One of the most exciting developments in the semiconductor field is the emergence of printed flexible electronics, which are poised to shape the future in various ways. Let’s start by exploring the most intriguing use of printed flexible electronics and the potential it holds for the future: electronic textiles.
E-textiles, simply put, are electronically embedded fabrics. Theoretically, any component can be embedded, however, the most used in e-textiles are sensors such as the Velostat® Pressure-Sensitive Conductive Sheet or Flexpoint Bend Sensors, LEDs, batteries and most recently FPCBs (Flexible Printed Circuit Boards) like Kapton® or Pyralux®.
These novel textiles have a wide range of properties, including flexibility, large surface area for sensing and invisibility to others, making them ideal for various applications, most notably textile heating, textile lighting, biometric sensing and monitoring, health monitoring and worker safety. The manufacturing of e-textiles involves the use of conductive materials such as metals like silver or copper, as well as the integration of flexible electronic components directly into the textile substrates.
To integrate flexible electronic components directly into textile substrates, a key challenge lies in efficiently routing electronic circuits on flexible materials. The integration of flexible electronic components into textile substrates involves advanced interconnection technologies, material considerations for flexibility and performance, and innovative methods like inkjet printing to create conductive patterns on e-textiles. These developments aim to overcome challenges in routing electronic circuits on flexible substrates efficiently while ensuring optimal performance and reliability of the integrated components.
Various methods and technologies have been developed to address this challenge:
1. Interconnection Technologies:
  - Modified Mill and Fill (M&F) Interconnect Technology: Proposed for high-resolution, high-throughput and high-density conductive trace patterns on flexible substrates.
  - Different Interconnect Structures: Utilized such as serpentine, buckled geometry, and honeycomb structure, each with its own merits and demerits in terms of electrical and mechanical performance.
  - Stretchable Indium Interconnects: Demonstrated as a cost-effective fabrication process on an elastomer PDMS (Polydimethylsiloxane) substrate.
  - Conductive Adhesives: Offer an alternative for connecting components without generating heat or stress, although they may have varying electrical properties.
  - Inkjet Printing: Commonly used to create conductive patterns using conductive inks catered for e-textiles.
2. Materials and Integration:
  - Flexible Substrates: Materials like polyimide are considered for better flexibility and processability.
  - Integration Challenges: Ensuring all electronic components and ICs are integrated optimally on the flexible substrate with minimal space and power requirements.
  - Hybrid Solutions: Combining rigid semiconductor/metal/dielectric components with soft fibrous materials to achieve flexibility and optimal performance.
The field of e-textiles can be divided into two main types:
1. E-textiles with classical electronic devices such as conductors, integrated circuits, LEDs and conventional batteries embedded into garments.
2. E-textiles with electronics integrated directly into the textile substrates, including passive and active components such as transistors, diodes and solar cells.Â
Most research and commercial e-textile projects are hybrids, where electronic components embedded in the textile are connected to classical electronic devices or components. Examples include touch buttons constructed entirely in textile forms using conductive textile weaves, which are then connected to devices like music players or LEDs mounted on woven conducting fiber networks to create displays. Printed sensors for both physiological and environmental monitoring have been integrated into various textiles, including cotton, Gore-Tex and neoprene.
The manufacturing of e-textiles involves the use of various conductive materials and electronic components. Conductive fabrics and textiles are plated or woven with metallic elements such as silver, nickel, tin, copper and/or aluminum. These textiles exhibit excellent electrical properties and can be used to create flexible and soft electrical circuits within garments or other products, as well as pressure and position-sensing systems. Conductive threads, yarns, coatings and inks like the Shieldex® Silver Plated Nylon Yarn or Gore® Conductive Yarn are also used to create conductive paths and convert traditional textiles into electrically conductive materials.
Recent advanced functions in e-textiles include the development of organic fiber transistors, organic solar cells on fibers, and the use of materials such as shape memory alloys (SMOs), piezoelectric materials, chromic materials and nano-materials. This has significantly expanded the capabilities of e-textiles and opened new possibilities for their use in various applications, most notably, aerospace, military and sports.
