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SQUID作为一种超灵敏的磁通传感器，在生物磁探测、低场核磁共振、地球物理探矿等领域得到广泛应用。本文设计开发了一种用于脑磁（MEG）系统的集成SQUID芯片，并进行了批量封装测试。其中，每个芯片上集成了两个一阶平面梯度计和一个磁强计，采用亚微米约瑟夫森结制备技术，实现0.7 μm ×0.7 μm的亚微米结尺寸。SQUID与探测线圈采用Nb超导引线连接，集成到同一芯片上。我们对171个SQUID器件的测试结果显示，这些器件在磁场白噪声、I-V特性、V-Φ特性等方面表现优异。我们制备的SQUID器件工作电流集中在15~20μA区间，电压摆幅集中在80~120 μV之间。此外，超过80%的SQUID器件的磁场白噪声低于5 fT/√Hz，能够满足多通道SQUID脑磁系统的要求。The Superconducting Quantum Interference Device (SQUID) is one of the most sensitive flux sensors, which is critical in fields such as biomagnetism, low-field nuclear magnetic resonance (NMR), and geophysics. In this paper, we present a detailed investigation of the integrated magnetoencephalography (MEG) SQUID chip, which consists of a magnetometer and two gradiometers. The SQUID and pick-up coils are fabricated on different-sized wafers. The SQUID is fabricated on a commercial silicon substrate using micro- and nano-fabrication processes, including thin-film growth, iline stepper photolithography, and reactive ion etching (RIE). The sub-micron Josephson junction technology is employed to acquire a junction size of 0.7 μm × 0.7 μm, with a junction capacitance of only 0.05 pF. The pick-up coil is designed as a single-turn coil for a magnetometer and a planar first-order gradient coil for a gradient sensor. The MEG SQUID chips are tested in a well-shielded room with the heliumliquid temperature (4.2 K). Customized low-voltage noise readout circuit and source measure units are used to characterize the magnetic field white noise, current-voltage (IV) characteristics, and voltage modulation amplitude of 171 SQUID channels. The results show that 81% of the SQUID chips exhibit the lower magnetic field noise (< 5 fT/√Hz), and the high modulation amplitudes (in the range of 80 ~ 120 μV) with the low working currents of 15 ~ 20 μA, yielding a wafer yield rate of 78%. In summary, the SQUIDs show excellent performance in terms of magnetic field white noises, modulation amplitudes, and working currents, which are suitable for the very weak magnetic signal detection. One future work will focus on optimizing the SQUID chip fabrication process to minimize performance variations between chips on the same wafer.
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Keywords:
- DC-SQUID /
- Magnetometer /
- Gradiometer /
- Magnetic field noise
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