Physically responsive field-effect transistors (physi-FETs), which are sensitive to physical stim... more Physically responsive field-effect transistors (physi-FETs), which are sensitive to physical stimuli, have been studied for decades. However, the primary issue of separating responses by sensing materials from interferences by other subcomponents in a FET transducer under global physical stimuli has not been completely resolved. Recent challenges of structural design and employing smart materials with a large electro-physical coupling effect for flexible physi-FETs still remain. In this article, we propose directly integrating nanocomposites of barium titanate (BT) nanoparticles (NPs) and highly crystalline poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) as gate dielectrics into flexible organic FETs to precisely separate and quantify tiny variations of remnant polarization caused by mechanical stimuli. Investigations under static stimuli resulted in first-reported giant-positive piezoelectric coefficients of d33 up to 960 pC/N, presumably due to significant contribution o...
Electronic skin (e-skin) is designed to mimic the comprehensive nature of human skin. Various adv... more Electronic skin (e-skin) is designed to mimic the comprehensive nature of human skin. Various advances in e-skin continue to drive the development of the multimodal tactile sensor technology on flexible and stretchable platforms. e-skin incorporates pressure, temperature, texture, photographic imaging, and other sensors as well as data acquisition and signal processing units formed on a soft substrate for humanoid robots, wearable devices, and health monitoring electronics that are the most critical applications of soft electronics. This artificial skin has developed very rapidly toward becoming real technology. However, the complex nature of e-skin technology presents significant challenges in terms of materials, devices, sophisticated integration methods, and interference-free data acquisition. These challenges range from functional materials, device architecture, pixel design, array structure, and data acquisition method to multimodal sensing performance with negligible interference. In this article, we present recent research trends and approaches in the field of flexible and stretchable multimodal sensors for e-skin focusing on the following aspects: 1) flexible and stretchable platforms; 2) operating principles and materials suitable for pressure, temperature, strain, photograph, and hairy sensor devices; 3) device and integration architectures, including multimodal single cells, three-axis tactile sensors, vertical-stacked sensor arrays, active matrix sensor arrays, and integration electronics; 4) reliable acquisition methods for various texture sensing and machine-learning algorithms for processing tactile sensing data; and 5) future outlook.
A conformal patch biosensor that can detect biomolecules is one promising technology for wearable... more A conformal patch biosensor that can detect biomolecules is one promising technology for wearable sweat glucose self-monitoring. However, developing such a patch is challenging because conferring stretchability to its components is difficult. Herein, we demonstrate a platform for a nonenzymatic, electrochemical sensor patch: a wrinkled, stretchable, nanohybrid fiber (WSNF) in which Au nanowrinkles partially cover the reduced graphene oxide (rGO)/polyurethane composite fiber. The WSNF has high electrocatalytic activity because of synergetic effects between the Au nanowrinkles and the oxygen-containing functional groups on the rGO-supporting matrix which promote the dehydrogenation step in glucose oxidation. The WSNF offers stretchability, high sensitivity, low detection limit, high selectivity against interferents, and high ambient-condition stability, and it can detect glucose in neutral conditions. If this WSNF sensor patch were sewn onto a stretchable fabric and attached to the human body, it could continuously measure glucose levels in sweat to accurately reflect blood glucose levels.
Fiber-based sensors integrated on textiles or clothing systems are required for the next generati... more Fiber-based sensors integrated on textiles or clothing systems are required for the next generation of wearable electronic platforms. Fiber-based physical sensors are developed, but the development of fiber-based temperature sensors is still limited. Herein, a new approach to develop wearable temperature sensors that use freestanding single reduction graphene oxide (rGO) fiber is proposed. A freestanding and wearable temperature-responsive rGO fiber with tunable thermal index is obtained using simple wet spinning and a controlled graphene oxide reduction time. The freestanding fiber-based temperature sensor shows high responsivity, fast response time (7 s), and good recovery time (20 s) to temperature. It also maintains its response under an applied mechanical deformation. The fiber device fabricated by means of a simple process is easily integrated into fabric such as socks or undershirts and can be worn by a person to monitor the temperature of the environment and skin temperature...
