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- Feng, Yi
(författare)
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Printed RFID Humidity Sensor Tags for Flexible Smart Systems
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Radio frequency identification (RFID) and sensing are two key technologies enabling the Internet of Things (IoT). Development of RFID tags augmented with sensing capabilities (RFID sensor tags) would allow a variety of new applications, leading to a new paradigm of the IoT. Chipless RFID sensor technology offers a low-cost solution by eliminating the need of an integrated circuit (IC) chip, and is hence highly desired for many applications. On the other hand, printing technologies have revolutionized the world of electronics, enabling cost-effective manufacturing of large-area and flexible electronics. By means of printing technologies, chipless RFID sensor tags could be made flexible and lightweight at a very low cost, lending themselves to the realization of ubiquitous intelligence in the IoT era.This thesis investigated three construction methods of printable chipless RFID humidity sensor tags, with focus on the incorporation of the sensing function. In the first method, wireless sensing based on backscatter modulation was separately realized by loading an antenna with a humidity-sensing resistor. An RFID sensor tag could then be constructed by combining the wireless sensor with a chipless RFID tag. In the second method, a chipless RFID sensor tag was built up by introducing a delay line between the antenna and the resistor. Based on time-domain reflectometry (TDR), the tag encoded ID in the delay time between its structural-mode and antenna-mode scattering pulse, and performed the sensing function by modulating the amplitude of the antenna-mode pulse.In both of the above methods, a resistive-type humidity-sensing material was required. Multi-walled carbon nanotubes (MWCNTs) presented themselves as promising candidate due to their outstanding electrical, structural and mechanical properties. MWCNTs functionalized (f-MWCNTs) by acid treatment demonstrated high sensitivity and fast response to relative humidity (RH), owing to the presence of carboxylic acid groups. The f-MWCNTs also exhibited superior mechanical flexibility, as their resistance and sensitivity remained almost stable under either tensile or compressive stress. Moreover, an inkjet printing process was developed for the f-MWCNTs starting from ink formulation to device fabrication. By applying the f-MWCNTs, a flexible humidity sensor based on backscatter modulation was thereby presented. The operating frequency range of the sensor was significantly enhanced by adjusting the parasitic capacitance in the f-MWCNTs resistor. A fully-printed time-coded chipless RFID humidity sensor tag was also demonstrated. In addition, a multi-parameter sensor based on TDR was proposed.The sensor concept was verified by theoretical analysis and circuit simulation.In the third method, frequency-spectrum signature was utilized considering its advantages such as coding capacity, miniaturization, and immunity to noise. As signal collision problem is inherently challenging in chipless RFID sensor systems, short-range identification and sensing applications are believed to embody the core values of the chipless RFID sensor technology. Therefore a chipless RFID humidity sensor tag based on near-field inductive coupling was proposed. The tag was composed of two planar inductor-capacitor (LC) resonators, one for identification, and the other one for sensing. Moreover, paper was proposed to serve as humidity-sensing substrate for the sensor resonator on accounts of its porous and absorptive features.Both inkjet paper and ordinary packaging paper were studied. A commercial UV-coated packaging paper was proven to be a viable and more robust alternative to expensive inkjet paper as substrate for inkjet-printed metal conductors. The LC resonators printed on paper substrates showed excellent sensitivity and reasonable response time to humidity in terms of resonant frequency. Particularly, the resonator printed on the UV-coated packaging paper exhibited the largest sensitivity from 20% to 70% RH, demonstrating the possibilities of directly printing the sensor tag on traditional packages to realize intelligent packaging at an ultra-low cost.
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| 2. |
- Lopez Cabezas, Ana, 1980-
(författare)
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Nanofibrillar Materials for Organic and Printable Electronics
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent years, organic electronics have attracted great attention due to their multiple advantages such as light weight, flexibility, large area fabrication and cost-effective production processes. The recent progress in fabricating organic electronic devices has been achieved with the development of new materials which provide competing functionalities to the electronics devices. However, as it happens with all type of technologies, organic electronics is not free from challenges. In the latest OE-A Roadmap for organic and printed electronics (2011), the “red brick walls” were identified, and the following three main challenges were pointed out as the potential roadblocks from the material point of view: electrical performance, solution processability (especially formulations in non-toxic solvents) and environmental stability. Currently there is a significant increasing interest in optimizing or developing novel materials to meet those requirements. This thesis presents processing development and study of nanofibrillar materials and deals with the optimization for its applicability for organic electronics. The overall work presented in the thesis is based on three nanofibrillar materials: Polyaniline (PANI), carbon nanotubes (CNTs) and the CNT/PANI composite. First, the solution processability of carbon nanotubes and polyaniline is studied respectively, and through covalent and non-covalent methods, stable aqueous dispersions of these materials are successfully achieved. Second, a composite consisting of multi-walled carbon nanotubes (MWCNTs) and PANI with a core-shell structure is developed and characterized. The investigation of the effects of the loading and type of nanotubes incorporated in the composite material, led to understanding on the fundamental theory underlying the composite morphology. Based on those findings and by carefully optimizing the synthesis procedure, water dispersible MWCNT/PANI nanofibrillar composite is successfully synthesized becoming compatible with solution processable techniques, such as spray coating and potentially with printing technology. With the incorporation of carbon nanotubes, the nanofibrillar composite reaches conductivities 20 times higher than that of the pure polymer. Moreover, the presence of the nanotubes in the composite material decelerates up to 60 times the thermal ageing of its conductivity, making the polymer more robust and suitable for possible manufacturing processes. Furthermore, the composite material still retains the advantageous properties of PANI: electrochromism, tunable conductivities, and sensing capabilities. Third, the stable dispersions of PANI, CNTs and MWCNT/PANI composite were effectively deposited by spray coating technique on several low-cost substrates (PET, PEN, polyimide and papers), and homogeneous, flexible, large-area films were fabricated. Additionally, by spraying the materials on pre-fabricated inkjet printed electrodes, a pH sensor based on the MWCNT/PANI composite and a humidity sensor based on functionalized MWCNTs capable of working at GHz range were demonstrated, which shows that the nanofibrillar materials studied in this thesis work are promising sensor materials for wireless application at ultra-high frequency (UHF) band. Finally, the humidity sensor was integrated into a sensor-box demonstrating a hybrid interconnection platform where printed electronics can be seamlessly integrated with silicon-based electronics. The integration closes the gap between the two technologies, anticipating the adaption of organic electronic technologies.
