3-dimensional silicon image sensor and LED display formed by selective solvent plasticization and origami transformation of acrylonitrile-butadiene-styrene substrate

Abstract

3-dimensional (3D) optoelectronics based on the shape transformation of flexible electronics have emerged as an innovative technology that exhibits versatile optical benefits, such as low optical aberration or a wide field of view (FOV). Compared to direct fabrication methods such as 3D printing, the shape transformation has a significant advantage in that the initial planar shape can serve to mount electronic devices formed by the conventional planar semiconductor process. However, the transformation of shape in optoelectronic devices encounters three challenging issues; First, the devices should be soft for transformation but rigid to maintain the final shape. Second, the transforming technique should ensure a high degree of freedom in designing without electrical failure. Third, the transformation should not hamper the circuit layout, which is important in the optoelectronic devices with common row and column control lines. This thesis addresses the three issues by introducing an acrylonitrile-butadiene-styrene (ABS) substrate to the membrane-type electronic device and plasticizing the ABS selectively to induce a mechanical hard-soft-hard transition. It is envisioned that the addition of solvent induces viscoplastic property to accommodate most of stress/strain during transformation, otherwise concentrated to the device layer, which is critical when the device layer is placed on the top surface of the ABS for optoelectronic applications. Chapter 1 reviews current progress on flexible electronics and 3D optoelectronics with diverse approaches to minimize mechanical stress on the electronics parts. Moreover, this chapter summarises that the chemical and mechanical properties of ABS and the previous work on the hard-to-soft transition of the solvent-plasticized ABS substrate and stress reduction in the electronic components mostly highlighted in metal electrodes during the deformation. Chapter 2 presents a tetrahedral image sensor manufactured by transforming a flexible silicon image sensor on an ABS substrate with hinges and facets that can be selectively plasticized by limiting solvent diffusion time for sufficient plasticization in the hinges only. Concerning the device configuration of the image sensor, a passive-type pixel with a photodiode and a blocking diode and an active-type pixel with a photodiode and a transistor are fabricated and characterized. The tetrahedral image sensor shows the omnidirectional capability of detecting image. This chapter includes a detailed study on improvement in resolution of the image, collaborated detection capability in the neighboring faces, and the consideration of the required FOV for omnidirectional detection of regular polyhedrons. Chapter 3 demonstrates a tucking-based origami using selective plasticization through a microfluidic channel to form various 3D shapes. Confined plasticization on an ABS film allows extremely inward and outward folding and thereby tucking-based origami in the electronics level without losing common row and column control lines. As applications, this chapter presents three types of 3D display systems, including a double-sided display, a holographic display, and a hexahedral LED array.