Enhanced Limit-of-Detection of Current Sensor Based on Tunneling Magnetoresistive Effect With Multichips Differential Design
Jiaming Liu, Mengmeng Guan, Yiwei Xu, Shuang Zhao, Wei Su, Cuiling Zhang, Zhiguang Wang, Xiaohui Zhang, Zhongqiang Hu, Zhuangde Jiang, Ming Liu
Abstract
Accurately measuring weak electric currents in the order of mA in a non-invasive manner is crucial yet challenging for industrial electronics. In this work, we first fabricated low-noise magnetic field sensor chips based on the tunneling magnetoresistive (TMR) effect. A composite free layer and a three-step annealing process were used to improve performance, resulting in a sensitivity of 30 V/V/T (3 mV/V/Oe), non-linearity below 0.5%, and reduce the noise density from 1.4 μV/V/√Hz to 0.7 μV/V/√Hz at 1 Hz, in comparison with the traditional two-step annealing process. We then developed a weak-current sensing module with a differential design using two TMR sensor chips arranged antiparallelly. Equipped with a magnetic flux concentration structure and a low-noise signal processing circuit, we demonstrated transient measurement of weak current well below 1 mA with a wide bandwidth of DC-16 kHz, a dynamic range of ±150 mA (51 dB), and a rapid response time of ~30 μs. The limit-of-detection (LoD) of the sensing module for DC and AC current reached 800 μA and 300 μA (RMS), respectively, which is about 30% lower than the single-chip design. This weak-current sensor based on differential TMR has the potential to be useful for industrial applications in smart grids and green energy.