Omnidirectionally stretchable photodetectors are limited by difficulties in designing material an... more Omnidirectionally stretchable photodetectors are limited by difficulties in designing material and fabrication processes that enable stretchability in multiaxial directions. Here, we propose a new approach involving an organic-inorganic p-n heterojunction photodetector comprised of free-standing ZnO nanorods (NRs) grown on a poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate transport layer coated on a three-dimensionally micro-patterned stretchable substrate containing bumps and valleys. This structure allows for efficient absorption of stretching strain. This approach allows the device to accommodate large tensile strain in all directions. The device behaves as a photogated p-n heterojunction photodetector, in which current modulation was obtained by sensing mechanisms that rely on photovoltage and photogating effects. The device exhibits a high photoresponse to UV light and reliable electrical performance under applied stretching in uniaxial and omni-axial directions. Furthermore, the device can be easily and conformally attached to a human wrist. This allowed us to investigate the response of the device to UV light during human activity.
Herein, we review recent advances in transparent stretchable electronic materials and transparent... more Herein, we review recent advances in transparent stretchable electronic materials and transparent stretchable electronic devices. Some representative examples that highlight the unique optical, electrical and mechanical properties of transparent stretchable materials and devices are also discussed in detail.
Advanced materials (Deerfield Beach, Fla.), Jan 14, 2016
Stretchable electronic devices with intrinsically stretchable components have significant inheren... more Stretchable electronic devices with intrinsically stretchable components have significant inherent advantages, including simple fabrication processes, a high integrity of the stacked layers, and low cost in comparison with stretchable electronic devices based on non-stretchable components. The research in this field has focused on developing new intrinsically stretchable components for conductors, semiconductors, and insulators. New methodologies and fabrication processes have been developed to fabricate stretchable devices with intrinsically stretchable components. The latest successful examples of stretchable conductors for applications in interconnections, electrodes, and piezoresistive devices are reviewed here. Stretchable conductors can be used for electrode or sensor applications depending on the electrical properties of the stretchable conductors under mechanical strain. A detailed overview of the recent progress in stretchable semiconductors, stretchable insulators, and oth...
Flexible chemical sensors utilizing chemically sensitive nanomaterials are of great interest for ... more Flexible chemical sensors utilizing chemically sensitive nanomaterials are of great interest for wearable sensing applications. However, obtaining high performance flexible chemical sensors with high sensitivity, fast response, transparency, stability, and workability at ambient conditions is still challenging. Herein, a newly designed flexible and transparent chemical sensor of reduced graphene oxide (R-GO) coupled with organic dye molecules (bromophenol blue) is introduced. This device has promising properties such as high mechanical flexibility (>5000 bending cycles with a bending radius of 0.95 cm) and optical transparency (>60% in the visible region). Furthermore, stacking the water-trapping dye layer on R-GO enables a higher response as well as workability in a large relative humidity range (up to 80%), and dual-mode detection capabilities of colorimetric and electrical sensing for NH3 gas (5–40 ppm). These advantageous attributes of the flexible and transparent R-GO sensor coupled with organic dye molecules provide great potential for real-time monitoring of toxic gas/vapor in future practical chemical sensing at room conditions in wearable electronics.
Abstract A flexible photodetector based on methylammonium lead iodide perovskite-graphene (Gr) hy... more Abstract A flexible photodetector based on methylammonium lead iodide perovskite-graphene (Gr) hybrid channel field-effect transistors (FETs) are studied under broadband incident light and at various photon intensities (515 nm). The combination of high light absorption of the antenna material (perovskite) and excellent mobility and conduction of the transport layer (Gr) in the hybrid channel enables the photodetector to reach high responsivities (up to 115 A W−1) at 515 nm. The change in transfer characteristics of the hybrid channel phototransistor under light exposure allows for a deep understanding of the sensing mechanism and carrier transport properties of Gr based on the shifting of Dirac points (VDirac). Additionally, the as-fabricated device on polyimide substrates yields good mechanical flexibility, electrical stability, and endurance with the responsivity being unaffected under flexure and the photocurrent being unchanged after 3000 bending cycles at a 12 mm bending radius. This work demonstrates the promising potential of these materials for future application in next generation optoelectronic devices.
