| Author: | Liu, Su |
| Title: | Heterogeneously integrated microelectronic systems on one-dimensional circuit board for wearable applications |
| Advisors: | Tao, Xiao-ming (ITC) |
| Degree: | Ph.D. |
| Year: | 2022 |
| Subject: | Electronic textiles Microelectronics Wearable technology Smart materials Hong Kong Polytechnic University -- Dissertations |
| Department: | Institute of Textiles and Clothing |
| Pages: | xx, 202 pages : color illustrations |
| Language: | English |
| Abstract: | Textiles are important to humans as they not only offer protection from the cold but also provide aesthetics and comfort. The emergence of smart textiles provides additional functions to the wearer by integrating microelectronic devices or incorporating a nanostructure within the materials that form them. In wearable smart textile systems, microelectronic devices are essential, which are assembled on flexible substrates. Fibre-based materials like fabrics and papers have contributed to the development of flexible wearable electronics as substrates. Yet, the porous structure of fabric and large surface roughness limit its application in high precision flexible circuits. On the other hand, fibre-based paper is regarded as an alternative and biocompatible substrate that can be integrated as miniature electronic components for wearable textiles. However, applications of fibre-based electronics are inhibited by the mechanical properties of paper, fabrication methods and limited integrability. In response, this thesis aims to develop a high resolution, low resistance and highly efficient fibre-based circuit board (FCB), to explore the connection between microelectronic chips and FCB, and FCB and external circuits for optimum connections. Then, one such microelectronic system protype will be designed and fabricated, i.e. a monitoring diaper system for babies. Even impermeable thin plastic films generating uncomfortable experience to wearer and having poor fatigue resistance, this disadvantage will be eliminated by integrating film-based microelectronics into textile structure. Finally, a textile display prototype which integrated flexible printed circuit assembly (FPCA) into textile structure will be developed. An FCB with exceptional performance is realised by exploring the use of different substrates, photolithography and metal plating. First, fibre aramid paper sheets are studied due to their excellent properties, such as high mechanical strength and excellent resistance to water. The excellent properties of aramid paper will ensure the stability and durability of paper electronics. Then, photolithography is used to transfer a high resolution pattern onto the paper. Thirdly, metal is electroless deposited on the paper and electroplated to develop the FCB. A scanning electron microscope (SEM) analysis is conducted to investigate the layer of metal tracks. The SEM results demonstrate that the surface of the paper is entirely coated by the deposited metal particles. The ratio of metal elements is Cu 98.9/Ni 0.4/Ag 0.7. The developed FCB only has two layers, that is: the paper substrate and deposited metal particles. The error of the metal tracks is less than 0.01 mm. The tracks have a resistance of 0.2 Ω/cm. The deposited metal tracks show a small increase in the resistance parameters after 2000 cycles of a bending test. Finally, an FCB for light-emitting diode (LED) arrays is designed and developed. The results show that all the LEDs on the FCB could give light normally regardless of the folding and bending cycles. Circuit boards have now evolved so that they are highly accurate and thin, and have multiple layers with small holes known as vias that are small openings to allow conductive connections between the layers. Thus, to expand the applications of FCBs in wearable electronics, a novel double sided FCB has been developed in this study. To establish the connection between the FCB and scaled down sensors, surface mount technology (SMT) is adopted. During the progression of surface mounting, a custom-made system is used to support and fix the FCB. To reduce the deformation of the FCB during reflow soldering, a solder paste with the lowest melting temperature among all of the commercial products is used. After surface mounting is carried out, the FCB assembly (FCBA) is constructed. With respect to new-borns with jaundice, a wearable urine analysis system (WUAS) is required to identify related diseases in the early stages. To build the WUAS, a heterogeneous integration method is used to interface a flexible conformal sensor unit and rigid control units. Particularly, a sensor unit on an FCB that includes a temperature/humidity sensor, colour sensor and LEDs with a scaled down printed circuit board (PCB) that consists of a variety of processing and power components. A circuit bridge constructed on polyimide (PI) is designed to connect the sensor and control units. An analysis software is also developed for the WUAS and installed onto a mobile phone. Real-time display on the mobile phone is used to obtain parameter information such as the temperature, humidity, and R/G/B values of the colour sensor. The completed WUAS can be attached to the external surface of the diaper. After conducting experiments, it is found that when artificial urine is increased to a temperature of 37.2°C on the inner side of the diaper, the temperature and humidity of the external surface of the diaper increase from 24°C to 32°C, and 77% to 100%, respectively. Thus, urination events can be perceived by comparing ambient temperature/humidity and the temperature/humidity of the diaper. Several kinds of bilirubin and urobilinogen solutions are also prepared with different gradient concentrations and determined the corresponding R, G, and B value range of the test result as "+", "++", etc. Another one-dimensional circuit boards based on PI irritate human skin when in direct contact. Also, the roughness of fabric has inhibited the use of fabric in the development of high precision circuits. To combine the advantages of the high precision of PI circuits and softness of textile, PI circuits could be integrated into textile structures to develop functional wearable electronics. In this study, a prototype system that comprises an e-textile modular display of full 2563 colours is proposed. The FPC for the display is designed on a double sided circuit board to reduce the size of the circuits with RGB LED. A continuous length FPC is required to reduce the number of electrical connections for the display module. A serpentine track is designed on a circuit board and the adjacent tracks are connected at the corner of the circuits. RGB LEDs are mounted on the double sided FPC as the illuminating elements of display. A precision cutting machine is used to fabricate the FPCA into a certain length of FPCA strips. After cutting, the FPCA strips have straighter linkages at the corners of the circuit. One strip of FPCA is utilised as the inlay yarn to fabricate a programmable full-colour textile with an 8*8 LED display module. The modules are connected in two layers: (1) electronically with specially designed connection ports at the ends of the FPCA, and (2) mechanically with a connecting yarn network using crocheting. After connecting the four display modules into an e-textile display, the serial numbers of the RGB LED are not the same as their location in the display fabric module. Thus, the serial numbers of the RGB have to be determined in the e-textile display. Python software is then used to process the video into photos frame by frame, and then divide the photo into four patterns which correspond to the four display modules. The pixel information is obtained through Python software. Then, the pixel information is inputted into Arduino software which is used to drive e-textile displays and realise different functions. |
| Rights: | All rights reserved |
| Access: | open access |
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