs) are novel sens... more Sensing sheets based on Large Area Electronics (LAE) and Integrated Circuits (ICs) are novel sensors designed to enable reliable early-stage detection of local unusual structural behaviors. Such a device consists of a dense array of strain sensors, patterned onto a flexible polyimide substrate along with associated electronics. Previous tests performed on steel specimens equipped with sensing sheet prototypes and subjected to fatigue cracking pointed to a potential issue: individual sensors that were on or near a crack would immediately be damaged by the crack, thereby rendering them useless in assessing the size of the crack opening or to monitor future crack growth. In these tests, a stiff adhesive was used to bond the sensing sheet prototype to the steel specimen. Such an adhesive provided excellent strain transfer, but it also caused premature failure of individual sensors within the sheet. Therefore, the aim of this paper is to identify an alternative adhesive that survives min...
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2015
ZnO thin film transistors (TFTs) are fabricated on Si substrates using atomic layer deposition te... more ZnO thin film transistors (TFTs) are fabricated on Si substrates using atomic layer deposition technique. The growth temperature of ZnO channel layers are selected as 80, 100, 120, 130, and 250 °C. Material characteristics of ZnO films are examined using x-ray photoelectron spectroscopy and x-ray diffraction methods. Stoichiometry analyses showed that the amount of both oxygen vacancies and interstitial zinc decrease with decreasing growth temperature. Electrical characteristics improve with decreasing growth temperature. Best results are obtained with ZnO channels deposited at 80 °C; Ion/Ioff ratio is extracted as 7.8 × 109 and subthreshold slope is extracted as 0.116 V/dec. Flexible ZnO TFT devices are also fabricated using films grown at 80 °C. ID–VGS characterization results showed that devices fabricated on different substrates (Si and polyethylene terephthalate) show similar electrical characteristics. Sub-bandgap photo sensing properties of ZnO based TFTs are investigated; it...
Thin film transistors (TFT's) on flexible large-area substrates enable large-scale deployment... more Thin film transistors (TFT's) on flexible large-area substrates enable large-scale deployment of form-fitting embedded and tactile sensors. However, the combination of insulating substrates (e.g., glass, plastics), long metal traces for distributed sensors and circuits over large areas, plasma processing and packaging/assembly for hybrid (CMOS-TFT) systems makes anomalous breakdown in TFT gate dielectrics a prominent limiter of yield in complex systems. In this work, we use layout modifications, shielding layers, and temporary “shorting bars” to enable high-yield processing and assembly of distributed sensor-acquisition circuits, in which 161 ZnO TFT's are used per sensor (Fig. 1) to implement compressed sensing (i.e., matrix projection). Although this is a large number of TFT's, compressed sensing greatly enhances critical system metrics, e.g., reduces the number of acquisition cycles and physical interfaces to a readout CMOS IC, as demonstrated in a tactile force-sensing system [1].
2017 75th Annual Device Research Conference (DRC), 2017
Besides traditional RFID [1], an emerging application of large-area electronics is hybrid systems... more Besides traditional RFID [1], an emerging application of large-area electronics is hybrid systems [2], where we need to transfer power and signals from one flexible sheet to another. This is driven by manufacturing considerations: sheets providing different functionality, via different materials and devices, can simply be laminated together. Hard-wired metallurgical bonds between flexible sheets are expected to be problematic, especially for reliability, motivating the use of non-contact inductively-coupled interfaces between adjacent sheets [2-3]. For efficiency of such interfaces, high-frequency thin-film diodes (HF-TFDs) are required, since inductive losses are lower at high frequencies [3].
Damage detection, localization and prognosis are fundamentally important for a comprehensive stru... more Damage detection, localization and prognosis are fundamentally important for a comprehensive structural health monitoring (SHM) process. Damage is often associated with an anomalous strain changes or jumps. These changes are best captured if sensors are in direct contact with the damage. However, one-dimensional direct sensing is often expensive to cover the whole structure. Two-dimensional sensors, on the other hand, show promise to allow direct sensing on a large scale. Researchers at Princeton University have developed a flexible thin-film resistive strain sensor based on the principles on large area electronics (LAE). These two-dimensional sheets are suitable for covering large areas ( 10m2) and, hence, could be used for direct damage detection. In this work, the authors explore the suitability of such sheets for real-life applications. Results of laboratory experiments conducted using an aluminum cantilever beam for evaluation of performance in ideal conditions are presented. T...