Advanced materials (Deerfield Beach, Fla.), Jan 3, 2016
Flexible and stretchable physical sensors that can measure and quantify electrical signals genera... more Flexible and stretchable physical sensors that can measure and quantify electrical signals generated by human activities are attracting a great deal of attention as they have unique characteristics, such as ultrathinness, low modulus, light weight, high flexibility, and stretchability. These flexible and stretchable physical sensors conformally attached on the surface of organs or skin can provide a new opportunity for human-activity monitoring and personal healthcare. Consequently, in recent years there has been considerable research effort devoted to the development of flexible and stretchable physical sensors to fulfill the requirements of future technology, and much progress has been achieved. Here, the most recent developments of flexible and stretchable physical sensors are described, including temperature, pressure, and strain sensors, and flexible and stretchable sensor-integrated platforms. The latest successful examples of flexible and stretchable physical sensors for the ...
Advanced materials (Deerfield Beach, Fla.), Jan 26, 2015
A transparent stretchable (TS) gated sensor array with high optical transparency, conformality, a... more A transparent stretchable (TS) gated sensor array with high optical transparency, conformality, and high stretchability of up to 70% is demonstrated. The TS-gated sensor array has high responsivity to temperature changes in objects and human skin. This unprecedented TS-gated sensor array, as well as the integrated platform of the TS-gated sensor with a transparent and stretchable strain sensor, shows great potential for application to wearable skin electronics for recognition of human activity.
Photodetectors using optically responsive graphene (Gr) or reduced graphene oxide (R-GO) on rigid... more Photodetectors using optically responsive graphene (Gr) or reduced graphene oxide (R-GO) on rigid substrates have showed promising results for detection of broad band light including infrared (IR). However, there have been only a few reports on Gr or R-GO photodetectors with new functionalities such as optical transparency and/or flexibility. Herein, a new kind of transparent and flexible IR photodetector is presented using a field-effect transistor (FET) structure in which an IR-responsive nanocomposite layer of R-GO and poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) is employed as the channel. The IR photodetector exhibits high IR responsivity, stability, and reproducibility under mechanical strain and ambient conditions. In addition, the capability of measuring the distribution of responses from each device in the transparent and flexible nanocomposite FET array under IR radiation from the human body is also demonstrated. Therefore, the development of a flexible IR photodetector with high responsivity, transparency, ease of integration, and stability in an ambient environment is a suitable alternative approach for achieving the stable monitoring of IR in many flexible and transparent electronic systems.
Ultraviolet (UV) photodetectors based on ZnO nanostructure/graphene (Gr) hybrid-channel field-eff... more Ultraviolet (UV) photodetectors based on ZnO nanostructure/graphene (Gr) hybrid-channel field-effect transistors (FETs) are investigated under illumination at various incident photon intensities and wavelengths. The time-dependent behaviors of hybrid-channel FETs reveal a high sensitivity and selectivity toward the near-UV region at the wavelength of 365 nm. The devices can operate at low voltage and show excellent selectivity, high responsivity (RI ), and high photoconductive gain (G). The change in the transfer characteristics of hybrid-channel FETs under UV light illumination allows to detect both photovoltage and photocurrent. The shift of the Dirac point (V Dirac ) observed during UV exposure leads to a clearer explanation of the response mechanism and carrier transport properties of Gr, and this phenomenon permits the calculation of electron concentration per UV power density transferred from ZnO nanorods and ZnO nanoparticles to Gr, which is 9 × 10(10) and 4 × 10(10) per mW, respectively. The maximum values of RI and G infer from the fitted curves of RI and G versus UV intensity are 3 × 10(5) A W(-1) and 10(6) , respectively. Therefore, the hybrid-channel FETs studied herein can be used as UV sensing devices with high performance and low power consumption, opening up new opportunities for future optoelectronic devices.
