Ultra-wideband 1–20 GHz Non-contact FMR Test System for TMR HGA
The read sensor of hard disk drive abnormality at the bar level is detected by a ferromagnetic resonant analyzer (FMRA) system requiring a galvanic contact to the sensor. After the read head is assembled to the slider, a quasistatic tester is used to check the slider functionality. At this stage, the FMR information of the read sensor cannot be easily accessed since there is no suitable measurement technique available. In this research, an innovative non-contact ferromagnetic resonant (FMR) measurement for the read head sensor quality control at slider level is reported for the first time. The proposed test system is designed for detecting the FMR from 1 to 20 GHz. The FMR is interpreted from the peak of read sensor resistance over the frequency span. This new measurement technique has been applied to a model of tunneling magnetoresistance (TMR) sensor and compared with the FMRA. The FMR frequency at 5.4 GHz can be detected by the proposed measurement system with only 1 MHz difference from the value obtained from conventional FMRA. The higher effective stiffness field of the read sensor is also observed from the lower FMR resistance in the shorter stripe height head.