Low frequency noise in MgO magnetic tunnel junctions with magnetic flux concentrator

Magnetic tunnel junctions (MTJ) have been widely studied as ultra-sensitive magnetic sensors, due to their high sensitivity, low power consumption, and small size. Field detectability of MTJ sensor, particularly at low frequency, is primarily limited by its intrinsic 1/f noise. Hence understanding in the noise performance of MTJ sensor is important for its application. Also, magnetic flux concentrator can enhance signal level of MTJ sensor, yet its role in the noise performance of the sensor system is not fully investigated. In this work, we have measured sensitivity and low-frequency noise spectrum (1 Hz – 10 kHz) of MgO-based MTJ sensor incorporated with an on-chip magnetic flux concentrator. We have found that 1/f noise strongly depends on the bias magnetic field, and a linear relationship between 1/f noise and sensitivity is observed. This result indicates that 1/f noise in highly-sensitive MTJ sensor is dominated by magnetic noise, originated from thermal magnetic fluctuations. Role of magnetic flux concentrator in noise performance will also be discussed.