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2019, 2019
Damage characterization often requires direct sensing due to the localization of the anomalous be... more Damage characterization often requires direct sensing due to the localization of the anomalous behavior near the cracks. Direct sensing, however, is expensive because of the need to deploy a dense array of individual sensors. Sensing sheets based on Large Area Electronics (LAE) and Integrated Circuits (ICs) are a novel solution to this problem. Such sensing sheets could span several square meters, with a dense array of strain sensors embedded on a polyimide substrate along with the relevant electronics allowing for direct sensing while keeping the costs low. Current studies on LAE based sensing sheets are limited to laboratory experiments. This paper explores the question of suitability of the sensing sheets as a viable option for real-life SHM based on LAE and ICs. Results of laboratory experiments on an aluminum beam are provided to demonstrate the performance of sensing sheets in ideal conditions. Then, the sensing sheets are employed on a pedestrian bridge already equipped with fiber-optic sensors. The strain measurements from the sensing sheets and the fiber-optic sensors are compared and sources of differences are discussed.
IABSE Congress, New York, New York 2019: The Evolving Metropolis, 2019
Damage detection in structures is an important part of structural health monitoring (SHM). Two ap... more Damage detection in structures is an important part of structural health monitoring (SHM). Two approaches for detecting damages are indirect and direct sensing. Indirect sensing uses sparse array of sensors and complex algorithms to determine the extent and localization of damage. Crack initiation can best be captured with direct sensing as it provides resolved information about the anomalous behavior near cracks. Direct sensing, however, is expensive because of the need to install a large array of densely packed sensors. A novel solution developed recently is the use of two-dimensional sensing sheets designed to cover large areas of structures. Such sheets are based on large area electronics (LAE) with flexible thin film resistive strain sensors embedded in polyimide substrate along with the relevant electronics. This paper explores the use of sensing sheets for damage detection using static and dynamic measurement. Laboratory testing on aluminum beam is used to demonstrate the per...
Damage significantly influences response of a strain sensor only if it occurs in the proximity of... more Damage significantly influences response of a strain sensor only if it occurs in the proximity of the sensor. Thus, two-dimensional (2D) sensing sheets covering large areas offer reliable early-stage damage detection for structural health monitoring (SHM) applications. This paper presents a scalable sensing sheet design consisting of a dense array of thin-film resistive strain sensors. The sensing sheet is fabricated using flexible printed circuit board (Flex-PCB) manufacturing process which enables low-cost and high-volume sensors that can cover large areas. The lab tests on an aluminum beam showed the sheet has a gauge factor of 2.1 and has a low drift of 1.5 μ ϵ / d a y . The field test on a pedestrian bridge showed the sheet is sensitive enough to track strain induced by the bridge’s temperature variations. The strain measured by the sheet had a root-mean-square (RMS) error of 7 μ ϵ r m s compared to a reference strain on the surface, extrapolated from fiber-optic sensors embedd...
Sensing sheets based on Large Area Electronics (LAE) and Integrated Circuits (ICs) are novel sens... more Sensing sheets based on Large Area Electronics (LAE) and Integrated Circuits (ICs) are novel sensors designed to enable reliable early-stage detection of local unusual structural behaviors. Such a device consists of a dense array of strain sensors, patterned onto a flexible polyimide substrate along with associated electronics. Previous tests performed on steel specimens equipped with sensing sheet prototypes and subjected to fatigue cracking pointed to a potential issue: individual sensors that were on or near a crack would immediately be damaged by the crack, thereby rendering them useless in assessing the size of the crack opening or to monitor future crack growth. In these tests, a stiff adhesive was used to bond the sensing sheet prototype to the steel specimen. Such an adhesive provided excellent strain transfer, but it also caused premature failure of individual sensors within the sheet. Therefore, the aim of this paper is to identify an alternative adhesive that survives min...
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2015
ZnO thin film transistors (TFTs) are fabricated on Si substrates using atomic layer deposition te... more ZnO thin film transistors (TFTs) are fabricated on Si substrates using atomic layer deposition technique. The growth temperature of ZnO channel layers are selected as 80, 100, 120, 130, and 250 °C. Material characteristics of ZnO films are examined using x-ray photoelectron spectroscopy and x-ray diffraction methods. Stoichiometry analyses showed that the amount of both oxygen vacancies and interstitial zinc decrease with decreasing growth temperature. Electrical characteristics improve with decreasing growth temperature. Best results are obtained with ZnO channels deposited at 80 °C; Ion/Ioff ratio is extracted as 7.8 × 109 and subthreshold slope is extracted as 0.116 V/dec. Flexible ZnO TFT devices are also fabricated using films grown at 80 °C. ID–VGS characterization results showed that devices fabricated on different substrates (Si and polyethylene terephthalate) show similar electrical characteristics. Sub-bandgap photo sensing properties of ZnO based TFTs are investigated; it...
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Papers by Levent E Aygun