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| 3. |
- Xie, Li
(författare)
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Heterogeneous Integration of Silicon and Printed Electronics for Intelligente Sensing Devices
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Driven by the exploding popularity of the Internet-of-Things (IoT), the demand for thin, flexible, lightweight intelligent sensingdevices is growing rapidly. Two attractive examples are intelligent packaging and wearable healthcare monitoring devices, which help to connect and track / monitor everything / everybody at any time and in any place. The remarkably swift development of flexible and printed electronics is promoting new possibilities for cost-effective manufacturing of such devices. However, compared with silicon-based circuits, state-of-the-art all-printed circuits are encountering low integration density, long switching time and corresponding high cost per function. Therefore, a heterogeneous platform is in great demand, which employs a cost-effective, large-area manufacturing technique while keeping the same complex functionality and processing capability as silicon-based systems. Due to temperature and mechanical reasons, traditional silicon integration methods, such as solder bonding and wire bonding, are not suitable for flexible printed electronics. This thesis aims to develop a generally applicable hetero-geneous integration platform for the realization of intelligent sensing devices on flexible substrates.First, inkjet printing technique is introduced and studied. As the basic and key element, inkjet printing technology is employed to fabricate interconnections as well as electrodes of the printed sensors. Novel flexible media, plastic and paper, are evaluated as the substrates of printed electronic systems from two aspects: the electrical characteristics and performance reliability. In addition to widely used inkjet/photo paper, packaging paper is presented as a promising candidate for intelligent packaging applications due to the advantages in terms of lower price, higher temperature endurance and better reliability against 85◦/85% RH aging.Second, the heterogeneous integration platform enabled byinkjet printing is presented. Benefiting from the non-contact, accurate alignment and fine resolution features, this integration technique has the advantages of simplified fabrication process and multi-substrate compatibility. The design rules have been studied and the integration process is optimized for silicon chips with/without packaging.Finally, to verify the suitability, the heterogeneous integration platform is applied to two representative applications, each with unique emphasis and requirements.For intelligent packaging, low-cost is one crucial requirement. Paper substrate is selected because it is cost-effective, recyclableand a commonly-used packaging material in industry. In order to fit into non-regular shape pack-ages, the intelligent packaging needs to be bent or folded, which brings about reliability concern for paper electronics. Therefore, bending and folding tests are applied to reveal the capability and the limitation of paper electronics in terms of flexibility. For applications such as fresh food tracking, humidity is an important physical quantity to monitor during transportation and storage. Therefore, a resistive humidity sensor based on multi-walled carbon nanotubes is fabricated and integrated. A commercial packaged microcontroller is used to sense and store the resistance of the sensor and control the LEDs to indicate the ambient humidity level. By integratingthe microcon-troller, LEDs and a switch with the printed sensor and battery, a prototype of a paper-based humidity sensor card is implemented.For the healthcare application, user comfort is an essential element. Future long-term healthcare devices require a bio-sensing system which is small, thin, lightweight and wearable, has a long-battery life, and is easy to customize. The heterogeneous platform offers a promising solution for such systems from three aspects. 1) A fully integrated system-on-chip (SoC) is embedded to detect and process the bio-signal. The SoC solution features tiny size and low-power consumption, which contribute to system miniaturization and long battery lifetime. 2) Inkjet printing offers a cost-effective approach to fabricate personalized electrodes. 3) Inkjet printed interconnections enable the direct integration of the bare die instead of the packaged chip. This significantly reduces the physical size of the system, simplifies the manufacture process and lowers the cost. The concept is demonstrated by aminiaturized wearable Bio-Patch with the size of 4.5 cm×2.5 cm.
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