A fully MEMS-compatible process for 3D high aspect ratio micro coils obtained with an automatic wire bonder

• Published in: Journal of micromechanics and microengineering 2010-01, Vol.20 (1), p.015021-015021 (11)
• Main Authors: Kratt, K, Badilita, V, Burger, T, Korvink, J G, Wallrabe, U
• Format: Article
• Language: English
• Subjects: Applied sciences; Bonding; Coils; Electronics; Exact sciences and technology; High aspect ratio; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Lithography; Mechanical engineering. Machine design; Mechanical instruments, equipment and techniques; Microelectronic fabrication (materials and surfaces technology); Micromechanical devices and systems; Physics; Precision engineering, watch making; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Spin coating; Three dimensional; Winding; Wire
• ISSN: 0960-1317; 1361-6439
• DOI: 10.1088/0960-1317/20/1/015021

We report the fabrication of 3D micro coils made with an automatic wire bonder. Using standard MEMS processes such as spin coating and UV lithography on silicon and Pyrex(R) wafers results in high aspect ratio SU-8 posts with diameters down to 100 mum that serve as mechanical stabilization yokes for the coils. The wire bonder is employed to wind 25 mum insulated gold wire around the posts in an arbitrary (e.g. solenoidal) path, yielding arrays of micro coils. Each micro coil is bonded directly on-chip, so that loose wire ends are avoided and, compared to other winding methods, coil re-soldering is unnecessary. The manufacturing time for a single coil is about 200 ms, and although the process is serial, it is batch fabrication compatible due to the high throughput of the machine. Despite the speed of manufacture we obtain high manufacturing precision and reliability. The micro air-core solenoids show an RF quality factor of over 50 when tested at 400 MHz. We present a flexible coil making method where the number of windings is only limited by the post height. The coil diameter is restricted by limits defined by lithography and the mechanical strength of the posts. Based on this technique we present coils ranging from 100 mum diameter and 1 winding up to 1000 mum diameter and 20 windings.