Physically responsive field-effect transistors (physi-FETs), which are sensitive to physical stim... more Physically responsive field-effect transistors (physi-FETs), which are sensitive to physical stimuli, have been studied for decades. However, the primary issue of separating responses by sensing materials from interferences by other subcomponents in a FET transducer under global physical stimuli has not been completely resolved. Recent challenges of structural design and employing smart materials with a large electro-physical coupling effect for flexible physi-FETs still remain. In this article, we propose directly integrating nanocomposites of barium titanate (BT) nanoparticles (NPs) and highly crystalline poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) as gate dielectrics into flexible organic FETs to precisely separate and quantify tiny variations of remnant polarization caused by mechanical stimuli. Investigations under static stimuli resulted in first-reported giant-positive piezoelectric coefficients of d33 up to 960 pC/N, presumably due to significant contribution o...
Electronic skin (e-skin) is designed to mimic the comprehensive nature of human skin. Various adv... more Electronic skin (e-skin) is designed to mimic the comprehensive nature of human skin. Various advances in e-skin continue to drive the development of the multimodal tactile sensor technology on flexible and stretchable platforms. e-skin incorporates pressure, temperature, texture, photographic imaging, and other sensors as well as data acquisition and signal processing units formed on a soft substrate for humanoid robots, wearable devices, and health monitoring electronics that are the most critical applications of soft electronics. This artificial skin has developed very rapidly toward becoming real technology. However, the complex nature of e-skin technology presents significant challenges in terms of materials, devices, sophisticated integration methods, and interference-free data acquisition. These challenges range from functional materials, device architecture, pixel design, array structure, and data acquisition method to multimodal sensing performance with negligible interference. In this article, we present recent research trends and approaches in the field of flexible and stretchable multimodal sensors for e-skin focusing on the following aspects: 1) flexible and stretchable platforms; 2) operating principles and materials suitable for pressure, temperature, strain, photograph, and hairy sensor devices; 3) device and integration architectures, including multimodal single cells, three-axis tactile sensors, vertical-stacked sensor arrays, active matrix sensor arrays, and integration electronics; 4) reliable acquisition methods for various texture sensing and machine-learning algorithms for processing tactile sensing data; and 5) future outlook.
A conformal patch biosensor that can detect biomolecules is one promising technology for wearable... more A conformal patch biosensor that can detect biomolecules is one promising technology for wearable sweat glucose self-monitoring. However, developing such a patch is challenging because conferring stretchability to its components is difficult. Herein, we demonstrate a platform for a nonenzymatic, electrochemical sensor patch: a wrinkled, stretchable, nanohybrid fiber (WSNF) in which Au nanowrinkles partially cover the reduced graphene oxide (rGO)/polyurethane composite fiber. The WSNF has high electrocatalytic activity because of synergetic effects between the Au nanowrinkles and the oxygen-containing functional groups on the rGO-supporting matrix which promote the dehydrogenation step in glucose oxidation. The WSNF offers stretchability, high sensitivity, low detection limit, high selectivity against interferents, and high ambient-condition stability, and it can detect glucose in neutral conditions. If this WSNF sensor patch were sewn onto a stretchable fabric and attached to the human body, it could continuously measure glucose levels in sweat to accurately reflect blood glucose levels.
Fiber-based sensors integrated on textiles or clothing systems are required for the next generati... more Fiber-based sensors integrated on textiles or clothing systems are required for the next generation of wearable electronic platforms. Fiber-based physical sensors are developed, but the development of fiber-based temperature sensors is still limited. Herein, a new approach to develop wearable temperature sensors that use freestanding single reduction graphene oxide (rGO) fiber is proposed. A freestanding and wearable temperature-responsive rGO fiber with tunable thermal index is obtained using simple wet spinning and a controlled graphene oxide reduction time. The freestanding fiber-based temperature sensor shows high responsivity, fast response time (7 s), and good recovery time (20 s) to temperature. It also maintains its response under an applied mechanical deformation. The fiber device fabricated by means of a simple process is easily integrated into fabric such as socks or undershirts and can be worn by a person to monitor the temperature of the environment and skin temperature...