Military and Aerospace: A novel wearable electronic textile (WET) incorporating S-ST/MWCNT/Kevlar demonstrates enhanced safeguarding and force-sensing capabilities. Stab resistance tests reveal a 90% increase in maximum resistance force (18 N) and a 50% increment in penetration impact energy (11.76 J) compared to neat Kevlar, while dynamic impact resistance tests show a 190% improvement (1052 N) with the WET, attributing its performance to stable electrical conductivity enabled by multi-walled carbon nanotubes, making it an ideal candidate for wearable monitoring devices providing both body protection and movement analysis. As for space wear, NASA's innovative method seamlessly integrates conventional embroidery with automated milling to create fabric-based circuits and antennas, offering enhanced surface conductivity, improved impedance control, and expanded design and application possibilities. This cost-effective approach facilitates the production of e-textiles with higher geometric complexity, paving the way for applications in aerospace, military and textiles/wearables, including fabric skin aircraft antennas, digital battlefield apparel with embedded electronics, and advanced sensors for spacesuits.
Sports:Â The latest in e-textile activewear is a novel self-powered and self-functional sock (S2-sock) that integrates a poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) coated fabric triboelectric nanogenerator (TENG) and lead zirconate titanate (PZT) piezoelectric chips. This hybrid mechanism enables the sock to harvest energy and sense physiological signals, such as gait, contact force and sweat level. It also demonstrates successful walking pattern recognition and motion tracking under various environmental conditions, emphasizing the feasibility of utilizing everyday cotton socks as a power source for self-sustained smart socks with wireless transmission modules and integrated circuits.
The diversity of e-textiles isn’t limited to the sports and defense industries. On the contrary, it is being widely considered for niche and commercial applications alike. Thus, it's not surprising that e-textiles and smart fabrics are used in clothing. The European Commission's STARTS Program initiated the Re-FREAM project, where artists, designers and scientists collaborated to innovate the fashion industry's manufacturing process. They aimed to create techniques and aesthetics that are both inclusive and sustainable. Here are some standout products:
Footwear Time-Based Design: A biodegradable shoe with replaceable parts and integrated sensors. Users can customize settings via an app or let the shoe adjust autonomously, reducing waste and carbon footprint.
Second Skins: Garments with responsive textile elements, allowing wearers to create personalized light displays. Made using printed circuit boards and LEDs, they're easily repairable or disassembled.
Touch (and staying in Touch):Â Sweaters with conductive yarns and e-textile bonding, enabling wearers to communicate through touch or Bluetooth, inspired by social distancing.
In the medical industry, smart textiles and e-textiles depend greatly on biosensors. These sensors are incorporated into garments and have been gaining a lot of fame and are being used in various applications:
Measuring muscle activity for rehabilitation.
The DynaFeed smart garment for athletes to track biometric data.
Biosensors for rapid medical diagnosis, like Monrod Bio, offering on-the-spot diagnostics.
In terms of occupational safety, workers also benefit from e-textiles:
Elitac Wearables' SmartShoulder vest for service engineers, featuring a panic button and LED lights for low-light visibility.Â
The Mission Navigation Belt for soldiers, providing haptic feedback for GPS navigation.
Exoskeletons: Industrial wearables assisting workers in lifting heavy objects and reducing physical strain during repetitive tasks. These devices boost efficiency and also mitigate the risk of injuries in the workplace.
Despite their potential, challenges like washability and affordability remain. Overall, wearable technology, including e-textiles and smart fabrics, is on its way towards significant development.
Although currently considered a niche market, smart textiles are poised for exponential growth and will project a surge in demand, expected to drive advancements in manufacturing techniques and lower costs. As forecasts suggest that by 2025 a significant portion (10%) of the population will integrate internet-connected clothing into their daily lives, we, at McKinsey Electronics, are here to witness this marvel take place. Our expert circuit design engineers will guide your e-textile and flexible electronics projects from the design phase to sourcing your components and testing them. Contact McKinsey Electronics today!