A Study on the Design and Process of CMOS Flip-Chip Micro Fluxgate Magnetometers

• Main Authors: Fang-Yu Jhao, 趙方毓
• Other Authors: Chih-Cheng Lu
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/jma636

碩士 === 國立臺北科技大學 === 機電整合研究所 === 100 === This paper presents a dual-core (Förster-type) micro-fluxgate magnetic field sensor fabricated on a silicon chip based on CMOS technology, electroless plating and flip-chip technology. The silicon chip is 2.5 mm × 2.5 mm in dimension. The sensor consists of magnetic cores, planar pick-up coils, bottom excitation coils (CMOS Al interconnections) and upper excitation coils (wire-bonding Al wires). By using Ansoft Maxwell to simulate the magnetic flux (Φ), it is found that by using a smaller core width it is able to obtain a higher magnetic flux density (B) at the expense of a reduced total magnetic flux (Φ). The simulation result helps optimizing the core size of microfluxgate in the future designs. In addition to the wire-bonded microfluxgate, we make use of the micro solder balls method to realize the flip-chip microfluxgate. Before collocating micro solder balls on to the pads, we tried two methods to improve the electrical contact between solder balls and pads. The first method is electroless plating of copper films, and the second one is sputtering deposition of silver films on the pads. Through experiments, it was found that the excitation circuit tends to open for both methods. The electroless-plated copper rapidly becomes insulating copper oxide on the surface, making it difficult to bond the solder balls. By using the silver coating process can successfully connect most of the pads of upper and lower chips. The experiment showed that the sensing coils in the upper and lower chips are successfully connected in series via solder balls, but the multi-turn excitation coil of the flip-chip sensor is an open circuit. Further works on improving the yield and efficiency of solder ball plating and wafer-to-wafer bonding with solder balls will be valuable for realization of the practical flip-chip microfluxgate.