Omnidirectionally stretchable photodetectors are limited by difficulties in designing material an... more Omnidirectionally stretchable photodetectors are limited by difficulties in designing material and fabrication processes that enable stretchability in multiaxial directions. Here, we propose a new approach involving an organic-inorganic p-n heterojunction photodetector comprised of free-standing ZnO nanorods (NRs) grown on a poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate transport layer coated on a three-dimensionally micro-patterned stretchable substrate containing bumps and valleys. This structure allows for efficient absorption of stretching strain. This approach allows the device to accommodate large tensile strain in all directions. The device behaves as a photogated p-n heterojunction photodetector, in which current modulation was obtained by sensing mechanisms that rely on photovoltage and photogating effects. The device exhibits a high photoresponse to UV light and reliable electrical performance under applied stretching in uniaxial and omni-axial directions. Furthermore, the device can be easily and conformally attached to a human wrist. This allowed us to investigate the response of the device to UV light during human activity.
Herein, we review recent advances in transparent stretchable electronic materials and transparent... more Herein, we review recent advances in transparent stretchable electronic materials and transparent stretchable electronic devices. Some representative examples that highlight the unique optical, electrical and mechanical properties of transparent stretchable materials and devices are also discussed in detail.
Advanced materials (Deerfield Beach, Fla.), Jan 14, 2016
Stretchable electronic devices with intrinsically stretchable components have significant inheren... more Stretchable electronic devices with intrinsically stretchable components have significant inherent advantages, including simple fabrication processes, a high integrity of the stacked layers, and low cost in comparison with stretchable electronic devices based on non-stretchable components. The research in this field has focused on developing new intrinsically stretchable components for conductors, semiconductors, and insulators. New methodologies and fabrication processes have been developed to fabricate stretchable devices with intrinsically stretchable components. The latest successful examples of stretchable conductors for applications in interconnections, electrodes, and piezoresistive devices are reviewed here. Stretchable conductors can be used for electrode or sensor applications depending on the electrical properties of the stretchable conductors under mechanical strain. A detailed overview of the recent progress in stretchable semiconductors, stretchable insulators, and oth...
Flexible chemical sensors utilizing chemically sensitive nanomaterials are of great interest for ... more Flexible chemical sensors utilizing chemically sensitive nanomaterials are of great interest for wearable sensing applications. However, obtaining high performance flexible chemical sensors with high sensitivity, fast response, transparency, stability, and workability at ambient conditions is still challenging. Herein, a newly designed flexible and transparent chemical sensor of reduced graphene oxide (R-GO) coupled with organic dye molecules (bromophenol blue) is introduced. This device has promising properties such as high mechanical flexibility (>5000 bending cycles with a bending radius of 0.95 cm) and optical transparency (>60% in the visible region). Furthermore, stacking the water-trapping dye layer on R-GO enables a higher response as well as workability in a large relative humidity range (up to 80%), and dual-mode detection capabilities of colorimetric and electrical sensing for NH3 gas (5–40 ppm). These advantageous attributes of the flexible and transparent R-GO sensor coupled with organic dye molecules provide great potential for real-time monitoring of toxic gas/vapor in future practical chemical sensing at room conditions in wearable electronics.
Abstract A flexible photodetector based on methylammonium lead iodide perovskite-graphene (Gr) hy... more Abstract A flexible photodetector based on methylammonium lead iodide perovskite-graphene (Gr) hybrid channel field-effect transistors (FETs) are studied under broadband incident light and at various photon intensities (515 nm). The combination of high light absorption of the antenna material (perovskite) and excellent mobility and conduction of the transport layer (Gr) in the hybrid channel enables the photodetector to reach high responsivities (up to 115 A W−1) at 515 nm. The change in transfer characteristics of the hybrid channel phototransistor under light exposure allows for a deep understanding of the sensing mechanism and carrier transport properties of Gr based on the shifting of Dirac points (VDirac). Additionally, the as-fabricated device on polyimide substrates yields good mechanical flexibility, electrical stability, and endurance with the responsivity being unaffected under flexure and the photocurrent being unchanged after 3000 bending cycles at a 12 mm bending radius. This work demonstrates the promising potential of these materials for future application in next generation optoelectronic devices.
