Noise characteristics of tunneling magnetoresistive sensors

Summary form only given. The noise of tunneling magnetoresistive sensors (TMR) has been measured in the frequency domain as a function of applied magnetic field (up to 4 T), temperature (4 K to 400 K), and bias current (up to 5 mA). The bias current was applied to a sensor through a bias tee. The AC noise signal from the sensor was decoupled from DC signal by the bias tee with a low cut off frequency of 5 kHz, and was measured by a spectrum analyzer. Noise voltage-spectral density (S/sub v/) was measured with a resolution bandwidth of 30 kHz for two types of sensors with different permanent magnet biases. The position of the noise peaks was in the range from 100 MHz to a few GHz, which is close to a typical data rate of hard disk drives. More detailed analyses revealed that these noise peaks may result from a uniform precession of magnetization in the free layer, possibly due to poor bias. Shot noise of the TMR sensors was also measured at room temperature with bias current of 3 mA under a very high magnetic field of 4 T. Sv observed under 4 T was very close to that of a 49 ohm non magnetic resistor at frequencies above 100 kHz, suggesting that shot noise may not be a dominant noise source in good TMR sensors.