Abstract
Ultra-thin chips (UTCs) are needed to meet the performance and packaging related requirements of flexible electronics and 3D integrated circuits (ICs). However, handling of UTCs (<50 μm thick), particularly after thinning, is a challenging task as the excessive mechanical stresses could lead to cracking. Such damages could be prevented by restricting the stresses to acceptable levels. Herein, we present a new reliable and cost-effective method based on a polymethylmethacrylate (PMMA) sacrificial layer (20 μm-thick). The PMMA layer results in 4 order of magnitude lower stress on UTCs and, as a result, the reliable removal or debonding of UTCs (35 μm-thick) from the glass substrate has been achieved. The distinctive features of the presented method are high reliability and cost-effectiveness (an order of magnitude cheaper) with respect to conventional methods that use UV curable tapes. The UTCs with metal-oxide-semiconductor capacitors (MOSCAPs) devices were also obtained using this approach and were evaluated under different bending conditions. The stable and uniform performance (134 pF) observed under bending conditions demonstrates that the presented technique could be useful for integration of high-performance flexible UTCs on flexible printed circuit boards for various practical application.
Highlights
Silicon has been the workhorse material for electronics industry, owing to its excellent electrical and mechanical properties which has led to today's fast computation and communication through highperformance devices and integrated circuits (ICs) [1]
The International Technology Roadmap for Semiconductor suggests that Moore's law may be flattening soon, and a further value addition could come from a vertical growth i.e. 3-dimentional (3D) ICs through the stacking of chips via new form factors such as flexible electronics [4,5,6,7]
Ultra-thin chip (UTC) technology has emerged as a key solution, enabling high density packaging as well as high performance flexible electronic systems [7]
Summary
Silicon has been the workhorse material for electronics industry, owing to its excellent electrical and mechanical properties which has led to today's fast computation and communication through highperformance devices and integrated circuits (ICs) [1]. As an example, during thinning by lapping the chips are placed firmly on a wax-based substrate and vacuum-based pick and transfer does not work because of higher fragility of the chip or wafer after thinning. During the transfer or removal of UTCs from wax, the PMMA-based sacrificial layer acts as a stress-relieving agent It can protect the active device region from impurities or damages during thinning and transferring processes.
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