Advanced materials (Deerfield Beach, Fla.), Jan 3, 2016
Flexible and stretchable physical sensors that can measure and quantify electrical signals genera... more Flexible and stretchable physical sensors that can measure and quantify electrical signals generated by human activities are attracting a great deal of attention as they have unique characteristics, such as ultrathinness, low modulus, light weight, high flexibility, and stretchability. These flexible and stretchable physical sensors conformally attached on the surface of organs or skin can provide a new opportunity for human-activity monitoring and personal healthcare. Consequently, in recent years there has been considerable research effort devoted to the development of flexible and stretchable physical sensors to fulfill the requirements of future technology, and much progress has been achieved. Here, the most recent developments of flexible and stretchable physical sensors are described, including temperature, pressure, and strain sensors, and flexible and stretchable sensor-integrated platforms. The latest successful examples of flexible and stretchable physical sensors for the ...
Advanced materials (Deerfield Beach, Fla.), Jan 26, 2015
A transparent stretchable (TS) gated sensor array with high optical transparency, conformality, a... more A transparent stretchable (TS) gated sensor array with high optical transparency, conformality, and high stretchability of up to 70% is demonstrated. The TS-gated sensor array has high responsivity to temperature changes in objects and human skin. This unprecedented TS-gated sensor array, as well as the integrated platform of the TS-gated sensor with a transparent and stretchable strain sensor, shows great potential for application to wearable skin electronics for recognition of human activity.
Photodetectors using optically responsive graphene (Gr) or reduced graphene oxide (R-GO) on rigid... more Photodetectors using optically responsive graphene (Gr) or reduced graphene oxide (R-GO) on rigid substrates have showed promising results for detection of broad band light including infrared (IR). However, there have been only a few reports on Gr or R-GO photodetectors with new functionalities such as optical transparency and/or flexibility. Herein, a new kind of transparent and flexible IR photodetector is presented using a field-effect transistor (FET) structure in which an IR-responsive nanocomposite layer of R-GO and poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) is employed as the channel. The IR photodetector exhibits high IR responsivity, stability, and reproducibility under mechanical strain and ambient conditions. In addition, the capability of measuring the distribution of responses from each device in the transparent and flexible nanocomposite FET array under IR radiation from the human body is also demonstrated. Therefore, the development of a flexible IR photodetector with high responsivity, transparency, ease of integration, and stability in an ambient environment is a suitable alternative approach for achieving the stable monitoring of IR in many flexible and transparent electronic systems.
Ultraviolet (UV) photodetectors based on ZnO nanostructure/graphene (Gr) hybrid-channel field-eff... more Ultraviolet (UV) photodetectors based on ZnO nanostructure/graphene (Gr) hybrid-channel field-effect transistors (FETs) are investigated under illumination at various incident photon intensities and wavelengths. The time-dependent behaviors of hybrid-channel FETs reveal a high sensitivity and selectivity toward the near-UV region at the wavelength of 365 nm. The devices can operate at low voltage and show excellent selectivity, high responsivity (RI ), and high photoconductive gain (G). The change in the transfer characteristics of hybrid-channel FETs under UV light illumination allows to detect both photovoltage and photocurrent. The shift of the Dirac point (V Dirac ) observed during UV exposure leads to a clearer explanation of the response mechanism and carrier transport properties of Gr, and this phenomenon permits the calculation of electron concentration per UV power density transferred from ZnO nanorods and ZnO nanoparticles to Gr, which is 9 × 10(10) and 4 × 10(10) per mW, respectively. The maximum values of RI and G infer from the fitted curves of RI and G versus UV intensity are 3 × 10(5) A W(-1) and 10(6) , respectively. Therefore, the hybrid-channel FETs studied herein can be used as UV sensing devices with high performance and low power consumption, opening up new opportunities for future optoelectronic devices.
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Papers by Tran Quang Trung