Stretchable electronics, which can maintain electric components’ function while being stretched, extend the application of electronics to nonplanar surface, human skin and robotic joint et. al. The stretchable components are requested to be stretched, twisted, and conformed to adapt the nonplanar surfaces, the elongation of skin and robotic joints. Currently, wearable electronics are developing rapidly in various aspects, encouraging the development of stretchable technologies. Two main strategies are explored for the stretchable electronics. One method is nano material doped elastomer and organic stretchable materials, making use of nano particles and functional groups to manufacture stretchable electronics. The other method is specific structure designs, such as wavy structure, origam...[ Read more ]

Stretchable electronics, which can maintain electric components’ function while being stretched, extend the application of electronics to nonplanar surface, human skin and robotic joint et. al. The stretchable components are requested to be stretched, twisted, and conformed to adapt the nonplanar surfaces, the elongation of skin and robotic joints. Currently, wearable electronics are developing rapidly in various aspects, encouraging the development of stretchable technologies. Two main strategies are explored for the stretchable electronics. One method is nano material doped elastomer and organic stretchable materials, making use of nano particles and functional groups to manufacture stretchable electronics. The other method is specific structure designs, such as wavy structure, origami structure, kirigami structure, achieving stretchability via the deformation of the specified structures. Among these typical structures, wavy structure is the simplest one, beneficial to models’ fabrication and devices’ mass production.

This thesis mainly focuses on the stretchable wavy structure design and the fabrication of stretchable electronics via MEMS based technology. Primarily, wavy structure-based electronics are designed and simulated to give a comprehensive study of the wavy structured stretchable electronic device. Wherein, one type of stretchable strain sensor and one type of stretchable display device was proposed, making use of the different designed wavy structures. Besides, the electric properties and mechanical properties are evaluated for the two types of wavy structure based electronic devices. The proposed MEMS based fabrication method is applicable for both stretchable electronic devices.

In the first work, a stretchable thin film capacitive strain sensor based on wavy-structured interdigitated metal electrodes was successfully demonstrated. Wavy-shape metal electrodes were patterned using bulk silicon micromachining, endowing the electrodes with high stretchability and reliability. The electrodes were also protected with a layer of parylene C to prevent damage during stretching and embedded in polydimethylsiloxane (PDMS) stretchable package layers. The interdigitated electrodes sitting on the wavy structures experienced a waving angle change under external strain resulting in capacitive change, which is the sensing mechanism of the wavy structured interdigitated capacitive strain sensor (WICSS). The sensitivity and stretchability of the WICSS is dependent on the design of interdigitated electrodes and the dimension of the wavy structures. The gauge factor (GF) of the WICSS was 0.27 at 25% strain. There was little hysteresis during the stretching and releasing process in the range of 25% strain. The sensing property remained stable within a 1000 cycling test. The applications of the high-performance WICSS are also demonstrated by detecting the motion of human fingers and wrists.

In the second work, we fabricated a biaxially stretchable LED display based on wavy structured metal grid together with LED chips. MEMS based fabrication process was utilized to fabricate the wavy-structured connection metal and rigid island of the LED display. The resulting LED display can be readily bent, rolled, washed, and stretched with no degradation of its image quality. And repeated cycles can be tolerated at 10% strain. This work demonstrates the potential of inorganic materials as stretchable displays and MEMS compatible processes as stretchable electronics fabrication processes.

In the above two projects, electronic devices’ stretchability is successfully achieved via special designed wavy structure. The wavy structure in both projects is stable, reliable, and compatible with micro fabrication process. This study shows inorganic materials’ promising potential in the application of stretchable electronic devices with the help of wavy structure.